Inborn Metabolic Diseases Diagnosis and Treatment - part 9 docx

The three most common porphyrias, acute intermittent por-phyria, porphyria cutanea tarda and erythropoietic pro-toporphyria, differ considerably from each other.. Measurement of urina

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36 Disorders of Heme Biosynthesis

Norman G Egger, Chul Lee, Karl E Anderson

36.1 X-Linked Sideroblastic Anemia – 453

36.2 Classification of Porphyrias – 453

36.3 Diagnosis of Porphyrias – 454

36.4 5-Aminolevulinic Acid Dehydratase Porphyria – 454

36.5 Acute Intermittent Porphyria – 455

36.6 Congenital Erythropoietic Porphyria (Gunther Disease) – 458 36.7 Porphyria Cutanea Tarda – 459

36.8 Hepatoerythropoietic Porphyria – 460

36.9 Hereditary Coproporphyria and Variegate Porphyria – 461 36.10 Erythropoietic Protoporphyria – 462

References – 463

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Chapter 36 · Disorders of Heme Biosynthesis

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The Heme Biosynthetic Pathway

Heme (iron protoporphyrin), a metalloporphyrin with

iron as the central metal atom, is the prosthetic group

for many hemoproteins It is produced mainly in the

bone marrow (for hemoglobin), and in the liver (for

cytochrome P450 enzymes) The pathway ( Fig 36.1)

consists of eight enzymes; the first and last three are

mitochondrial, the other four cytosolic

The first enzyme of the pathway, 5-aminolevulinic acid synthase (ALAS), has a house keeping form (termed

ALAS1), and an erythroid form (termed ALAS2)

en-coded by a separate gene on the X chromosome ALAS1

is especially active in liver, where it is subject to negative

feedback by heme, and induced by a variety of drugs,

steroids and other chemicals that also induce chrome P450 enzymes [1, 2] ALAS2 is induced by heme and erythropoietin but not by the factors that in-duce liver cytochrome P450 enzymes This explains why such factors are important deter minants of the clinical expression in hepatic porphyrias but not in erythropoietic porphyrias

cyto-Mutations of ALAS2 are found in X-linked blastic anemia Mutations in genes for the other seven enzymes are found in the porphyrias Deficiency of hepatic uroporphyrinogen decarboxylase, which occurs

sidero-in porphyria cutanea tarda, can develop sidero-in the absence

of a mutation of its gene

Fig 36.1 Pathway of heme biosynthesis Intermediates and

enzymes of the heme biosynthetic pathway are listed ALA,

by the various enzyme deficiencies (indicated by solid bars across the arrows) are given in bold

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X-linked sideroblastic anemia is due to a deficiency

of the erythroid form of the first enzyme in the heme

biosynthetic pathway, 5-aminolevulinic acid synthase

Characteristics of the disease are variable, but typically

include adult onset anemia, ineffective erythropoiesis

with formation of ring sideroblasts, iron accumulation

and pyridoxine responsiveness

Porphyrias are metabolic disorders due to

deficien-cies of other enzymes of this pathway, and are

associat-ed with striking accumulations and excess excretion of

heme pathway intermediates and their oxidized

prod-ucts Symptoms and signs of the porphyrias are almost

all due to effects on the nervous system or skin The

three most common porphyrias, acute intermittent

por-phyria, porphyria cutanea tarda and erythropoietic

pro-toporphyria, differ considerably from each other The

first presents with acute neurovisceral symptoms and

can be aggravated by some drugs, hormones and

nutri-tional changes, and is treated with intravenous heme

and carbohydrate loading The skin is affected in the

latter two although the lesions are usually distinct and

treatment is different Porphyrias are more often

mani-fest in adults than are most metabolic diseases All

por-phyrias are inherited, with the exception of porphyria

cutanea tarda, which is due to an acquired enzyme

de-ficiency in liver, although an inherited dede-ficiency is a

predisposing factor in some cases.

36.1 X-Linked Sideroblastic Anemia

36.1.1 Clinical Presentation

Sideroblastic anemia is a variable condition and can be

either acquired or inherited Its presence is suggested by

hypochromic anemia in the presence of increases in serum

iron concentration and transferrin saturation The bone

marrow contains nucleated erythrocyte precursors with

iron-laden mitochondria surrounding the nucleus (ring

sideroblasts) Progressive iron accumulation may occur as

a result of ineffective erythropoiesis, leading to organ

dam-age

The inherited form is due to a deficiency of the erythroid

form of 5-aminolevulinic acid synthase (ALAS2) Acquired

forms have been attributed to alcohol, chemotherapy and to

early stages of a myelodysplastic syndrome, which might

affect one or more steps in heme synthesis However,

ALAS2 mutations have not been excluded in many of these

cases

X-linked sideroblastic anemia is due to mutations of the ALAS2 gene This disorder is heterogeneous, in that multi-ple mutations have been described [3, 4] Phenotypic ex-pression is variable [5] Point mutations may occur in the pyridoxine binding site of the enzyme, and enzyme activity may be at least partially restored and anemia corrected by high doses of this vitamin

36.1.4 Diagnostic Tests

Hypochromic anemia with evidence of iron overload gests this diagnosis Ring sideroblasts in the bone marrow and pyridoxine responsiveness is further evidence De-tection of an ALAS2 mutation and demonstration of its X-linked inheritance is important for a definite diagnosis Screening for mutations of the gene associated with hemo-

sug-chromatosis (HFE) may identify patients at greater than

expected risk for iron accumulation

36.1.5 Treatment and Prognosis

Treatment consists of administration of pyridoxine and folic acid The starting dose of pyridoxine is 100-300 mg/day followed by a maintenance dose of 100 mg/day Phle-botomy to remove excess iron not only prevents organ dam-age, which is the primary cause of morbidity in this disease, but also may increase responsiveness to pyridoxine

36.2 Classification of Porphyrias

These metabolic disorders are due to deficiencies of heme biosynthetic pathway enzymes and characterized by accu-mulation and excess excretion of pathway intermediates and their oxidized products The photosensitizing effects of excess porphyrins cause cutaneous manifestations Neuro-logical effects are poorly explained, but are associated with increases in the porphyrin precursors, 5-aminolevulinic acid (also known as G-aminolevulinic acid) and porpho-bilinogen

5-Aminolevulinic acid and porphobilinogen are soluble and are excreted almost entirely in urine, as are porphyrins with a large number of carboxyl side chains (e.g uroporphyrin, an octacarboxyl porphyrin) Protopor-phyrin (a dicarboxyl porphyrin) is not soluble in water and is excreted entirely in bile and feces Coproporphyrin (a tetracarboxyl porphyrin) is found in both urine and bile, and its urinary excretion increases when hepatobiliary function is impaired Most of the porphyrin intermediates are porphyrinogens (reduced porphyrins) and these un-dergo autooxidation if they leave the intracellular environ-

water-36.2 · Classification of Porphyrias

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ment and are then excreted primarily as the corresponding

porphyrins 5-Aminolevulinic acid, porphobilinogen and

porphyrinogens are colorless and non-fluorescent, whereas

oxidized porphyrins are reddish and fluoresce when

ex-posed to ultraviolet light [6]

The porphyrias are classified with regard to the

tissue where the metabolic defect is primarily expressed

(hepatic and erythropoietic porphyrias), or the clinical

presenta tion (acute neurovisceral or cutaneous porphyrias)

( Table 36.1)

Acute porphyrias (acute intermittent porphyria,

varie-gate porphyria, hereditary coproporphyria and

5-aminole-vulinic acid dehydratase porphyria) can cause acute attacks

of potentially life-threatening neurovisceral symptoms (e.g

abdominal pain, neuropathy, and mental disturbances) All

are associated with striking increases in 5-aminolevulinic

acid, and three with increases in porphobilinogen

Porphyrias accompanied by skin manifestations are

termed cutaneous porphyrias In these conditions,

excita-tion of excess porphyrins in the skin by long-wave

ultravio-let light (UV-A) leads to generation of singultravio-let oxygen and

cell damage The two most common cutaneous porphyrias

are porphyria cutanea tarda and erythropoietic

protopor-phyria Variegate porphyria, and much less commonly

hereditary coproporphyria, can also cause cutaneous

symptoms

Acute porphyria should be considered in patients with

unexplained neurovisceral symptoms, such as abdominal

pain Diagnosis of active cases is based on measurement

of porphyrin precursors and porphyrins in urine, blood

and feces Measurements of deficient enzymes and DNA

methods are available for confirmation and for family

studies

36.3 Diagnosis of Porphyrias

In contrast to the nonspecific nature of symptoms,

labora-tory tests, if properly chosen and interpreted, can be both

sensitive and specific [6] The initial presentation

deter-mines the type of initial laboratory testing ( Table 36.2)

In a severely ill patient with symptoms suggesting acute

porphyria, it is very important to confirm or exclude this

diagnosis promptly, because treatment is more successful

if started soon after the onset of symptoms Measurement

of urinary porphyrin precursors (5-aminolevulinic acid

and porphobilinogen) and total porphyrins is

recom-mended when neurovisceral symptoms are suggestive of

acute porphyria Urinary porphobilinogen (and

5-ami-nolevulinic acid) is always markedly increased during

attacks of acute intermittent porphyria but may be less

increased in hereditary coproporphyria and variegate

por-phyria 5-Aminolevulinic acid but not porphobilinogen is

increased in 5-amino levulinic acid dehydratase porphyria

The finding of normal levels of 5-aminolevulinic acid,

por-phobilinogen and total porphyrins effectively excludes all acute porphyrias as potential causes of current symptoms Current recommendations are that all major medical cent-ers should have capabilities for rapid screening of spot urine samples for excess porphobilinogen, and 5-amino-levulinic acid and total porphyrins be measured later on the same sample [7]

Total plasma porphyrins are increased in virtually all patients with blistering skin lesions due to porphyrias, and should be measured when a cutaneous porphyria is sus-pected [8, 9] Plasma porphyrins may not be increased in all patients with the nonblistering photosensitivity found in erythropoietic protoporphyria, and measurement of eryth-rocyte protoporphyrin is more sensitive Unfortunately, erythrocyte protoporphyrin is increased in many other erythrocytic disorders, and because this test lacks specifi-city, it does not alone confirm a diagnosis of erythropoietic protoporphyria

Further laboratory evaluation is necessary if the tial tests are positive in order to distinguish between the different types of porphyria and establish a precise diagno-sis This is essential for management and genetic coun-seling

ini-36.4 5-Aminolevulinic Acid

Dehydratase Porphyria36.4.1 Clinical Presentation

This is the most recently described porphyria, and only

6 cases have been documented by molecular methods Symptoms resemble those of acute intermittent porphyria, including abdominal pain and neuropathy The disease may begin in childhood and in severe cases be accompanied by failure to thrive and anemia Other causes of 5-amino-levulinic acid dehydratase deficiency and increased urinary 5-aminolevulinic acid need to be excluded, such as lead poi-soning and hereditary tyrosinemia; these conditions can also present with symptoms resembling those in acute porphyrias

This disorder is due to a homozygous or compound zygous deficiency of 5-aminolevulinic acid dehydratase, the second enzyme in the heme biosynthetic pathway ( Fig 36.1) The enzyme is markedly reduced (<5% of normal) in affected individuals, and approximately half-normal in both parents, which is consistent with autosomal recessive inheritance ( Table 36.1) Lead poisoning can

hetero-be distinguished by showing reversal of the inhibition of 5-amino levulinic acid dehydratase in erythrocytes by the in-vitro addition of dithiothreitol Hereditary tyrosinemia

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type 1 leads to accumulation of succinylacetone

(2,3-dioxo-heptanoic acid, a structural analog of 5-aminolevulinic acid

and a potent inhibitor of the dehydratase, 7 Chap 18) Other

heavy metals and styrene can also inhibit 5-aminolevulinic

acid dehydratase

36.4.3 Genetics

All well-documented cases were unrelated, and most had

different mutations Immunological studies to date have

indicated that most mutant alleles produce a defective

en-zyme protein [10]

Characteristic findings include increases in urinary

5-ami-nolevulinic acid and coproporphyrin and erythrocyte zinc

protoporphyrin, normal or slightly increased urinary

por-phobilinogen, and a marked decrease in erythrocyte

5-ami-nolevulinic acid dehydratase Other causes of

5-amino-levulinic acid dehydratase deficiency must be excluded and

the diagnosis confirmed by DNA studies [10] The increase

in urinary coproporphyrin (mostly isomer III) is probably

due to metabolism of 5-aminolevulinic acid via the heme

biosynthetic pathway in tissues other than the liver

Copro-porphyrin III also increases in normal subjects after loading

with exogenous 5-aminolevulinic acid [11] Erythrocyte

zinc protoporphyrin content is also increased, as in other

homozygous cases of porphyria

There is little experience in treating this porphyria In general, the approach is the same as in acute intermittent porphyria Heme therapy was effective in most cases It is prudent to avoid drugs that are harmful in other acute por-phyrias

36.5 Acute Intermittent Porphyria36.5.1 Clinical Presentation

Symptoms appear during adult life and are more common

in women than in men Acute attacks of neurovisceral symptoms and signs are the most common presentation, although subacute and chronic manifestations can also occur Attacks usually last for several days or longer, often require hospitalization, and are usually followed by com-plete recovery Severe attacks may be much more prolonged and are sometimes fatal, especially if the diagnosis is de-layed Abdominal pain, the most common symptom, is usu-ally steady and poorly localized, but is sometimes crampy Tachycardia, hypertension, restlessness, fine tremors, and excess sweating suggest sympathetic overactivity Nausea, vomiting, constipation, pain in the limbs, head, neck or chest, muscle weakness and sensory loss are also common Dysuria, bladder dysfunction and ileus, with abdominal distention and decreased bowel sounds, may occur How-ever, increased bowel sounds and diarrhea are sometimes seen Because the abdominal symptoms are neurological

Table 36.1 Enzyme deficiencies and classification of human porphyrias Classifications are based on the major tissue site of

overpro-duction of heme pathway intermediates (hepatic vs erythropoietic) or the type of major symptoms (acute neurovisceral vs cutaneous),

but are not mutually exclusive

5-Aminolevulinic acid dehydratase ? X X

Acute intermittent porphyria Porphobilinogen deaminase1 X X

Congenital erythropoietic porphyria Uroporphyrinogen III cosynthase X X

Porphyria cutanea tarda 2 Uroporphyrinogen decarboxylase X X

Hepatoerythropoietic porphyria Uroporphyrinogen decarboxylase X X X

Hereditary coproporphyria Coproporphyrinogen oxidase X X X

1 This enzyme is also known as hydroxymethylbilane synthase, and formerly as uroporphyrinogen I synthase.

2 Inherited deficiency of uroporphyrinogen decarboxylase is partially responsible for familial (type 2) porphyria cutanea tarda.

36.5 · Acute Intermittent Porphyria

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rather than inflammatory, tenderness, fever and

leukocyto-sis are characteristically mild or absent A peripheral

neu-ropathy that is primarily motor can develop, and is

mani-fested by muscle weakness that most often begins

proxi-mally in the upper extremities It may progress to involve all

extremities, respiratory muscles and even lead to bulbar

pa-ralysis Tendon reflexes may be little affected or hyperactive

in early stages, but are usually decreased or absent with

ad-vanced neuropathy Muscle weakness is sometimes focal

and asymmetric Cranial and sensory nerves can be

affect-ed Advanced motor neuropathy and death are rare unless

porphyria is not recognized and appropriate treatment not

instituted Seizures may occur as an acute neurological

manifestation of acute porphyrias, as a result of

hyponatrem-ia, or due to other causes unrelated to porphyria

Hy-ponatremia can be due to electrolyte depletion from

vo-miting or diarrhea, poor intake, renal sodium loss, or

in-appropriate antidiuretic hormone secretion Persistent

hypertension and impaired renal function may occur over

the long term Chronic abnormalities in liver function tests,

particularly transaminases, are common, although few

pa-tients develop significant hepatic impairment The risk of

hepatocellular carcinoma is increased in this and other

acute porphyrias, as well as in porphyria cutanea tarda

[6, 12, 13]

Acute intermittent porphyria (AIP) is due to mutations that

lead to loss of activity of porphobilinogen deaminase (also

known as hydroxymethylbilane synthase and formerly as

uroporphyrinogen I synthase), the third enzyme in the

heme biosynthetic pathway ( Fig 36.1, Table 36.1)

In-heritance is autosomal dominant, and the residual ~50%

enzyme activity is mostly due to enzyme produced from the

normal allele Most heterozygotes remain asymptomatic

with normal levels of urinary porphyrin precursors When

the disease is clinically expressed, accumulation of heme

pathway intermediates in liver leads to increased excretion

primarily in urine

Apparently, the partial deficiency of porphobilinogen

deaminase does not of itself greatly impair hepatic heme

synthesis However, when drugs, hormones, or nutritional

factors increase the demand for hepatic heme, the deficient

enzyme can become limiting Induction of hepatic ALAS1

is then accentuated and 5-aminolevulinic acid and

porpho-bilinogen accumulate Excess porphyrins originate

nonen-zymatically from porphobilinogen, and perhaps

enzymati-cally from 5-aminolevulinic acid transported to tissues

other than the liver

Most drugs that are harmful to patients with this and

other acute hepatic porphyrias are known to have the

ca-pacity to induce the synthesis of cytochrome P450 enzymes

and ALAS1 in the liver [2]

36.5.3 Genetics

More than 200 different mutations of the porphobilinogen deaminase gene have been identified in unrelated families [14] The gene has two promoters, one of which is ery-throid-specific Erythroid-specific and housekeeping forms

of this enzyme are derived from the same gene by tive splicing of two primary transcripts Most mutations in AIP lead to a deficiency of both isozymes Mutations lo-cated in or near the first of the 15 exons in this gene can impair the synthesis of the housekeeping form but not the erythroid-specific form of porphobilinogen deaminase Homozygous cases of acute intermittent porphyria are ex-tremely rare, but should be suspected particularly if the disease is active early in childhood [15]

alterna-36.5.4 Diagnostic Tests

A substantial increase in urinary porphobilinogen is a sitive and specific indication that a patient has either acute intermittent porphyria, hereditary coproporphyria or vari-egate porphyria ( Table 36.2) A kit is available for the rapid detection of porphobilinogen at concentrations great-

sen-er than 6 mg/l with a color chart for semiquantitative mation of higher levels [16]; this enables major medical centers to provide for rapid in-house testing for these disor-ders [7] Porphobilinogen remains increased between at-tacks of acute intermittent porphyria and becomes normal only after prolonged latency Fecal total porphyrins are gen-erally normal or minimally increased in acute intermittent porphyria, and markedly increased in the other two condi-tions Total plasma porphyrins are charactistically increased

esti-in variegate porphyria, as discussed later, but are normal or only slightly increased in acute intermittent porphyria Urinary porphyrins, and particularly coproporphyrin is generally more increased in hereditary coproporphyria and variegate porphyria Urinary uroporphyrin can be in-creased in all of these disorders, especially when porpho-bilinogen is increased

Decreased erythrocyte porphobilinogen deaminase helps to confirm a diagnosis of acute intermittent porphy-ria However, falsely low activity may occur if there is a problem with processing or storing the sample The eryth-rocyte enzyme is not deficient in all patients because some mutations of the porphobilinogen deaminase gene only re-duce the housekeeping form of the enzyme Furthermore, erythrocyte porphobilinogen deaminase has a wide normal range (up to 3-fold) that overlaps the range of patients with acute intermittent porphyria

Measuring erythrocyte porphobilinogen deaminase is very useful for detecting asymptomatic carriers, if it is known that the propositus has a deficiency of the erythro-cyte enzyme Urinary porphobilinogen should also be measured when relatives are screened for this porphyria

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Identification of the specific mutation in a known case

en-ables the same mutation to be detected in relatives, most of

whom are likely to be asymptomatic and can then be

ad-vised to take precautions to avoid exacerbating the disease

Intravenous hemin (heme arginate or hematin) is

consid-ered specific therapy for acute attacks because it represses

hepatic ALAS1, and markedly reduces levels of

5-aminole-vulinic acid and porphobilinogen Severe attacks, with

fea-tures such as nausea, vomiting, motor weakness and

hy-ponatremia should be treated initially with hemin

Carbo-hydrate loading, usually accomplished by intravenous

ad-ministration of 10% glucose, also has some repressive effect

on ALAS1, but is much less effective Glucose may be

start-ed initially until hemin is obtainstart-ed Heme arginate is the

preferred form of hemin [17] Degradation products of

hematin (heme hydroxide) commonly cause phlebitis at the

site of infusion and a transient anticoagulant effect In

countries where heme arginate is not available, hematin can

be reconstituted with human albumin to stabilize the heme

as heme albumin, which confers many of the advantages of

heme arginate [18]

The standard regimen for hemin is 3–4 mg per kg body

weight infused intravenously once daily for 4 days

Treat-ment of a newly diagnosed patient should be started only

after a marked increase in urinary porphobilinogen is

demonstrated using a rapid and reliable method Recurrent

attacks can be diagnosed on clinical grounds, since

porpho-bilinogen remains elevated in most AIP patients between

attacks, and the presenting signs and symptoms are often

similar from one attack to the next A longer course of

treatment is seldom necessary if treatment is started early

Efficacy is reduced and recovery less rapid when treatment

is delayed and neuronal damage is more advanced Heme

therapy is not effective for chronic symptoms of acute phyrias [19]

por-Most acute attacks are severe enough to require talization for administration of intravenous hemin and ob-servation for neurological complications and electrolyte imbalances Narcotic analgesics are commonly required for abdominal, back or extremity pain, and small doses of a phenothiazine are useful for nausea, vomiting, anxiety, and restlessness Chloral hydrate can be administered for in-somnia Diazepam in low doses is safe if a minor tranqui-lizer is required, although it needs to be kept in mind that benzodiazepines have some inducing effect on hepatic heme synthesis and may act in an additive fashion to other inducing influences Bladder distention may require cath-eterization

hospi-Carbohydrate loading can be tried instead of hemin for mild attacks At least 300 g daily is recommended, and

>500 g daily may be more effective Carbohydrate can sometimes be given orally However, nausea, vomiting and ileus usually prevent this approach More complete parenteral nutrition should be considered for patients when oral intake is not possible for more than several days

Abdominal pain may disappear within hours, and sis begin to improve within days Muscle weakness due to severe motor neuropathy may gradually resolve, but there may be some residual weakness

pare-Treatment of seizures is problematic, because almost all anticonvulsant drugs can exacerbate acute porphyrias Bro-mides, gabapentin and probably vigabatrin can be given safely [20] EAdrenergic blocking agents may control tach-ycardia and hypertension in acute attacks of porphyria, but

do not have a specific effect on the underlying ology [19]

pathophysi-An allogeneic liver transplant in a woman with severe, recurrent attacks of acute intermittent porphyria led to complete biochemical and clinical remission [21] This ex-perience supports the role of hepatic overproduction of

Table 36.2 First-line laboratory tests for screening for porphyrias and second-line tests for further evaluation when initial testing is

positive

Testing Symptoms suggesting porphyria

First-line Urinary 5-aminolevulinic acid, porphobilinogen

and total porphyrins 1 (quantitative; random or 24 h urine)

Blistering skin lesions: Total plasma porphyrins2

Nonblistering: Erythrocyte porphyrins3

Second-line Total fecal porphyrins 1

Erythrocyte porphobilinogen deaminase Total plasma porphyrins 2

Urinary 5-aminolevulinic acid, porphobilinogen and total porphyrins 1

Total fecal porphyrins 1

1 Fractionation of urinary and fecal porphyrins is usually not helpful unless the total is increased.

2 The preferred method is by direct fluorescence spectrophotometry.

3 Erythrocyte porphyrins are generally expressed as protoporphyrin, however the method detects other porphyrins as well This test

lacks specificity, because erythrocyte protoporphyrin is increased in many erythrocytic disorders.

36.5 · Acute Intermittent Porphyria

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porphyrin precursors in causing the neurological

manifes-tations, but is not sufficient evidence for broad application

of hepatic transplantation for acute porphyrias [7]

Identification and correction of precipitating factors

such as certain drugs, inadequate nutrition, cyclic or

exog-enous hormones (particularly progesterone and progestins),

and intercurrent infections can hasten recovery from an

attack and prevent future attacks Frequent cyclic attacks

occurring in some women during the luteal phase of the

cycle when progesterone levels are highest can be prevented

by administration of a gonadotropin-releasing hormone

analogue to prevent ovulation [22]

With prompt treatment of acute attacks and precautions

to prevent further attacks, the outlook for patients with

acute porphyrias is usually excellent Fatal attacks have

be-come much less common [12] However, some patients

continue to have attacks in the absence of identifiable

pre-cipitating factors Some develop chronic pain and other

symptoms, and may become addicted to narcotic

analge-sics Such patients need to be followed closely because there

is often coexistent depression and an increased risk of

suicide

36.6 Congenital Erythropoietic

Porphyria (Gunther Disease)36.6.1 Clinical Presentation

This is usually a severe disease with manifestations noted

soon after birth, or even in utero But clinical expression is

variable and is determined in part by the degree of enzyme

deficiency Cutaneous features resemble those in porphyria

cutanea tarda but in most cases are much more severe

Le-sions include bullae and vesicles on sun-exposed skin,

hypo- or hyperpigmented areas, hypertrichosis, and

scar-ring The teeth are reddish brown (erythrodontia) because

of porphyrin deposition, and may fluoresce when exposed

to long-wave ultraviolet light Porphyrins are also deposited

in bone Hemolysis is almost invariably present and results

from the markedly increased erythrocyte porphyrin levels,

and is accompanied by splenomegaly Life expectancy is

often shortened by infections or hematological

complica-tions There are no neurological manifestacomplica-tions

Congenital erythropoietic porphyria can present in

utero as nonimmune hydrops [23] When this is recognized,

intrauterine transfusion is possible, and after birth severe

photosensitivity can be prevented by avoiding phototherapy

for hyperbilirubinemia Rarely, the disease develops in

adults, and is associated with a myeloproliferative

disor-der

This rare disorder is due to a severe deficiency of phyrinogen III cosynthase, the fourth enzyme of the heme synthesis pathway ( Fig 36.1, Table 36.1) Hydroxymeth-ylbilane (the substrate of the deficient enzyme) accumulates and is converted nonenzymatically to uroporphyrinogen I,

uropor-a nonphysiologicuropor-al intermediuropor-ate, which curopor-annot be meturopor-abo-lized to heme Therefore, uroporphyrin, coproporphyrin and other porphyrins accumulate in bone marrow, plasma, urine, and feces Porphyrin accumulation in erythroid cells results in intramedullary and intravascular hemolysis, which leads to increased erythropoiesis As a result, heme synthesis is actually increased in spite of the inherited en-zyme deficiency, in order to compensate for porphyrin-in-duced hemolysis Although the porphyrins that accumulate

metabo-in this disease are primarily type I porphyrmetabo-in isomers, type III isomers are also increased

36.6.3 Genetics

Congenital erythropoietic porphyria is an autosomal sive disorder Patients have either homozygous or com-pound heterozygous mutations of the uroporphyrinogen III cosynthase gene Like other porphyrias, this disease is genetically heterogeneous, and many different mutations have been identified [24] Parents and other heterozygotes display intermediate deficiencies of the cosynthase The disease can be diagnosed in utero by porphyrin measure-ments and DNA methods Expansion of a clone of erythroid cells that carry a uroporphyrinogen III cosynthase muta-tion often accounts for adult-onset cases

reces-36.6.4 Diagnostic Tests

Erythrocyte and plasma porphyrins are markedly increased and usually consist mostly of uroporphyrin I Copropor-phyrin and even zinc protoporphyrin may be increased in erythrocytes Porphyrins in urine are primarily uroporphy-rin I and coproporphyrin I, and in feces mostly copropor-phyrin I Porphyrin precursors are not increased The diag-nosis should be confirmed by finding a marked deficiency

in uroporphyrinogen III cosynthase activity and by tion analysis

muta-36.6.5 Treatment and Prognosis

Protection of the skin from sunlight is essential Minor trauma can lead to denudation of fragile skin Bacterial infections should be treated promptly to prevent scarring and mutilation Improvement in hemolysis has been re-ported after splenectomy Oral charcoal may be helpful by

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increasing fecal excretion of porphyrins High level blood

transfusions and hydroxyurea may be effective by

suppress-ing erythropoiesis and porphyrin synthesis [25, 26] Bone

marrow or stem cell transplantation is effective current

therapy, and gene therapy may eventually be possible [27,

28]

36.7 Porphyria Cutanea Tarda

This is the most common and readily treated form of

por-phyria and is manifested primarily by chronic, blistering

skin lesions, especially on the backs of the hands, forearms,

face and (in women) the dorsa of the feet Neurological

effects are not observed Sun-exposed skin is also friable,

and minor trauma may precede the formation of bullae or

cause denudation of the skin Small white plaques (milia)

may precede or follow vesicle formation Hypertrichosis

and hyperpigmentation are also noted Thickening, scarring

and calcification of affected skin may be striking, and is

re-ferred to as pseudoscleroderma Skin lesions are

indistin-guishable clinically from all other cutaneous porphyrias,

except for erythropoietic protoporphyria (7 later discussion)

In pseudoporphyria, skin lesions resemble porphyria

cuta-nea tarda but porphyrins are not significantly increased;

presumably other photosensitizers are responsible

Multiple susceptibility factors for porphyria cutanea

tarda are commonly identified in an individual patient A

normal or increased amount of hepatic iron is a

require-ment for the disease Others include moderate or heavy

alcohol intake, hepatitis C infection, estrogen use and

smoking Infection with HIV is a less common association

There are geographic differences in the association with

hepatitis C; in some locations more than 80% of patients are

infected with this virus

A large outbreak of this porphyria occurred in eastern

Turkey in the 1950s from ingestion of wheat that was

in-tended for planting, and had been previously treated with

hexachlorobenzene as a fungicide Porphyria cutanea tarda

has been reported after exposure to other chemicals

includ-ing di- and trichlorophenols and

2,3,7,8-tetrachlorodiben-zo-p-dioxin (TCDD, dioxin) These halogenated polycyclic

aromatic hydrocarbons induce an experimental porphyria

in laboratory animals that biochemically closely resembles

human porphyria cutanea tarda Such toxic exposures are

not evident in most human cases of sporadic porphyria

cu-tanea tarda [29, 30]

This porphyria is caused by a profound deficiency of

he-patic uroporphyrinogen decarboxylase, the fifth enzyme of

the heme biosynthetic pathway ( Fig 36.1, Table 36.1).Sporadic (type 1) and familial (types 2 and 3) forms of the disease have been described These do not differ substan-tially in terms of clinical features or treatment In all cases,

a specific inhibitor of hepatic uroporphyrinogen ylase, which has not yet been characterized, is generated from an intermediate of the heme biosynthetic pathway by

decarbox-an iron-dependent oxidative mechdecarbox-anism Certain chrome P450 enzymes and low levels of ascorbic acid and carotenoids may contribute to this oxidative process within hepatocytes The prevalence of HFE mutations is increased [30] Individuals with type 2 disease from birth have half the normal enzyme activity and are therefore more susceptible

cyto-to developing a more profound enzyme deficiency in the liver [29]

Patterns of excess porphyrins in this disease are plex and characteristic Uroporphyrinogen, (an octacar-boxyl porphyrinogen) undergoes a sequential, four-step decarboxylation to coproporphyrinogen (a tetracarboxyl porphyrinogen) Uroporphyrinogen and the hepta-, hexa-, and pentacarboxyl porphyrinogens accumulate To compli-cate the porphyrin pattern further, pentacarboxyl porphy-rinogen can be metabolized by coproporphyrinogen oxi-dase to a tetracarboxyl porphyrinogen termed isocopropor-phyrinogen These porphyrinogens accumulate first in liver, are mostly oxidized to the corresponding porphyrins, and then appear in plasma and are excreted in urine, bile and feces Successful treatment may require some time be-fore the massive porphyrin accumulations in liver are cleared

com-36.7.3 Genetics

Porphyria cutanea tarda results from a liver-specific, parently acquired deficiency of uroporphyrinogen decar-boxylase No mutations in this gene have been found in sporadic (type 1) porphyria cutanea tarda The amount of hepatic uroporphyrinogen decarboxylase protein in type 1 disease, as measured immunochemically, is normal, as might be expected with an inhibitor of the enzyme

ap-An inherited partial deficiency of this enzyme utes in type 2, which accounts for approximately 20% of patients with porphyria cutanea tarda In these cases eryth-rocyte uroporphyrinogen decarboxylase is approximately 50% of normal in erythrocytes, and this feature is inherited

contrib-as an autosomal dominant trait affecting all tissues Type 2 becomes clinically manifest when hepatic uroporphyrino-gen decarboxylase becomes profoundly inhibited, as in type 1 A number of mutations of the uroporphyrinogen decarboxylase gene have been identified in type 2 disease Cases classified as type 3 disease, which are rare, have nor-mal erythrocyte uroporphyrinogen decarboxylase activity but one or more relatives also have the disease A genetic defect has not been clearly identified in type 3, and it is

36.7 · Porphyria Cutanea Tarda

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Blistering skin lesions are found in all cutaneous

porphyri-as, except erythropoietic protoporphyria Skin

histopathol-ogy is not specific and does not establish a diagnosis of

porphyria cutanea tarda or exclude pseudoporphyria It is

important to differentiate these conditions by laboratory

testing before starting therapy

Plasma porphyrins are increased in all patients with

blistering skin lesions due to porphyria The fluorescence

spectrum of plasma porphyrins can readily distinguish

variegate porphyria and erythropoietic protoporphyria

from porphyria cutanea tarda ( Table 36.2) The diagnosis

is best confirmed by increased total urinary porphyrins

with a predominance of uroporphyrin and heptacarboxyl

porphyrin Total fecal porphyrins are usually less increased

than in hereditary coproporphyria and variegate porphyria

In porphyria cutanea tarda, an increase in the proportion of

fecal isocoproporphyrin, which can be expressed as a ratio

to coproporphyrin, is distinctive

Repeated phlebotomy is standard treatment at most

cent-ers, although low-dose hydroxychloroquine (or

chloro-quine) is also effective Patients are also advised to

distinue alcohol, estrogens, iron supplements, and other

con-tributing factors Phlebotomies remove iron and stimulate

erythropoiesis, and utilization of storage iron for

hemo-globin formation gradually reduces the serum ferritin to a

target range of 15–20 ng/ml This can usually be achieved

by removal of only 5–6 units (450 ml each) of blood at 1–2

week intervals Further iron depletion is of no additional

benefit and may cause anemia and associated symptoms

Many more phlebotomies may be needed in patients who

have marked iron overload, which is likely to be due to

fa-milial hemochromatosis The plasma or serum porphyrin

level falls somewhat more slowly than ferritin, and may not

yet be normal when the target ferritin level is reached

With treatment the activity of hepatic

uroporphyrino-gen decarboxylase gradually increases to normal After

re-mission, ferritin can return to pretreatment values without

recurrence, in most cases Postmenopausal women who

have been treated for porphyria cutanea tarda can usually

resume estrogen replacement without recurrence Relapses

seem to be more common in patients who resume alcohol

intake, but will respond to further phlebotomies

A low dose of hydroxychloroquine (100 mg twice

weekly) or chloroquine (125 mg twice weekly) for several

months gradually removes excess porphyrins from the liver

This is a suitable alternative when phlebotomy is indicated or difficult, and is preferred at some centers Standard doses of these 4-aminoquinolines exacerbate pho-tosensitivity and cause hepatocellular damage, and should not be used Both may produce retinal damage, although this risk is very low, and may be lower with hydroxychloro-quine than chloroquine The mechanism by which these drugs remove porphyrins from the liver in this condition is not known [31] This treatment is not effective in other por-phyrias [19]

contra-36.8 Hepatoerythropoietic Porphyria36.8.1 Clinical Presentation

This rare disease is clinically similar to congenital poietic porphyria and usually presents with red urine and blistering skin lesions shortly after birth Mild cases may present later in life and more closely resemble porphyria cutanea tarda Concurrent conditions, such as viral hepati-tis, may accentuate porphyrin accumulation

Hepatoerythropoietic porphyria is the homozygous form of familial (type 2) porphyria cutanea tarda, and is due to a substantial deficiency of uroporphyrinogen decarboxylase Intermediate deficiencies of the enzyme are found in the parents, as expected for an autosomal recessive disorder ( Fig 36.1, Table 36.1) The disease has features of both hepatic and erythropoietic porphyrias

This porphyria results from a homozygous or compound heterozygous state for mutations of the gene encoding uro-porphyrinogen decarboxylase The disease is genetically heterogeneous Mutations found in this disease generally result in marked decreases in uroporphyrinogen decarbox-ylase activity, but some activity remains, so heme formation can occur [30]

The excess porphyrins found in urine, plasma and feces are similar to those in porphyria cutanea tarda In addi-tion, erythrocyte zinc protoporphyrin is increased, as in

a number of other autosomal recessive porphyrias This finding probably reflects an earlier accumulation of uro-porphyrinogen in erythroblasts, which after completion of hemoglobin synthesis is metabolized to protoporphyrin

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Erythrocyte porphyrins in congenital erythropoietic

por-phyria are usually mostly uroporphyrin I and

coproporphy-rin I, but in some cases there is a predominance of zinc

protoporphyrin Hepatoerythropoietic porphyria is

dif-ferentiated from congenital erythropoietic porphyria also

by excess isocoproporphyrins in feces and urine, and by

decreased erythrocyte uroporphyrinogen decarboxylase

activity It is important to document the diagnosis by

mo-lecular methods

Therapeutic options are essentially the same as in

congeni-tal erythropoietic porphyria

36.9 Hereditary Coproporphyria

and Variegate Porphyria

These disorders can present with acute attacks that are

iden-tical to those in acute intermittent porphyria However,

un-like the latter disease, variegate porphyria and more rarely

hereditary coproporphyria may cause blistering skin lesions

that are indistinguishable from those of porphyria cutanea

tarda Symptoms are most common after puberty Factors

that exacerbate acute intermittent porphyria are important

in both of these porphyrias Variegate porphyria is

particu-larly common in South Africa where most cases are

de-scendants of a couple who emigrated from Holland and

arrived in Cape Town in 1688 [32] In rare homozygous

cases of these porphyrias clinical manifestations begin in

childhood

Hereditary coproporphyria and variegate porphyria result

from approximately 50% deficiencies of

coproporphyrin-ogen oxidase and of protoporphyrincoproporphyrin-ogen oxidase,

respec-tively, which are the sixth and seventh enzyme of the heme

biosynthetic pathway ( Fig 36.1, Table 36.1) In

heredi-tary coproporphyria there is marked accumulation of

co-proporphyrin III (derived from autooxidation of

copro-porphyrinogen III), and urinary porphyrin precursors

and uroporphyrin are increased particularly in association

with acute attacks Similar abnormalities are seen in

vari-egate porphyria, but in addition protoporphyrin (derived

from autooxidation of protoporphyrinogen) is increased

in feces (and bile), and plasma porphyrins are increased

Protoporphyrinogen has been shown to inhibit

porpho-bilinogen deaminase, which along with induction of

he-patic ALAS1, may account for the increase in porphyrin

precursors during acute attacks, at least in variegate phyria

Urinary 5-aminolevulinic acid and porphobilinogen are increased during acute attacks of these porphyrias, although the increases may be less and more transient than in acute intermittent porphyria Urinary coproporphyrin increases may be more prominent and prolonged However, copro-porphyrinuria is a highly nonspecific finding It can be seen

in many medical conditions, especially when hepatic or bone marrow function is affected

A marked, isolated increase in fecal coproporphyrin (especially isomer III) is distinctive for hereditary copro-porphyria Fecal coproporphyrin and protoporphyrin are about equally increased in variegate porphyria An increase

in fecal pseudo-pentacarboxyl porphyrin, which is a boxyl porphyrin derived from protoporphyrin, is also diag-nostically useful in variegate porphyria

dicar-Increased plasma porphyrins and a fluorescence trum of plasma porphyrins (at neutral pH) is characteristic and very useful for rapidly distinguishing variegate porphyria from the other porphyrias This is at least as sensitive as fecal porphyrin measurement for detecting variegate porphyria, although not as sensitive as a reliable assay for lymphocyte protoporphyrinogen oxidase or mutation analysis [33, 34] Reliable assays for protoporphyrinogen oxidase and coproporphyrinogen oxidase in cultured fibroblasts or lymphocytes are available only in a few research laborato-ries Erythrocytes cannot be used to measure these mito-chondrial enzymes, because mature erythrocytes do not contain mitochondria As in other porphyrias, identifica-tion of a mutation in an index case facilitates detection of relatives who carry the same mutation

spec-36.9.5 Treatment and Prognosis

Acute attacks are treated as in acute intermittent porphyria (7 above) Cutaneous symptoms are more difficult to treat, andtherapies that are effective for porphyria cutanea tarda (phle-botomy and low-dose hydroxychloroquine) are not effective

in these conditions Protection from sunlight is important

36.9 · Hereditary Coproporphyria and Variegate Porphyria

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462

36.10 Erythropoietic Protoporphyria

36.10.1 Clinical Presentation

Erythropoietic protoporphyria is the third most common

porphyria Cutaneous symptoms begin in childhood, and

are generally much more prominent than objective

chang-es by examination Symptoms such as burning, itching,

erythema, and swelling can occur within minutes of sun

exposure, and the diffuse edema of sun-exposed areas may

resemble angioneurotic edema Other more chronic skin

changes may include lichenification, leathery

pseudo-vesicles, labial grooving, and nail changes In contrast to

other cutaneous porphyrias, blistering, milia, friability, and

chronic skin changes such as scarring and hypertrichosis

are not prominent There is no fluorescence of the teeth and

no neuropathic manifestations Mild anemia with

hy-pochromia and microcytosis is noted in some cases

The severity of the symptoms is remarkably stable over

time Drugs that exacerbate hepatic porphyrias are not

known to worsen this disease, although they are generally

avoided as a precaution Gallstones containing

protopor-phyrin may also develop Some patients develop liver

dis-ease, which can progress rapidly to death from hepatic

failure This complication is accompanied by marked

dep-osition of protoporphyrin in liver and increased levels in

plasma and erythrocytes A motor neuropathy may further

complicate the course of liver decompensation in this

dis-ease, and is unexplained [35]

36.10.2 Metabolic Derangement

The inherited deficiency of ferrochelatase, the eighth and

last enzyme in the heme biosynthetic pathway ( Fig 36.1,

Table 36.1) leads to increases in protoporphyrin in bone

marrow, circulating erythrocytes, plasma, bile, and feces in

this disease Ferrochelatase is deficient in all tissues, but the

deficient enzyme is rate-limiting for protoporphyrin

me-tabolism primarily in bone marrow reticulocytes, which

are the primary source of the excess protoporphyrin

Circu-lating erythrocytes and perhaps the liver contribute smaller

amounts Excess protoporphyrin is transported in plasma

and excreted in bile and feces

Erythrocyte protoporphyrin is mostly chelated with

zinc in normal erythrocytes as well as in many other

condi-tions where protoporphyrin in increased (e.g lead

poison-ing, iron deficiency, and homozygous forms of porphyria)

Formation of both heme and zinc protoporphyrin is

cata-lyzed by ferrochelatase Protoporphyrin accumulates

most-ly as free protoporphyrin in protoporphyria, because this

enzyme is deficient Free protoporphyrin diffuses more

readily from erythrocytes into plasma than does zinc

pro-toporphyrin, most of which remains in the erythrocyte for

its full life span Therefore, primarily reticulocytes and

young circulating erythrocytes fluoresce when observed under long wave ultraviolet light

Protoporphyrin is excreted in bile and may undergo enterohepatic circulation Liver protoporphyrin content is not increased in uncomplicated protoporphyria But large amounts of protoporphyrin derived primarily from the bone marrow can cause cholestasis and severe liver failure

in some patients with protoporphyria

de-~10% of normal Caucasians, and has no consequence in the absence of a mutant ferrochelatase allele that results in little

or no enzyme activity [38] Therefore, ferrochelatase ity is only 10-25% of normal in patients with manifest dis-ease, rather than the expected ~50% for autosomal domi-nant inheritance, and many heterozygotes in a family have higher enzyme activity and no increase in erythrocyte pro-toporphyrin Autosomal recessive inheritance, with two disabling mutations has been documented in a few families, where at least one of the two mutant ferrochelatase alleles expresses some enzyme activity [35]

activ-36.10.4 Diagnostic Tests

The most sensitive screening test for this disorder is a mination of erythrocyte protoporphyrin, which under most circumstances is the predominant porphyrin in erythro-cytes This test lacks specificity because standard assays reflect all porphyrins that might be increased in many dis-eases, including free protoporphyrin (in protoporphyria), zinc protoporphyrin (in iron deficiency, lead poisoning, most homozygous cases of porphyria, and many other erythrocyte disorders), and very rarely uroporphyrin I and coproporphyrin I (in congenital erythropoietic porphyria)

deter-To gain specificity for protoporphyria, an increased rocyte protoporphyrin result is followed by a determination whether the protoporphyrin is free or complexed with zinc, using a simple ethanol extraction method

eryth-The plasma porphyrin concentration is almost always increased, but less so than in other cutaneous porphyrias Moreover, the excess protoporphyrin in plasma in this con-

Trang 13

dition is particularly sensitive to light exposure, which may

increase the chance of a falsely normal measurement It is

especially important to shield plasma samples from light if

protoporphyria is suspected The fluorescence spectrum of

plasma porphyrins at neutral pH can distinguish

erythro-poietic protoporphyria from other porphyrias

Total fecal porphyrins may be normal or increased in

protoporphyria, with a predominance of protoporphyrin

Urinary porphyrins and porphyrin precursors are normal,

unless the patient has liver impairment, in which case

uri-nary porphyrins (especially coproporphyrin) may increase

Hepatic complications of the disease are often preceded by

increasing levels of erythrocyte and plasma

protoporphy-rin, abnormal liver function tests, marked deposition of

protoporphyrin in liver cells and bile canaliculi, and

in-creased photosensitivity

36.10.5 Treatment and Prognosis

Photosensitivity is managed by avoidance of sunlight Oral

E-carotene and cysteine improve tolerance to sunlight in

some patients, perhaps by quenching singlet oxygen or free

radicals.E-Carotene seems to be more effective in

erythro-poietic protoporphyria than in other cutaneous porphyrias

Cholestyramine may reduce protoporphyrin levels by

inter-rupting its enterohepatic circulation Iron deficiency,

ca-loric restriction, and drugs or hormone preparations that

impair hepatic excretory function should be avoided

Treatment of liver complications is difficult

Transfu-sions or heme therapy may suppress erythroid and hepatic

protoporphyrin production Liver transplantation is

some-times required, but there is some risk that the new liver will

also accumulate excess protoporphyrin and develop

im-paired function [39] Operating room lights have produced

severe skin and peritoneal burns in some patients with

pro-toporphyria, liver failure, and marked increases in

erythro-cyte and plasma protoporphyrin concentrations A patient

with erythropoietic protoporphyria who underwent bone

marrow transplantation for leukemia experienced

com-plete remission of the porphyria [40] Therefore, there is

potential benefit from bone marrow replacement and gene

therapy in this and other erythropoietic porphyrias [35]

References

1 Granick S (1966) The induction in vitro of the synthesis of

G-ami-nolevulinic acid synthetase in chemical porphyria: a response to

certain drugs, sex hormones, and foreign chemicals J Biol Chem

241:1359-1375

2 Anderson KE, Freddara U, Kappas A (1982) Induction of hepatic

cytochrome P-450 by natural steroids: relationships to the

induc-tion of G-aminolevulinate synthase and porphyrin accumulainduc-tion in

the avian embryo Arch Biochem Biophys 217:597-608

3 Bekri S, May A, Cotter PD et al (2003) A promoter mutation in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene caus-

es X-linked sideroblastic anemia Blood 102:698-704

4 Cazzola M, May A, Bergamaschi G et al (2000) Familial-skewed chromosome inactivation as a predisposing factor for late-onset X-linked sideroblastic anemia in carrier females Blood 96:4363- 4365

5 Cazzola M, May A, Bergamaschi G et al (2002) Absent phenotypic expression of X-linked sideroblastic anemia in one of 2 brothers with a novel ALAS2 mutation Blood 100:4236-4238

6 Anderson KE (2003) The porphyrias In: Zakim D, Boyer T (eds) tology Saunders, Philadelphia, chap 11, pp 291-346

7 Anderson KE, Bloomer JE, Bonkovsky HL et al (2005) tions for the diagnosis and treatment of the acute porphyrias Ann Intern Med 142:439-450

8 Poh-Fitzpatrick MB, Lamola AA (1976) Direct spectrophotometry

of diluted erythrocytes and plasma: a rapid diagnostic method in primary and secondary porphyrinemias J Lab Clin Med 87:362-370

9 Poh-Fitzpatrick MB (1980) A plasma porphyrin fluorescence marker for variegate porphyria Arch Dermatol 116:543-547

10 Sassa S (1998) ALAD porphyria Semin Liver Dis 18:95-101

11 Shimizu Y, Ida S, Naruto H, Urata G (1978) Excretion of porphyrins in urine and bile after the administration of delta-aminolevulinic acid

J Lab Clin Med 92:795-802

12 Kauppinen R, Mustajoki P (1992) Prognosis of acute porphyria: currence of acute attacks, precipitating factors, and associated diseases Medicine 71:1-13

oc-13 Andant C, Puy H, Bogard C et al (2000) Hepatocellular carcinoma in patients with acute hepatic porphyria: frequency of occurrence and related factors J Hepatol 32:933-939

14 Human Gene Mutation Database (www.hgmd.org).

15 Solis C, Martinez-Bermejo A, Naidich TP et al (2004) Acute tent porphyria: studies of the severe homozygous dominant disease provides insights into the neurologic attacks in acute porphyrias Arch Neurol 61:1764-1770

intermit-16 Deacon AC, Peters TJ (1998) Identification of acute porphyria: uation of a commercial screening test for urinary porphobilinogen Ann Clin Biochem 35:726-732

eval-17 Tenhunen R, Mustajoki P (1998) Acute porphyria: treatment with heme Semin Liver Dis 18:53-55

18 Bonkovsky HL, Healey BS, Lourie AN, Gerron GG (1991) Intravenous heme-albumin in acute intermittent porphyria: evidence for reple- tion of hepatic hemoproteins and regulatory heme pools Am J Gastroenterol 86:1050-1056

19 Anderson KE (2003) Approaches to treatment and prevention of human porphyrias In: Kadish KM, Smith K, Guilard R (eds) Porphy- rin handbook, part II, vol 14 Academic Press, San Diego, chap 94,

pp 247-284

20 Hahn M, Gildemeister OS, Krauss GL et al (1997) Effects of new ticonvulsant medications on porphyrin synthesis in cultured liver cells: potential implications for patients with acute porphyria Neu- rology 49:97-106

an-21 Soonawalla ZF, Orug T, Badminton MN (2004) Liver transplantation

as a cure for acute intermittent porphyria Lancet 363:705-706

22 Anderson KE, Spitz IM, Bardin CW, Kappas A (1990) A GnRH logue prevents cyclical attacks of porphyria Arch Intern Med 150:1469-1474

ana-23 Verstraeten L, Van Regemorter N, Pardou A et al (1993) Biochemical diagnosis of a fatal case of Gunther‹s disease in a newborn with hydrops-fetalis Eur J Clin Chem Clin Biochem 31:121-128

24 Desnick RJ, Glass IA, Xu W et al (1998) Molecular genetics of genital erythropoietic porphyria Semin Liver Dis 18:77-84

con-25 Piomelli S, Poh-Fitzpatrick MB, Seaman C et al (1986) Complete suppression of the symptoms of congenital erythropoietic porphyria by long-term treatment with high-level transfusions N Engl J References

Trang 14

VIII

464

26 Guarini L, Piomelli S, Poh-Fitzpatrick MB (1994) Hydroxyurea in genital erythropoietic porphyria (letter) N Engl J Med 330:1091- 1092

con-27 Zix-Kieffer I, Langer B, Eyer D (1996) Successful cord blood stem cell transplantation for congenital erythropoietic porphyria (Gunther's disease) Bone Marrow Transplant 18:217-220

28 Fritsch C, Lang K, Bolsen K et al (1998) Congenital erythropoietic porphyria Skin Pharmacol Appl Skin Physiol 11:347-357

29 Elder GH (2003) Porphyria cutanea tarda and related disorders In: Kadish KM, Smith K, Guilard R (eds) Porphyrin handbook, part II, vol

14 Academic Press, San Diego, chap 88, pp 67-92

30 Egger NG, Goeger DE, Payne DA et al (2002) Porphyria cutanea tarda: multiplicity of risk factors including HFE mutations, hepatitis

C, and inherited uroporphyrinogen decarboxylase deficiency Dig Dis Sci 47:419-426

31 Egger NG, Goeger DE, Anderson KE (1996) Effects of chloroquine in hematoporphyrin-treated animals Chem Biol Interact 102:69-78

32 Meissner P, Hift RJ, Corrigall A (2003) Variegate porphyria In: Kadish

KM, Smith K, Guilard R (eds) Porphyrin handbook, part II, vol 14 Academic Press, San Diego, chap 89, pp 93-120

33 Da Silva V, Simonin S, Deybach JC et al (1995) Variegate porphyria: diagnostic value of fluorometric scanning of plasma porphyrins Clin Chim Acta 238:163-168

34 Long C, Smyth SJ, Woolf J et al (1993) Detection of latent variegate porphyria by fluorescence emission spectroscopy of plasma Br J Dermatol 129:9-13

35 Cox TM (2003) Protoporphyria In: Kadish KM, Smith K, Guilard R (eds) Porphyrin handbook, part II, vol 14 Academic Press, San Di- ego, chap 90, pp 121-149

36 Went LN, Klasen EC (1984) Genetic aspects of erythropoietic toporphyria Ann Hum Genet 48:105-117

pro-37 Gouya L, Puy H, Robreau AM et al (2002) The penetrance of nant erythropoietic protoporphyria is modulated by expression of wildtype FECH Nat Genet 30:27-28

domi-38 Bloomer J, Wang Y, Singhal A, Risheg H (2005) Molecular studies of liver disease in erythropoietic protoporphyria J Clin Gastroenterol 39:S167-175

39 Do KD, Banner BF, Katz E (2002) Benefits of chronic plasmapheresis and intravenous heme-albumin in erythropoietic protoporphyria after orthotopic liver transplantation Transplantation 73:469-472

40 Poh-Fitzpatrick MB, Wang X, Anderson KE et al (2002) etic protoporphyria: altered phenotype after bone marrow transplantation for myelogenous leukemia in a patient heteroallelic for

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Erythropoi-IX Disorders of

Metal Transport

Zinc and Magnesium – 467

Roderick H.J Houwen

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37 Disorders in the Transport of

Copper, Zinc and Magnesium

37.2.2 Zink Deficiency in Breastfed Babies – 473

37.2.3 Hyperzincemia with Hypercalprotectinemia – 473

37.2.4 Autosomal Dominant Hyperzincemia Without Symptoms – 473

37.3.1 Primary Hypomagnesemia with Secondary Hypocalcemia – 47437.3.2 Hypomagnesemia with Hypercalciuria and Nephrocalcinosis – 47437.3.3 Isolated Dominant Hypomagnesemia – 475

37.3.4 Isolated Autosomal Recessive Hypomagnesemia – 475

37.3.5 Other Metals – 475

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Chapter 37 · Disorders in the Transport of Copper, Zinc and Magnesium

IX

468

Copper, Zinc and Magnesium

Copper is an essential component for a number of

im-portant metalloenzymes Its absorption in the intestine,

and excretion by the liver are tightly regulated to

main-tain adequate serum levels This balance is disturbed in

two inborn errors: Wilson disease and Menkes disease

Wilson disease, or hepatolenticular degeneration, is due

to mutations in the ATP7B gene, encoding a

copper-transport protein essential for the export of copper from

the liver into bile It is characterized by a gradual copper

accumulation in the liver and, secondarily, in other

organs, such as brain, kidney and cornea Clinical

symptoms result from copper accumulation in the liver

and/or the brain Early treatment with copper chelators

or zinc is generally effective

Menkes disease is a X-linked disorder due to

muta-tions in the ATP7A gene, encoding a copper-transport

protein required for the efflux of copper from cells The

disorder is characterized by a general copper deficiency

Patients manifest progressive neurodegeneration, which

is usually fatal in infancy or childhood Early therapy

with copper histidine might have some benefits in

Zinc is a cofactor for over 100 enzymes and, as such, is

involved in all major metabolic pathways It is also

essential for nucleic acid metabolism and protein

syn-thesis and their regulation through so-called

zinc-finger proteins Zinc deficiency, either hereditary or

acquired, has major detrimental effects, whereas high

serum zinc has few, probably because of binding to

al-bumin and D2-macroglobulin

Acrodermatitis enteropathica is due to mutations in

the SLC39A4 gene, encoding the major zinc importing

carrier in the intestine Symptoms typically start in

infancy after the introduction of bottle feeding, and include periorificial and acral dermatitis, diarrhea, in-fections, and growth retardation Therapy with zinc is extremely effective

Zinc deficiency in breast fed babies presents with the

same dermatological symptoms as acrodermatitis teropathica, although the basic defect is probably dif-ferent Nevertheless, zinc therapy is equally effective

en-Hyperzincemia with hypercalprotectinemia is

cha-racterized by extremely elevated levels of calprotectin thought to cause uncontrolled, harmful inflammatory reactions

Autosomal dominant hyperzincemia without toms is most likely a non-disease.

symp-Magnesium is the second most abundant intracellular

cation and plays an essential role in many biochemical processes as well as neuromuscular excitability Its homeostasis is regulated by the interplay between intes-tinal absorption and renal excretion

Primary hypomagnesemia with secondary cemia generally presents in the first months of life with

hypocal-increased neuromuscular irritability or even frank

con-vulsions It is caused by mutations in the TRPM6 gene,

reducing uptake of magnesium from the gut Magnesium suppletion is highly effective

Hypomagnesemia with hypercalciuria and calcinosis provokes calcium deposition in the kidney,

nephro-leading to renal failure, with few symptoms of

hypo-magnesemia It is caused by mutations in the CLDN16

gene, encoding a calcium and magnesium sensitive pore

in the loop of Henle Magnesium supplements do not prevent the development of end stage renal disease

Isolated dominant hypomagnesemia provokes

gen-eralized convulsions and is caused by mutations in the

FXYD2 gene.

Isolated autosomal recessive hypomagnesemia has no

other symptoms

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37.1 Copper

37.1.1 Wilson Disease

Clinical Presentation

The overwhelming majority of cases display either hepatic

or neurological symptoms, and the disease should be

suspected in patients with liver disease without obvious

cause or a movement disorder [1, 2] In addition, the

diag-nosis is often made when siblings of a patient are screened

Occasionally, Wilson disease presents with isolated raised

transaminases, Kayser-Fleischer rings or haemolysis

Patients with hepatic symptoms generally present

be-tween 8 and 20 years of age, but may be as young as 3 or over

50 The presentation can be acute and severe with hepatitis,

jaundice and impending liver failure Transaminases,

al-though raised, generally are much lower than in

autoim-mune or viral hepatitis [3] While liver disease is rapidly

progressive in some patients, in others jaundice can persist

for months without progression to liver failure, or even

sub-side These patients ultimately develop liver cirrhosis and

present several years later with neurological disease

Neurological symptoms usually develop in the second

or third decade, although patients may be as young as

8 years of age Symptoms include dysarthria and

dimin-ished control of movements, accompanied in a later stage

by tremors, rigidity and drooling in combination with

swallowing problems A frequent early sign is a

deteriora-tion in the quality of handwriting In some patients

psy-chiatric symptoms predominate, ranging from behavioural

disturbances, often characterized by impulsivity and

irrita-bility, to frank psychosis

Most patients have aminoaciduria in combination with

excessive loss of bicarbonate, calcium and phosphate, and

may develop renal stones or osteoporosis Haemolytic

anaemia, leading to gall-stones, may be present

Cardiomy-opathy has also been described

The greenish brown Kayser-Fleischer ring, located in

the membrane of Descemet at the limbus of the cornea, can

be seen with the naked eye in the majority of patients with

full-blown neurological disease Careful slit lamp

examina-tion will reveal this ring in almost all these patients In

con-trast, in a substantial proportion of the patients presenting

with liver disease and in most pre-symptomatic patients,

the Fleischer ring is absent Conversely, a

Kayser-Fleischer ring is occasionally found in patients with

chole-static liver disease Its absence thus does not rule out Wilson

disease, while its presence does not confirm the disorder

Metabolic Derangement

Wilson disease is caused by reduced excretion of copper into

bile, resulting in a gradual accumulation of copper in the

liver and, secondarily, in the brain, kidneys and eye A

number of patients exhibit severe liver disease, while others

redistribute copper to the brain, especially the basal ganglia,

causing neurological disease Copper excess exerts its patic toxicity by generating free radicals that oxidize the mi-tochondrial membranes, resulting in their swelling and loss

he-of oxidative phosphorylation capacity The characteristic Kayser-Fleischer ring is a deposit of copper and sulphur The renal dysfunction is a consequence of copper accu mulation

in the renal tubules The increased urinary copper excretion, characteristic for Wilson disease, is due to the loss of un-bound, dialysable copper through the kidneys This un-bound copper can cause hemolysis in some patients

The primary defect in Wilson disease is a lesion of a protein localized in the Golgi network, ATP7B, an adeno-sine triphosphatase (ATPase), which is responsible for the excretion of copper [4, 5] and for the incorporation of cop-per into ceruloplasmin Owing to the reduced half-life of ceruloplasmin without copper, the concentration of serum ceruloplasmin is subnormal in Wilson disease Rare patients, although unable to excrete copper into bile, can incorporate copper into ceruloplasmin and have normal serum cerulo-plasmin [6]

Genetics

Wilson disease in an autosomal recessive condition caused

by mutations in the ATP7B gene, localized on chromosome

13q14 [4, 5] Its transcript, ATP7B, has six copper binding domains and is expressed predominantly in liver and kid-ney ATP7B is highly homologous to APT7A, the protein defective in Menkes disease

More than 200 mutations in the ATP7B gene have been

described so far and are listed in the Wilson Disease tation Database (www.uofa-medical-genetics.org/wilson) The distribution of mutations within various racial groups

Mu-is quite different, with the R778L mutation being common amongst Asian patients [7], the H1069Q mutation amongst European patients [8], and still other mutations being pre-valent elsewhere Most patients are compound heterozy-gotes Mutations that completely destroy the function of the protein are generally found in patients who present early, while residual function is associated with late presentation For example, patients homozygous for the non-functional R778L mutation tend to present earlier, with hepatic mani-festations [7], whereas those homozygous for the H1069Q mutation present relatively late (i.e around 21 years of age), with neurological symptoms, indicative of a relative slow build up of copper [8]

Diagnostic Tests

Wilson disease is characterized by low serum cerulo plasmin and serum copper, elevated urinary copper, and increased liver copper ( Table 37.1) These laboratory results should only be interpreted in combination, because each individual parameter can be abnormal in situations other than Wilson disease [9] For example, liver copper is raised in liver cir-rhosis, whereas serum ceruloplasmin is low in a substantial proportion of heterozygotes for Wilson disease, and in

37.1 · Copper

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IX

470

patients with hereditary aceruloplasminemia Conversely,

serum ceruloplasmin is normal in a small proportion of

patients with Wilson disease

Since over 90% of serum copper is normally bound to

ceruloplasmin, it is generally low when serum

ceruloplas-min is low, as is the case in Wilson disease

Characteris-tically the fraction of serum copper not bound to

cerulo-plasmin, called free serum copper, is raised This sensitive

parameter can be calculated with the knowledge that each

mg of ceruloplasmin contains 3.4 µg of copper, provided the

laboratory can reliably measure ceruloplasmin

concentra-tions in the subnormal ranges, i.e <200 mg/l

Urinary copper excretion is determined in a 24 h

collec-tion, but is sensitive to contamination Excretion is always

increased in symptomatic patients, but may be normal or

only borderline elevated in presymptomatic individuals

The diagnostic value of this parameter might be improved

by administering a loading dose of penicillamine

When Wilson disease is diagnosed in a family, siblings

should be investigated Analysis of mutations, or using

closely linked markers, is more reliable than laboratory

investigations of copper metabolism which cannot always

distinguish between carriers and young patients who still

have a low copper load

Treatment and Prognosis

Prognosis is excellent for patients who start treatment

be-fore severe tissue damage has occurred, i.e when

presymp-tomatic or diagnosed at an early stage Prognosis can still be

good for those with more advanced disease, provided

ag-gressive decoppering treatment is instituted immediately

after diagnosis Several therapeutic agents are available:

penicillamine, trien and zinc Tetrathiomolybdate is a

rela-tive new agent and experience is limited so far

The first agent, penicillamine, has provided the largest

experience Penicillamine chelates copper by forming a

stable complex that is subsequently excreted in urine The

initial dose for adults is 1–2 g/day, divided in four doses,

together with 25 mg/day of pyridoxine Approximately half

of the patients with liver disease will recover, while the other

half will need a transplant [10] Of patients with neurological disease, approximately half will totally recover, 25% will re-cover but still have some residual disabilities, and 25% will either recover with severe remaining disabilities or die [11]

Of note, a significant proportion of patients with cal disease will have an initial worsening of symptoms after starting penicillamine therapy For these patients the chances of a total recovery are less In addition, side effects and toxic reactions are seen in up to 20% of the patients treated with penicillamine and therapy has to be stopped in many Given this suboptimal safety profile, alternatives for penicillamine have been sought, with trien (trientine) being the first to be introduced This agent is also a copper chelator, with an efficacy that is approximately similar to penicil-lamine However side effects seem less common [12].Oral zinc has been used in the treatment of Wilson disease for more than 25 years It induces metallothionein synthesis in the small intestinal epithelium Since metallo-thionein binds copper preferentially over zinc, copper balance will become negative through faecal excretion, as villus cells are lost into the intestinal lumen As compared

neurologi-to penicillamine, zinc does not have any serious side effects, although some patients experience gastric complaints on zinc sulphate This can generally be solved by switching to zinc gluconate or zinc acetate Given its favourable side effect profile, zinc seems the agent of choice in presympto-matic individuals In patients with symptomatic disease (particularly with neurological symptoms) a small non-randomized, non-blinded trial showed similar outcomes for zinc and penicillamine [13] Given the side effects of penicillamine and the frequency of initial deterioration in patients with neurological disease, zinc should be seriously considered in this group In patients with hepatic disease, which can evolve rapidly, zinc seems less appropriate be-cause it may have a slower effect on copper overload Ob-viously, more trials are needed before final conclusions can

be drawn The initial dose of zinc sulphate for adults is

600 mg/day, divided in 3 doses; this dose can be doubled if insufficient effect is obtained Urinary copper excretion should be followed: it should fall rapidly initially, and more slowly thereafter A reasonable goal is to achieve an ex-cretion below 2 µmol/day [1] Copper depletion should be avoided: in the maintenance phase, 300 mg/day or even less can be sufficient

Tetrathiomolybdate, a copper chelating agent with greater affinity for copper than penicillamine, has been used mainly for initial decoppering of patients with neuro-logical symptoms [14] The initial detioration, often seen in patients treated with penicillamine, appears to occur less frequently Based on theoretical considerations and animal experiments, this agent could also have a place in the treat-ment of patients with liver disease, as current treatment modalities are suboptimal

In patients presenting with severe liver disease, cient experience is only available for penicillamine In this

suffi- Table 37suffi-.1suffi- Laboratory results in Wilson disease and

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group, at least half will require a liver transplant [10]

There-fore other treatment modalities have been tried, such as the

combination of zinc and penicillamine (or trien),

tetra-thiomolybdate, or addition of high dose vitamin E to the

copper chelating therapy Restoring normal plasma vitamin

E levels seems to protect liver mitochondria against

oxi-dative damage, and might be helpful in reversal of liver

damage However, none of these interventions have been

investigated in a substantial number of patients

37.1.2 Menkes Disease

Clinical Presentation

Symptoms generally appear at the age of 2 to 3 months, in

males, when the neurodegeneration provoked by the

di-sease becomes manifest with seizures and hypotonia [15]

Sometimes, non-specific signs can be present at birth,

in-cluding prematurity, large cephalhematomas, skin laxicity

and hypothermia, which are often not recognized as Menkes

disease at that time The hair, if present, can already exhibit

the characteristic pili torti, which will appear later on in all

Patients loose earlier developmental milestones and,

pro-gressively, hypotonia is replaced by spasticity A typical

facial appearance, with sagging cheeks and frontal bossing,

gradually becomes prominent Feeding difficulties,

vomit-ing and/or chronic diarrhea are common, and weight gain

is generally insufficient; nevertheless, linear growth is

rela-tively preserved The loose skin, which is particularly

pro-minent at the back of the neck and on the trunk, is a

con-sequence of defective collagen crosslinking, as are the

vas-cular tortuosity and bladder diverticula, which are present

in virtually all patients The latter are a frequent source

of infection Umbilical or inguinal hernias and/or a pectus

excavatum are also commonly encountered

Besides the more prevalent, severe Menkes phenotype,

less severe forms occur in 10–15% of the patients, with the

occipital horn syndrome being the mildest This syndrome

is characterized by connective tissue abnormalities with

minimal effects on neurodevelopment [16] Bone disease

with demineralization, deformities and exostoses,

partic-ularly at the occipital insertion of the paraspinal muscles

(hence its name), are characteristic Furthermore, patients

have urinary tract diverticuli, orthostatic hypotension and

chronic diarrhea Skin and joint laxicity are common, but

pili torti are rarely seen

In Menkes disease, cellular copper uptake is normal, but

copper cannot be exported from cells due to a defect of the

ATP7A protein, a copper transporter localized in the Golgi

network When intracellular copper rises, the normal ATP7A

protein is redistributed to a cytoplasmic vesicular

compart-ment and the plasma membrane [17] This renders copper

available for excretion and incorporation into the enzymes

that require copper When ATP7A is defective, these ways are blocked Consequently, copper efflux from the in-testinal cells is severely reduced, and insufficient copper will reach the circulation, pass the blood-brain barrier, and be incorporated into the cuproenzymes (although specific mutations exist in which this latter function is spared [18]) Among the affected copper-requiring enzymes in the brain are dopamine Ehydroxylase, which is essential for cate-cholamine biosynthesis, peptidyl glycine monooxygenase, involved in the processing of neuropeptide precursors, and cytochrome-c-oxidase Deficient activity of these enzymes is probably responsible for a significant part of the cerebral pathology in Menkes disease Dys function of Cu/Zn super-oxide dismutase seems to be compensated for by an in-creased activity of manganese superoxide dismutase, and as such probably does not contribute much to the neurodegen-eration Other enzymes influenced by copper deficiency are lysyloxidase, a critical enzyme in collagen cross-linking, and tyrosinase which is necessary for melanin formation

path-Genetics

A rare condition with an incidence of approximately 1:250,000 [15], Menkes disease is inherited as an X-linked

recessive trait It is caused by mutations in the ATP7A gene,

localized on chromosome Xq13.3, and expressed in all tissues, except liver Its protein product, ATP7A, is highly homologous to APT7B, the protein defective in Wilson di-sease The mutation spectrum in Menkes disease is wide, with lesions throughout the gene, without predominant mutations Seven patients have been reported with chromo-some abnormalities, mostly X-autosome translocations, visible on cytogenetic examination [19] Gross deletions in the gene, encompassing one or more exons, or even almost the whole coding sequence, are found in approximately 15% of the cases [19] Many single base pair changes or in-sertion/deletions of a few base pairs have been described The vast majority of these mutations are predicted to intro-duce a premature stop codon, probably resulting in a trun-cated, non-functional protein No straightforward genotype/phenotype correlations have been found so far, although most patients with the occipital horn syndrome have splice site mutations that potentially permit small amounts of

ATP7A to be transcribed [20].

Reduced levels of serum copper (<11 µmol/l) and serum ceruloplasmin (<200 mg/l) support the diagnosis, but are not specific, since infants in the first months of life gener-ally have low levels An abnormal ratio between catecho-lamine metabolites in plasma and cerebrospinal fluid seems

to be quite specific for Menkes disease [21], as is reduced urinary excretion of deoxypyridinoline, a metabolite formed

in the cross-linking of collagen [22] The copper retention, characteristic of Menkes disease, can be demonstrated by measuring the increased accumulation and reduced efflux

37.1 · Copper

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IX

472

of radiocopper in cultured fibroblasts [23] Final diagnosis

requires identification of the mutation

Prenatal diagnosis is preferably done by mutation

ana-lysis If the mutation is unknown DNA studies can still be

informative by using intragenic microsatellite markers

Carrier detection too should be done by DNA analysis,

especially as biochemical studies of copper accumulation in

fibroblasts can give false negative results due to random

inactivation of the X-chromosome

Classically, most patients die before three years of age due

to infections or vascular complications, although with

cur-rent medical care (improved feeding techniques) longer

survival is not uncommon Treatment is mainly

sympto-matic Nevertheless, since symptoms can be attributed to

insufficient copper for synthesis of cuproenzymes, a logical

approach would be to administer parenteral copper to

bypass the intestinal block, thereby making more copper

available for incorporation into cuproenzymes To this aim

a number of inorganic copper salts have been used without

clinical improvement However, treatment with copper

his-tidine, the physiological copper complex in humans, had

significant clinical effects in four patients, resulting in near

normal intellectual development, although the connective

tissue abnormalities persisted [24] Treatment in these

patients was initiated in the first few months of life, which

might have been a crucial factor, since copper treatment

of brindled mice, a model for Menkes disease, prevented

neurological damage, but only if started at day 7, while

administration at day 10 was ineffective Unfortunately

however, early treatment with copper histidine in a larger

series of 11 infants did not prevent death in 5 [15] This

therapy should nevertheless be considered for patients

identified at an early age When treatment is started after

the onset of symptoms, meaningful neurological recovery

seems impossible, although reduced irritability has been

reported Some evidence suggests that active ATP7A

pro-tein, albeit at a very low level, should be present for copper

histidine therapy to work [18] Still, 2 out of 4 patients

succesfully treated by Christodoulou et al [24] had

pre-mature stop codons in ATP7A, reasonably preventing any

functional protein to be synthesized

37.1.3 Other Copper Storage Disorders

Indian Childhood Cirrhosis (ICC), is characterized by a

nor-mal serum ceruloplasmin and an extremely high liver

cop-per (800–6500 µg/g dry weight) [25] It is seen solely in

young children The usual outcome is liver failure, although

this can be reverted by early decoppering therapy The

disorder is caused by an increased dietary copper intake in

genetically susceptible individuals, due to the use of copper

utensils when cooking milk Eliminating this practice has

virtually eradicated ICC Although the disease is confined

to India (hence its name) a similar disease has been seen in

Tyrol (Endemic Tyrolean Infantile Cirrhosis, ETIC), which is

also caused by using copper vessels when preparing milk [26] Sporadic cases from all over Europe and Northern

America have been described (generally labelled Idiopathic

Copper Toxicosis, ICT), mostly associated with a high copper

content of water in certain wells Given the similarities in clinical and biochemical characteristics it seems possible that all three entities are in fact one and the same disease Since many of the patients are from consanguineous fami-lies, it is probable that an autosomal recessive mutation is

responsible MURR1, the gene mutated in the copper

toxi-cosis seen in Bedlington terriers, has been excluded as a didate gene [27] A human equivalent of the copper storage disease in Bedlington terriers has not yet been identified

can-37.2 Zinc37.2.1 Acrodermatitis EnteropathicaClinical Presentation

Children with acrodermatitis enteropathica (AE) are healthy at birth, but develop symptoms some weeks after breast feeding has been stopped The most striking clinical feature is a severe dermatitis, classically localized at the acral and periorificial sites [28, 29] At onset, these skin lesions are erythematous, while after the first year of life pustular and hyperkeratotic changes become more prominent

Secondary infection with Candida Albicans and/or

Staphy-lococcus Aureus is not uncommon In addition to the skin

lesions, seen in almost all patients, intermittent diarrhea can develop, which in more advanced stages can progress

to intractable watery diarrhea and failure to thrive If treated, a significant fraction of the patients will have a gradual downhill course, although the majority seems to be able to survive without treatment into adulthood Mood changes are an early sign of zinc deficiency, presenting as apathy and irritability in infancy and later on as depression Infections are also frequent, and can be life threatening Other clinical features include alopecia and nail defor mities,

un-as well un-as ophthalmological symptoms such un-as blepharitis, conjunctivitis and photophobia

AE is caused by a partial block in the intestinal absorption

of zinc, as demonstrated in vivo by oral application of

65Zn [30] Likewise, zinc absorption in intestinal biopsies of patients is reduced [31] This defect is due to dysfunction of the protein involved in AE (ZIP4) The insufficient zinc absorption results in severe zinc deficiency with impair-ment of the function of many enzymes that have zinc as cofactor Tissues with a high cellular turnover, such as skin, intestine, and lymphoid system are most severely affected

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Genetics

AE is an autosomal recessive disease caused by mutations

in the SLC39A4 gene localized on chromosome 8q24.3

[32, 33] SLC39A4 encodes a zinc transporter, ZIP4, with

eight transmembrane domains, which probably form a zinc

channel, and is expressed at the apical membrane of the

enterocytes Over 20 mutations have been identified so far,

mainly in families from Europe, the Middle-East and

North-Africa [34]

In most patients, serum zinc levels are lower (7.1±5.0 µmol/l)

than normal (11.9–19.4 µmol/l) although values within

the normal range are found in at least 15 % of patients [29]

Measurements of zinc in other tissues, such as hair and red

or white blood cells, do not seem to improve diagnostic

accuracy In addition, several conditions, such as chronic

diarrhea due to other causes, can present with low serum

zinc Therefore the diagnosis of AE can never be based on

serum zinc Other tests may contribute to a certain extent:

low urinary zinc excretion (reflecting a low serum zinc

level), low serum alkaline phosphatase activity, changes

in the serum fatty acid profile, hypobetalipoproteinemia,

reduction of serum vitamin A, and elevation of blood

ammonia In many patients, both humoral and

cell-medi-ated immunity are depressed [35] Small bowel biopsy

gen-erally shows partial to subtotal villous atrophy and Paneth

cell inclusions on electron microscopy

The defect in active zinc transport can be proven with

radiolabeled zinc [30] However, since this might not be

available in most settings, a practical approach is to start

zinc therapy when the clinical diagnosis is suspected, and

await the response, which should occur within one week

When the clinical signs of acrodermatitis were equivocal

one may consider to temporarily withdraw zinc therapy

after some time to provoke a relapse, and in this way

dif-ferentiate between true AE (which will relapse quickly) and

acquired zinc deficiency

Before zinc supplementation was serendipitously found to

correct the abnormalities in AE, patients were given breast

milk and later on iodo-hydroxyquinolines This generally

resulted in partial or even total remission Zinc therapy was

introduced in 1975 [36], and is now used in all patient with

AE The usual dose is 150–400 mg zinc sulphate/day

(equi-valent to 35–90 mg elemental zinc/day), on which patients

will start to show clinical improvement within days

Simul-taneously, laboratory abnormalities such as serum zinc

levels, urinary zinc excretion and alkaline phosphatase

activity will normalize Generally, the initial dose can be

maintained throughout childhood, although some patients

may need an increase during their growth spurt After

pu-berty, the requirements for zinc may be lower, but during

pregnancy and lactation 400–500 mg zinc sulphate/day is

needed If the preparation causes gastric problems it may be encapsulated, or alternatively zinc gluconate or other zinc salts may be used As zinc therapy will decopper patients it

is necessary to monitor serum copper, and either reduce the dose of zinc or supplement copper if a deficiency is found Prognosis is excellent since the introduction of zinc sup-plementation

37.2.2 Zinc Deficiency in Breastfed Babies

Rarely, zinc deficiency with acrodermatitis can occur in breast-fed babies, especially in premature infants, as they have an increased zinc requirement in combination with a reduced capacity for zinc uptake in the gut [37] Although this condition responds rapidly to oral zinc supplements, it

is clearly different from AE, as it is seen exclusively during breast feeding and no impairment of intestinal zinc uptake can be found The deficiency is caused by reduced levels

of zinc in maternal milk, and its inheritance might be somal recessive [38]

auto-37.2.3 Hyperzincemia with

Hyper-calprotectinemia

Sampsom [39] described 5 patients with a new syndrome defined by high plasma zinc (77–200 µmol/l), recurrent in-fections, hepatosplenomegaly, arthritis, anemia and per-sistently raised concentrations of C-reactive protein The majority of these patients also had severe growth retarda-tion Levels of serum calprotectin, the major zinc binding protein of phagocytes, were more than 1000 times the upper limit of normal It is speculated that the very high con-centration of this protein results in the uncontrolled and harmful inflammatory reactions which characterize this syndrome, while the hyperzincemia is caused by the zinc capturing properties of calprotectin Inheritance of this syn-drome is not clear yet

37.2.4 Autosomal Dominant

Hyper-zincemia Without Symptoms

Elevated serum zinc (40–70 µmol/l) was described by Smith

et al in seven family members from one large pedigree The condition seems to be inherited in an autosomal dominant fashion Zinc concentrations in hair and erythocytes were normal, as was serum albumin, to which most of the excess zinc seemed to be bound There were no clinical symptoms, nor additional biochemical abnormalities, so this condition appears to be benign [40]

37.2 · Zinc

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Primary hypomagnesemia with secondary hypocalcemia

(HSH) is a rare autosomal recessive disorder It was first

recognized in 1965 and since then more than 50 infants

from all over the world have been described [41, 42]

Pa-tients commonly present in the first months of life with

generalized seizures or other symptoms of increased

neu-romuscular excitability such as irritability, poor sleeping,

muscle spasms and/or tetany

Primary hypomagnesemia is caused by impaired magnesium

uptake from the gut [43] A lowered renal threshold for

magnesium may be a contributing factor [44] The disease

is caused by a defect of a protein, TRPM6, a member of the

long transient receptor potential channel (TRPM) family,

which complexes with its closest homolog, TRPM7, to form

an ion-channel for magnesium at the cell surface Genetic

lesions of TPRM6 prevent assembly of this complex and

hence impair magnesium transport [45]

Severe hypomagnesemia blocks synthesis and/or

re-lease of parathormone In addition, when

hypomagnesem-ia is present, the administration of parathormone (PTH)

fails to induce a rise in serum calcium The hypocalcemia

in HSH is thus secondary to low parathormone levels in

combination with some form of end organ resistance

Genetics

Although a male/female ratio of 4 in the first reported

patients led to the initial proposal of X-linked inheritance,

further genetic investigations indicated autosomal recessive

inheritance This was clearly established when the gene

was localized to a small interval on chromosome 9q22

by homozygosity mapping in three interrelated Bedouin

kindreds Within this interval, two groups subsequently

identified mutations of the TRPM6 gene [44, 46] This gene

is expressed in the small and large intestine as well as in the

cells lining the distal tubules

Primary hypomagnesemia is characterized by a very low

serum magnesium (0.24 ± 0.11 mmol/l; normal 0.65–

1.20 mmol/l) in combination with a low serum calcium

(1.64 ± 0.41 mmol/l; normal 2.12–2.70 mmol/l) In the

pre-sence of serum hypomagnesemia, the urinary excretion of

magnesium is reduced, and PTH levels are inappropriately

low No evidence for malabsorption of other nutrients is

found, and renal function is not otherwise compromised

Untreated, the disorder will result in permanent cal damage or death However, magnesium supplementation corrects all clinical symptoms Initially, magnesium should

neurologi-be given intravenously The exact dose depends on the response of the patient, but is usually in the range of 0.5–1.5 ml/kg/day of a MgSO4 10% solution After stabilization, therapy can be continued orally in an amount that must be adjusted to the clinical response In a series of 15 patients the individual dosage varied between 0.7 and 3.5 mmol/kg/day

of elemental magnesium On this regimen, serum calcium normalized, but serum magnesium remain ed just below normal (0.53 ± 0.12 mmol/l) [42] Dividing oral magnesium supplementation in three to five doses will reduce fluctua-tions of serum magnesium and will prevent the develop-ment of chronic diarrhea in many, but not all patients The prognosis of primary hypomagnesemia is good if the diagnosis is made early; with treatment growth and development is normal However, patients who have fre-quent hypomagnesemia/hypocalcemia-induced convul-sions, either before or after the diagnosis is made, are at risk for developing psychomotor retardation

37.3.2 Hypomagnesemia with

Hyper-calciuria and NephrocalcinosisClinical Presentation

Over 80 patients with familial hypomagnesemia with percalciuria and nephrocalcinosis (FHHNC) have been reported [47, 48] Patients usually present during childhood with recurrent urinary tract infections, polyuria/polydipsia and/or hematuria At presentation, renal stones are seen

hy-in 13–25% of patients, while nephrocalchy-inosis, rare at sentation, will ultimately develop in all Clinical signs of hypomagnesemia such as seizures are less common, in line with only moderately depressed serum magnesium level Ocular involvement, e.g severe myopia and macular colo-bomata, is seen in a significant proportion of patients

pre-Metabolic Derangement

FHHNC is caused by a defect of paracellin-1, a protein calized in the thick ascending limb of Henle and the distal tubulus [49] This is where magnesium and calcium are pas-sively reabsorbed through the paracellular pathway Para-cellin-1, as part of the tight junction, is thought to contri-bute to the formation of a calcium and magnesium sensitive pore, through which this reabsorption takes place Distur-bance of this process leads to renal loss of magnesium and calcium, with secondary development of nephrocalcinosis and ultimately renal failure

lo-Genetics

The gene encoding paracellin-1, CLDN16 (formerly

PCLN-1), belongs to the claudin multigene family [49] and is

Trang 24

ized on chromosome 3q27-q29 So far, over 20 distinct

mutations have been identified, all single base pair changes

First degree family members of patients with FHHNC have

a tendency towards mild hypomagnesemia, hypercalciuria

and renal stone formation, indicating that heterozygosity for

CLDN16 mutations also predisposes to a mildly disturbed

renal handling of magnesium and calcium Interestingly,

CLDN16 is also expressed in the cornea and retinal

epithelium, thereby providing a link between defects in paracel

-lin-1 and the ocular pathology observed in some patients

Serum magnesium is low (mean 0.40 mmol/l, range 0.23–

0.61 mmol/l) [48], but less so than in primary

hypomag-nesemia Median calcium excretion is 10.0 mg/kg/24 h

(normal 4–6 mg/kg/24 h) Serum calcium is somewhat

below the lower level of normal in about half of the patients

Other biochemical abnormalities include hypocitraturia

and mild hyperuricemia At diagnosis, glomerular filtration

rate is already reduced in the majority of patients, and

sub-sequently deteriorates further Renal sonography shows

nephrocalcinosis, with its characteristic medullary

distri-bution, early in the course of the disease

Oral magnesium salts are used to supplement renal loss,

while thiazide diuretics are given to reduce calcium

excre-tion rates in an effort to prevent the progression of

nephro-calcinosis, which correlates with development of renal

failure However, these strategies do not seem to

significant-ly influence the progression of renal failure In a recent series

of 33 patients, all showed a deterioration in glome rular

fil-tration rate, and one third developed end stage renal disease

during adolescence [48] The median age at end stage renal

disease in this group was 14.5 years (range 5.5–37.5 years)

37.3.3 Isolated Dominant

Hypo-magnesemia

This disorder was first described by Geven et al in two Dutch

families [50] The index cases presented with generalized

convulsions, which led to the detection of the

hypomagnes-emia (0.40 mmol/l; normal 0.65–1.20 mmol/l) Subsequent

evaluation showed a reduced tubular threshold for

magne-sium in combination with lowered calcium ex cretion

Auto-somal dominant inheritance was evidenced by investigation

of the families of the two probands: the same combination

of hypomagnesemia and hypocalciuria was found in 22 out

of 47 family members Interestingly, none of them had any

clinical symptom of magnesium deficiency

In the two families, a locus for this disorder was mapped

to chromosome 11q23, revealing a similar haplotype for all

cases in both pedigrees, which suggests a common ancestor

Within the FXYD2 gene, residing in this interval, a

hetero-zygous G123A mutation was identified [51] This gene codes the J-subunit of a Na+K+-ATPase, which is expressed

en-in the distal tubules, the maen-in site of renal magnesium reabsorption Obviously normal function of the Na+K+-AT-Pase is necessary for adequate renal magnesium hand ling, and the mutation identified in the J-subunit specifically impairs its activity, accounting for the dominant negative effect of the mutation seen in these families The exact pathophysiologic mechanism leading to the low serum mag-nesium and the associated low urinary calcium excretion is not yet clear The disorder seems genetically heterogeneous since an American family with a similar phenotype has been described that does not map to the 11q23 locus [52]

37.3.4 Isolated Autosomal Recessive

Hypomagnesemia

Isolated autosomal recessive hypomagnesemia has been described in two children from a consanguineous family [53] Apart from the hypomagnesemia due to increased urinary magnesium excretion, no biochemical abnormality was report ed This disorder can be distinguished from autosomal dominant hypomagnesemia by the normal cal-cium excretion in the urine

37.3.5 Other Metals

Aceruloplasminemia is an autosomal recessive disorder characterized by accumulation of iron in liver, spleen, pan-creas, retina and basal ganglia by the fourth or fifth decade

of life [54, 55] Clinically the disease consists of the triad of adult-onset neurological disease (chorea, cerebellar ataxia, dystonia, Parkinsonism and psychiatric signs), retinal de-generation and diabetes mellitus The elevated iron con-centration is associated with increased lipid peroxidation suggesting that increased oxidative stress is involved in neuronal cell death More than 30 aceruloplasminemia-causing mutations in the ceruloplasmin gene have been identified Desferrioxamine, a high-affinity iron chelator, reduces body iron stores and may therefore ameliorate dia-betes as well as hepatic and neurological symptoms [56]

Manganese-related disease (prolidase deficiency) is cussed in 7 Chap 30; molybdenum-related disease (com-bined deficiency of sulfite oxidase and xanthine oxidase)

References

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IX

476

4 Bull PC, Thomas GR, Rommens JM et al (1993) The Wilson disease

gene is a putative copper transporting P-type ATPase similar to the

Menkes gene Nat Genet 5:327-337

5 Tanzi RE, Petrukhin K, Chernov I, et al (1993) The Wilson disease

gene is a copper transporting ATPase with homology to the Menkes

disease gene Nat Genet 5:344-350

6 Forbes JR, Cox DW (2000) Copper-dependent trafficking of Wilson

disease mutant ATP7B proteins Hum Mol Genet 9:1927-1935

7 Liu XQ, Zhang YF, Liu TT et al (2004) Correlation of ATP7B genotype

with phenotype in Chinese patients with Wilson disease World J

Gastroenterol 10:590-593

8 Stapelbroek JM, Bollen CW, Ploos van Amstel JK, et al (2004) The

H1069Q mutation in ATP7B is associated with late and neurologic

presenttaion in Wilson disease: results of a meta-analysis J Hepatol

41:758-763

9 Ferenci P, Caca K, Loudianos G et al (2003) Diagnosis and phenotypic

classification of Wilson disease Liver International 23:139-142

10 Nazer H, Ede RJ, Mowat AP, Williams R (1986) Wilson’s disease:

clini-cal presentation and use of prognostic index Gut 27:1377-1381

11 Walshe JM, Yealland M (1993) Chelation treatment of neurological

Wilson’s disease Q J Med 86:197-204

12 Dahlman T, Hartvig P, Löfholm M et al (1995) Long-term treatment

of Wilson’s disease with triethylene tetramine dihydrochloride

(trientine) Q J Med 88:609-616

13 Czlonkowska A, Gajda J, Rodo M (1996) Effects of long-term

treat-ment in Wilson’s disease with D-penicillamine and zinc sulphate

Neurol 243:269-273

14 Brewer GJ, Hedera P, Kluin KJ et al (2003) Treatment of Wilson

di-sease with Ammonium Tetrathiomolybdate III Initial therapy in a

total of 55 neurologically affected patients and follow-up with zinc

therapy Arch Neurol 60:379-385

15 Kaler SG (1998) Diagnosis and therapy of Menkes syndrome,

a genetic form of copper deficiency Am J Clin Nutr

67:1029S-1034S

16 Tsukahara M, Imaizumi K, Kawai S, Kajii T (1994) Occipital horn

syn-drome: report of a patient and review of the literature Clin Genet

45:32-35

17 Petris MJ, Mercer JFB (1999) The Menkes protein (ATP7A;MNK)

cycles via the plasma membrane both in basal and elevated

extra-cellular copper using a C-terminal di-leucine endocytic signal Hum

Mol Genet 8:2107-2115

18 Kim BE, Smith K, Petris MJ (2003) A copper treatable Menkes

di-sease mutation associated with defective trafficking of a

function-al Menkes copper ATPase J Med Genet 40:290-295

19 Tümer Z, Møller LB, Horn N (2003) Screening of 383 unrelated

patients affected with Menkes disease and finding of 57 gross

dele-tions in ATP7A Hum Mutat 22:457-464

20 Møller LB, Tümer Z, Lund C et al (2000) Similar splice-site mutations

of the ATP7A gene lead to different phenotypes: classical Menkes

disease or occipital horn syndrome Am J Hum Genet

66:1211-1220

21 Kaler SG, Goldstein DS, Holmes C et al (1993) Plasma and

cerebro-spinal fluid neurochemical pattern in Menkes disease Ann Neurol

33:171-175

22 Kodoma H, Sato E, Yanagawa Y et al (2003) Biochemical indicator

for evaluation of connective tissue abnormalities in Menkes’

di-sease J Pediatr 142:726-728

23 Tümer Z, Horn N (1998) Menkes disease: Underlying genetic defect

and new diagnostic possibilities J Inherit Metab Dis 21:604-612

24 Christodoulou J, Danks DM, Sarkar B et al (1998) Early treatment

of Menkes disease with parenteral cooper-histidine: long-term

follow-up of four treated patients Am J Med Genet 76:154-164

25 Tanner MS (1998) Role of copper in Indian childhood cirrhosis Am

J Clin Nutr 67:1074S-1081S

26 Müller T, Feichtinger H, Berger H, Müller W (1996) Endemic Tyrolean

infantile cirrhosis: an ecogenetic disorder Lancet 347:877-880

27 Müller T, van de Sluis B, Zhernakova A et al (2003) The canine

cop-per toxicosis gene MURR1 does not cause non-Wilsonian hepatic

copper toxicosis J Hepatol 38:164-168

28 Aggett PJ (1983) Acrodermatitis enteropathica J Inherit Metab Dis

6:39S-43S

29 Van Wouwe JP (1989) Clinical and laboratory diagnosis of

acroder-30 Lombeck I, Schnippering HG, Ritzl F et al (1975) Absorption of zinc

in acrodermatitis enteropathica Lancet i:855

31 Atherton DJ, Muller DPR, Aggett PJ, Harries JT (1979) A defect in zinc uptake by jejunal biopsies in acrodermatitis enteropathica Clin Sci 56:505-507

32 Küry S, Dréno B, Bézieau S et al (2002) Identification of SLC39A4, a gene

involved in acrodermatitis enteropathica Nat Genet 31:239-240

33 Wang K, Zhou B, Kuo YM et al (2002) A novel member of a zinc transporter family is defective in acrodermatitis enteropathica Am

J Hum Genet 71:66-73

34 Küry S, Kharfi M, Kamoun R et al (2003) Mutation spectrum of human SLC39A4 in a panel of patients with Acrodermatitis Entero-

pathica Hum Mutat 22:337-338

35 Antilla PH, Von Willebrand E, Simell O (1986) Abnormal immune responses during hypozincaemia in acrodermatitis enteropathica Acta Paediatr Scand 75:988-992

36 Neldner KH, Hambidge KM (1975) Zinc therapy of acrodermatitis enteropathica N Engl J Med 292:879-882

37 Stevens J, Lubitz L (1998) Symptomatic zinc deficiency in breast-fed term and premature infants J Paed Child Health 34:97-100

38 Sharma NL, Sharma RC, Gupta KR, Sharma RP (1988) Self-limiting acrodermatitis enteropathica A follow-up study of three interrelated families Int J Dermatol 27:485-486

39 Sampsom B, Fagerhol MK, Sunderkötter C et al (2002) aemia and hypercalprotectinaemia: a new disorder of zinc metabolism Lancet 360:1742-1745

Hyperzinc-40 Smith JC, Zeller JA, Brown ED, Ong SC (1976) Elevated plasma zinc:

a heritable anomaly Science 193:496-498

41 Dudin KI, Teebi AS (1987) Primary hypomagnesaemia A case report and literature review Eur J Pediatr 146:303-305

42 Shalev H, Phillip M, Galil A et al (1998) Clinical presentation and outcome in primary familial hypomagnesaemia Arch Dis Child 78:127-130

43 Milla PJ, Aggett PJ, Wolff OH, Harries JT (1979) Studies in primary hypomagnesaemia: evidence for defective carrier-mediated small intestinal transport of magnesium Gut 20:1028-1033

44 Walder RY, Landau D, Meyer P et al (2002) Mutation of TRPM6 causes

familial hypomagnesemia with secondary hypocalcemia Nat Genet 31:171-174

45 Chubanov V, Waldegger S, Schnitzler MM et al (2004) Disruption of TRPM6/TRPM7 complex formation by a mutation in the TRPM6

gene causes hypomagnesemia with secondary hypocalcemia Proc Natl Acad Sci USA 101:2894-2899

46 Schlingmann KP, Weber S, Peters M et al (2002) Hypomagnesemia with secondary hypocalcemia is caused by mutations in TRPM6,

a new member of the TRPM family Nat Genet 31:166-170

47 Benigno V, Canonica CS, Bettinelli A et al (2000) aemia-hypercalciuria-nephrocalcinosis: a report of nine cases and

Hypomagnes-a review Nephrol DiHypomagnes-al TrHypomagnes-ansplHypomagnes-an 15:605-610

48 Weber S, Schneider L, Peters M et al (2001) Novel paracellin-1 tions in 25 families with familial hypomagnesemia with hypercalciuria and nephrocalcinosis J Am Soc Nephrol 12:1872-1881

muta-49 Simon DB, Lu Y, Choate KA et al (1999) Paracellin-1 a renal tight junction protein required for paracellular Mg2+ resorption Science 285:103-106

50 Geven WB, Monnens LA, Willems HL et al (1987) Renal magnesium wasting in two families with autosomal dominant inheritance Kidney Int 31:1140-1144

51 Meij IC, Koenderink JB, van Bokhoven H et al (2000) Dominant isolated renal magnesium loss is caused by misrouting of the

Na + K + -ATP-ase γ-subunit Nat Genet 26:265-266

52 Kantorovich V, Adams JS, Gaines JE et al (2002) Genetic neity in familial renal magnesium wasting J Clin Endocrinol Metab 87:612-617

heteroge-53 Geven WB, Monnens LAH, Willems JL et al (1987) Isolated autosomal recessive renal magnesium loss in two sisters Clin Genet 32:398-402

54 Miyajima H, Nishimura Y, Mizoguchi K et al (1987) Familial plasmin deficiency associated with blepharospasm and retinal degeneration Neurology 37:761-767

apocerulo-55 Kono S, Miyajima H (2006) Molecular and pathological basis of aceruloplasminemia Biol Res 39:15-23

56 Miyajima H, Takahashi Y, Kamata T et al (1997) Use of desferrioxamine

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X Organelle-Related

Disorders: Lysosomes, Peroxisomes, and Golgi and Pre-Golgi Systems

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