The Wilson disease gene: spectrum of mutations and their consequences

Cell-specific trafficking suggests a new role for renal ATP7B in the intracellular copper storage

Human Cu-ATPases ATP7A and ATP7B maintain copper homeostasis through regulated trafficking between intracellular compartments. Inactivation of these transporters causes Menkes disease and Wilson disease, respectively. In Menkes disease, copper accumulates in kidneys and causes tubular damage, indicating that the renal ATP7B does not compensate for the loss of ATP7A function. We show that this is likely due to a kidney-specific regulation of ATP7B. Unlike ATP7A (or hepatic ATP7B) which traffics from the TGN to export copper, renal ATP7B does not traffic and therefore is unlikely to mediate copper export. The lack of ATP7B trafficking is not on account of the loss of a kinase-mediated phosphorylation or simultaneous presence of ATP7A in renal cells. Rather, the renal ATP7B appears 2-3 kDa smaller than hepatic ATP7B. Recombinant ATP7B expressed in renal cells is similar to hepatic protein in size and trafficking. The analysis of ATP7B mRNA revealed a complex behavior of exon 1 upon amplification, suggesting that it could be inefficiently translated. Recombinant ATP7B lacking exon 1 traffics differently in renal and hepatic cells, but does not fully recapitulate the endogenous phenotype. We discuss factors that may contribute to cell-specific behavior of ATP7B and propose a role for renal ATP7B in intracellular copper storage.

Estimation of Wilson's disease incidence and carrier frequency in the Korean population by screening ATP7B major mutations in newborn filter papers using the SYBR green intercalator method based on the amplification refractory mutation system

Wilson's disease (WD), an autosomal recessive disorder of copper transport, is one of the most common inherited metabolic disorders in Korea. Despite its frequency, the incidence and carrier frequency of WD has not yet been estimated in the Korean population. We therefore screened for four major missense mutations (p.Arg778Leu, p.Ala874Val, p.Leu1083Phe, and p.Asn1270Ser) of the ATP7B gene in 476 newborn filter papers by real-time multiplex PCR and melting curve analysis using the SYBR Green intercalator method based on the amplification refractory mutation system test. Newborn filter papers with abnormal melting curves were subjected to subsequent sequence analysis. Three mutated alleles, one p.Arg778Leu and two p.Ala874Val, were detected among the 476 newborn filter papers (952 alleles). The carrier frequency and incidence of WD in the Korean population were determined as 1 in 88.2 and 30,778, respectively, by reversely calculating based on the Hardy-Weinberg law.

Copper-induced translocation of the Wilson disease protein ATP7B independent of Murr1/COMMD1 and Rab7

Wilson disease is a genetic disorder of copper metabolism. Impaired biliary excretion results in a gradual accumulation of copper, which leads to severe disease. The specific gene defect lies in the Wilson disease protein, ATP7B, a copper-transporting ATPase that is highly active in hepatocytes. The two major functions of ATP7B in the liver are the copper loading of ceruloplasmin in the Golgi apparatus, and the excretion of excess copper into the bile. In response to elevated copper levels, ATP7B shows a unique intracellular trafficking pattern that is required for copper excretion from the Golgi apparatus into dispersed vesicles. We analyzed the translocation of ATP7B by both confocal microscopy and RNA interference, testing current models that suggest the involvement of Murr1/COMMD1 and Rab7 in this pathway. We found that although the ATP7B translocation is conserved among nonhepatic cell lines, there is no co-localization with Murr1/COMMD1 or the Rab marker proteins of the endolysosomal system. Consistent with this finding, the translocation of ATP7B was not impaired by the depletion of either Murr1/COMMD1 or Rab7, or by a dominant-negative Rab7 mutant. In conclusion, our data suggest that the translocation of ATP7B takes place independently of Rab7-regulated endosomal traffic events. Murr1/COMMD1 plays a role in a later step of the copper excretion pathway but is not involved in the translocation of the Wilson disease protein.

Diagnosis of Wilson's disease: a comprehensive review

Wilson's disease is an autosomal recessive disorder of copper metabolism. The culprit gene is ATP7B. The worldwide prevalence is about 1 in 30,000, which may vary by population. Higher prevalence rates were reported using more sensitive screening techniques and pilot population screening. Typical presentations include neuropsychiatric and hepatic dysfunction, whereas atypical presentations are protean. Diagnosis relies on a high clinical suspicion, typical neurological symptoms, presence of Kayser-Fleischer rings, and reduced serum ceruloplasmin concentration. The conventional value of < 0.20 g/l is not a universal diagnostic value. Age of the subjects and analytical variations should be considered when interpreting these levels. Patients with inconclusive findings require further investigations such as 24 h urinary free-copper excretion, penicillamine challenge test, liver copper measurement, and detection of gene mutations. Direct molecular diagnosis remains the most decisive tool. Other tests such as non-ceruloplasmin-bound copper are unreliable. Potential pitfalls and limitations of these diagnostic markers are critically reviewed in this paper. The mainstays of therapy are trientine, penicillamine, and/or zinc. Liver transplantation is lifesaving for those with advanced disease. Ceruloplasmin oxidase activity and serum free-copper concentration should be monitored in patients on long-term de-coppering therapy to prevent iatrogenic copper deficiency.

Quantitative relationship between mutated amino-acid sequence of human copper-transporting ATPases and their related diseases

Copper-transporting ATPase 1 and 2 (ATP7A and ATP7B) are two highly homologous P-type copper ATPase exporters. Mutations in ATP7A can lead to Menkes disease which is an X-linked disorder of copper deficiency. Mutations in ATP7B can cause Wilson disease which is an autosomal recessive disorder of copper toxicity. In this study, we attempt to build a quantitative relationship between mutated ATPase and Menkes/Wilson disease. First, we use the amino-acid distribution probability as a measure to quantify the difference in ATPase before and after mutation. Second, we use the cross-impact analysis to define the quantitative relationship between mutant ATPase protein and Menkes/Wilson disease, and compute various probabilities. Finally, we use the Bayesian equation to determine the probability that Menkes/Wilson disease is diagnosed under a mutation. The results show (i) the vast majority of mutations lead to the amino-acid distribution probability increase in mutant ATP7As and decrease in ATP7Bs, and (ii) the probability that a mutation causes Menkes/Wilson disease is about nine tenth. Thus we provide a way to use the descriptively probabilistic method to couple the mutation with its clinical outcome after quantifying mutations in proteins.

Genotype phenotype correlation in Wilson's disease within families--a report on four south Indian families

AIM

To study the genotype phenotype correlation in Wilson's disease (WD) patients within families.

METHODS

We report four unrelated families from South India with nine members affected with WD. Phenotype was classified as per international consensus phenotypic classification of WD. DNA was extracted from peripheral blood and 21 exons of ATP7B gene and flanking introns were amplified by polymerase chain reaction (PCR). The PCR products were screened for mutations and the aberrant products noted on screening were sequenced.

RESULTS

Four separate ATP7B mutations were found in the four families. ATP7B mutations were identical amongst affected members within each family. Three families had homozygous mutations of ATP7B gene while one family had compound heterozygous mutation, of which only one mutation was identified. We noted concordance between ATP7B gene mutation and Wilson's disease phenotype amongst members within each family. The age of onset of symptoms or of detection of asymptomatic disease, baseline serum ceruloplasmin and baseline urinary copper levels were also similar in affected members of each family. Minor differences in phenotype and baseline serum ceruloplasmin level were noted in one family.

CONCLUSION

We report concordance between ATP7B mutation and WD phenotype within each family with > 1 member affected with WD. Homozygous ATP7B mutation was present in 3 of the 4 families studied. Our report supports allelic dominance as a determinant of WD phenotype. However, in one family with compound heterozygous mutation, there was a similar WD phenotype which suggests that there may be other factors determining the phenotype.

New mutations in the Wilson disease gene, ATP7B: implications for molecular testing

Wilson disease (WND), an autosomal recessive disorder of copper transport with a broad range of genotypic and phenotypic characteristics, results from mutations in the ATP7B gene. ATP7B encodes a copper transporting P-type ATPase involved in the transport of copper into the plasma protein ceruloplasmin, and for excretion of copper from the liver. Defects in ATP7B lead to copper storage in liver, brain and kidney. Mutation analysis was carried out on 300 WND patients of various origins, and new mutations not previously reported were identified: European white (p.L217X, c.918_931, c.1073delG, c.3082_3085delAAGAinsCG, p.V536A, p.S657R, p.A971V, p.T974M, p.Q1004P, p.D1164N, p.E1173G, p.I1230V, p.M1359I, c.2355+4A>G), Sephardic Jewish (p.Q286X), Filipino (p.G1149A), Lebanese (p.R1228T), Japanese (p.D1267V) and Taiwanese (p.A1328T). All but one missense variant have strong evidence for classification as disease-causing mutations. In the patients reported here, we also identified 20 nucleotide substitutions, six not previously reported, which cause silent amino acid changes or intronic changes. Documentation and characterization of all variants is essential for accurate DNA diagnosis in WND because of the wide range of clinical and biochemical variability.

Mutational analysis of ATP7B gene in Egyptian children with Wilson disease: 12 novel mutations

The aim of this work was to study the mutations within ATP7B in Egyptian children with Wilson disease and to evaluate any potential correlation between genotype and phenotype in this cohort. The study consisted of 48 children with Wilson disease from 32 independent families. The 21 exons of the ATP7B gene were amplified in a thermal cycler. Direct sequencing of the amplified polymerase chain reaction (PCR) products was performed by cycle sequencing using fluorescent dye terminators in an automatic ABI sequencer. Thirty-one different mutations in 96 chromosomes were detected (19 missense, three nonsense, seven frameshift deletions, and two splice-site mutations). Of these, 12 mutations have not been previously reported. The p.N1270S, p.C703Y, IVS18-2A > G, p.R1319X, c.2304-2305insC, and p.H1069Q were present in 7.8%, 6.2%, 6.2%, 6.2%, 4.7%, and 4.7%, respectively, of studied chromosomes in independent families. One patient was homozygous for both p.N1270S and p.T1434M mutations. Frameshift and nonsense mutations were found in 50% of patients with disease onset < or =8 years compared with only 26% in patients with onset >8 years. Despite mutation heterogeneity in Egyptian children, genotype-phenotype correlation analysis seems to be promising in this population, as many patients carry homozygous mutations, a situation that mandates a larger-scale population screening to identify the carrier rate in this community.

Analysis of the human Atox 1 homologue in Wilson patients

AIM: To analyze the metallochaperone antioxidant-1 (Atox1) gene sequence in Wilson disease patients.

METHODS: Mutation analysis of the four exons of the Atox1 gene including the intron- exon boundaries was performed in 63 Wilson disease patients by direct sequencing.

RESULTS: From 63 selected patients no mutations were identified after the entire coding region including the intron- exon boundaries of Atox1 were sequenced. One known polymorphism within the Atox1 gene (5’UTR -99 T>C) in 31 (49%) of the Wilson patients as well as one previously undescribed variation (5’UTR -68 C>T) in 2 of the Wilson patients could be detected. Statistical analyses revealed that the existence of a variation within the Atox1- gene showed a tendency towards an earlier onset of the disease.

CONCLUSION: Based on the data of this study, no major role can be attributed to Atox1 in the pathophysiology or clinical variation of Wilson disease.

Sequence variation in the ATP-binding domain of the Wilson disease transporter, ATP7B, affects copper transport in a yeast model system

ATP7B is a copper transporting P-type ATPase defective in the autosomal recessive copper storage disorder, Wilson disease (WND). Functional assessment of variants helps to distinguish normal from disease-causing variants and provides information on important amino acid residues. A total of 11 missense variants of ATP7B, originally identified in WND patients, were examined for their capacity to functionally complement a yeast mutant strain in which the yeast gene ortholog, CCC2, was disrupted. Solution structures of ATP7B domains were used to predict the effects of each variant on ATP7B structure. Three variants lie within the copper-binding domain and eight within the ATP-binding domain of ATP7B. All three ATP7B variants within the copper-binding domain and four within the ATP-binding domain showed full complementation of the yeast ccc2 phenotype. For the remaining four located in the ATP-binding domain, p.Glu1064Lys and p.Val1106Asp were unable to complement the yeast ccc2 high-affinity iron uptake deficiency phenotype, apparently due to mislocalization and/or change in conformation of the variant protein. p.Leu1083Phe exhibited a temperature-sensitive phenotype with partial complementation at 30 degrees C and a severe deficit at 37 degrees C. p.Met1169Val only partially complemented the ccc2 phenotype at 30 degrees C and 37 degrees C. Therefore, four variant positions were identified as important for copper transport and as disease-causing changes. Since the yeast assay specifically evaluates copper transport function, variants with normal transport could be defective in some other aspect of ATP7B function, particularly trafficking in mammalian cells. Functional assessment is critical for reliable use of mutation analysis as an aid to diagnosis of this clinically variable condition.

Sequence variation database for the Wilson disease copper transporter, ATP7B

Wilson disease (WND) is a disorder of copper transport resulting in copper accumulation in liver, kidney, and brain. This recessive disorder expresses variable clinical symptoms affecting liver, brain, and/or kidney. The age of onset of symptoms varies from 3 to almost 70 years, so the diagnosis for this treatable disorder is easily missed. The defective gene is a membrane P-type ATPase, with similar structure to the other metal transporting ATPases. Most patients with Wilson disease are compound heterozygotes. This report describes the database we have developed for reporting of mutations in ATP7B, the gene defective in WND. The database includes more than 518 variants (379 probable disease-causing and the remainder possible normal variants) from populations worldwide (Available at: www.medicalgenetics.med.ualberta.ca/wilson/index.php; Last accessed: 20 June 2007). The tables in this database are a valuable resource for the study of population variation and the function of the transporter, and will assist in the identification of disease and non-disease-causing sequence variants.

Psychopathology and personality traits in patients with treated Wilson disease grouped according to gene mutations

Wilson disease (WD) is a recessively inherited copper storage disorder mainly affecting liver and brain. Genotype/phenotype correlations have been report ed but as yet not regarding psychic symptoms. Our aim was to investigate if a correlation might exist between genotype and phenotype concerning psychopathology and/or personality traits in patients with treated WD. Nine homozygous and three compound heterozygous Swedish patients were retrospectively investigated, representing four different mutation settings. Psychopathological symptoms were studied using the Comprehensive Psychopathological Rating Scale (CPRS), personality traits using the Karolinska Scales of Personality (KSP) and mutations were analyzed by manifold sequencing. Psychopathological symptoms: Patients with the Trp779Stop mutation had the lowest scores on the total CPRS, due to less pronounced reported CPRS items, as compared to the other three groups of patients. Compound heterozygotes for the His1069Gln/Arg1319Stop mutation showed the highest total CPRS scores. Personality traits: Patients homozygous for the Trp779Stop and the Thr977Met mutations had high scores on Psychopathy related scales whereas patients with His1069Gln/Arg1319Stop mutations had the lowest scores on these scales. Serum ceruloplasmin levels were undetectable in all patients with the Trp779Stop and Thr977Met mutations. The results show a trend towards a genotype/phenotype correlation regarding psychopathological symptoms and personality traits in treated patients with WD. If replicable, these results might contribute to the elucidation of the possible clinical importance of functionally deleterious gene mutations in WD psychopathology and personality traits.

Molecular pathogenesis of Wilson disease among Indians: a perspective on mutation spectrum in ATP7B gene, prevalent defects, clinical heterogeneity and implication towards diagnosis

AIMS

We aim to identify the molecular defects in the ATP7B, the causal gene for Wilson disease (WD), in eastern Indian patients and attempt to assess the overall mutation spectrum in India for detection of mutant allele for diagnostic purposes.

METHODS

Patients from 109 unrelated families and their first-degree relatives comprising 400 individuals were enrolled in this study as part of an ongoing project. Genomic DNA was prepared from the peripheral blood of Indian WD patients. PCR was done to amplify the exons and flanking regions of the WD gene followed by sequencing, to identify the nucleotide variants.

RESULTS

In addition to previous reports, we recently identified eight mutations including three novel (c.3412 + 1G > A, c.1771 G > A, c.3091 A > G) variants, and identified patients with variable phenotype despite similar mutation background suggesting potential role of modifier locus.

CONCLUSIONS

So far we have identified 17 mutations in eastern India including five common mutations that account for 44% of patients. Comparative study on WD mutations between different regions of India suggests high genetic heterogeneity and the absence of a single or a limited number of common founder mutations. Genotype-phenotype correlation revealed that no particular phenotype could be assigned to a particular mutation and even same set of mutations in different patients showed different phenotypes.

Developmental expression of Commd1 in the liver of the Jackson toxic milk mouse

Wilson disease (WD) is due to mutations in ATP7B, which encodes an intracellular metal-transporting P-type ATPase. In WD holoceruloplasmin production and biliary excretion of copper are decreased, leading to copper overload, oxidative stress and apoptotic cell death. Other copper-binding proteins include COMMD1, which is inactive in the Bedlington terrier hereditary copper toxicosis, and XIAP, which regulates apoptosis. We examined developmental expression of Commd1 and Xiap in the Jackson toxic milk mouse (Atp7b(tx-J), G712D missense mutation in Atp7b). Expression of Commd1 mRNA appeared unchanged by PCR but real-time PCR demonstrated 3- to 4-fold increase over the first 6 months of life. Immunodetectable Xiap dropped over the first 8 months of life and was nearly undetectable from 6 months onward. Cytosolic NF-kappaB rose then dropped precipitously at 5-6 months. In tx-j mice hepatic copper accumulation leads to decreased Xiap, increased Commd1; these responses ultimately fail to prevent progressive apoptotic cell damage.

Identification of novelATP7Bgene mutations and their functional roles in Korean patients with Wilson disease

Wilson disease (WND), an autosomal recessive disorder of copper transport, is characterized by excessive accumulation of intracellular copper in liver and extrahepatic tissues because of impaired biliary copper excretion and disturbed incorporation of copper into ceruloplasmin. Hepatic cirrhosis and neuronal degeneration are the major symptoms of WND, and mutations in the ATP7B gene are associated with WND. We have identified 28 different mutations in the ATP7B gene, including six novel variations, in 120 unrelated Korean patients with WND. Molecular defects in ATP7B were present in only 75.0% of Korean WND patients, with the most common mutation, p.Arg778Leu, having an allele frequency of 39.2%. To evaluate the functional defects of ATP7B caused by novel mutations, we used a yeast complementation system, and we used confocal microscopy to localize each mutation after transient expression in mammalian cells. Six novel variations were cloned into a yeast expression vector and two into a mammalian expression vector for confocal analysis. We found that c.2785A>G (p.Ile929Val) and c.3316G>A (p.Val1106Ile) were rare polymorphisms, whereas the others were novel variations disturbing ATP7B function.

Wilson disease: Identification of two novel mutations and clinical correlation in Eastern Chinese patients

AIM: To study mutations in the P-type ATPase (ATP7B) gene responsible for Wilson disease (WD) in the Eastern Chinese population, and the possible correlation of specific mutations with clinical characteristics.

METHODS: Mutations of the ATP7B gene were sought by means of direct sequencing in 50 Eastern Chinese WD patients of Han ethnic origin.

RESULTS: Two novel mutations, Asp96Gly and Asp196Glu, were first identified. We also compared the characterization of mutations in ATP7B with the clinical findings, and a significant correlation with hepatic manifestations between patients carrying the Arg778Leu mutation and those without was found.

CONCLUSION: Gene sequencing analysis was shown to have a high detection rate and accuracy. It may become the first priority in screening of WD patients.

Genetic background of Japanese patients with adult-onset storage diseases in the liver

In contrast to primary lysosomal diseases in young subjects, adult-onset liver storage disorders may be explained by non-lysosomal genetic defects. The aim of the present review is to summarize the genetic backgrounds of Japanese patients with hemochromatosis of unknown etiology, Wilson disease of primary copper toxicosis, and the black liver of Dubin-Johnson syndrome. Three patients with middle-age onset hemochromatosis were homozygous for mutations of HJV and two patients were homozygous for mutations of TFR2. Minor genes other than HJV and TFR2 might be involved in Japanese patients. Five of the six patients with Wilson disease were compound heterozygous, while the remaining patient was heterozygous for the mutation in ATP7B responsible for copper toxicosis. Involvement of MURR1 was not proved in the heterozygote of ATP7B. Because of ferroxidase deficiency,most patients had secondary lysosomes shared by cuprothioneins and iron complex. Six patients with Dubin-Johnson syndrome were homozygous or compound heterozygous for mutant MRP2. Despite complex metabolic disorders, the syndrome had a single genetic background. Thus, most patients with adult-onset lysosomal proliferation in the liver had genetic defects in non-lysosomal organelles, named the secondary lysosomal diseases. The proliferating lysosomes in these conditions seemed to be heterogeneous in their matrices.

Analysis of the T1288R mutation of the Wilson disease ATP7B gene in four generations of a family: possible genotype-phenotype correlation with hepatic onset

Wilson disease, an autosomal recessive disorder due to mutations of the ATP7B gene, is characterized by copper accumulation and toxicity in the liver and subsequently in other organs, mainly the brain and cornea. A new missense mutation (T1288R) of the ATP7B gene has recently been discovered in a Wilson disease patient in our laboratory. The aim of the present study was to analyze clinical and genetic features of more generations of the family of the patient in which the new mutation T1288R was discovered. A total of 19 subjects were studied; in particular, four generations of the patient's family were analyzed. The ATP7B gene was analyzed by single-strand conformational polymorphism followed by direct sequencing. Two brothers presented a clinical diagnosis of Wilson disease with an hepatic phenotype and a genotype characterized by the homozygotic mutation T1288R. The heterozygotic mutation T1288R was found in seven subjects belonging to all four generations. The present study represents the first screening for a Wilson disease mutation through four generations of a nonconsanguineous family. All the patients with the homozygotic T1288R mutation in the present pedigree presented an hepatic phenotype without a neurological presentation. Consequently, a genotype-phenotype correlation could be hypothesized, although further studies are necessary to clarify this topic.

Neurological manifestations and ATP7B mutations in Wilson's disease

Wilson's disease (WD) is a rare inborn metabolic error characterized by deficient biliary copper excretion secondary to ATP7B gene mutations. Neurological presentations are variable in respect to both pattern and age of onset; commonly a movement disorder presents in the second or third decade. The aim of this study was to ascertain genotype correlations with distinct neurological manifestations in 41 WD patients in a Brazilian center for WD. A total of 23 distinct mutations were detected, and the frameshift 3402delC had the highest allelic frequency (31.7%). An association between 3402delC and dysphagia was detected (p=0.01) but the limited number of patients is insufficient to allow one to draw conclusions. Both clinical studies analyzing larger cohorts and basic research on ATP7B protein function could potentially shed more light on our understanding of WD.

Molecular pathogenesis of Wilson and Menkes disease: correlation of mutations with molecular defects and disease phenotypes

The trace metal copper is essential for a variety of biological processes, but extremely toxic when present in excessive amounts. Therefore, concentrations of this metal in the body are kept under tight control. Central regulators of cellular copper metabolism are the copper-transporting P-type ATPases ATP7A and ATP7B. Mutations in ATP7A or ATP7B disrupt the homeostatic copper balance, resulting in copper deficiency (Menkes disease) or copper overload (Wilson disease), respectively. ATP7A and ATP7B exert their functions in copper transport through a variety of interdependent mechanisms and regulatory events, including their catalytic ATPase activity, copper-induced trafficking, post-translational modifications and protein-protein interactions. This paper reviews the extensive efforts that have been undertaken over the past few years to dissect and characterise these mechanisms, and how these are affected in Menkes and Wilson disease. As both disorders are characterised by an extensive clinical heterogeneity, we will discus how the underlying genetic defects correlate with the molecular functions of ATP7A and ATP7B and with the clinical expression of these disorders.

Late-onset Wilson's disease

BACKGROUND & AIMS

The clinical symptoms and age at onset of Wilson's disease (WD) are highly variable. This study investigated patients who became symptomatic at >40 years of age.

METHODS

Clinical features, laboratory data, and mutation analysis were evaluated in 46 (3.8%) of 1223 patients who were investigated in a multinational study on genotype-phenotype correlations (1053 index patients, 170 siblings) who were >40 years of age at onset of symptoms and, in 2 asymptomatic siblings, diagnosed at >40 years of age.

RESULTS

Thirty-one patients presented with neurologic symptoms (mean age, 44.5 years; range, 40-52; male/female, 14/17), 15 presented with liver disease (mean age, 47.1 years; range, 40-58; male/female, 6/9), and 2 were asymptomatic siblings. Hepatic copper content was measured in 17 patients and was above 250 microg/g dry weight in 13. One patient with hepatic presentation had "fulminant" WD, the remaining 14 abnormal liver function tests and/or hepatomegaly. Liver biopsy specimens were available in 13 patients presenting with liver disease (cirrhosis, 10; chronic hepatitis, 2; steatosis, 1; no abnormalities, 1) and in 14 neurologic patients (cirrhosis, 9; advanced fibrosis, 1; chronic hepatitis, 2; no abnormalities, 2). Twenty-seven of the 46 index cases had mutations on both chromosomes (including 13 H1069Q/H1069Q), 13 on just 1 chromosome.

CONCLUSIONS

Late-onset WD is a frequently overlooked condition. The diagnostic features and the frequency of late-onset WD gene mutations were not different than in patients with an earlier onset of disease. Factors other than ATP7B mutations may modify the phenotypic presentation of WD.

Diagnostic criteria for acute liver failure due to Wilson disease

AIM: To describe the diagnostic criteria for acute liver failure due to Wilson disease (WD), which is an uncommon cause of acute liver failure (ALF).

METHODS: We compared findings of patients presenting with ALF due to WD to those with ALF of other etiologies.

RESULTS: Previously described criteria, such as low alkaline phosphatase activity, ratio of low alkaline phosphatase to total bilirubin or ratio of high aspartate aminotransferase (AST) to alanine aminotransferase (ALT), failed to identify patients with ALF due to WD. There were significant differences in low ALT and AST activities (53 ± 43 vs 1982 ± 938, P < 0.0001 and 87 ± 44 vs 2756 ± 2941, P = 0.037, respectively), low choline esterase activity (1.79 ± 1.2 vs 4.30 ± 1.2, P = 0.009), high urine copper concentrations (93.4 ± 144.0 vs 3.5 ± 1.8, P = 0.001) and low hemoglobin (7.0 ± 2.2 vs 12.6 ± 1.8, P < 0.0001) in patients with ALF caused by WD as compared with other etiologies. Interestingly, 4 of 7 patients with ALF due to WD survived without liver transplantation.

CONCLUSION: In ALF, these criteria can help establish a diagnosis of WD. Where applicable, slit-lamp examination for presence of Kayser-Fleischer rings and liver biopsy for determination of hepatic copper concentration still remain important for the diagnosis of ALF due to WD. The need for liver transplantation should be evaluated carefully as the prognosis is not necessarily fatal.

Novel mutations of the ATP7B gene among 109 Hungarian patients with Wilson's disease

BACKGROUND/AIMS

Diagnosis of Wilson's disease may be difficult in patients presenting with liver disease and in asymptomatic siblings. The aim of the present study was to assess the impact of genetic testing for diagnosis of the disease in a large cohort (n=109) from Hungary.

PATIENTS/METHODS

One hundred and nine patients with Wilson's disease were studied (65 men and 44 women; mean age at onset of symptoms: 20+/-9 years). Diagnosis of the disease was based on typical clinical and laboratory features (all had a Wilson's disease score of >or=4). H1069Q was assessed by the semi-nested polymerase chain reaction-based restriction fragment length polymorphism assay. H1069Q heterozygotes and H1069Q negative samples were then screened for mutations (on exons 6 to 20) by denaturating high-performance liquid chromatography and than sequenced on a genetic analyser.

RESULTS

Twenty-three different mutations were found. H1069Q was the most frequent mutation in Hungary, detected in 77 patients (71%). Fourteen further known mutations were found by sequencing. We identified eight new mis-sense mutations not described before: N676I, S693Y, Y715H, M769L, W939C, P1273S, G1281D and G1341V. In 36/109 patients (33%) the diagnosis of Wilson's disease was established by adding mutational analysis. The Kayser-Fleischer ring was more frequent in H1069Q homozygous patients and their mean age at the time of diagnosis was higher than in patients heterozygous or negative for H1069Q.

CONCLUSION

Eight novel mutations in addition to the 15 that are already known were found in Hungarian patients with Wilson's disease. Our results underline the importance and usefulness of genetic testing for patients presenting with liver disease and for family screening.

Clinical and molecular characterization of Wilson disease in Spanish patients

Wilson disease (WD) results when specific mutations occur at the ATP7B gene. The presence of mutations in the ATP7B gene was studied in the coding region and the intron-exon boundaries in 15 WD Spanish patients, and their first-degree relatives when possible. A total of 20 nucleotide sequence changes were detected, 18 missense and two splicing mutations. Six of these variants were classified as disease-causing mutations, five missense, and one splicing; four of them have been previously described (M645R, A1065P, H1069Q, and 3060 + 5G > T), whereas two were novel (P768L and A990P). No mutation was clearly prevalent, although the H1069Q mutation predominated, nor did a good phenotype-genotype correlation exist. The two new mutations described were manifested as an asymptomatic increase in serum transaminases. The remaining 14 changes were classified as polymorphisms and their potential effects on protein function are discussed. The identification of mutations in the ATP7B gene has allowed a conclusive diagnosis to be made of WD in patients presenting neurological phenotype or neurological of hepatic phenotype, who would otherwise not have been diagnosed using classical criteria. WD patients could start chelating treatment earlier on and possibly modify the natural progression of the disease.

Mechanisms of Acute Liver Failure

Acute liver failure is characterized by the sudden onset of liver failure in a patient without evidence of chronic liver disease. This definition is important, as it differentiates patients with acute liver failure from patients who suffer from liver failure owing to end-stage chronic liver disease.

Late neurological presentations of Wilson disease patients in French population and identification of 8 novel mutations in the ATP7B gene

Wilson disease (WD) is an autosomal recessive disorder of copper biliary excretion caused by an impaired function of ATP7B, a metal-transporting P-type ATPase encoded by WD gene. It results in copper accumulation, mostly in liver and brain tissues. Mutation analysis was carried out on 11 WD French unrelated patients presenting a predominant neurological form of this illness. SSCP and dHPLC analysis followed by sequencing of the 21 exons and their flanking introns were performed. Thirteen different mutations in a total of 17, and, among them, 10 novel variants were evidenced. Two deletions (c.654_655delCC and c.1745_1746delTA), 4 missense mutations (p.F763Y, p.G843R, p.D918A and p.L979Q), 1 nonsense mutation (p.Q1200X), 1 splice site mutation (c.1947-1G>C) and 2 intronic silent substitutions (c.2448-25G>T and c.3412+13T>A) were detected. These data extend the mutational spectrum of the disease, already known to be a very heterogeneous genetic disorder. As compared to hepatic manifestations, the phenotypes associated to these mutations confirm that neurological presentations associated with other mutations than p.H1069Q are also often late in their onset. Most of these neurological forms probably correspond to an attenuated impairment of copper metabolism, as compared to hepatic forms of the disease, mostly diagnosed earlier.

Intracellular copper does not catalyze the formation of oxidative DNA damage in Escherichia coli

Because copper catalyzes the conversion of H(2)O(2) to hydroxyl radicals in vitro, it has been proposed that oxidative DNA damage may be an important component of copper toxicity. Elimination of the copper export genes, copA, cueO, and cusCFBA, rendered Escherichia coli sensitive to growth inhibition by copper and provided forcing circumstances in which this hypothesis could be tested. When the cells were grown in medium supplemented with copper, the intracellular copper content increased 20-fold. However, the copper-loaded mutants were actually less sensitive to killing by H(2)O(2) than cells grown without copper supplementation. The kinetics of cell death showed that excessive intracellular copper eliminated iron-mediated oxidative killing without contributing a copper-mediated component. Measurements of mutagenesis and quantitative PCR analysis confirmed that copper decreased the rate at which H(2)O(2) damaged DNA. Electron paramagnetic resonance (EPR) spin trapping showed that the copper-dependent H(2)O(2) resistance was not caused by inhibition of the Fenton reaction, for copper-supplemented cells exhibited substantial hydroxyl radical formation. However, copper EPR spectroscopy suggested that the majority of H(2)O(2)-oxidizable copper is located in the periplasm; therefore, most of the copper-mediated hydroxyl radical formation occurs in this compartment and away from the DNA. Indeed, while E. coli responds to H(2)O(2) stress by inducing iron sequestration proteins, H(2)O(2)-stressed cells do not induce proteins that control copper levels. These observations do not explain how copper suppresses iron-mediated damage. However, it is clear that copper does not catalyze significant oxidative DNA damage in vivo; therefore, copper toxicity must occur by a different mechanism.

Analysis of most common mutations R778G, R778L, R778W, I1102T and H1069Q in Indian Wilson disease patients: correlation between genotype/phenotype/copper ATPase activity

The present study was intended to estimate the frequencies of the most common mutations (R778L, R778W, R778G, I1102T and H1069Q) of ATP7B in Indian Wilson disease (WD) population and to explore the correlation between genotype/phenotype and copper ATPase activity. A total of 33 WD patients and their family members from North West states of India were examined. The H1069Q, R778W and R778L mutations were absent in these WD patients. R778W and I1102T mutations were present in 36% of WD patients. Family analysis for these mutations using PCR-RFLP documented 5 carriers and 2 asymptomatic WD patients. The copper ATPase activity in WD patients was significantly reduced (50%) than that of control individuals. No significant difference was observed in copper stimulated ATPase activity between homozygous (R778W/R778W, I1102T/I1102T) and compound heterozygous (R778W/unknown mutation, I1102T/unknown mutation) WD patients. Serum ceruloplasmin, serum copper levels were significantly lower in homozygous WD patients than that of compound heterozygous. However, no significant difference was observed in liver copper contents between heterozygous and homozygous patients. In conclusion, the data suggest that R778W and I1102T are most common mutations and provide the basis of genetic (PCR-RFLP) diagnostic tool for Indian WD patients as well as in siblings/parents where biochemical parameters are ambiguous.

A cadmium-transporting P1B-type ATPase in yeast Saccharomyces cerevisiae

Detoxification and homeostatic acquisition of metal ions are vital for all living organisms. We have identified PCA1 in yeast Saccharomyces cerevisiae as an overexpression suppressor of copper toxicity. PCA1 possesses signatures of a P1B-type heavy metal-transporting ATPase that is widely distributed from bacteria to humans. Copper resistance conferred by PCA1 is not dependent on catalytic activity, but it appears that a cysteine-rich region located in the N terminus sequesters copper. Unexpectedly, when compared with two independent natural isolates and an industrial S. cerevisiae strain, the PCA1 allele of the common laboratory strains we have examined possesses a missense mutation in a predicted ATP-binding residue conserved in P1B-type ATPases. Consistent with a previous report that identifies an equivalent mutation in a copper-transporting P1B-type ATPase of a Wilson disease patient, the PCA1 allele found in laboratory yeast strains is nonfunctional. Overexpression or deletion of the functional allele in yeast demonstrates that PCA1 is a cadmium efflux pump. Cadmium as well as copper and silver, but not other metals examined, dramatically increase PCA1 protein expression through post-transcriptional regulation and promote subcellular localization to the plasma membrane. Our study has revealed a novel metal detoxification mechanism in yeast mediated by a P1B-type ATPase that is unique in structure, substrate specificity, and mode of regulation.

Wilson's disease: an update

Wilson's disease (WD) is an inborn error of copper metabolism caused by a mutation to the copper-transporting gene ATP7B. The disease has an autosomal recessive mode of inheritance, and is characterized by excessive copper deposition, predominantly in the liver and brain. Diagnosis of the condition depends primarily on clinical features, biochemical parameters and the presence of the Kayser-Fleischer ring, and a new diagnostic scoring system has recently been proposed. Mutations in ATP7B can occur anywhere along the entire 21 exons, which makes the identification of gene defects particularly challenging. Identification of carriers and presymptomatic family members of affected individuals is achieved by polymerase-chain-reaction-based marker analysis. The traditional treatment for WD is based on copper chelation with agents such as D-penicillamine, but use of this drug has been questioned because of reported side effects. The use of agents such as trientine and ammonium tetrathiomolybdate has been advocated, although results of long-term trials are awaited. In selected cases, orthotropic hepatic transplantation can reverse the basic metabolic abnormality in WD and improve both hepatic and neurological symptoms. Studies of the underlying defects in ATP7B and its suspected modifiers ATOX1 and COMMD1 are expected to unravel the disease's genotype-phenotype correlation, and should lead to the design of improved drugs for ameliorating the suffering of patients.

Familial gene analysis for Wilson disease from north-west Indian patients

BACKGROUND

A number of polymerase chain reaction (PCR) based techniques like single-strand conformational polymorphism (SSCP), amplification refractory mutation system (ARMS)-PCR, semi-nested PCR and dinucleotide-repeat marker analysis have been used in the diagnosis of asymptomatic Wilson disease (WD) patients and the carrier status of WD families. In the present study, we explore the utility of mutation analysis in combination with restriction fragment length polymorphism (RFLP) in the genetic diagnosis of WD.

AIM

The study was planned to provide a molecular diagnostic tool for the diagnosis of asymptomatic WD patients as well as assessment of the carrier status of WD families.

SUBJECTS AND METHODS

Four WD families were analyzed in which parents and siblings showed no clinical manifestations or biochemical abnormalities. The parents of the WD patients were not consanguineous and had no family history of WD. Mutations in ATP7B were characterized using SSCP and DNA sequencing. Further, RFLP was developed for the analysis of characterized mutations in ATP7B from the WD patients, their parents and siblings.

RESULTS

Three mutations, Q1256R, A1003T and I1102T, were characterized in WD patients, using SSCP and DNA sequencing. These mutations created/deleted restriction sites for AccII, Bsh1236I and EcoRI restriction enzymes respectively. Despite having no clinical manifestations nor any significant alteration in biochemical investigations, eight carriers and one asymptomatic WD patient were diagnosed in 13 members of the patients families by restriction digestion analysis.

CONCLUSION

The report demonstrates that mutation analysis in combination with RFLP is useful for diagnosis of asymptomatic WD patients as well as for the elucidation of the carrier status of the patients' family members. It is noteworthy that this combinational methodology provides a positive diagnosis in siblings/parents where biochemical parameters are ambiguous.

Regional distribution of mutations of the ATP7B gene in patients with Wilson disease: impact on genetic testing

Wilson disease is an autosomal recessive inherited disorder of copper metabolism. The Wilson disease gene codes for a copper transporting P-type ATPase (ATP7B). Molecular genetic analysis reveals at least 300 distinct mutations. While most reported mutations occur in single families, a few are more common. The most common mutation in patients from Central, Eastern, and Northern Europe is the point mutation H1069Q (exon 14). About 50-80% of Wilson disease (WD) patients from these countries carry at least one allele with this mutation with an allele frequency ranging between 30 and 70%. Other common mutations in Central and Eastern Europe are located on exon 8 (2299insC, G710S), exon 15 (3400delC) and exon 13 (R969Q). The allele frequency of these mutations is lower than 10%. In Mediterranean countries there is a wide range of mutations, the frequency of each of them varies considerably from country to country. In Sardinia, a unique deletion in the 5' UTR (-441/-427 del) is very frequent. In mainland Spain the missense mutation M645R in exon 6 is particularly common. Data from non-European countries are scarce. Most data from Asia are from Far Eastern areas (China, South Korea and Japan) where the R778L missense mutation in exon 8 is found with an allele frequency of 14-49%. In summary, given the constant improvement of analytic tools genetic testing will become an integral part for the diagnosis of WD. Knowledge of the differences in the worldwide distribution of particular mutations will help to design shortcuts for genetic diagnosis of WD.

Frameshift and nonsense mutations in the gene for ATPase7B are associated with severe impairment of copper metabolism and with an early clinical manifestation of Wilson's disease

Wilson's disease (WD) is an autosomal recessive disorder of copper metabolism. The clinical phenotype of the disease is varied. It is proposed that this variation may be a result of differential functional disruption of ATPase7B (ATP7B) resulting from mutations in the gene ATP7B. We aimed to assess the relationship between specific mutational defects in ATP7B and divergence in the phenotypic expression of WD. One hundred and forty-two patients with clinically, biochemically and genetically diagnosed WD were included in the study. The phenotypic expression of WD was compared between patients with different types of mutations in ATP7B, detected by direct sequencing of exons 1-21 of the gene. Twenty-six mutations were identified in ATP7B; eleven of them were mutations predicted to result in the absence of a full-length normal protein [frameshift/nonsense mutations; classified as 'severe' mutations (SMs)], 14 were missense mutations (MMs) and one was a splice site mutation. Patients with one or two SMs on their alleles had lower serum copper and ceruloplasmin and were younger when the first symptoms of the disease appeared, compared with individuals with two MMs. The effect of SMs on the WD phenotype was dose-dependent. It is concluded that mutations within ATP7B are very heterogeneous. Frameshift and nonsense mutations are associated with a severe phenotype of WD.

Mutation analysis of Taiwanese Wilson disease patients

Wilson disease (WD) is an autosomal recessive disorder of copper metabolism, which is caused by mutation in copper-transporting ATPase (ATP7B). In the present study, we report a molecular diagnosis method to screen the WD chromosome in patients or in heterozygotic carriers in Taiwan. Exons 8, 11, 12, 13, 16, 17, and 18 of ATP7B are selected for the screening of mutations. The most common mutation, Arg778Leu or Arg778Gln, was first screened by PCR-RFLP then we combined single-stranded conformation polymorphism (SSCP) analysis followed by direct DNA sequencing on the DNA fragments with mobility shift on SSCP analysis. The diagnostic rate was compared with standard ATP7B whole gene sequencing analysis. Ten different mutations were identified among 29 WD patients; among them four were novel (Ala1168Pro, Thr1178Ala, Ala1193Pro, and Pro1273Gln). The false positive rates were tested against 100 normal individuals and listed as follows: exon 8: 5%; exon 11: 4%; exon 12: 6%; exon 13: 5%; exon 16: 5%; exon 17: 3%; exon 18: 4%. The Arg778Leu mutation exhibited the highest allelic frequency (43.1%). The detection rate of WD chromosomes is 65.52%, which is as sensitive as whole gene sequencing scanning. According to our results, WD chromosomes in Taiwan are predominantely located at exons 8, 11, 12, 13, 16, 17, and 18. The standard sequencing analysis on the entire gene is time consuming. We recommend screening these 7 exons first on those individuals who have a higher risk in having WD, before whole gene and promoter sequencing analysis in Taiwan.

Structure of human Wilson protein domains 5 and 6 and their interplay with domain 4 and the copper chaperone HAH1 in copper uptake

Human Wilson protein is a copper-transporting ATPase located in the secretory pathway possessing six N-terminal metal-binding domains. Here we focus on the function of the metal-binding domains closest to the vesicular portion of the copper pump, i.e., domain 4 (WLN4), and a construct of domains 5 and 6 (WLN5-6). For comparison purposes, some experiments were also performed with domain 2 (WLN2). The solution structure of apoWLN5-6 consists of two ferredoxin folds connected by a short linker, and (15)N relaxation rate measurements show that it behaves as a unit in solution. An NMR titration of apoWLN5-6 with the metallochaperone Cu(I)HAH1 reveals no complex formation and no copper exchange between the two proteins, whereas titration of Cu(I)HAH1 with WLN4 shows the formation of an adduct that is in fast exchange on the NMR time scale with the isolated protein species as confirmed by (15)N relaxation data. A similar interaction is also observed between Cu(I)HAH1 and WLN2; however, the relative amount of the adduct in the protein mixture is lower. An NMR titration of apoWLN5-6 with Cu(I)WLN4 shows copper transfer, first to WLN6 then to WLN5, without the formation of an adduct. Therefore, we suggest that WLN4 and WLN2 are two acceptors of Cu(I) from HAH1, which then somehow route copper to WLN5-6, before the ATP-driven transport of copper across the vesicular membrane.

Allele Dropout in PCR-Based Diagnosis of Wilson Disease: Mechanisms and Solutions

Background: We investigated the mechanisms leading to allele dropout—the nonamplification of 1 of the alleles—in PCR-based diagnosis of Wilson disease (WD).

Methods: We extracted genomic DNA from blood samples from 6 WD patients (P1–P6) with allele dropouts detected in a previous study of WD in a Hong Kong Chinese population. We amplified the ATP7B gene by PCR and performed direct DNA sequencing of all exons of the ATP7B gene. To support the proposed mechanism of allele dropout, we used proofreading DNA polymerase, primer design avoiding single-nucleotide polymorphism sites, and duplex PCR.

Results: Patients P1–P4 were all apparently homozygous for a known disease-causing mutation, c.2975C&gt;T (p.P992L) in exon 13. Patient P5 was apparently homozygous for a novel mutation, c.2524G&gt;A, and patient P6 was apparently homozygous for another known mutation, c.522_523insA (p.K175K-fs). In all cases, we determined that the patients were actually heterozygous for these mutations.

Conclusion: Our results confirm that allele dropout is the mechanism causing apparent homozygosity of heterozygous mutations in these WD patients.

ATP7B mediates vesicular sequestration of copper: insight into biliary copper excretion

BACKGROUND & AIMS

The Wilson protein (ATP7B) regulates levels of systemic copper by excreting excess copper into bile. It is not clear whether ATP7B translocates excess intrahepatic copper directly across the canalicular membrane or sequesters this copper into exocytic vesicles, which subsequently fuse with canalicular membrane to expel their contents into bile. The aim of this study was to clarify the mechanism underlying ATP7B-mediated copper detoxification by investigating endogenous ATP7B localization in the HepG2 hepatoma cell line and its ability to mediate vesicular sequestration of excess intracellular copper.

METHODS

Immunofluorescence microscopy was used to investigate the effect of copper concentration on the localization of endogenous ATP7B in HepG2 cells. Copper accumulation studies to determine whether ATP7B can mediate vesicular sequestration of excess intracellular copper were performed using Chinese hamster ovary cells that exogenously expressed wild-type and mutant ATP7B proteins.

RESULTS

In HepG2 cells, elevated copper levels stimulated trafficking of ATP7B to pericanalicular vesicles and not to the canalicular membrane as previously reported. Mutation of an endocytic retrieval signal in ATP7B caused the protein to constitutively localize to vesicles and not to the plasma membrane, suggesting that a vesicular compartment(s) is the final trafficking destination for ATP7B. Expression of wild-type and mutant ATP7B caused Chinese hamster ovary cells to accumulate copper in vesicles, which subsequently undergo exocytosis, releasing copper across the plasma membrane.

CONCLUSIONS

This report provides compelling evidence that the primary mechanism of biliary copper excretion involves ATP7B-mediated vesicular sequestration of copper rather than direct copper translocation across the canalicular membrane.

Mutation analysis of 218 Chinese patients with Wilson disease revealed no correlation between the canine copper toxicosis gene MURR1 and Wilson disease

Wilson disease (WD) is the most common disorder resulting in hepatic copper overload. A similar form of copper-associated cirrhosis caused by mutations of the canine copper toxicosis MURR1 gene is also observed in Bedlington terriers. Recent studies indicate that MURR1 might influence human copper metabolism and the clinical presentations of WD. However, the correlation between the MURR1 gene and the Chinese patients with WD has not been reported. In the present study, all three exons of the MURR1 gene including the intron-exon boundaries were directly sequenced in 120 unrelated healthy Chinese and 218 unrelated Chinese patients with WD. No mutations were detected in coding and splice site sequence in the human MURR1 gene. A novel polymorphism 3'+119T-->A in the 3' untranslated region (UTR) was identified in three healthy individuals and four patients with two disease-causing mutations in the ATP7B gene and a great diversity of clinical presentations. Of the ATP7B mutations reported here, Gly1268Arg is a novel one. Also, the previously described nucleotide change IVS2+63C-->G was detected in 31.66% of normal chromosomes and 26.15% of WD chromosomes. The results have indicated that there is no correlation between MURR1 and WD in the Chinese population.

Alteration of copper physiology in mice overexpressing the human Menkes protein ATP7A

The Menkes protein (ATP7A) is defective in the Cu deficiency disorder Menkes disease and is an important contributor to the maintenance of physiological Cu homeostasis. To investigate more fully the role of ATP7A, transgenic mice expressing the human Menkes gene ATP7A from chicken beta-actin composite promoter (CAG) were produced. The transgenic mice expressed ATP7A in lung, heart, liver, kidney, small intestine, and brain but displayed no overt phenotype resulting from expression of the human protein. Immunohistochemical analysis revealed that ATP7A was found primarily in the cardiac muscle, smooth muscle of the lung, distal tubules of the kidney, intestinal enterocytes, and patches of hepatocytes, as well as in the hippocampus, cerebellum, and choroid plexus of the brain. In 60-day- and 300-day-old mice, Cu concentrations were reduced in most tissues, consistent with ATP7A playing a role in Cu efflux. The reduction in Cu was most pronounced in the hearts of older T22#2 females (24%), T22#2 males (18%), and T25#5 females (23%), as well as in the brains of 60-day-old T22#2 females and males (23% and 30%, respectively).

Late onset of Wilson's disease in a family with genetic haemochromatosis

We report the coexistence of Wilson's disease and genetic haemochromatosis in one family. The diagnosis of genetic haemochromatosis was established in a 52-year-old man. Among his siblings, one 57-year-old sister and one 55-year-old brother had decreased copper and ceruloplasmin levels in serum and increased urinary copper excretion. The sister shared the same human leucocyte antigen haplotypes and was homozygous for the HFE mutation C282Y, like the propositus. However, she had normal liver iron content and increased liver copper content. Her dietary copper intake was probably excessive. The association of Wilson's disease and genetic haemochromatosis is rare and has only been described twice. The onset of Wilson's disease after 50 years of age is rare; Wilson's disease should be considered in any patient with unexplained chronic liver disease; an excess in liver copper content might be induced by excessive dietary input in a susceptible individual.

Apolipoprotein E genotype analysis in Chinese Han ethnic children with Wilson's disease, with a concentration on those homozygous for R778L

Wilson's disease (WD) is an autosomal recessive disorder of copper metabolism caused by a large number of different mutations in the ATP7B gene. R778L mutation is mostly observed in Chinese, Japanese and Korean patients, whereas the H1069Q point mutation in the ATP7B gene is the most frequent mutation in European patients with WD. In our previous study we did not find a significant correlation between genotype and phenotype (age of onset and clinical presentation) in patients homozygous (37 patients) or heterozygous (52 patients) for R778L. It was reported that European patients homozygous for H1069Q who were also homozygous for the ApoE genotype epsilon3/3 developed clinical symptoms 5-11 years later than did patients with genotypes other than ApoE epsilon3/3. In the present study (i) we firstly observed that ApoE epsilon3/3 did not delay the onset of WD; (ii) no association between ApoE genotype and WD clinical presentation in Chinese Han children, including those patients homozygous for R778L. Thus we conclude that the onset of WD in Chinese children is not related to ApoE epsilon3/3, although the high frequency of ApoE epsilon3/3 in Chinese Han children with WD was not significantly different from that in controls.

Molecular pathogenesis of Wilson disease: haplotype analysis, detection of prevalent mutations and genotype-phenotype correlation in Indian patients

Wilson disease (WD) is an autosomal recessive disorder caused by defects in the copper-transporting P-type ATPase gene (ATP7B) resulting in the accumulation of copper in the liver and the brain. We identified prevalent mutations in the ATP7B of Indian WD patients and attempted to correlate those with the disease phenotype. Patients from 62 unrelated families and their first-degree relatives comprising 200 individuals were enrolled in this study. Three dinucleotide repeat markers flanking WD locus and a few intragenic SNPs were used to determine the genotypes and construct haplotypes of the patients. Seven recurring haplotypes accounting for 58% of the total mutant chromosomes were identified, and four underlying defects in the ATP7B representing 37% of WD chromosomes were detected. In addition, five other rare mutations were characterized. Thus a total of nine mutations including five novel changes were identified in the ATP7B of WD patients. Interestingly, homozygotes for different mutations that would be expected to produce similar defective proteins showed significant disparity in terms of organ involvement and severity of the disease. We also observed WD patients with neurological symptoms with little or no manifestation of hepatic pathogenesis. In one WD family, the proband and a sib had remarkably different phenotypes despite sharing the same pair of mutant chromosomes. These findings suggest a potential role for yet unidentified modifying loci for the observed phenotypic heterogeneity among the WD patients.

N-acetyltransferase is not the rate-limiting enzyme of melatonin synthesis at night

Circadian melatonin production in the pineal gland and retina is under the control of serotonin N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase. Because NAT activity varies diurnally, it has been considered both the melatonin rhythm-generating enzyme and the rate-limiting enzyme of melatonin synthesis. In rats with dramatically reduced NAT activity due to a H28Y mutation in NAT, melatonin levels remained the same as in wildtype controls, suggesting that NAT does not determine the rate of melatonin production at night. Using a combination of molecular approaches with a sensitive in vivo measurement of pineal diurnal melatonin production, we demonstrate that (i) N-acetylserotonin (NAS), the enzymatic product of NAT, is present in vast excess in the night pineals compared with melatonin; (ii) the continuous increase in NAT protein levels at late night does not produce a proportional increase in melatonin; and (iii) an increase in NAS in the same animal over several circadian cycles do not result in corresponding increase in melatonin output. These results strongly suggest that NAT is not the rate-limiting enzyme of melatonin formation at night.

Absence of nigrostriatal degeneration in LEC rats up to 20 weeks of age

BACKGROUND

Long-Evans Cinnamon (LEC) rat has a genetic defect of copper metabolism that is similar to human Wilson's disease. We studied the pathological changes in the nigrostriatal system of the LEC rat to examine the feasibility of using the LEC rat as a model of neurological Wilson's disease.

METHODS

LEC and Long-Evans Agouti (LEA) rats were killed at 12 and 20 weeks of age. FluoroJade B staining and immunohistochemistry were performed and Western blot compared the amount of tyrosine hydroxylase (TH) protein.

RESULTS

Degenerating neurons were not found in the substantia nigra (SN) and striatum. Dopaminergic neurons were of the same number in the SN of both LEC and LEA rats. Gliosis was of a similar degree in both animals. Western blot showed the same amount of TH protein in both animals.

DISCUSSION

There was no evidence of neurodegeneration in the nigrostriatal system of the LEC rat up to developmental age 20 weeks. The LEC rat is not a suitable model for deposition of copper in the brain in human Wilson's disease.