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.     

The interactions between iron and copper in genetic iron overload syndromes and primary copper toxicoses in Japan

Iron and copper are trace elements essential for health, and iron metabolism is tightly regulated by cuproproteins. Clarification of the interactions between iron and copper may provide a better understanding of the pathophysiology and treatment strategy for hemochromatosis, Wilson disease, and related disorders. The hepcidin/ferroportin system was used to classify genetic iron overload syndromes in Japan, and ceruloplasmin and ATP7B were introduced for subtyping Wilson disease into the severe hepatic and classical forms. Interactions between iron and copper were reviewed in these genetic diseases. Iron overload syndromes were classified into pre‐hepatic iron loading anemia and aceruloplasminemia, hepatic hemochromatosis, and post‐hepatic ferroportin disease. The ATP7B‐classical form with hypoceruloplasminemia has primary hepatopathy and late extra‐hepatic complications, while the severe hepatic form is free from ATP7B mutation and hypoceruloplasminemia, and silently progresses to liver failure. A large amount of iron and trace copper co‐exist in hepatocellular dense bodies of all iron overload syndromes. Cuproprotein induction to stabilize excess iron should be differentiated from copper retention in Wilson disease. The classical form of Wilson disease associated with suppressed hepacidin25 secretion may be double‐loaded with copper and iron, and transformed to an iron disease after long‐term copper chelation. Iron disease may not be complicated with the severe hepatic form with normal ferroxidase activity. Hepatocellular dense bodies of iron overload syndromes may be loaded with a large amount of iron and trace copper, while the classical Wilson disease may be double‐loaded with copper and iron.     

A new variant deletion of a copper-transporting P-type ATPase gene found in patients with Wilson's disease presenting with fulminant hepatic failure

A candidate gene (ATP7B) for Wilson's disease, an autosomal recessive disorder of copper transport, has recently been identified. We examined the ATP7B gene in two Japanese sisters with Wilson's disease presenting with fulminant hepatic failure but who did not exhibit Kayser-Fleischer rings or abnormal neurological findings. Genomic DNA was isolated from the whole blood of the patients and their family. Entire exons of ATP7B, and their associated splice junctions, were amplified by polymerase chain reaction. The sequencing of all exons was performed by a non-radioactive sequencing method. The sequencing of exon 12 of ATP7B revealed a 9-bp deletion. The mutation deleted 922Gly, 923Tyr, and 924Phe, and three residues conserved in the Menkes gene, ATP7A, located in the fifth transmembrane region. Of the 14 family members tested, 7 were normal and 7 were heterozygous for the deletion. Mean serum copper and cerulopasmin levels were significantly lower in the family members who were heterozygous for the deletion than in the normal family members, and two heterozygous family members showed abnormally low ceruloplasmin levels; however, there were no differences in mean aspartate aminotransferase or alanine aminotransferase levels between the two groups. Received: February 13, 1999 / Accepted: October 22, 1999     

Pathogenesis and management of Wilson disease

Hepatolenticular degeneration, commonly known as Wilson disease, is an autosomal recessive inherited disease of abnormal copper metabolism, characterized by the accumulation of copper in the body due to decreased biliary excretion of copper from hepatocytes. Wilson disease protein, ATP7B, functions in copper excretion into bile and in copper secretion to the bloodstream coupled with ceruloplasmin synthesis. Various kinds of mutations of ATP7B cause Wilson disease. Wilson disease is a rare genetic disease that can be treated pharmacologically. Recognition and prompt diagnosis are very important, because Wilson disease is fatal if left untreated. In this review, I summarize the pathogenesis and management of Wilson disease.     

The canine copper toxicosis gene MURR1 is not implicated in the pathogenesis of Wilson disease

Background It has recently been demonstrated that the Wilson disease (WD) protein directly interacts with the human homolog of the MURR1 protein in vitro and in vivo, and that this interaction is specific for the copper transporter. The aim of the present study was to clarify the role of MURR1 in the pathogenesis of WD as well as in other WD-like disorders of hepatic copper metabolism of unknown origin. Methods Using the single-strand conformation polymorphism (SSCP) method followed by sequencing, we analyzed the 5′ untranslated region (UTR) and three exons of the MURR1 gene in three groups of patients: 19 wd patients in whom no mutations were detected in the ATP7B gene, 53 wd patients in whom only one mutation in the ATP7B gene was found, and 34 patients in whom clinical and laboratory data suggested a WD-like disorder of hepatic copper metabolism of unknown origin. Results We  detected in these patients six rare nucleotide substitutions, namely one splice-site consensus sequence and one missense and four silent nucleotide substitutions. All substitutions except one were found in the heterozygous state. No difference in the frequencies of the various substitutions was observed between patients and controls. Conclusions These data suggest that the MURR1 gene and its protein product are unlikely to play a primary role in the pathogenesis of Wilson disease. More extensive studies with larger numbers of clinically homogeneous patients should be carried out to establish whether nucleotide alterations in the MURR1 gene may have a role in causing WD or WD-like disorders or act as modifying factors in the phenotype variability in WD.     

Genetic Testing for Wilson Disease: Availability and Utility

Wilson disease, a genetic disorder of copper metabolism, presents typically in the second and third decades of life with hepatic or neuropsychiatric disease. Clinical presentations often vary depending on age and degree of onset; although clinical and biochemical testing can usually establish a diagnosis, the data are difficult to interpret in some patients. Correctly identifying patients from nonaffected carriers is important because treatment is lifelong. Genetic testing has greatly improved the ability to diagnose Wilson disease in affected patients and in their siblings even without clear-cut clinical and biochemical data. Direct sequencing of ATP7B for disease-specific mutations is now the standard for molecular diagnosis. However, haplotype analysis is useful when only a single mutation can be found. In specific populations with a higher frequency of a specific mutation, direct testing for these mutations can simplify and expedite molecular diagnosis. The molecular genetic test is now available commercially and in specific research laboratories; however, barriers to its use include cost, understanding when to perform it, and interpretation. This test eventually will be incorporated into the diagnostic armamentarium, allowing timely diagnosis and perhaps reversal or even prevention of further copper-induced injury.     

Long‐term follow‐up of Wilson Disease: natural history,treatment, mutations analysis and phenotypic correlation

Background and aims: Wilson disease (WD) is an inherited disorder of copper metabolism. When treated, the outcome can be excellent, although the long‐term survival has yet to be well documented. The aim of this study was to describe the long‐term outcome of a cohort of patients with WD and to assess those factors affecting the phenotypic manifestation of WD. Methods: The presence of mutations to the ATP7B gene, the clinical manifestations, treatments and the long‐term outcomes were analysed retrospectively in 117 patients with WD (59 men and 58 women, aged at evaluation 38.5 ± 11, range 16–63 years). Results: Fifty‐five patients with a neurological presentation, 51 patients with a hepatic presentation and 11 asymptomatic patients were followed up for an average of 15.1 ± 10 years (median 12 years, range 1–41 years). The H1069Q ATP7B gene mutation was the most frequent genetic variant (54.3%); the frequency of this mutation did not differ between patients with either the hepatic or the neurological presentation (P=0.099). d ‐penicillamine or zinc salts (81 and 17% respectively) were used for treatment, and three patients underwent liver transplantation. The majority of symptomatic patients became asymptomatic, or improved, during the follow‐up (82% patients with hepatic presentation, 69% with neurological presentation). The long‐term survival of patients with WD did not differ from that of the general Czech population (P=0.95). Conclusions: Long‐term follow‐up shows a satisfactory response in the great majority of adequately treated patients with WD and survival coincides with that of the general population.     

Prevalence of ATP7B Gene Mutations in Iranian Patients With Wilson Disease

Background

Wilson disease (WD) is an autosomal recessive disorder. The WD gene, ATP7B, encodes a copper-transporting ATPase involved in the transport of copper into the plasma protein ceruloplasmin and in excretion of copper from the liver. ATP7B mutations cause copper to accumulate in the liver and brain.

Objectives

We examined the ATP7B mutation spectrum in Wilson disease patients in Iran.

Patients and Methods

Genomic DNA was extracted from patients with Wilson disease. The entire coding region of the ATP7B gene was amplified using PCR and analyzed using direct sequencing.

Results

We identified five novel mutations in 5 Iranian patients with Wilson disease. The first was a transversion, c.2363C > T, which led to an amino acid change from threonine to isoleucine. The second mutation was a deletion, c.2532delA (Val845Ser), which occurred in exon 10. The third mutation was a transition mutation, c.2311C > G (Leu770Leu), which occurred in the TM4 domain of the ATP7B protein. The fourth mutation was a transversion, (c.3061G > A) (Lys1020Lys), in exon 14. Lastly, we identified a transversion, c.3206C > A (His1069Asn) in exon 14 which led to a change in function of the ATP loop domain of the ATP7B protein. The H1069Q mutation was identified as the most common mutation in our study population.

Conclusions

Based on our findings, the H1069Q may be a biomarker that can be used in a rapid detection assay for diagnosing WD patients     

High prevalence of the H1069Q mutation in East German patients with Wilson disease: rapid detection of mutations by limited sequencing and phenotype-genotype analysis.

BACKGROUND/AIMS: Wilson disease is caused by a large number of different mutations in the ATP7B gene. Wilson disease patients from a homogeneous ethnical background (Saxonia) were studied for distribution and phenotypes of ATP7B mutations. METHODS: Eighty-two patients were analyzed. The H1069Q mutation was assayed by a polymerase chain reaction-based restriction fragment length polymorphism test. Exons 8 and 15 were sequenced in all, and the entire gene in 30, non-H1069Q-homozygotes. RESULTS: Four novel and 12 known mutations were found. Thirty-two (39%) Wilson disease patients were homozygous and 39 (48%) heterozygous for the H1069Q mutation (allele frequency 63%). Together with sequence analysis of exons 8 and 15 mutations in both alleles were identified in 65% of patients. Only one patient had both mutations at other locations. In H1069Q homozygotes symptoms started later (21.3+/-7.2 years) than in H1069Q compound heterozygotes (14.6+/-5.8, P<0.001) or H1069Q negatives (10+/-4.4, P<0.001), and they had more frequently neurologic symptoms (93 vs. 47%, P<0.001) and Kayser-Fleischer rings (82 vs. 51%, P<0.001). Mutation status did not correlate with liver biopsy findings, serum ceruloplasmin levels or (64)Cu-assay results. CONCLUSIONS: In spite of many known ATP7B mutations, only few occur in this homogeneous population. Limited genetic testing is useful to confirm Wilson disease in this population.     

Multiplex ARMS PCR to Detect 8 Common Mutations of ATP7B Gene in Patients With Wilson Disease

Background

Wilson disease is a rare disorder of copper metabolism due to mutation in ATP7B gene. Proper counseling of patients with Wilson disease, and their families necessitates finding mutation in ATP7B gene. Finding mutations in ATP7B gene with 21 exons, and more than 500 mutations is expensive and time-consuming.

Objectives

The aim of this study was to provide a simple multiplex amplification refractory mutation system PCR (M-ARMS-PCR) for screening eight common mutations in ATP7B gene.

Patients and Methods

Two sets of ARMS mutant and normal specific primer pairs were designed for genotyping of p.R778L, p.R969Q, p.H1069Q, and p.3400delC mutations as Set 1 and p.W779G, c.3061-1G > A, p.I1102T, and p.N1270S mutations as Set 2. The Multiplex ARMS assay was then subsequently tested in 65 patients with Wilson disease with known and unknown ATP7B mutations.

Results

Using these two sets, we identified H1069Q mutation in four patients, c.2335T > G mutation in three, c.3061-1G > A splice site mutation in five, c.3305T > C mutation in one, and c.3809A > G mutation in two patients.

Conclusions

The Multiplex ARMS assay used in this study can be an efficient, reliable, and cost effective method as a primary screen for patients with Wilson disease.     

Genetics of Wilson’s disease: a clinical perspective

Hepatic Wilson??s disease is often a difficult diagnosis to confirm. This review examines the current role of genetic tests for Wilson??s disease and is aimed at clinicians caring for patients with this disease. We discuss how genetic testing is carried out for Wilson??s disease, indications for these tests, and genetic counseling for the family. In contrast to the advances in diagnosis of Wilson??s disease by testing for ATP7B mutations, genotype-phenotype correlations are not yet sufficiently established. The non-Wilsonian copper overload syndromes causing cirrhosis in children are another important area for study. The review also identifies further areas for research into the genetics of Wilson??s disease in India.     

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.     

Pathophysiology and Clinical Features of Wilson Disease

Wilson disease is an autosomal recessive inherited disorder of copper metabolism resulting in pathological accumulation of copper in many organs and tissues. ATP7B is the gene product of the Wilson disease gene located on chromosome 13 and resides in hepatocytes in the trans-Golgi network, transporting copper into the secretory pathway for incorporation into apoceruloplasmin and excretion into the bile. Mutations of the gene result in impaired trafficking of copper in and through the hepatocytes. More than 200 mutations of Wilson disease gene were found, the most common ones being H1069Q (in Europe) and R778L (in Asia). Wilson disease may present under a variety of clinical conditions, commonly as liver and/or neuropsychiatric disease. The pathogenesis of hepatic and neurologic Wilson disease is a direct consequence of copper accumulation. Presence of copper causes oxidative stress resulting in cell destruction. The diagnosis of Wilson disease requires a combination of a variety of clinical symptoms, biochemical tests, and detection of gene mutations, which are the basis of a score proposed by a group of international experts. Initial treatment for symptomatic patients should include a chelating agent (penicillamine or trientine). Treatment of presymptomatic patients or maintenance therapy can also be accomplished with zinc.     

Diagnosis and phenotypic classification of Wilson disease1

Wilson disease is an inherited autosomal recessive disorder of hepatic copper metabolism leading to copper accumulation in hepatocytes and in extrahepatic organs such as the brain and the cornea. Originally Wilson disease was described as a neurodegerative disorder associated with cirrhosis of the liver. Later, Wilson disease was observed in children and adolescents presenting with acute or chronic liver disease without any neurologic symptoms. While diagnosis of neurologic Wilson disease is straightforward, it may be quite difficult in non‐neurologic cases. Up to now, no single diagnostic test can exclude or confirm Wilson disease with 100% certainty. In 1993, the gene responsible for Wilson disease was cloned and localized on chromosome 13q14.3 (MIM277900) ( 1 , 2 ). The Wilson disease gene ATP7B encodes a P‐type ATPase. More than 200 disease causing mutations of this gene have been described so far ( 3 ). Most of these mutations occur in single families, only a few are more frequent (like H1069Q, 3400delC and 2299insC in Caucasian ( 4 - 6 ) or R778L in Japanese ( 7 ), Chinese and Korean patients). Studies of phenotype‐genotype relations are hampered by the lack of standard diagnostic criteria and phenotypic classifications. To overcome this problem, a working party discussed these problems in depth at the 8th International Meeting on Wilson disease and Menkes disease in Leipzig/Germany (April 16–18, 2001) ² 2This meeting was organized under the auspices of the European Association for the Study of the Liver (EASL) and was financially supported by the European Commission (High‐level Scientific Conference No. HPCF‐CT‐2000‐00327) and the Austrian Society of Gastroenterology and Hepatology (O¨GGH). . After the meeting, a preliminary draft of a consensus report was mailed to all active participants and their comments were incorporated in the final text.     

The H1069Q mutation in ATP7B is associated with late and neurologic presentation in Wilson disease: results of a meta-analysis

BACKGROUND AND AIMS: Wilson disease is an hereditary disorder of copper metabolism, caused by mutations in the ATP7B gene, and leading to hepatic or neurologic disease. We examined whether H1069Q, the most common ATP7B mutation, is associated with a specific phenotype. METHODS: Genotyping results in 70 Dutch patients were related to clinical presentation. Subsequently a meta-analysis for genotype-phenotype correlation was performed on all patients available from literature, combined with the current Dutch group, a total of 577 patients. RESULTS: The Dutch patients homozygous or heterozygous for the H1069Q mutation presented more frequently with neurologic disease (63% and 43% vs. 15%), and at a later age (20.9 and 15.9 vs. 12.6 years) than patients without the H1069Q mutation. In the meta-analysis the odds-ratio for neurologic presentation in homozygous or heterozygous H1069Q vs. non-H1069Q patients was 3.50 (95% CI 2.01-6.09) and 2.13 (95% CI 1.18-3.83), respectively. Age at presentation was 21.1, 19.2 and 16.5 years, respectively, corresponding to a weighted mean difference (WMD) of 4.41 (95% CI 1.56-7.26) for homozygous H1069Q vs. heterozygous patients and 6.68 (95% CI 4.33-9.38) for homozygous H1069Q vs. non-H1069Q patients. CONCLUSIONS: Our results indicate that the H1069Q mutation is associated with a late and neurologic presentation.     

Functional analysis and drug response to zinc and D-penicillamine in stable ATP7B mutant hepatic cell lines

AIM: To study the effect of anti-copper treatment for survival of hepatic cells expressing different ATP7B mutations in cell culture.METHODS: The most common Wilson disease (WD) mutations p.H1069Q, p.R778L and p.C271*, found in the ATP7B gene encoding a liver copper transporter, were studied. The mutations represent major genotypes of the United States and Europe, China, and India, respectively. A human hepatoma cell line previously established to carry a knockout of ATP7B was used to stably express WD mutants. mRNA and protein expression of mutant ATP7B, survival of cells, apoptosis, and protein trafficking were determined.RESULTS: Low temperature increased ATP7B protein expression in several mutants. Intracellular ATP7B localization was significantly impaired in the mutants. Mutants were classified as high, moderate, and no survival based on their viability on exposure to toxic copper. Survival of mutant p.H1069Q and to a lesser extent p.C271* improved by D-penicillamine (DPA) treatment, while mutant p.R778L showed a pronounced response to zinc (Zn) treatment. Overall, DPA treatment resulted in higher cell survival as compared to Zn treatment; however, only combined Zn + DPA treatment fully restored cell viability.CONCLUSION: The data indicate that the basic impact of a genotype might be characterized by analysis of mutant hepatic cell lines.     

Mutation analysis and characterization of alternative splice variants of the Wilson disease gene ATP7B

Wilson disease is a copper metabolism disorder caused by mutations in ATP7B, a copper-transporting adenosine triphosphatase. A molecular diagnosis was performed on 135 patients with Wilson disease in Taiwan. We identified 36 different mutations, eight of which were novel: five missense mutations (Ser986Phe, Ile1348Asn, Gly1355Asp, Met1392Lys, and Ala1445Pro), one deletion (2810delT) in the coding region, and two nucleotide substitutions (-133A→C and -215A→T) in the promoter region. These mutations were not observed in 100 control subjects and reduced the activity of the mutated protein by at least 50% when compared with wild-type ATP7B. In addition to exon 8, our data indicate another mutation hotspot in exon 12 where 9.62% of all mutations occurred. An alternative splice variant of ATP7B lacking exon 12 was observed in one patient who had a homozygous 2810delT mutation and very mild clinical symptoms. Clinical examination and functional characterization of alternative splice variants of ATP7B lacking exon 12 showed that they retained 80% of their biological activity. The 2810delT mutation increased the expression of these variants, which may have explained the mild symptoms in the patient with the 2810delT mutation. We also discovered that treating liver cancer cells with a Na(+)/H(+) exchanger inhibitor, 5-(N-ethyl-N-isopropyl)-amiloride, significantly enhanced the expression of the alternative splice variant of ATP7B lacking exon 12. CONCLUSION: This study suggests a novel therapeutic strategy for patients with mutations in exon 12.     

Hämochromatose und Morbus Wilson

Hereditary hemochromatosis and Wilson disease are both autosomal recessively inherited metabolic diseases that can lead to liver cirrhosis. Hereditary hemochromatosis is characterized by iron overload due to elevated duodenal iron absorption, while copper overload in Wilson disease results from an impaired copper excretion into bile. Especially in hemochromatosis but also in Wilson disease, the last decade has seen extraordinary growth in our understanding of the pathophysiology of both diseases. In hemochromatosis, hepatic and extrahepatic symptoms can occur. Extrahepatic symptoms include cardiomyopathy, diabetes mellitus, arthritis, and endocrine dysfunction. In Wilson disease, hepatic and/or neuropsychiatric symptoms are typical. While genetic testing for a homozygote HFE C282Y mutation (or a compound heterozygote C282Y/H63D mutation) is very helpful in hemochromatosis, genetic analysis of the Wilson gene, ATP7B, is limited by the existence of a plethora of individual mutations. Hemochromatosis is treated effectively with phlebotomies, whereas Wilson disease is treated medically with chelators (D-penicillamine and triethylenetetramine) or zinc salts. Liver transplantation is a therapeutic option for both diseases and shows excellent long-term results in Wilson disease, but less favorable results in hemochromatosis. The prognosis of sufficiently treated disease is very good for both diseases, especially when the diagnosis is established early in the disease course.     

Wilson disease: revision of diagnostic criteria in a clinical series with great genetic homogeneity

Background

Wilson disease is an autosomal recessive disorder of copper metabolism caused by mutations in the ATP7B gene. An early diagnosis is crucial to prevent evolution of the disease, as implantation of early therapeutic measures fully prevents its symptoms. As population genetics data predict a higher than initially expected prevalence, it was important to define the basic diagnostic tools to approach population screening.

Methods

A highly genetically homogeneous cohort of 70 patients, belonging to 50 unrelated families, has been selected as a framework to analyze all their clinical, biochemical and genetic characteristics, to define the disease in our population, with an estimated prevalence of 1 in 12,369, and determine the most useful features that reach diagnostic value.

Results

Serum ceruloplasmin below 11.5 mg/dL and cupremia below 60 μg/mL, were the best analytical predictors of the disease in asymptomatic individuals, while cupruria or hepatic copper determination were less powerful. Genetic analysis reached a conclusive diagnosis in all 65 patients available for complete testing. Of them, 48 were carriers of at least one p.Leu708Pro mutant allele, with 24 homozygotes. Nine patients carried a promoter deletion mutation, revealing that extended sequencing beyond the ATP7B gene-coding region is essential. All mutations caused hepatic damage since early ages, increasing its severity as diagnosis was delayed, and neurological symptoms appear.

Conclusion

Serum ceruloplasmin determination followed by genetic screening would reduce costs and favor the prioritization of non-invasive procedures to reach a definitive diagnosis, even for asymptomatic cases.

     

High prevalence of the very rare Wilson disease gene mutation Leu708Pro in the Island of Gran Canaria (Canary Islands, Spain): a genetic and clinical study

The molecular basis of Wilson disease (WD), an autosomal recessive disorder, is the presence of mutations in the ATP7B gene, a copper transporting ATPase. Hospital records indicated a higher prevalence of WD (1 in 2,600) in some counties in the northeastern region of the island of Gran Canaria (Canary Islands, Spain) that was around 10-fold higher than that described for European populations (1 in 30,000). The ATP7B gene was analyzed for mutations in 24 affected subjects, revealing a high prevalence of the rare Leu708Pro mutation present in 12 homozygous and 7 heterozygous individuals. In these patients, who constitute one of the largest described cohorts of WD homozygotes, we found a variable clinical presentation of the disease, although the biochemical picture was homogenous and characteristic, thereby confirming that the Leu708Pro change is indeed a mutation associated with WD. Haplotype analysis of subjects homozygous for the Leu708Pro mutation showed a conserved shared region smaller than 1 centimorgan (cM), and the region of linkage disequilibrium between the Leu708Pro mutation and neighboring microsatellite markers extended approximately 4.6 cM. When comparing the amount of linkage disequilibrium versus genetic distance from the disease mutation, it was estimated that a common ancestral Leu708Pro chromosome may have been introduced in Gran Canaria over 56 generations ago, dating it back to pre-Hispanic times. The prevalence, and the tight geographical distribution of the Leu708Pro chromosome suggests that the Canary Islands can be considered a genetic isolate for linkage disequilibrium studies.