Handbook of Clinical Neurology, Vol. 120 (3rd series) Neurologic Aspects of Systemic Disease Part II Jose Biller and Jose M. Ferro, Editors © 2014 Elsevier B.V. All rights reserved

Chapter 57

Disorders of heavy metals FRANCE WOIMANT* AND JEAN-MARC TROCELLO French National Wilson’s Disease Centre (CNR Wilson), Lariboisire Hospital, Paris, France

INTRODUCTION Heavy metals and trace elements play an important role in relation to the physiology and pathology of the nervous system. Metals are present in air, water, and diet. Input sources in humans are mainly respiratory and digestive and rarely dermal. Some metals have no biologic function but are toxic where there is excessive exposure (e.g., cadmium, lead, aluminum, mercury, manganese). The main features of these metal toxicities are summarized in Table 57.1. Other metals, such as iron and copper, are involved in biologic processes as cofactors of numerous enzymes. Disorders of metabolism of these metals will lead to various neurologic diseases.

COPPER DISORDERS Copper is an essential trace element, necessary for the activity of many key enzymes including superoxide dismutase, lysyloxidase, dopamine b-hydroxylase, cytochrome oxidase, and ceruloplasmin. Copper disorders can be divided into two groups: ● ●

ATP7A- or ATP7B-related inherited copper transport disorders acquired diseases associated with copper deficiency or copper excess.

Copper metabolism The main regulators of cellular copper metabolism are the copper-transporting P-type ATPases: ATP7A and ATP7B. Their transport activity is crucial for central nervous system (CNS) development, liver function, connective tissue formation, and many other physiologic processes (Barnes et al., 2005). The physiologic importance of Cu-ATPases is illustrated by the deleterious consequences of mutations or deletions in the gene encoding these proteins,

essentially Menkes disease for ATP7A and Wilson disease for ATP7B. Both Cu-ATPases have two main roles in cells, namely to provide copper to essential cuproenzymes and to mediate the excretion of excess intracellular copper (Lutsenko et al., 2007). They are expressed in most tissues. Their roles are probably not the same in all organs. In intestine where the two Cu-ATPases are expressed, ATP7B does not compensate for the deficiency of ATP7A function (Menkes disease). In contrast, in the cerebellum of ATP7B
/
mice, ATP7A appears to substitute for missing ATP7B (Barnes et al., 2005). The daily intake of copper is about 3 mg. Copper is absorbed by the intestinal cells and stored with metallothioneins in a nontoxic form (Fig. 57.1). It is exported from the enterocytes into the blood by Cu-ATPase ATP7A and transported via the portal vein to the liver, which is the main organ responsible for copper homeostasis. In hepatocytes and other cells, copper is absorbed by copper transporter 1 (CTR1) (Vulpe et al., 1993). In the cytoplasm, it is bound to metallothionein or to copper-specific chaperone proteins (CCS, ATOX 1, and COX17). Thus, cells are protected from the toxic effects of free copper. CCS and COX17 guide copper to mitochondria and ATOX1 to the trans-Golgi network (TGN). Under basal conditions, ATP7A and ATP7B are essentially localized within the TGN. Under increased copper concentrations, ATP7A is translocated to the vesicles or to the plasma membranes, allowing excretion of excess intracellular copper; in hepatocytes, ATP7B is relocalized toward canalicular membrane allowing excretion of copper into the bile and subsequently to feces (de Bie et al., 2007). In liver, ATP7B mediates also the incorporation of copper into the copper-dependant ferroxydase ceruloplasmin (CP), which is subsequently secreted into the blood. CP is the major copper-containing protein; however, it does not seem to play an essential role in copper metabolism. (Valentine and Gralla, 1997).

*Correspondence to: Dr France Woimant, Neurology Department, CNR Wilson, Lariboisie`re Hospital, 2 rue Ambroise Pare´. 75010 Paris, France. Tel: þ33-1-49-95-65-27, Fax: þ33-1-49-95-65-34, E-mail: [email protected]

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Table 57.1 Main features of excessive exposure to heavy metals Metal

Mode of intoxication

General features

Neurological features

Diagnosis

Cadmium (Sethi and Khandelwal, 2006) Lead (Brodkin et al., 2007)

Inhalation of fumes

Nephropathy Decreased bone density

Urinary cadmium level

Occupational exposure, (manufacturing of batteries, pigments, solder . . .) Diet Dental amalgam Fish consumption

Abdominal pain, anorexia, nausea and constipation, nephropathy, anemia with basophilic stippling

Occupational exposure Dialysis Intravenous boiled methadone Intravenous methcathinone Inhalation of fumes Acquired hepatocerebral degeneration (CAHD)

Bone pain, ostemalacia, pathological fractures, microcytic anemia

Neuropsychiatric manifestations, polyneuropathy Headache, concentration and memory difficulties, sleep disturbances, peripheral neuropathy Irritability, concentration and memory difficulties, sleep disturbances, sensory peripheral neuropathy Seizures, myoclonus, personality changes, tremor, ataxia Personality changes, irritability, sleep disturbances, Parkinsonism, chorea, dystonia, ataxia, tremor, myoclonus

Serum manganese level Hypersignal on T1-weighted brain MRI in globus palidus

Mercury (Brodkin et al., 2007)

Aluminum (Letzel et al., 2000; Yong et al., 2006)

Manganese (Jog and Lang, 1995; Stepens et al., 2008)

Gingivitis, stomatitis, hypersalivation, metallic taste, nephropathy

Weakness

Copper from Diet

Acquired copper toxicosis - Acute copper poisoning - chronic copper toxicosis

Metallothionein

CTR1

ATP7 A

Acquired copper deficiency - Malabsorption - Inflammatory disease - Drugs - Zinc excess

Atox 1

ATP7A-related copper transport disorders - Menkes disease - Occipital horn syndrome - ATP7A-related distal motor neuropathy (DMN)

Nucleus Enterocyte

Portal vein

Aceruloplasminemia

CTR1 ATP7 B Cp

Atox 1

Cp

Wilson’s disease Nucleus

Ferroxydasic activity

ATP7 B

Vesicle

Excretion of copper into the bile

Metallothionein Hepatocyte

CTR: copper transporter; ATOX 1: copper specific chaperone protein; ATP7: copper-transporting P-type ATPases; Cp: ceruloplasmin (Apoceruloplasmin, without copper, holoceruloplasmin with copper)

Fig. 57.1. Copper metabolism and disorders.

Blood lead level

Blood and urine mercury levels

Serum aluminium level

DISORDERS OF HEAVY METALS

ATP7A- or ATP7B-related inherited copper transport disorders ATP7A-RELATED COPPER TRANSPORT DISORDERS Menkes disease (MD), occipital horn syndrome (OHS), and ATP7A-related distal motor neuropathy are caused by mutations in the ATP7A gene, which is located on the long arm of the X chromosome (Xq13.1-q2). Over 200 mutations have been identified, among which are small deletions/ insertions, nonsense mutations, missense mutations, and splice site mutations. In one-third of cases, MD is caused by de novo mutations. Splice site mutations appear to be over-represented in patients with OHS (de Bie et al., 2007). ATP7A-related distal motor neuropathy involves unique missense mutations (Kennerson et al., 2010). Menkes disease (MD), also known as kinky hair disease, was first described by Menkes in 1962 (Menkes et al., 1962). Some 10 years later, Danks et al. (1972) found serum copper and ceruloplasmin levels to be reduced and suggested that the primary defect in Menkes disease involved copper metabolism. In 1993, three teams isolated the gene that encodes Cu-ATPase, the ATP7A gene (Chelly et al., 1993; Mercer et al., 1993; Vulpe et al., 1993). Defective ATP7A function results in: ● ●

dysfunction of several copper-dependant enzymes, due to inability to load these enzymes with copper reduction of elimination of copper from cells, and almost all the tissues except for liver and brain will accumulate copper to abnormal levels. As intestinal copper absorption is impaired, the copper level does not reach a toxic state (T€ umer and Mller, 2010). In the liver, low levels of copper are explained by the fact that ATP7A is not the main liver copper transporter.

The incidence of MD is estimated to range between 1:40 000 and 1:350 000. (Mller et al., 2009). Clinical features include progressive neurologic deterioration and marked connective tissue dysfunction. As in linked-X disease, MD typically occurs in males. Usually, patients are born at term. Developmental regression appears within the first 2 months of life as axial hypotonia,

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seizures, and psychomotor retardation. The appearance of the hair is often remarkable, being sparse, hypopigmented, and kinky (pili torti). Ligamentous hyperlaxity, skin hyperelasticity, and bladder and ureter diverticula are often associated. Skeletal findings are metaphyseal spurs and long bone fractures. Autonomic dysfunction, including temperature instability and hypoglycemia, may be present in the neonatal period. Because of abnormal development of the vessel walls (fragmentation of the internal elastic lamina and thickening of the intima), arterial tortuosities and aneurysms are frequent, leading to cerebral infarcts and intracranial and intestinal bleeds (Horn et al., 1992). There is important variability in the severity of clinical expression of MD. Mild MD forms with later onset, moderate symptoms, and longer survival are observed in 5–10% of the patients. Diagnosis of MD can be established by detecting low levels of copper (and ceruloplasmin) in the serum, and high levels in cutaneous fibroblasts (Table 57.2). However, in the neonatal period serum copper and ceruloplasmin should be interpreted with caution, as their levels are low in healthy newborns. In this period, plasma catecholamine analysis (ratio of dihydroxyphenylalanine to dihydroxyphenylglycol) indicative of dopamine b-hydroxylase deficiency allows a rapid diagnosis (T€ umer and Mller, 2010). The diagnosis can be confirmed by identification of the gene mutation, but because of the large size of the gene and the high number of mutations, genetic analysis may take time. Genetic analysis also allows screening of carrier females and antenatal diagnosis through chorionic villus sampling. Parenteral administration of histidine-copper improves the neurologic outcome and increases lifespan. The prognosis remains inevitably poor. The age at which treatment is started, the severity of the disease, and the presence of at least partially functional ATP7A seem to be among the main determinants for the prognosis. Death usually occurs by 3 years of age, but some patients survive to 10 years or even more (T€ umer and Mller, 2010). Occipital horn syndrome (or X-linked cutis laxa, or Ehlers–Danlos syndrome type 9) is a less severe allelic

Table 57.2 Cupric tests in copper disorders

Serum Cu Urinary Cu Serum Cp

Menkes disease

Occipital horn disease

ATP7A related neuropathy

Wilson’s disease

Copper deficiency

Aceruloplasminemia

& & &

NI / & NI / & NI / &

NI NI NI

& % &

& & &

& NI &&

Cu: copper; Cp: ceruloplasmin

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variant of the MD syndrome (Kaler, 1998). Its incidence is unknown. Individuals typically live to at least midadulthood. Its principal clinical features are related to connective tissue, with bladder diverticula, inguinal hernias, skin laxity and hyperelasticity. Neurologic abnormalities are far less severe or even absent. Characteristic is the formation of occipital exostoses resulting from calcification of the trapezius and sternocleidomastoid muscles at their attachments to the occipital bone (Peltonen et al., 1983). The symptoms result from alterations in the function of copper-dependant enzymes, in particular that of lysyloxidase. Serum copper and ceruloplasmin levels are normal or low (Table 57.2). A newly discovered allelic variant associated with ATP7A is ATP7A-related distal motor neuropathy (DMN). It is an adult-onset distal motor neuropathy resembling Charcot–Marie–Tooth disease, and characterized by atrophy and weakness of distal muscles in hands and feet. There is no sign of systemic copper deficiency. Serum copper and ceruloplasmin levels are normal (Table 57.2) (Kaler, 2010).

ATP7B-RELATED COPPER TRANSPORT DISORDERS Wilson disease (WD) is caused by mutations in the ATP7B gene, located on chromosome 13 (q14.3.-q21.1). Although missense mutations are most frequent, deletions, insertions, nonsense, and splice site mutations have been reported. More than 400 mutations and 100 polymorphisms have been documented. In the US and northern Europe, two mutations, His1069Gln and Gly1267Arg, represent 38% of identified mutations (Thomas et al., 1995). The worldwide prevalence of WD is estimated in the order of 30 per 1 million, with a carrier frequency of approximately 1 in 90. WD is more frequent in countries in which consanguineous marriages are common (Figus et al., 1995). In 1912, in a doctoral thesis published in Brain, S.A. Kinner Wilson gave a very detailed description of both the clinical and pathologic characteristics of “Progressive lenticular degeneration: a familial nervous disease associated with cirrhosis of the liver” (Wilson, 1912; Walshe, 2006). The therapeutic area of WD began with Cumings in 1948; he suggested an etiologic role for copper and proposed chelating therapy with British antiLewisite (BAL or dimercaptopropanol) (Cumings, 1948). In 1956, Walshe proposed the use of D-penicillamine (Walshe, 1956), and in 1961, Schouwink the use of zinc salts as decoppering agents (Hoogenraad, 2001). In 1985, Frydman reported that the WD gene was located on chromosome 13 (Frydman et al., 1985). The identification of the gene, ATP7B, was realized by three separate teams during year 1993 (Bull et al., 1993; Tanzi et al., 1993; Yamaguchi et al., 1993).

Physiopathology Defective ATP7B function leads a reduction of conversion of apoceruloplasmin into ceruloplasmin and of copper release into the bile, resulting in important copper accumulation in the liver, very low levels of copperbound ceruloplasmin in the serum, and low biliary copper. When the hepatic copper storage capacity into metallothioneins is exceeded, unbound copper spills out of the liver and is deposited in other organs and tissues (Trocello et al., 2010a). Clinical features WD begins with a presymptomatic period during which there is accumulation of copper in the liver that will cause hepatitis and, without treatment, will progress to liver cirrhosis and development of extrahepatic symptoms. In our series of 385 patients, the initial manifestations are hepatic dysfunction in 44% of cases, and neurologic or neuropsychiatric symptoms in 39%. Other patients present with Kayser–Fleischer rings, hematologic or renal syndromes. The mean age of first hepatic symptoms is 17 years and for initial neurologic symptoms 23 years. It is rare that the first symptoms appear before 5 years, but WD has been diagnosed as early as 2 years (Beyersdorff and Findeisen, 2006), and as late as 72 years in a patient with Kayser–Fleischer rings (Czonkowska et al., 2008). WD can be asymptomatic with abnormal serum aminotransferases or hemolytic anemia found incidentally. Isolated splenomegaly or thrombopenia due to clinical unapparent cirrhosis with portal hypertension or detection of Kayser–Fleischer rings can also reveal the disease. Nonspecific symptoms are often the first manifestations: nausea, anorexia, fatigue, abdominal pain, amenorrhea, or repeated miscarriages. Disease may also present as acute transient hepatitis that can mimic autoimmune hepatitis, as chronic liver disease and cirrhosis either compensated or decompensated, or as fulminant hepatic failure with an associated Coombs-negative hemolytic anemia and acute renal failure (Ala et al., 2007). First neurologic symptoms of WD include changes in behavior, deterioration in school or professional work, in handwriting, dysarthria, drooling, tremor, or dystonia. The main neurologic manifestations can be roughly distinguished in three movement disorder syndromes (Trocello and Woimant, 2008): ●

dystonic syndrome characterized by choreoathetosis and dystonic postures (Lorincz, 2010). It starts with focal signs or functional dystonia and may progress to generalized dystonia. It often affects facial muscles, resulting in a fixed sardonic smile. Dystonic

DISORDERS OF HEAVY METALS

●

●

dysarthria affects laryngeal or pneumophonatory muscles. Choreic movements are often associated. parkinsonian syndrome with rigidity and akinesia. Hypomimia is present, as well as dysarthria with hypophonia, tachylalia. Gait is unsteady with small steps, reduced postural reflexes, festination, and freezing. Rest tremor is rarely isolated. postural and action tremor with high amplitude and low frequency. Its proximal component can be well observed when a patient’s arms are outstretched, showing the “wing-beating tremor.” It is sometimes associated with cerebellar syndrome.

Behavioral abnormalities are common at diagnosis, particularly in case of neurologic presentation. Symptoms are apathy, irritability, aggressive behavior, obsession, and disinhibition. A recent study reported psychiatric disorders in 24% of patients: bipolar affection (18%), major depression (4%), and dysthymia (2%) (Shanmugiah et al., 2008). The frontier between subcortical disorders and psychiatric disease is imprecise. Many patients suffer from a dysexecutive syndrome linked to subcorticofrontal lesions. Corneal Kayser– Fleischer (KF) rings are detected by slit-lamp examination (Fig. 57.2). They are, in our experience, invariably present in patients with neurologic symptoms. They are detected in 42–62% of the hepatic forms (Roberts and Schilsky, 2008). They are very suggestive of WD, even if they are also seen in other chronic hepatopathies (Suvarna, 2008). Other ophthalmic findings are sunflower cataracts that do not impair vision and oculomotor abnormalities; vertical eye movements, in particular vertical pursuits, are often impaired (Ingster-Moati et al., 2007). Other extrahepatic features include renal manifestations (as lithiasis), osteoarticular disorders, myocardial abnormalities, endocrine disturbances (Hoogenraad, 2001).

Fig. 57.2. Corneal Kayser–Fleischer ring (Wilson disease).

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Wilson disease diagnosis There is no single test for the diagnosis of WD; its assessment should include history, clinical, biologic, radiologic and sometimes histologic data. WD is characterized by low serum ceruloplasmin and total copper concentrations and increased urinary copper excretion (Table 57.2). Normal serum ceruloplasmin concentration does not exclude the diagnosis, since about 10% of WD patients and up to 50% of patients with severe liver disease have normal serum ceruloplasmin (Steindl et al., 1997). The level of serum ceruloplasmin is low in healthy newborns, and in Menkes disease, aceruloplasminemia, nephritic syndrome, copper deficiencies, and severe chronic liver disease of any cause (Pfeiffer, 2007). Some 20% of subjects heterozygous for the Wilson disease gene have reduced levels. In contrast, serum ceruloplasmin concentrations are elevated by inflammation states, by estrogen supplementation, and during pregnancy. Therefore, the interpretation of serum ceruloplasmin is often difficult (Chappuis et al., 2005). Serum copper level measures bound and free serum copper. Copper bound to ceruloplasmin normally represents about 90% of total serum copper. In WD, the total serum copper is usually decreased in proportion to the decreased ceruloplasmin. In cases of acute hepatitis or hemolysis, however, the total serum copper concentration can be increased due to important release of copper from liver or red blood cells. It has been proposed that the level of free copper should be calculated using the following formula: nonbound ceruloplasmin copper (mmol/L) ¼ total serum copper (mmol/L)
0.047  serum holoceruloplasmin (mg/L). The result is dependent on the adequacy of the methods for measuring both serum copper and ceruloplasmin (Twomey et al., 2008) and so this method is not of great value in WD diagnosis or in monitoring therapy. Relative exchangeable copper (REC) (exchangeable copper/total serum copper) is probably the most useful screening method (El Balkhi et al., 2011). The majority of patients with WD have a level of urinary copper above 100 mg by 24 hours. Increased urinary copper levels are not specific for WD; they can be found in disorders with severe proteinuria and in heterozygotes for the Wilson disease gene. A provocative test for urinary copper excretion using D-penicillamine can be a useful diagnostic adjunctive test (Foruny et al., 2008). In suspected WD, if the clinical and biochemical parameters are not supportive, a hepatic biopsy with a measurement of its copper content can be carried out. The hepatic copper value in untreated WD patients is above 250 mg by gram of dry weight. Interpretation can be difficult because increased liver copper concentrations can be seen in long-term cholestasis, and hepatic copper concentrations can be falsely low in patients with extensive fibrosis (Ferenci et al., 2005).

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ATP7B mutation analysis makes an important contribution to the diagnosis. Unfortunately, the sequencing of the complete coding sequence and of the intron-exon junction of the gene allows confirmation of the diagnosis of WD in only 80% of the cases (Trocello et al., 2009). In our experience, brain magnetic resonance imaging (MRI) is always abnormal in patients with neurologic symptoms. It reveals widespread atrophy and on T2weighted, FLAIR, and diffusion sequences shows bilateral, symmetric high-signal intensity mainly in the globus pallidus, putamen, thalamus, mesencephalon, pons, and dentate nucleus (Fig. 57.3) (Sener, 2003). A characteristic feature is the “face of the giant panda” sign on FLAIR and T2-weighted images of the midbrain. White matter changes are observed in about 25–40% of patients, often asymmetric with frontal predilection; when these lesions are extensive, they are associated with worse prognosis (Mikol et al., 2005). Abnormalities in the posterior part of the corpus callosum are frequent, observed in 23% of cases (Trocello et al., 2010b). Cortical lesions are infrequent. In patients with hepatic symptoms, a decrease of the apparent diffusion coefficient in the putamen can be detected before the occurrence of neurologic manifestations (Favrole et al., 2006). Patients with hepatic insufficiency may have high-signal intensity lesions in the basal ganglia on T1-weighted images (van Wassenaer-van Hall et al., 1996). Wilson disease treatment Wilson disease was fatal before the use of the first chelating agents. Low copper diet is recommended; chocolate, liver, nuts, and shellfish containing high concentrations of copper should be avoided, as should alcohol because of its liver toxicity. The drug treatment is particularly effective if it is administered at an early stage of the disease and followed for life. It is based on the use of copper chelators to promote copper excretion from the body (D-penicillamine and

A

B

triethylenetetramine or Trientine) and zinc salts (Wilzin®) to reduce copper absorption. The improvement is not immediate and may appear only after 3–6 months of therapy. Furthermore, at the institution of treatment there is a risk of a worsening of the hepatic and/or neurologic disease (Woimant et al., 2006). This deterioration is observed with all treatments, more frequently under D-penicillamine (13.8%) than under triethylenetetramine (8%) or zinc salts (4.3%) (Merle et al., 2007). A gradual institution of treatment might prevent this. Initial neurologic worsening could be due to the mobilization of hepatic copper into the circulation and its redistribution in the brain. It can also be observed in very acute forms as treatment might act too slowly. In rare cases, this deterioration is not reversible, the disease continuing to evolve under treatment. Tetratiomolybdate could have a lower risk of neurologic deterioration since it acts by forming a tripartite complex with copper and protein, either in the intestinal lumen where it prevents copper absorption or in the circulation where it makes the copper unavailable for cellular uptake (Brewer et al., 2006). This drug remains an experimental agent and is unavailable for general use. The usual daily dose of D-penicillamine is 750–1500 mg/day. Regular monitoring of full blood count and urinary protein is recommended because of possible side-effects which occur in 30% of patients. Most of them are reversible when the drug is withdrawn. Early sensitivity reactions, with fever, rash, lymphadenopathy, proteinuria, or bone marrow depression with neutropenia, and thrombocytopenia, may occur during the first weeks. Later adverse effects include lupus-like syndrome, Goodpasture’s syndrome, and myasthenia gravis. Long-term use of D-penicillamine induces changes in elastic tissues and in collagen and might cause skin lesions including elastosis perforans serpiginosa. The usual daily dose of triethylenetetramine is 750– 1500 mg/day. Side-effects are rare but include lupus-like reactions and reversible sideroblastic anaemia (Pfeiffer,

C

D

Fig. 57.3. Wilson disease, FLAIR MRI. Hypersignals in lenticular and caudate nuclei (A), thalami and corpus callosum (B), dentate nuclei (C), and mesencephal aspect of the “face of the giant panda” sign (D).

DISORDERS OF HEAVY METALS 2007). The dose of zinc for adults is 150 mg/day of elemental zinc. Zinc is generally well tolerated although dyspepsia may occur; elevation in serum amylase and lipase, without clinical and radiologic evidence of pancreatitis, has been reported. These treatments are monitored by measuring 24 hour urinary copper excretion: high during D-penicillamine and Trientine therapy, and less than 2 micromoles per day during zinc therapy. The best therapeutic approach remains controversial because no controlled trials have compared these treatments. A recent systematic review showed no obvious differences in clinical efficacy of D-penicillamine and zinc as initial therapy in WD. The two drugs controlled the disease effectively in a majority of patients, with the best results being in presymptomatic patients (Wiggelinkhuizen et al., 2009). Therefore, the choice of drug varies from center to center, based on the opinion of the physicians and on drug availability and costs. When the disease is stabilized after several years of treatment, the initial treatment with chelator may be continued on a lower dosage or shifted to treatment with zinc salts because they are better tolerated. During pregnancy, the treatment by chelating agents or zinc salts must be maintained; however, dosages of drugs should be reduced and adapted to copper urinary excretion. The most difficult question is how to manage patients who deteriorate despite medical therapy. Liver transplantation is the treatment for acute fulminant liver failure and for decompensated cirrhosis unresponsive to medical treatment. In cases of neurologic deterioration, the decision on whether to continue with the chosen treatment or change to adding another agent is difficult. Indication of liver transplantation is still a matter of controversy in cases of neurologic worsening without liver failure. In the study by Medici and colleagues, 70% of these patients improved after transplantation (Medici et al., 2005). The follow-up of WD patients is essential to make sure of observance, efficiency, and tolerance of the treatment. A clinical or biologic deterioration may provoke poor compliance with treatment. In the longer term, patients may develop hepatocellular carcinoma (Walshe et al., 2003). Family screening is essential in this autosomal recessive disease; indeed, early diagnosis of WD is essential as treatment is more effective if initiated early. The probability of finding a homozygote in siblings is 25%. The interpretation of cupric analysis can be difficult in WD heterozygotes and therefore molecular genetic analyses are very important. For families in which both mutations have been detected in the index patient, these mutations are researched in siblings. In the absence of indications on the mutations, haplotype analysis of

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markers around the ATP7B gene on chromosome 13 is used (Chappuis et al., 2005).

Acquired diseases associated with copper deficiency or copper excess ACQUIRED COPPER DEFICIENCY Copper deficiency is exceptional in developed countries because copper is present in numerous foods. However, nutritional copper deficiency is well documented in premature newborns and in patients maintained on parenteral nutrition for long periods of time without copper supplementation. Copper malabsorption is observed in other conditions such as upper gastrointestinal surgery or inflammatory bowel disease. An unusual cause of acquired copper deficiency is excess zinc intake, for example chronic use of denture cream containing zinc (Nations et al., 2008; Trocello et al., 2011). Manifestations of acquired copper deficiency are almost always neurologic and hematologic (Madsen and Gitlin, 2007). Patients present with a spastic gait and prominent sensory ataxia related to a myelopathy, similar to subacute combined degeneration observed in vitamin B12 deficiency. Associated peripheral neuropathy is common. Spinal MRI typically shows a longitudinal high T2 signal lesion in the dorsal cervical and thoracic cord. Cytopenias are found in 78% of cases, particularly anemia. Low serum copper and ceruloplasmin levels confirmed the diagnosis and, in contrast to WD, urinary copper levels were typically low (Table 57.2). Copper supplementation resolves the anemia and neutropenia promptly and completely. But, improvement of neurologic deficits is slight and often subjective (Jaiser and Winston, 2010).

ACQUIRED COPPER TOXICOSIS The first case of fatal copper intoxication was reported by Percival in 1785. Acute copper poisoning may occur accidentally or intentionally with suicidal objective, although the lethal dose is about 1000 times normal dietary intakes (Bremner, 1998). It manifests by a metallic taste, vomiting, diarrhea, gastrointestinal bleeding, hemolysis, oliguria, hematuria, seizures, coma, and death. The low incidence of chronic copper toxicosis reflects the efficiency of the copper homeostatic control mechanisms. Nevertheless, copper poisoning can develop under certain conditions. Liver copper accumulation has been observed in Indian childhood cirrhosis, nonIndian disease termed idiopathic copper toxicosis, and Tyrolean childhood cirrhosis. D-penicillamine, if given early, reduces mortality. The excess copper found in these childhood types of cirrhosis was believed to be due to increased dietary intake of copper associated with an autosomal recessive inherited defect in copper

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metabolism; this genetic disorder is as yet uncharacterized (Haywood et al., 2001).

IRON DISORDERS Iron is essential in multiple functions in CNS, including DNA synthesis, gene expression, myelinization, neurotransmission, and mitochondrial functions. Either brain accumulation or depletion of intracellular iron may impair normal function and promote cell death (Benarroch, 2009). Iron brain disorders can be divided into: ● ● ● ●

genetic neurodegeneration with brain iron accumulation genetic systemic iron accumulation with neurologic features (hemochromatosis) acquired neurodegenerative disorders such as Alzheimer disease and Parkinson disease acquired diseases associated with iron excess (superficial siderosis) or iron deficiency (restless leg syndrome).

Iron metabolism (Fig. 57.4) Dietary iron (Fe3þ) is first reduced to Fe2þ by duodenal cytochrome B (DcytB), a ferrireductase present on the apical membranes of enterocytes. Fe2þ then enters the enterocytes by divalent metal transporter-1 (DMT1) expressed on the apical membrane. Once inside, Fe2þ can be stored as ferritin or can leave the enterocyte through ferroportin (Fpn, Ireg1, MTP1), expressed on the basolateral membrane. Prior to the transport of iron outside the cell, intracellular iron must be converted to Fe3þ via either hephaestin or ceruloplasmin, both of which have ferroxidase activity (Mills et al., 2010). Intracellular iron is regulated by the IRE (iron regulatory element)–IRP (iron regulatory proteins) system. So, in case of elevation of intracellular iron, and particularly

Fig. 57.4. Brain iron metabolism.

of the LIP (labile iron pool), the synthesis of ferritin is increased (allowing the storage of the overload iron) and the expression of the receptor for transferrin (RTf1) reduced (limiting the entrance of iron to the cell). Hepcidin produced by hepatocytes is an important regulator of cellular iron export by controlling the amount of ferroportin that is the primary determinant of gastrointestinal absorption and iron release from reticuloendothelial stores. Ceruloplasmin is a major copper-containing protein in the serum (Lutsenko et al., 2007). This a-2glycoprotein is synthesized in the hepatic microsomes, as apoceruloplasmin. Loaded with six copper atoms per molecule, it is excreted into the circulation as holoceruloplasmin. Its essential function is a ferroxidase activity which is necessary to release iron from storage. The cellular and intercellular iron transport mechanisms in the CNS are still poorly understood. Blood–brain barrier limits iron entry to the brain from the blood, so disturbances of systemic iron homeostasis exhibit minimal effects on CNS iron content or metabolism (Moos and Morgan, 2004). Molecular mechanisms of iron transport seem similar to those described in the peripheral tissues; ferritine, DMT 1, ferroportine, hephaestine, and ceruloplasmin are all expressed in the CNS. Brain endothelial cells express the transferrin receptor 1 in their luminal membrane; this receptor binds iron-loaded transferrin and internalizes this complex in endosomes. Then ceruloplasmin, which acts as a ferroxidase, oxidizes ferrous iron to ferric iron, which binds to the transferrin in brain interstitial fluid (Benarroch, 2009).

Disorders INHERITED NEURODEGENERATION WITH BRAIN IRON ACCUMULATION

Inherited neurodegeneration with brain iron accumulation (NBIA) includes neurologic progressive disorders with basal ganglia iron accumulation and axonal dystrophy (spheroid bodies).

DISORDERS OF HEAVY METALS

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NBIA type 1: pantothenate kinase-associated neurodegeneration In 1922, Hallervorden and Spatz described the Hallervorden–Spatz disease (HSD) (Hallervorden and Spatz, 1922). Since the discovery of the PANK2 gene, the eponym HSD is no longer used. Classic pantothenate kinase-associated neurodegeneration (PKAN) begins with gait abnormalities, usually before 6 years of age. Dystonia, often asymmetric, is the major feature. Others symptoms include dysarthria, extrapyramidal syndrome, cognitive deterioration, or psychiatric disorder. About two-thirds of patients have clinical or electroretinographic evidence of retinopathy (Gregory et al., 2009). Death occurs about 30 years of age, related to decubitus complications. Approximately 25% of affected individuals have an atypical presentation with later onset (teenage) and slower progression. Presenting features include speech difficulties and extrapyramidal syndrome; psychiatric disorders are more prominent than in the classic form of the disease, including depression, emotional lability and impulsivity (Gregory et al., 2010). PKAN gene mutations have also been described in the HARP syndrome (hypo-blipoproteinemia, acanthocyosis, retinitis pigmentosa and pallidal degeneration) (Ching et al., 2002). Iron tests are normal. Classic and atypical PKAN patients show the same brain MRI findings. In globus pallidus, the “eye of the tiger” sign consists of bilateral areas of hyperintensity (corresponding to necrosis tissue) surrounded by a ring of hyposignal (high iron) on T2*-weighted sequences (Fig. 57.5) (Angelini et al., 1992; Grabli et al., 2011). Hypointensity of the substantia nigria and dentate nucleus are also described. PKAN is a recessive autosomal disease caused by a mutation of the gene (20p13-p12.3) encoding panthotenate kinase 2 (PANK2), an essential mitochondrial enzyme involved in coenzyme A biosynthesis (Zhou et al., 2001). Pantothenate kinase deficiency is thought to cause accumulation of N-pantothenoyl-cysteine and pantetheine, which may cause cell toxicity directly or via free radical damage as chelators of iron (Yoon et al., 2000). PANK2 mutations (essentially missense) are present in all patients with the classic form of the disease and in one-third of those with atypical disease and late onset (Hayflick et al., 2003).

NBIA type 2: classic infantile neuroaxonal dystrophy and atypical neuroaxonal dystrophy Infantile neuroaxonal dystrophy (INAD), sometimes called Seitelberger disease, was considered for a long time as an early form of Hallervorden–Spatz disease. The classic form begins generally in early childhood, before the age of 2 years, mostly with a regression of

Fig. 57.5. PKAN disease. T2-weighted brain MRI. Aspect of the “eye of the tiger” sign (Grabli© 2010, Elsevier Masson SAS).

psychomotor acquisitions, delayed walking, or gait disturbance. Other presenting signs are cerebellar syndrome with ataxia, pyramidal signs, and bulbar dysfunction. Disease progression is rapid with axial hypotonia and severe spastic tetraparesis. Strabismus, nystagmus, and optic atrophy are common. Death occurs generally during the first decade, but some patients can survive up to the age of 20 years (Aicardi and Castelein, 1979; Kurian et al., 2008). In the atypical form of INAD (ANAD), the onset is often later and the evolution slower. Ataxia remains the main symptom (Kurian et al., 2008). Denervation atrophy is seen on the electromyogram (Johnson et al., 2004). T2-weighted MRI demonstrates cerebellar cortical atrophy, white matter abnormalities, and corpus callosum changes. T2*-weighted MRI can show hypointense globus pallidus and substantia nigra (indicating iron accumulation). These abnormalities are more severe with increasing age (Kurian et al., 2008). Biological investigations do not indicate the presence of a metabolic disorder. Before the finding of the PLA2G6 gene, the diagnosis of INAD was established by tissue biopsy (sural nerve, skin, muscles, rectal). Indeed, unlike the neurodegeneration associated with pantothenate-kinase deficit, typical dystrophic axons are not limited to the CNS.

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INAD is inherited in an autosomal recessive manner related to mutations in the PLA2G6 gene (22q13.1) encoding a calcium-independent phospholipase A2 group VI that is thought to play a key role in cell membrane homeostasis. The sequencing of the gene allows detecting approximately 85% of the mutations. The less severe atypical NAD phenotype is caused by compound heterozygosity for missense mutations (Gregory et al., 2008). Idiopathic neurodegeneration with brain iron accumulation In recent years, progress has been made in the discovery of gene mutations and phenotypes. However, a large population of idiopathic cases caused by undiscovered genes remains to be investigated. Neuroferritinopathy Neuroferritinopathy was described for the first time in 2001 in a family from the north of England; it results from mutations in the ferritin light polypeptide gene (FTL) encoding the light chain of ferritin (Curtis et al., 2001). Clinical onset is around 40–50 years of age, with chorea, dystonia, and extrapyramidal syndrome. A cerebellar syndrome is sometimes associated (Ory-Magne et al., 2009). The evolution of the disease is slowly progressive; the majority of patients develop a characteristic orofacial dystonia leading to dysarthrophonia,and the gait is generally lost more than 20 years after the first symptoms. Serum ferritin concentrations are low (