High frequency of two mutations in codon 778 in exon 8 of the ATP7B gene in Taiwanese families with Wilson disease

Decoding Neurodegeneration: A Comprehensive Review of Molecular Mechanisms, Genetic Influences, and Therapeutic Innovations

Neurodegenerative disorders often acquire due to genetic predispositions and genomic alterations after exposure to multiple risk factors. The most commonly found pathologies are variations of dementia, such as frontotemporal dementia and Lewy body dementia, as well as rare subtypes of cerebral and cerebellar atrophy-based syndromes. In an emerging era of biomedical advances, molecular-cellular studies offer an essential avenue for a thorough recognition of the underlying mechanisms and their possible implications in the patient's symptomatology. This comprehensive review is focused on deciphering molecular mechanisms and the implications regarding those pathologies' clinical advancement and provides an analytical overview of genetic mutations in the case of neurodegenerative disorders. With the help of well-developed modern genetic investigations, these clinically complex disturbances are highly understood nowadays, being an important step in establishing molecularly targeted therapies and implementing those approaches in the physician's practice.

Three novel mutations in the ATP7B gene of unrelated Vietnamese patients with Wilson disease

Background

Wilson disease (OMIM # 277900) is a autosomal recessive disorder characterized by accumulation of copper in liver and brain. The accumulation of copper resulting in oxidative stress and eventually cell death. The disease has an onset in a childhood and result in a significant neurological impairment or require lifelong treatment. Another serious consequence of the disease is the development of liver damage and acute liver failure leading to liver transplant. The disorder is caused by mutations in the ATP7B gene, encoding a P-type copper transporting ATPase.

Case presentation

We performed genetic analysis of three unrelated patients from three different Vietnamese families. These patients had clinical features such as numbness of hands and feet, vomiting, insomnia, palsy, liver failure and Kayser–Fleischer (K–F) rings and were diagnosed with Wilson disease in the Human Genetics Department, Vietnam National Children’s Hospital. The entire coding region and adjacent splice sites of ATP7B gene were amplified and sequenced by Sanger method. Sequencing data were analyzed and compared with the ATP7B gene sequence published in Ensembl (ENSG00000123191) by using BioEdit software to detect mutations.

Conclusions

In this study, five mutations in the ATP7B gene were found. Among of these, three mutations were novel: c.750_751insG (p.His251Alafs*19) in exon 2, c.2604delC (p.Pro868Profs*5) in exon 11, and c.3077 T > A (p.Phe1026Tyr) in exon 14. Our results of the mutations associated with Wilson disease might facilitate the development of effective treatment plans.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0619-4) contains supplementary material, which is available to authorized users.

Epidemiology and introduction to the clinical presentation of Wilson disease

Our understanding of the epidemiology of Wilson disease has steadily grown since Sternlieb and Scheinberg's first prevalence estimate of 5 per million individuals in 1968. Increasingly sophisticated genetic techniques have led to revised genetic prevalence estimates of 142 per million. Various population isolates exist where the prevalence of Wilson disease is higher still, the highest being 885 per million from within the mountainous region of Rucar in Romania. In Sardinia, where the prevalence of Wilson disease has been calculated at 370 per million births, six mutations account for around 85% of Wilson disease chromosomes identified. Significant variation in the patterns of presentation may however exist, even between individuals carrying the same mutations. At either extremes of presentation are an 8-month-old infant with abnormal liver function tests and individuals diagnosed in their eighth decade of life. Three main patterns of presentation have been recognized - hepatic, neurologic, and psychiatric - prompting their presentation to a diverse range of specialists. Deviations in the family history from the anticipated autosomal-recessive mode of inheritance, with apparent "pseudodominance" and mechanisms of inheritance that include uniparental isodisomy (the inheritance of both chromosomal copies from a single parent), may all further cloud the diagnosis. It can therefore take the efforts of an astute clinician with a high clinical index of suspicion to clinch the diagnosis of this eminently treatable condition.

Disorders of metal metabolism

Trace elements are chemical elements needed in minute amounts for normal physiology. Some of the physiologically relevant trace elements include iodine, copper, iron, manganese, zinc, selenium, cobalt and molybdenum. Of these, some are metals, and in particular, transition metals. The different electron shells of an atom carry different energy levels, with those closest to the nucleus being lowest in energy. The number of electrons in the outermost shell determines the reactivity of such an atom. The electron shells are divided in sub-shells, and in particular the third shell has s, p and d sub-shells. Transition metals are strictly defined as elements whose atom has an incomplete d sub-shell. This incomplete d sub-shell makes them prone to chemical reactions, particularly redox reactions. Transition metals of biologic importance include copper, iron, manganese, cobalt and molybdenum. Zinc is not a transition metal, since it has a complete d sub-shell. Selenium, on the other hand, is strictly speaking a nonmetal, although given its chemical properties between those of metals and nonmetals, it is sometimes considered a metalloid. In this review, we summarize the current knowledge on the inborn errors of metal and metalloid metabolism.

ATP7B Mutation Detection and Pathogenicity Analysis: One Atypical Case of Wilson's Disease with Adrenocortical Insufficiency

Wilson's disease (WD) is an autosomal recessive disorder caused by defective function of the copper-transporting ATP7B protein. Symptoms are typically related to the brain and liver, while endocrinologic abnormalities are rare. Here, we reported a 12-year-old female patient that was initially presented with unusual skin darkening and low serum level of adrenocorticotropic hormone and diagnosed as having adrenocortical insufficiency. We further screened the mutation in ATP7B by direct DNA sequencing and found compound heterozygous mutations: a known pathogenic mutation in exon8:c.2333G>T (Arg778Leu) inherited from her mother and a variant in intron4:c.1707 + 5G>A inherited from her father. To explore the pathogenicity of the intronic variant, a minigene splicing assay was used to determine the effects of the splicing variant by analyzing reverse transcription PCR of ATP7B minigene transcript production. The result indicated that the c.1707 + 5G>A variant resulted in exon 4 skipping. We herein identified that 1707 + 5G>A intron 4 variant is a pathogenic mutation. Molecular genetic analysis and laboratory examination definitely confirmed the patient's condition as WD. Clinical status improved considerably after penicillamine treatment. Our results extended the mutation spectrum of ATP7B gene and highlighted the importance of molecular genetic analysis for the accurate diagnosis of atypical WD. WD may have diverse presentations and should be considered in children especially presenting with adrenocortical insufficiency as initial symptom, and this study highlights the importance of screening for hormone abnormal in WD.

Wilson's Disease: Clinical, Genetic and Pharmacological Findings

Wilson's disease (WD) is an autosomal recessive disorder characterized by copper accumulation and toxicity in the liver and in other tissues. WD presents with liver disease, neurological or psychiatric disturbances or other less common clinical features. Diagnosis of WD is often difficult and may be formulated through clinical, biochemical, imaging, histochemical and genetic evaluations. Pharmacological approach in WD consists in copper chelating agents such as D-penicillamine, trientine, dimercaprol and tetrathiomolybdate. In 1997 zinc was approved for maintenance therapy of WD by the U.S. FDA. Orthotopic Liver Transplantation is indicated in fulminant hepatic failure, progressive hepatic insufficiency despite therapy, cirrhosis with complications of portal hypertension. However the most appropriate therapy, including OLT, remains controversial in WD and further studies are needed especially in order to differentiate the possibility of specific therapies for different WD phenotypes.

Mutational analysis of ATP7B in Chinese Wilson disease patients

Wilson Disease (WD) is an inborn error of copper metabolism inherited in an autosomal recessive manner caused by the mutations in the P-type ATPase gene (ATP7B). In this study, we screen and detect the mutations of the ATP7B gene in unrelated Chinese WD patients. A total of 68 individuals from ten provinces of China with WD were recruited. Of them, 43 were males and 25 were females, and their onset ages were from 1 to 48 years with a median onset age of 22.2 years. All the exons and exon/intron boundaries of ATP7B gene of the patients were sequenced and aligned to the referred ATP7B gene sequence. The results suggested that 66 of the 68 patents carried with at least one mutation and 48 different mutations were identified including 34 missense, one synonymous, two nonsense, two splicing, and nine frameshift mutations (five insertion and four deletion). Among these mutations, c.2333G>T, c.2310C>G, c.2975C>T, and c.3443T>C were the most prevalent mutants and c.2310C>G always linked with c.2333G>T. The eighth, 11(th), and 18(th) exons carried more mutations (6/48, 5/48, and 5/48, respectively) than others. After comparing with the mutations reported previously, 22 out of the 48 mutations were identified as novel mutations. A popular algorithm, Polyphen-2, was used to predict the effects of the amino-acid substitution due to the mutations on the structure and function of ATP7B function and the predicted results indicated that all the missense mutations were unfavorable except c.121A>G and c.748G>A. Phenotype/genotype correlation analysis suggested that the patients with c.2975C>T or c.3809A>G often presented WD features before 12 years old while the patients with c.3443T>C almost presented WD after 12 years old. This is the first time to identify the common mutations contributing to early onset age in Chinese WD patients. Our study will broaden our knowledge about ATP7B mutations in WD patients.

Currently Clinical Views on Genetics of Wilson's Disease

Objective:

The objective of this study was to review the research on clinical genetics of Wilson's disease (WD).

Data Sources:

We searched documents from PubMed and Wanfang databases both in English and Chinese up to 2014 using the keywords WD in combination with genetic, ATP7B gene, gene mutation, genotype, phenotype.

Study Selection:

Publications about the ATP7B gene and protein function associated with clinical features were selected.

Results:

Wilson's disease, also named hepatolenticular degeneration, is an autosomal recessive genetic disorder characterized by abnormal copper metabolism caused by mutations to the copper-transporting gene ATP7B. Decreased biliary copper excretion and reduced incorporation of copper into apoceruloplasmin caused by defunctionalization of ATP7B protein lead to accumulation of copper in many tissues and organs, including liver, brain, and cornea, finally resulting in liver disease and extrapyramidal symptoms. It is the most common genetic neurological disorder in the onset of adolescents, second to muscular dystrophy in China. Early diagnosis and medical therapy are of great significance for improving the prognosis of WD patients. However, diagnosis of this disease is usually difficult because of its complicated phenotypes. In the last 10 years, an increasing number of clinical studies have used molecular genetics techniques. Improved diagnosis and prediction of the progression of this disease at the molecular level will aid in the development of more individualized and effective interventions, which is a key to transition from molecular genetic research to the clinical study.

Conclusions:

Clinical genetics studies are necessary to understand the mechanism underlying WD at the molecular level from the genotype to the phenotype. Clinical genetics research benefits newly emerging medical treatments including stem cell transplantation and gene therapy for WD patients.

Update on Wilson disease

Wilson disease (WD) is an inherited disorder of chronic copper toxicosis characterized by excessive copper deposition in the body, primarily in the liver and the brain. It is a progressive disease and fatal if untreated. Excessive copper accumulation results from the inability of liver to excrete copper in bile. Copper is an essential trace metal and has a crucial role in many metabolic processes. Almost all of the body copper is protein bound. In WD, the slow but relentless copper accumulation overwhelms the copper chaperones (copper-binding proteins), resulting in high levels of free copper and copper-induced tissue injury. Liver is the central organ for copper metabolism, and copper is initially accumulated in the liver but over time spills to other tissues. WD has protean clinical manifestations mainly attributable to liver, brain, and osseomuscular impairment. Diagnosis of WD is challenging and based on combination of clinical features and laboratory tests. Identification of various high-frequency mutations identified in different population studies across the world has revived interest in developing DNA chips for rapid genetic diagnosis of WD. All symptomatic and all presymptomatic patients require lifelong decoppering with careful clinical tracking. Decoppering ensures that presymptomatic individuals remain symptom free. With judicious decoppering, given time, even patients with severe neurological disability improve and can return to normal life and resume school or work at par with their peers. Treatment regimens and tracking patients using the WD-specific Global Assessment Scale for WD (GAS for WD) are discussed.

Family screening for a novel ATP7B gene mutation, c.2335T>G, in the South of Iran

BACKGROUND

Wilson disease (WD) is a rare autosomal recessive disorder, which leads to copper metabolism, due to mutations in ATP7B gene. The gene responsible for WD consists of 21 exons that span a genomic region of about 80 kb and encodes a copper transporting P-type ATPase (ATP7B), a protein consisting of 1465 amino acids. Identifying mutation in ATP7B gene is important to find carrier individuals for proper counseling. A novel mutation in exon 8 of ATP7B gene, c.2335T>G (p.Trp779Gly), with severe neuropsychiatric condition in the South of Iran, was recently identified. The aim of this study was to screen 120 individuals from a large family using a simple amplification refractory mutation system PCR (ARMS-PCR) for carrier screening in the South of Iran.

MATERIALS AND METHODS

120 individuals from family relatives of an index case in the Nasr Abad, south of Iran, were studied for screening of the c.2335T>G mutation. One patient with homozygous mutation and one homozygous normal individual were used as controls in this experiment.

RESULTS

Altogether, 16 out of 120 (13.3%) individuals within this region had heterozygous mutation. One individual with homozygote mutation was also identified.

CONCLUSION

Identification of carriers in families with affected individuals is of great importance for counseling before marriage. The results of this study can be used for further counseling programs in this population.

Metal storage disorders: Wilson disease and hemochromatosis

Hereditary hemochromatosis and Wilson disease are autosomal recessive storage disorders of iron and copper overload, respectively. These metals are involved in multiple redox reactions, and their abnormal accumulation can cause significant injury in the liver and other organs. Over the last few decades clinicians have developed a much better understanding of these metals and their mechanism of action. Moreover, sophisticated molecular genetic testing techniques that make diagnostic testing less invasive are now available. This article updates and discusses the pathogenesis, diagnosis, and management of these metal storage disorders.

Identification of one novel and nine recurrent mutations of the ATP7B gene in 11 children with Wilson disease

BACKGROUND

Wilson disease (WND), also called hepatolenticular degeneration, is an autosomal recessive genetic disorder in which copper abnormally accumulates in several organs. WND arises from the defective ATP7B gene, which encodes a copper transporting P-type ATPase.

METHODS

The molecular defects in 11 unrelated Chinese WND patients aged from 3 to 12 years were investigated. The diagnosis of these patients was based on typical clinical symptoms and laboratory testing results. All 21 exons and exon-intron boundaries of the ATP7B gene were amplified by polymerase chain reaction from the genomic DNA of the patients and then analyzed by direct sequencing. One hundred healthy subjects served as controls to exclude gene polymorphism.

RESULTS

In one novel (c.3605 C>G) and nine recurrent mutations of ATP7B identified, there were eight missense mutations, one splice-site mutation, and one nonsense mutation. The novel c.3605 C>G mutation resulted in the substitution of alanine by glycine at amino acid position 1202 (p.Ala1202Gly). The most frequent ATP7B mutation was c.2333 G>T (p.Arg778Leu), followed by c.2975 C>T (p.Pro992Leu), which accounted for 63.6% of the WND mutated alleles.

CONCLUSIONS

The novel c.3605 C>G mutation in. ATP7B is one of the molecular mechanisms of WND.

Wilson disease mutation pattern with genotype-phenotype correlations from Western India: confirmation of p.C271* as a common Indian mutation and identification of 14 novel mutations

Wilson disease (WD) is an autosomal recessive disorder resulting from mutations in the ATP7B gene, with over 600 mutations described. Identification of mutations has made genetic diagnosis of WD feasible in many countries. The heterogeneity of ATP7B mutants is, however, yet to be identified in the Indian population. We analyzed the mutational pattern of WD in a large region of Western India. We studied patients (n = 52) for ATP7B gene mutations in a cohort of families with WD and also in first-degree relatives (n = 126). All 21 exon-intron boundaries of the WD gene were amplified and directly sequenced. We identified 36 different disease-causing mutations (31 exonic and five intronic splice site variants). Fourteen novel mutations were identified. Exons 2, 8, 13, 14, and 18 accounted for the majority of mutations (86.4%). A previously recognized mutation, p.C271*, and the novel mutation p.E122fs, were the most common mutations with allelic frequencies of 20.2% and 10.6%, respectively. Frequent homozygous mutations (58.9%) and disease severity assessments allowed analysis of genotype-phenotype correlations. Our study significantly adds to the emerging data from other parts of India suggesting that p.C271* may be the most frequent mutation across India, and may harbor a moderate to severely disabling phenotype with limited variability.

A new ATP7B gene mutation with severe condition in two unrelated Iranian families with Wilson disease

Wilson disease is associated with a defect in copper metabolism and caused by different mutations in ATP7B gene. The aim of this study was to determine mutation frequency of ATP7B exons 8 and 14 in Wilson disease patients from the south of Iran. The exons 8 and 14 of ATP7B gene were analyzed in 65 unrelated Wilson disease patients by Denaturing High Performance Liquid Chromatography, and samples with abnormal peak profile were selected for direct DNA sequencing. Seven out of 65 (10.8%) patients had mutations at exon 14, including c.3061-1G>A in four and c.3207C>A in three patients. In addition, four different mutations were identified at exon 8 of six patients (9.2%). Three of these mutations have been previously reported, including c.2304delC in two patients, c.2293G>A and 2304dupC each in one patient. Furthermore, a novel mutation, c.2335T>G (p.Trp779Gly), was identified in two unrelated patients. The patients with this novel mutation demonstrated severe neuropsychiatric condition. All together, 13 out of 65 (20%) patients had mutations within exons 8 and 14. We also identified a lower frequency of the most common mutations of exons 8 and 14 in the southern Iranian population.

A structural model of the copper ATPase ATP7B to facilitate analysis of Wilson disease-causing mutations and studies of the transport mechanism

The copper-transporting ATPase ATP7B has an essential role in human physiology, particularly for the liver and brain function. Inactivation of ATP7B is associated with a severe hepato-neurologic disorder, Wilson disease (WD). Hundreds of WD related mutations have been identified in ATP7B to date. The low frequency and the compound-heterozygous nature of causative mutations complicate the analysis of individual mutants and the establishment of genotype-phenotype correlations. To facilitate studies of disease-causing mutations and mechanistic understanding of WD, we have homology-modelled the ATP7B core (residues 643-1377) using the recent structure of the bacterial copper-ATPase LCopA as a template. The model, supported by evolutionary conservation and hydrophobicity analysis, as well as existing and new mutagenesis data, allows molecular interpretations of experimentally characterized clinical mutations. We also illustrate that structure and conservation can be used to grade potential deleterious effects for many WD mutations, which were clinically detected but have not yet been experimentally characterized. Finally, we compare the structural features of ATP7B and LCopA and discuss specific features of the eukaryotic copper pump.

Mutation analysis of 73 southern Chinese Wilson's disease patients: identification of 10 novel mutations and its clinical correlation

This study was designed to investigate the molecular basis and the correlation between genotype and phenotype in the southern Chinese patients with Wilson's disease (WD). Genotypes of the ATP7B gene in 73 WD patients were examined by denaturing high-performance liquid chromatography (DHPLC) and DNA sequencing. A total of 38 different disease-causing mutations were identified, including 10 novel mutations: missense mutations (p.Gln707Arg, p.Cys1079Phe, p.Gly1149Glu, p.Ser855Tyr, p.Ala874Pro and p.Ser921Arg), nonsense mutation (p.Arg1228Stop), splice-site mutations (2121+3A>T and 3244-2A>G) and frameshift mutation (1875_1876insAATT). We found that a pair of siblings carried the same genotype but different clinical type, and two patients were found to have three mutations. In addition, we compared the clinical data for p.Arg778Leu homozygotes and compound heterozygotes. Our research has enriched the mutation spectrum of the ATP7B gene in the Chinese population and can serve as the basis for genetic counseling and clinical/prenatal diagnosis to prevent WD in China.

Association between the c. 2495 A>G ATP7B Polymorphism and Sporadic Alzheimer's Disease

Nonceruloplasmin-bound copper (“free”) is reported to be elevated in Alzheimer's disease (AD). In Wilson's disease (WD) Cu-ATPase 7B protein tightly controls free copper body levels. To explore whether the ATP7B gene harbours susceptibility loci for AD, we screened 180 AD chromosomes for sequence changes in exons 2, 5, 8, 10, 14, and 16, where most of the Mediterranean WD-causing mutations lie. No WD mutation, but sequence changes corresponding to c.1216 T>G Single-Nucleotide Polymorphism (SNP) and c.2495 A>G SNP were found. Thereafter, we genotyped 190 AD patients and 164 controls for these SNPs frequencies estimation. Logistic regression analyses revealed either a trend for the c.1216 SNP (P = .074) or a higher frequency for c.2495 SNP of the GG genotype in patients, increasing the probability of AD by 74% (P = .028). Presence of the GG genotype in ATP7B c.2495 could account for copper dysfunction in AD which has been shown to raise the probability of the disease.

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.

Six novel ATP7B mutations in Thai patients with Wilson disease

WD is an autosomal recessive disorder of copper transport resulting in excessive copper deposition in the liver and brain. It is caused by defects of ATP7B encoding a copper transporting P-type ATPase. To identify the mutations in ATP7B in Thai patients with WD, DHPLC analysis was applied to detect mutations and polymorphisms of the entire ATP7B gene in 19 Thai patients with WD. Mutations in ATP7B were identified in 14 of 19 patients: 2 homozygotes, 8 compound heterozygotes and 4 heterozygotes. Eighteen mutations distributed throughout the entire coding region of ATP7B gene including 11 missense, 3 nonsense, 1 splice-site, 1 deletion and 2 insertions. Of 18 different mutations identified, 6 were found to be novel. Twelve single nucleotide polymorphisms (SNPs) were also identified and two SNPs have not yet previously been reported. Segregation analysis using DHPLC analysis showed mutation transmission patterns within each family of Thai patients with WD. Mutations in ATP7B in Thai patients with WD are worth adding into the public database for genetic epidemiology and population genetics.

Genetics of Wilsons disease

Wilson's disease is a rare autosomal recessive disorder of copper transport due to mutations in the ATP7B gene, responsible for transport of copper into bile from hepatocytes and its incorporation into apoceruloplasmin to form ceruloplasmin resulting in excessive accumulation of copper in the liver and extrahepatic tissues. Clinical features of WD result from toxic accumulation of copper in liver, brain and kidney. Early diagnosis is mandatory to initiate early treatment to prevent morbidity and mortality. More than 400 mutations have been reported, some of which are rather characteristic of geographical regions and ethnic population. Genetic testing is not useful as a routine procedure, but has its role in at risk individuals such as siblings and children of probands and in individuals with suggestive symptoms but where other tests are contradictory.

Copper- and Iron-rich Matrices in Hepatocellular Lipofuscin Particles of a Young Male Patient: Diagnostic Ultrastructures for Wilson Disease

A 17-year-old male patient appeared with the biochemical liver damage associated with hypoceruloplasminemia and mild iron overload. Genetic analysis identified a compound heterozygosity of ATP7B responsible for the primary copper toxicosis of Wilson disease without mutations in HFE. A liver specimen consisted of cirrhotic nodules of large-sized hepatocytes with fatty change and those of fat-free small-sized hepatocytes. Histochemically, iron was distributed diffusely in the small-sized hepatocytes, while copper grains appeared in a few of the hepatocytes near the fibrous bands. X-ray microanalysis on the liver tissue fixed with a 0.1% osmium tetroxide solution and embedded in epoxy resin disclosed (1) complex formation of copper with sulfur, and iron with phosphorus in the hepatocyte lipofuscin particles, (2) intraparticle localization of the cuprothionein in the less dense matrix and ferric proteins in the dense matrix, and (3) high affinity of the cuprothionein to lead staining. Considering the fact that ceruloplasmin is the major ferroxidase essential for iron efflux, iron deposits in the hypoceruloplasminemic patients with Wilson disease are not a complication, but a natural event. This study disclosed for the first time the diagnostic ultrastructures of Wilson disease, which might represent different detoxification processes to the reactive metals of copper and iron.

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.

Mutational analysis of 65 Wilson disease patients in Hong Kong Chinese: identification of 17 novel mutations and its genetic heterogeneity

Wilson disease (WD), an autosomal recessive disorder of copper transport, is the most common inherited liver disorder in Hong Kong Chinese. This was the first local study to elucidate the molecular basis and establish an effective DNA-based diagnostic protocol. The ATP7B genes of 65 patients were amplified by polymerase chain reaction (PCR) and sequenced. Haplotype analysis was performed using D13S301, D13S314, and D13S316. The p.L770L/p.R778L status in 660 subjects was determined to estimate WD prevalence. Allele age of p.R778L was determined by the smallest homozygosity region between D13S301 and D13S270. We identified 42 different mutations with 17 being novel. p.R778L (17.3%) was the most prevalent. Exons 2, 8, 12, 13, and 16 harbored 70% mutations. Thirty-two haplotypes were associated with WD chromosomes. The estimated prevalence rate was 1 in 5,400. Three out of 660 normal subjects had p.L770L/p.R778L. In the remaining 657 individuals, neither p.L770L nor p.R778L was found. We characterized a Hong Kong Chinese-specific ATP7B mutation spectrum with great genetic diversity. Exons 2, 8, 12, 13, and 16 should be screened first. The perfect linkage disequilibrium suggested that p.R778L and its private polymorphism p.L770L originated from a single ancestor. This East-Asian-specific mutation p.R778L/p.L770L is aged at least 5,500 years.

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.

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.

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.

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.

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.

Characterization of the molecular defect in the ATP7B gene in Wilson disease patients from Yugoslavia

Wilson disease (WD) is an autosomal recessive disorder of copper metabolism resulting from the absence or dysfunction of a copper transporting P-type ATPase (ATP7B). Approximately 150 mutations of the ATP7B have been identified to date. In this paper, we report the results of molecular characterization and genotype-phenotype analysis, which we have carried out on 35 patients from Yugoslavia affected by WD. Using single-strand conformational polymorphism (SSCP) followed by direct sequencing, we characterized the molecular defect in 80% of WD chromosomes and found 11 different mutations, three of which are novel. The most common mutations that accounted for the molecular defect in 71.3% of WD chromosomes were H1069Q (48.9%), 2304-2305insC (11.4%), R616Q (5.7%), and A1003T (5.7%). The results produced in this paper indicate that the best strategy for mutation detection in Yugoslavian patients with WD is an SSCP analysis of exons 14, 8, 5, and 13, where most of the defects (73.1%) lie, followed by mutation analysis of the remaining exons in ATP7B in patients in whom the mutation was not detected by the finitial screening. These data can be used to develop straightforward genetic testing in this population or in other countries composed of a genetically mixed population like the United States, where a significant number of immigrants came from Central and Eastern Europe.

Correlation of ATP7B genotype with phenotype in Chinese patients with Wilson disease

AIM: To determine the mutational characterization of P-type ATP7B gene and to explore the correlation of ATP7B genotype to phenotype in Chinese patients with Wilson disease (WD).

METHODS: Seventy-five patients with WD from 72 no-kinship families, 44 males and 31 females, were enrolled in this study. The age of onset ranged from 4 to 39 years, ≤ 18 years in 72 patients. Some exons of ATP7B gene mutations were analyzed in patients with WD by using biochemical methods, polymerase chain reaction-single strand configuration polymorphism (PCR-SSCP) and DNA sequence analysis. A total of 778 coding regions were identified with restriction enzyme Msp I. The activity of Cu-ATPase was assessed by measuring inorganic phosphorus.

RESULTS: Sixty-six of 75 patients (88%) had with hepatic manifestations, 39 of them had only hepatic manifestations, 27 patients had hepatic and neurological manifestations or other symptoms at the same time (16 patients had associated neurological manifestation, 3 patients had osteopathy, 8 patients had other symptoms). Eight of the 75 patients (10.7%) had only neurological symptoms, one patient (5 years old) had no symptom. Twelve changing patterns were detected in ATP7B gene by DNA sequencing, including seven mutations (R778L, C656X, G943D, V1140A, V1106I V1216M and 1384del17), six polymorphisms (IVS4-5t/c, A2495G, C2310G, IVS18 + 6c/t and IVS20 + 5a/g). R778L occurred in 49/66 patients (74%) with hepatic manifestations, homozygosis of R778L in 16 patients, heterozygosity of R778L in 33 patients. V1106I mutation of ATP7B gene occurred in 2 patients with delaying onset of clinical symptoms. Cu-ATPase activity of three patients with known mutations (R778L/ V1106I/A2495G, R778L/V1216M and R778L/R778L) were determined, and the activity of Cu-ATPase was decreased by 44.55%, 88.23% and 69.49% respectively.

CONCLUSION: 1384del17bp is a novel mutation found in WD patients. R778L is the most common mutation of ATP7B gene. There is a correlation between R778L and hepatic manifestations in WD patient.

Identification of novel mutations and the three most common mutations in the human ATP7B gene of Korean patients with Wilson disease

PURPOSE

Wilson disease, an autosomal recessive disorder of copper transport, is probably the most common inherited metabolic disorder in Korea. In Wilson disease, synthesis of a defective copper transporting enzyme leads to the accumulation of copper in the liver, brain, and kidney. The product of the Wilson disease gene is a copper transporting P-type ATPase (ATP7B). In this study, efforts were made to identify novel mutations and investigate the frequency of the common mutations in Korean patients with Wilson disease.

METHODS

This study includes 37 patients from 33 unrelated Korean families with Wilson disease. Genomic DNA from peripheral leukocytes or skin fibroblasts and cDNA from liver tissue were polymerase chain reaction-amplified exon by exon and subsequently analyzed using heteroduplex or single-strand conformation polymorphism analysis. Specimens showing mobility shift on those studies were directly sequenced.

RESULTS

Twelve different mutations in 33 Korean families with Wilson disease were identified: Arg778Leu (R778L), Asn1270Ser (N1270S), Ala874Val (A874V), 2303-2305delC, 2630-2656del, 2460-2462insC, Cys656Stop (C656X), Pro768His (P768H), Leu1083Phe (L1083F), Ala1168Ser (A1168S), Leu1255Ile (L1255I), and Asp1267Ala (D1267A). Among these, six mutations (2630-2656del, 2460-2462insC, C656X, P768H, A1168S, and L1255I) are novel. The R778L mutation is known to be highly prevalent in Asian patients. The allele frequency of R778L in Korean patients with Wilson disease was 37.9%, which was significantly higher than those of Japanese and Taiwanese patients. The N1270S mutation, originally described in an Italian patient, was the next most common mutation in Korean patients, with an allele frequency of 12.1%, which was presumed to disrupt the ATP hinge domain of the ATP7B protein. The A874V mutation was the third most common mutation with an allele frequency of 9.4%, which was presumed to disrupt the Td domain of the ATP7B protein.

CONCLUSION

The R778L, N1270S, and A874V mutations are three major mutations representing approximately 60% of mutated alleles, although Korean patients with Wilson disease are genetically heterogeneous.

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.

Delineation of the spectrum of Wilson disease mutations in the Greek population and the identification of six novel mutations

In this study, we report the further results of an ongoing project on the delineation of the spectrum of mutations on the ATP7B gene in Wilson disease (WD) patients of Greek origin. We have analyzed 24 additional families and detected 16 mutations (five frameshifts, two splice site, two nonsense, and seven missense), of which six are novel. On adding these results to the ones already published by us, we conclude that WD shows a marked allelic heterogeneity in the Greek population. Of the total number of mutations so far detected, the most common eight account for the molecular defect in 72.8% of the WD chromosomes. The most frequent mutation is the His0169Gln, which has a frequency of 28.5%, similar to those reported in North European populations. Using these data, an efficient strategy of mutation screening for WD is possible in this population, thus improving the possibility of preclinical diagnosis.

Further delineation of the molecular pathology of Wilson disease in the Mediterranean population

This study presents the update results of an ongoing project on the delineation of the spectrum of mutations at the Wilson disease (WD) gene in WD patients of Mediterranean origin. In studying 59 patients, of whom were 26 Continental Italians, 22 Sardinians, 9 Turkish, and 2 Albanians, we have found 31 novel and three known mutations. Of the novel mutations, 3 are deletions, two nonsense, 2 splice or consensus splice site, and 24 missense. The large majority of the missense mutations lie in evolutionary conserved regions of the WD gene of documented functional importance. Most of our patients were compound heterozygotes, and only a few were homozygotes. In addition, three polymorphisms were detected. By adding the new data to those previously reported by our group, we have to date detected 85% of mutations in the WD chromosomes from Continental Italians, 30% from Sardinians, 81.7% from Turkish and 66.7% from Albanians. Most of the mutations characterized are rare, and only a limited number are common. Of the common mutations 5 were found in Continental Italians, two in Sardinians and a single one in Turkish. Because there are so many causative mutations of the disease, the preclinical and prenatal diagnosis of WD should be carried out by a combination of mutation and linkage analysis.

Mutation analysis of Wilson disease in Taiwan and description of six new mutations

Wilson disease is an autosomal recessive disorder of copper metabolism. Mutation screening in Wilson disease has led to the detection of at least 89 disease-specific mutations. Some mutations appear to be population specific, while others are common to many populations. In this study, 38 Taiwanese patients with Wilson disease were screened using single-strand conformation polymorphism analysis, followed by direct DNA sequencing. We found 12 different mutations, six of which were novel. All our detected mutations were found to be in eight exons. Four mutations in three loci (Arg778Gln, Arg778Leu, Gly943Asp, and Pro992Leu) accounted for about 58% of the mutant alleles we detected. Using an RNA transcriptional assay, we confirmed that both of our detected splice-site mutations resulted in exon skipping.

Identification of three novel mutations and a high frequency of the Arg778Leu mutation in Korean patients with Wilson disease

Four mutations--R778L, A874V, L1083F, and 2304delC--in the copper-transporting enzyme, P-type ATPase (ATP7B), were identified in Korean Patients with Wilson disease. Arg778Leu, the most frequently reported mutation of this enzyme, was found in six of eight unrelated patients studied, an allele frequency of 37.5%, which is considerably higher than those in other Asian populations. The novel single nucleotide deletion, 2304delC, was found in one patient. Since a mutation at cDNA nucleotide 2302 (2302insC) had been previously described, this region of the ATP7B gene may be susceptible to gene rearrangements causing Wilson disease.

Mutational analysis of ATP7B and genotype-phenotype correlation in Japanese with Wilson's disease

The gene ATP7B responsible for Wilson's disease (WD) produces a protein which is predicted to be a copper-binding P-type ATPase, homologous to the Menkes disease gene (ATP7A). Various mutations of ATP7B have been identified. This study aimed to detect disease-causing mutations, to clarify their frequency and distribution, to determine whether genotype correlates with phenotype, and to determine the rate of abnormal findings in heterozygotes for the WD gene. We analyzed 41 unrelated Japanese WD families, including 47 patients. Twenty-one mutations, including nine novel ones, were identified. 2871delC (15.9%), 1708-5T-->G (11. 0%), and Arg778Leu (13.4%) were the most common mutations. 2871delC was detected mainly in eastern Japan and 1708-5T-->G in western Japan. The homozygotes for the 1708-5T-->G, 2871delC, or Arg778Leu mutations did not show a correlation with their phenotypes. Ceruloplasmin and copper levels were abnormally low in 28.6% and 35. 0% of heterozygotes, respectively. When patients and their families are screened for WD, a high rate of abnormal laboratory data in heterozygotes must be taken into account.

Mutation analysis in patients of Mediterranean descent with Wilson disease: identification of 19 novel mutations

In this study, we report further results of mutation analysis of the ATP7B gene in Wilson disease (WD) patients of Mediterranean origin. A total of 136 WD chromosomes, 73 of which were of Italian, 43 of Turkish, 18 of Sardinian, and two of Spanish origin, were analysed and the mutation characterised in 84.5% of them. We found 50 different mutations of which 19 are novel, including three nonsense, one frameshift, and 15 missense mutations. The mutations detected were rare and mostly found in the compound heterozygous state together with other mutations and only rarely in homozygosity. Most of these mutations lie in the transmembrane and ATP binding loop regions. These data expand our knowledge of both the structure-function relationships of the WD protein and the molecular pathology of WD, thus improving our capability of prevention and genetic counselling.

Molecular characterization of wilson disease in the Sardinian population--evidence of a founder effect

Wilson disease (WD) in the Sardinian population has an approximate incidence of 1:7,000 live births. Mutation analysis of the WD gene in this population reported in our previous articles led us to the characterization of two common mutations and a group of 13 rare mutations accounting for the molecular defect of 8.5, 7.9, and 15.1% of the WD chromosomes. However, molecular analysis of the WD chromosomes containing the most common haplotype, which accounts for 60.5% of the WD chromosomes, failed to define the disease-causing mutation. In this study, we characterized the promoter and the 5' UTR of the WD gene sequence and carried out a mutation analysis in this DNA region from patients with the most common haplotype. The promoter is contained in a GC-rich island and shows a TATA and a CAAT consensus sequence as well as potential binding sites for transcription factors and metal response elements. In all the analyzed 92 chromosomes with this haplotype, we detected a single mutation consisting of a 15-nt deletion from position -441 to position -427 relative to the translation start site. Expression assays demonstrated a 75% reduction in the transcriptional activity of the mutated sequence compared to the normal control. By adding this mutation to those that have been already characterized, we have now defined the molecular defect in 92% of the WD chromosomes in Sardinians. The high frequency, the expected prevention by preclinical diagnosis and early treatment of the devastating effect of WD on the nervous system and liver tissue, and the feasibility to detect most of molecular defects by DNA analysis indicate that WD in the Sardinian population should be added to the list of diseases currently detected by newborn screening.

A study of Wilson disease mutations in Britain

Wilson disease (WD) is an autosomal recessive disease of copper transport. The disease is caused by a large number of mutations in the ATP7B gene, some of which appear to be population specific, whereas others are found in probands from a variety of different ethnic backgrounds. This study presents the results of screening the ATP7B gene by SSCP and sequencing in order to define the spectrum of mutations seen in British referrals for WD. The 52 patients screened included 10 with a non-British mixed ethnicity origin. This study identified 19 novel mutations and 18 mutations that had been previously described. The novel mutations included seven nonconservative missense mutations, eight small insertions, or deletions causing frameshift, two nonsense mutations, and two splice-site mutations. Seven of the 10 mixed ethnicity patients harboured homozygous mutations, whereas only four of the larger British group were homozygotes. The detection rate by SSCP analysis in the British group of 42 consecutive unrelated WD probands was 70%. However, SSCP screening of just three exons (exons 8, 14, and 18) is predicted to identify 60% of mutations present in WD referrals.

Molecular analysis and diagnosis in Japanese patients with Wilson's disease

BACKGROUND

Wilson's disease is characterized by the toxic accumulation of copper in the liver, brain, cornea and other organs. It is caused by both impaired excretion via the bile and impaired incorporation of copper into ceruloplasmin in the liver. The Wilson's disease gene (ATP7B) has been cloned as a putative copper-transporting P-type ATPase gene. We therefore analysed mutations of ATP7B in Japanese patients with Wilson's disease.

METHODS

Twenty-three Japanese patients with Wilson's disease were investigated. In all patients, the ATP7B coding sequence, including exon-intron junctions, was analysed by restriction endonuclease digestion, mutation detected enhancement gel electrophoresis and/or direct sequencing analysis of amplified fragments.

RESULTS

Thirteen mutations were identified, including seven missense mutations, four detections, one insertion and one exon skipping in the coding region. The most common mutations were 2874deletion(del)C in exon 13 and arginine (Arg)778 leucine (Leu) in exon 8.

DISCUSSION

None of the observed mutations, except for 2302insertion(ins)C, have been previously detected in either European or North American patients. We conclude that the mutation spectrum of Wilson's disease may thus indicate a population-dependent pattern. Based on the population-dependent manner of the occurrence of ATP7B gene mutations, it may be possible to establish a molecular diagnosis system. A molecular diagnosis system is considered to be very effective for making a definitive diagnosis in very young patients and for also detecting carriers.

Mutation spectrum of ATP7A, the gene defective in Menkes disease

Our knowledge about Menkes disease (MD) has expanded greatly since its description in 1962 as a new X-linked recessive neurodegenerative disorder of early infancy. Ten years later a defect in copper metabolism was established as the underlying biochemical deficiency. In the beginning of 1990s efforts were concentrated on the molecular genetic aspects. The disease locus was mapped to Xq13.3 and the gene has been isolated by means of positional cloning. This was the beginning of a series of new findings which have greatly enhanced our understanding of copper metabolism not only in human, but also in other species. This review will focus on the molecular genetic aspects of Menkes disease and its allelic form occipital horn syndrome. The mutations will be compared briefly with those described in the animal model mottled mouse, and in Wilson disease, the autosomal recessive disorder of copper metabolism.

Functional characterization of missense mutations in ATP7B: Wilson disease mutation or normal variant?

Wilson disease is an autosomal recessive disorder of copper transport that causes hepatic and/or neurological disease resulting from copper accumulation in the liver and brain. The protein defective in this disorder is a putative copper-transporting P-type ATPase, ATP7B. More than 100 mutations have been identified in the ATP7B gene of patients with Wilson disease. To determine the effect of Wilson disease missense mutations on ATP7B function, we have developed a yeast complementation assay based on the ability of ATP7B to complement the high-affinity iron-uptake deficiency of the yeast mutant ccc2. We characterized missense mutations found in the predicted membrane-spanning segments of ATP7B. Ten mutations have been made in the ATP7B cDNA by site-directed mutagenesis: five Wilson disease missense mutations, two mutations originally classified as possible disease-causing mutations, two putative ATP7B normal variants, and mutation of the cysteine-proline-cysteine (CPC) motif conserved in heavy-metal-transporting P-type ATPases. All seven putative Wilson disease mutants tested were able to at least partially complement ccc2 mutant yeast, indicating that they retain some ability to transport copper. One mutation was a temperature-sensitive mutation that was able to complement ccc2 mutant yeast at 30 degreesC but was unable to complement at 37 degreesC. Mutation of the CPC motif resulted in a nonfunctional protein, which demonstrates that this motif is essential for copper transport by ATP7B. Of the two putative ATP7B normal variants tested, one resulted in a nonfunctional protein, which suggests that it is a disease-causing mutation.