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

Navigating the CRISPR/Cas Landscape for Enhanced Diagnosis and Treatment of Wilson's Disease

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system continues to evolve, thereby enabling more precise detection and repair of mutagenesis. The development of CRISPR/Cas-based diagnosis holds promise for high-throughput, cost-effective, and portable nucleic acid screening and genetic disease diagnosis. In addition, advancements in transportation strategies such as adeno-associated virus (AAV), lentiviral vectors, nanoparticles, and virus-like vectors (VLPs) offer synergistic insights for gene therapeutics in vivo. Wilson's disease (WD), a copper metabolism disorder, is primarily caused by mutations in the ATPase copper transporting beta (ATP7B) gene. The condition is associated with the accumulation of copper in the body, leading to irreversible damage to various organs, including the liver, nervous system, kidneys, and eyes. However, the heterogeneous nature and individualized presentation of physical and neurological symptoms in WD patients pose significant challenges to accurate diagnosis. Furthermore, patients must consume copper-chelating medication throughout their lifetime. Herein, we provide a detailed description of WD and review the application of novel CRISPR-based strategies for its diagnosis and treatment, along with the challenges that need to be overcome.

CRISPR/Cas9-mediated correction of mutated copper transporter ATP7B

Wilson's disease (WD) is a monogenetic liver disease that is based on a mutation of the ATP7B gene and leads to a functional deterioration in copper (Cu) excretion in the liver. The excess Cu accumulates in various organs such as the liver and brain. WD patients show clinical heterogeneity, which can range from acute or chronic liver failure to neurological symptoms. The course of the disease can be improved by a life-long treatment with zinc or chelators such as D-penicillamine in a majority of patients, but serious side effects have been observed in a significant portion of patients, e.g. neurological deterioration and nephrotoxicity, so that a liver transplant would be inevitable. An alternative therapy option would be the genetic correction of the ATP7B gene. The novel gene therapy method CRISPR/Cas9, which has recently been used in the clinic, may represent a suitable therapeutic opportunity. In this study, we first initiated an artificial ATP7B point mutation in a human cell line using CRISPR/Cas9 gene editing, and corrected this mutation by the additional use of single-stranded oligo DNA nucleotides (ssODNs), simulating a gene correction of a WD point mutation in vitro. By the addition of 0.5 mM of Cu three days after lipofection, a high yield of CRISPR/Cas9-mediated ATP7B repaired cell clones was achieved (60%). Moreover, the repair efficiency was enhanced using ssODNs that incorporated three blocking mutations. The repaired cell clones showed a high resistance to Cu after exposure to increasing Cu concentrations. Our findings indicate that CRISPR/Cas9-mediated correction of ATP7B point mutations is feasible and may have the potential to be transferred to the clinic.

The Prevalence of Wilson's Disease: An Update

BACKGROUND AND AIMS

In 1984, Scheinberg and Sternlieb estimated the prevalence of Wilson's disease to be 1:30,000 based on the limited available data. This suggested a large number of overlooked cases with potentially fatal consequences. The "Scheinberg-Sternlieb Estimate" is still widely used, although more recent clinical and genetic studies of higher quality are now available. In the present study, we included these data to update the prevalence estimate.

APPROACH AND RESULTS

A MEDLINE Ovid, Science Citation Index Expanded, and PubMed systematic search for all relevant studies on the prevalence of Wilson's disease was conducted. In total, 59 studies (50 clinical and 9 population-based genetic) were included in the final analysis. We identified 4 recent clinical studies based on nationwide databases of high quality, providing prevalence estimates from 1:29,000 to 1:40,000. Higher frequency populations do exist because of frequent first-cousin marriages and/or a higher mutation frequency. When calculating prevalence from the incidence related to number of births, estimates were 1:40,000-1:50,000. Clinical screening studies, including examination for Kayser-Fleischer rings or ceruloplasmin, did not improve these estimates because of insufficient sample size or selection biases. Population-based genetic studies in US and UK populations were not in disagreement with the clinically based estimates. At the same time, studies from France and Sardinia suggested that the genetic prevalence may be 3-4 times higher than the clinical disease prevalence. This raises the question whether the penetrance is indeed 100% as generally assumed.

CONCLUSIONS

The original prevalence estimate from 1984 of 1:30,000-1:50,000 still appears valid, at least for the United States, Europe, and Asia. In some population-based studies, the genetic prevalence was 3-4 times higher than clinically based estimates. The question of penetrance needs further evaluation.

A novel gross deletion and breakpoint junction sequence analysis of ATP7B in a Chinese family with Wilson disease using next‑generation sequencing and Sanger sequencing

Wilson disease (WD) is a rare autosomal recessive genetic disorder that causes abnormal copper metabolism, resulting in pathological accumulation of copper in the liver, brain and other organs. Mutations in the ATPase copper transporter 7B (ATP7B) gene, which encodes a membrane P-type adenosine triphosphatase, have been identified as being responsible for WD. The present study analyzed clinical data and collected DNA samples from a pediatric patient with WD and her healthy parents. Mutation screening for ATP7B was performed using direct sequencing, multiplex ligation-dependent probe amplification(MLPA), next-generation sequencing (NGS) and Sanger sequencing of the breakpoint junction sequence. The patient (age, 2.7 years) presented with early-onset hepatic disease. The present study identified compound heterozygous mutations of ATP7B, including a heterozygous mutation (p.Arg1,041Trp) and a novel heterozygous gross deletion of a 57,771 bp fragment (chr13: 52490972-52548742) (GRCh37) from partial exon2- exon21 to external ATP7B sequence (15.833bp) in the patient. Analysis of the family members of the patient showed that the missense mutation and the gross deletion mutation were inherited from her mother and father, respectively. Microhomology and inverted repeat sequences, which may mediate the deletion mutation, were identified through sequence analysis on both sides of the breakpoints of this deletion. The present study provided additional information on the genotypic spectrum of the ATP7B gene, particularly with regard to early onset hepatic disease, as observed in the present patient with WD. The identification of the precise breakpoint junction sequence warrants further investigation of DNA break and recombination mechanisms. In detecting precise deletions, the NGS associated with Sanger sequencing of breakpoint junction sequence have been found to have more advantages than MLPA.

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.

Production of Wilson Disease Model Rabbits with Homology-Directed Precision Point Mutations in the ATP7B Gene Using the CRISPR/Cas9 System

CRISPR/Cas9 has recently been developed as an efficient genome engineering tool. The rabbit is a suitable animal model for studies of metabolic diseases. In this study, we generated ATP7B site-directed point mutation rabbits to simulate a major mutation type in Asians (p. Arg778Leu) with Wilson disease (WD) by using the CRISPR/Cas9 system combined with single-strand DNA oligonucleotides (ssODNs). The efficiency of the precision point mutation was 52.94% when zygotes were injected 14 hours after HCG treatment and was significantly higher than that of zygotes injected 19 hours after HCG treatment (14.29%). The rabbits carrying the allele with mutant ATP7B died at approximately three months of age. Additionally, the copper content in the livers of rabbits at the onset of WD increased nine-fold, a level similar to the five-fold increase observed in humans with WD. Thus, the efficiency of precision point mutations increases when RNAs are injected into zygotes at earlier stages, and the ATP7B mutant rabbits are a potential model for human WD disease with applications in pathological analysis, clinical treatment and gene therapy research.

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.

Carrier frequency of Wilson's disease in the Korean population: a DNA-based approach

Wilson's disease (WD) is an autosomal recessive disorder caused by ATP7B gene mutation. The frequency of WD is about 1 in 30 000 worldwide. In the present study, we screened 14 835 dried blood spots (DBSs) from asymptomatic Korean neonates and retrospectively reviewed massively parallel sequencing of 1090 control individuals to estimate carrier frequency. TaqMan real-time PCR assays were conducted to detect six mutations that account for 58.3% of mutations in Korean WD patients: c.2333G>T (p.Arg778Leu), c.2621C>T (p.Ala874Val), c.3086C>T (p.Thr1029Ile), c.3247C>T (p.Leu1083Phe), c.3556G>A (p.Gly1186Ser) and c.3809A>G (p.Asn1270Ser). We also retrospectively reviewed data from 1090 individuals with various indications other than WD for whom whole-exome or panel sequencing data were available. Mutant allele frequency based on the six most common mutations was 0.0067 among the total of 14 835 DBSs screened. Given that these six mutations account for 58.3% of mutations in Korean WD patients, the corrected mutant allele frequency is 0.0115 (95% confidence interval (CI): 0.0103-0.0128). Corresponding incidence (q²) and carrier frequency (2pq) were estimated to be 1:7561 and 1:44, respectively. In retrospective data analysis of 1090 control individuals, allele frequency of pathogenic or likely pathogenic variants was 0.0096 (95% CI: 0.0063-0.0146). Corresponding carrier frequency was estimated to be 1:53. Estimated allele and carrier frequencies based on DNA screening were relatively higher than those reported previously based on clinical ascertainment.

Spectrum of ATP7B mutations and genotype-phenotype correlation in large-scale Chinese patients with Wilson Disease

Wilson disease (WD), an inherited disorder associated with ATP7B gene, has a wide spectrum of genotypes and phenotypes. In this study, we developed a rapid multiplex PCR-MassArray method for detecting 110 mutant alleles of interest, and used it to examine genomic DNA from 1222 patients and 110 healthy controls. In patients not found to have any mutation in the 110 selected alleles, PCR-Sanger sequencing was used to examine the ATP7B gene. We identified 88 mutations, including 9 novel mutations. Our analyses revealed p.Arg778Leu, p.Arg919Gly and p.Thr935Met showed some correlations to phenotype. The p.Arg778Leu was related to younger onset age and lower levels of ceruloplasmin (Cp) and serum copper, while p.Arg919Gly and p.Thr935Met both indicated higher Cp levels. Besides, the p.Arg919Gly was related to neurological subtype, and p.Thr935Met showed significant difference in the percentage of combined neurological and visceral subtype. Moreover, for ATP7B mutations, the more severe impact on ATP7B protein was, the younger onset age and lower Cp level presented. The feasibility of presymptomatic DNA diagnosis and predicting clinical manifestation or severity of WD would be facilitated with identified mutations and genotype-phenotype correlation precisely revealed in the study.

The genetics of Wilson disease

Wilson disease (WD) is an autosomal-recessive disorder of hepatocellular copper deposition caused by pathogenic variants in the copper-transporting gene, ATP7B. Early detection and treatment are critical to prevent lifelong neuropsychiatric, hepatic, and systemic disabilities. Due to the marked heterogeneity in age of onset and clinical presentation, the diagnosis of Wilson disease remains challenging to physicians today. Direct sequencing of the ATP7B gene is the most sensitive and widely used confirmatory testing method, and concurrent biochemical testing improves diagnostic accuracy. More than 600 pathogenic variants in ATP7B have been identified, with single-nucleotide missense and nonsense mutations being the most common, followed by insertions/deletions, and, rarely, splice site mutations. The prevalence of Wilson disease varies by geographic region, with higher frequency of certain mutations occurring in specific ethnic groups. Wilson disease has poor genotype-phenotype correlation, although a few possible modifiers have been proposed. Improving molecular genetic studies continue to advance our understanding of the pathogenesis, diagnosis, and screening for Wilson disease.

Diagnosis of Wilson disease

Clinical presentation of Wilson disease can vary widely; therefore diagnosis is not always straightforward. Wilson disease is not just a disease of children and young adults, but may present at any age. The key features of Wilson disease are liver disease and cirrhosis, neuropsychiatric disturbances, Kayser-Fleischer rings, and acute episodes of hemolysis, often in association with acute liver failure. Diagnosis is particularly difficult in children and in adults presenting with active liver disease. None of the available laboratory tests is perfect and may not be specific for Wilson disease. A detailed neurologic examination is required for all cases. Neuroimaging and electrophysiologic methods are helpful. To overcome the diagnostic challenge, several clinical signs (Kayser-Fleischer rings, neurologic symptoms) and laboratory features (copper in serum, urine, liver; serum ceruloplasmin; genetic testing) are scored 0 (absent) to 2 (present) and the Leipzig score is calculated. If the score is ≥4, the diagnosis of Wilson disease is very likely. For asymptomatic siblings of index patients, mutation analysis is the most reliable approach.

Clinical Use of Next-Generation Sequencing in the Diagnosis of Wilson's Disease

Objective. Wilson's disease is a disorder of copper metabolism which is fatal without treatment. The great number of disease-causing ATP7B gene mutations and the variable clinical presentation of WD may cause a real diagnostic challenge. The emergence of next-generation sequencing provides a time-saving, cost-effective method for full sequencing of the whole ATP7B gene compared to the traditional Sanger sequencing. This is the first report on the clinical use of NGS to examine ATP7B gene. Materials and Methods. We used Ion Torrent Personal Genome Machine in four heterozygous patients for the identification of the other mutations and also in two patients with no known mutation. One patient with acute on chronic liver failure was a candidate for acute liver transplantation. The results were validated by Sanger sequencing. Results. In each case, the diagnosis of Wilson's disease was confirmed by identifying the mutations in both alleles within 48 hours. One novel mutation (p.Ala1270Ile) was found beyond the eight other known ones. The rapid detection of the mutations made possible the prompt diagnosis of WD in a patient with acute liver failure. Conclusions. According to our results we found next-generation sequencing a very useful, reliable, time-saving, and cost-effective method for diagnosing Wilson's disease in selected cases.

Whom and how to screen for Wilson disease

Wilson disease is a genetic disorder of hepatic copper excretion leading to copper accumulation in various tissues. The disease expression is highly variable, ranging from totally asymptomatic subjects to patients with severe liver disease or movement disorders. Thus, it is difficult to define in which patient Wilson disease has to be considered as diagnosis. The suspicion should be high in patients presenting with extrapyramidal disorders or with liver diseases or of unknown origin. For diagnosis, in many patients a combination of tests reflecting disturbed copper metabolism may be needed. Not a single test is per se specific and, thus, a range of tests has to be applied (presence or absence of Kayser-Fleischer rings or neurologic symptoms, serum ceruloplasmin, liver copper content, urinary copper excretion, mutation analysis; rated -1 to 4 depending on the test) and clinical symptoms. A diagnostic sum score of ≥ 4 confirms the diagnosis.

New mutations and polymorphisms of the ATP7B gene in sporadic Wilson disease

Wilson's disease (WD) is a rare autosomal recessive genetic disorder of copper metabolism resulting in brain damage, liver failure, and neurological impairment and psychiatric disturbances, as a result of excessive copper accumulation in the brain, liver, kidneys and eyes. ATP7B, encoding a copper transporter P-ATPase was identified as the causative gene of WD. Mutations in the ATP7B gene lead to the defection of the transmembrane transporter so that it can not metabolize copper effectively. We reported the clinical and molecular features of three unrelated and non-consanguineous WD patients. We performed molecular genetic analysis of the ATP7B gene in all cases by DNA sequencing, and revealed 7 novel single nucleotide polymorphisms (SNPs) and 8 well known mutations. Among them, that novel SNP (c. -520 C>T) and two well known mutations (c. 2310 C>G/p. Leu700Leu, c. 2333 G>T/A/p. Arg778Leu/Gln) coexisted in all patients and they were heterozygous and homozygous in the youngest case, respectively, indicating that they may be correlated to the pathogenesis and potentially used as a genetic biomarker for early WD diagnosis.

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.

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.

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.

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.

Identification of a novel Wilson disease gene mutation frequent in Upper Austria: a genetic and clinical study

Wilson disease (WD), a disorder of copper metabolism is caused by mutations in the ATP7B gene, a copper transporting ATPase. In the present study we describe a novel mutation in exon 9 of the ATP7B gene. The ATP7B gene was analyzed for mutations by denaturing HPLC and direct sequencing. DNA from 100 healthy blood donors from the same geographic area was examined as control. Sixteen (7.4%) out of the 216 patients diagnosed with WD in Austria carried the newly identified R816S(c.2448G>T) point mutation in exon 9 (4 male, age: 19 (6-30) years, median (range)). One patient was homozygous for R816S(c.2448G>T). Thirteen patients were compound heterozygotes (p.H1069Q(c.3207C>A)/R816S(c.2448G>T) (N=6), P539L/R816S(c.2448G>T) (N=3), each one G710S/R816S(c.2448G>T), P767P(2299insC)/R816S(c.2448G>T), W779G/R816S(c.2448G>T), T1220M/R816S(c.2448G>T)). In two patients no second mutation was identified. Interestingly, all but three of the patients originated within a distinct geographical area in Austria. Eleven patients presented with hepatic disease, 3 patients with neurological disease and 2 were asymptomatic sisters of an index case. A liver biopsy was available in 14 patients. Three patients showed advanced liver disease with liver transplantation for acute hepatic failure in two. The remaining patients had only mild histological changes, most commonly steatosis. Chronic hepatitis was described in five patients. Kayser-Fleischer ring was present in five patients. None of the 100 healthy controls carried the mutation. We describe a novel mutation in the ATP7B gene, occurring in patients originated from a distinct geographical area in Austria associated with a variable course of the disease.

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.

Molecular analysis of Wilson patients: direct sequencing and MLPA analysis in the ATP7B gene and Atox1 and COMMD1 gene analysis

ATP7B mutations result in Cu storage in the liver and brain in Wilson disease (WD). Atox1 and COMMD1 were found to interact with ATP7B and involved in copper transport in the hepatocyte. To understand the molecular etiology of WD, we analyzed ATP7B, Atox1 and COMMD1 genes. Direct sequencing of (i) ATP7B gene was performed in 112 WD patients to identify the spectrum of disease-causing mutations in the French population, (ii) Atox1 gene was performed to study the known polymorphism 5'UTR-99T>C in 78 WD patients with two ATP7B mutations and (iii) COMMD1 gene was performed to detect the nucleotide change c.492GAT>GAC. MLPA (Multiplex Ligation-dependent Probe Amplification) analysis was performed in WD patients presenting only one ATP7B mutation. Among our 112 WD unrelated patients, 83 different ATP7B gene mutations were identified, 27 of which were novel. Two ATP7B mutations were identified in 98 WD cases, and one mutation was identified in 14 cases. In two of these 14 WD patients, we identified the deletion of exon 4 of the ATP7B gene by MLPA technique. In 78 selected patients of the cohort with two mutations in ATP7B, we have examined genotype-phenotype correlation between the detected changes in Atox1 and COMMD1 genes, and the presentation of the WD patients. Based on the data of this study, no major role can be attributed to Atox1 and COMMD in the pathophysiology or clinical variation of WD.

Metals and the liver

PURPOSE OF REVIEW

Hereditary liver diseases resulting in copper and iron overload may cause significant morbidity and mortality if not diagnosed and treated early. The goal of this review is to highlight the key publications on genetics, diagnosis and management of hemochromatosis and Wilson disease over the past 18 months.

RECENT FINDINGS

Several recent advancements have been made in the genetic diagnosis of hemochromatosis and Wilson disease. Uncommon HFE mutations resulting in phenotypic hemochromatosis among C282Y heterozygotes have been identified from HFE gene sequencing. A serum ferritin less than 1000 μg/l in C282Y homozygotes was found to be associated with milder symptoms of hemochromatosis. Deferasirox was shown to reduce iron overload in patients with hemochromatosis and may be an option for patients who cannot tolerate phlebotomy. There was found to be evidence of genotype and phenotype correlation in Wilson disease, which can be diagnosed by genetic sequencing. A modified diagnostic guideline has been developed for children with Wilson disease with mild liver disease that increases the sensitivity and specificity of diagnosis. Also treatment with copper chelating agents has less hepatic treatment failures when compared with zinc monotherapy.

SUMMARY

Advancements in diagnosis of hemochromatosis and Wilson disease may lead to earlier diagnosis and treatment with resulting decrease in morbidity and mortality.

EASL Clinical Practice Guidelines: Wilson's disease

This Clinical Practice Guideline (CPG) has been developed to assist physicians and other healthcare providers in the diagnosis and management of patients with Wilson's disease. The goal is to describe a number of generally accepted approaches for diagnosis, prevention, and treatment of Wilson's disease. Recommendations are based on a systematic literature review in the Medline (PubMed version), Embase (Dialog version), and the Cochrane Library databases using entries from 1966 to 2011. The Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) system used in other EASL CPGs was used and set against the somewhat different grading system used in the AASLD guidelines (Table 1A and B). Unfortunately, there is not a single randomized controlled trial conducted in Wilson's disease which has an optimal design. Thus, it is impossible to assign a high or even a moderate quality of evidence to any of the questions dealt with in these guidelines. The evaluation is mostly based on large case series which have been reported within the last decades.

Elucidation of the ATP7B N-domain Mg2+-ATP coordination site and its allosteric regulation

The diagnostic of orphan genetic disease is often a puzzling task as less attention is paid to the elucidation of the pathophysiology of these rare disorders at the molecular level. We present here a multidisciplinary approach using molecular modeling tools and surface plasmonic resonance to study the function of the ATP7B protein, which is impaired in the Wilson disease. Experimentally validated in silico models allow the elucidation in the Nucleotide binding domain (N-domain) of the Mg²⁺-ATP coordination site and answer to the controversial role of the Mg²⁺ ion in the nucleotide binding process. The analysis of protein motions revealed a substantial effect on a long flexible loop branched to the N-domain protein core. We demonstrated the capacity of the loop to disrupt the interaction between Mg²⁺-ATP complex and the N-domain and propose a role for this loop in the allosteric regulation of the nucleotide binding process.

DNA capturing machinery through spore-displayed proteins

AIMS

The purpose of this study was to develop a general method for the facile development of a new DNA biosensor which utilizes streptavidin-displayed spores as a molecular machinery.

METHODS AND RESULTS

Fluorescence spectroscopy was used as a monitoring tool for the streptavidin displayed on the surface of Bacillus thuringiensis spores and as a diagnosis method for DNA detection. As a proof-of-concept, four pathogenic bacteria including Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli and Klebsiella pneumonia were used for the detection of pathogenic species. In addition, a set of mutant variants of Wilson's disease were also used for the detection of single nucleotide polymorphism (SNP) in this system.

CONCLUSIONS

This strategy, utilizing streptavidin-displayed spores, is capable of capturing DNA targets for the detection of pathogenic bacteria and for mutation analysis in Wilson's disease.

SIGNIFICANCE AND IMPACT OF THE STUDY

This approach could be useful as a simple platform for developing sensitive spore-based biosensors for any desired DNA targets in diagnostic applications.

Distinct clinical courses according to presenting phenotypes and their correlations to ATP7B mutations in a large Wilson's disease cohort

INTRODUCTION AND AIMS

Wide phenotypic and genotypic heterogeneities in Wilson's disease (WD) have been reported, hampering the study of their correlations. The goal of this study was to identify the factors related to these diversities.

METHODS

Clinical courses and molecular genetic characteristics were analysed in 237 unrelated Korean WD families. The average follow-up period was 8.2 ± 5.8 years.

RESULTS

Presenting phenotypes were classified as H1 (12.2%), H2 (42.4%), N1 (21.6%), N2 (0.4%), NX (0.4%), presymptomatic (22.4%) and other (0.4%), modifying the guidelines by Ferenci and colleagues. Age at presentation was youngest and cirrhosis was rarest in the presymptomatic group. Decompensated cirrhosis was the highest in the H1 group. Favourable outcome was rarest in the N1 group. Forty-seven (11 novel) ATP7B mutations were identified in 85% of the 474 alleles. Multiplex ligation-dependent probe amplification assays in ATP7B and analyses of ATOX1 and COMMD1 genes identified no additional mutations. Yeast complementation assays demonstrated functional perturbation of the seven novel missense mutants. Five major mutations, p.Arg778Leu, p.Ala874Val, p.Asn1270Ser, p.Lys838SerfsX35 and p.Leu1083Phe, accounted for 63% of the alleles. H1 was more common, age at presentation was younger and N1+N2+NX tended to be less common in patients with nonsense, frame shifting or splicing mutations than in those with missense mutations alone. Patients with both mutations in the transduction (Td) or the ATP hinge domain showed presymptomatic or hepatic manifestations but no neurological manifestation.

CONCLUSIONS

The presenting phenotype strongly affects the clinical outcome of WD, and is related to the ATP7B mutation type and location, providing an evidence for genotype-phenotype correlations in WD.

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.

Membrane transporters and drug development: relevance to pharmacogenomics, nutrigenomics, epigenetics, and systems biology

The study of membrane transporters may result in breakthroughs in the discovery of new drugs and the development of safer drugs. Membrane transporters are essential for fundamental cellular functions and normal physiological processes. These molecules influence drug absorption and distribution and play key roles in drug therapeutic effects. A primary goal of current research in drug discovery and development is to fully understand the interactions between transporters and drugs at both the system levels in the human body and the individual level for personalized therapy. Systematic studies of membrane transporters will help in not only better understanding of diseases from the systems biology point of view but also better drug design and development. The exploration of both pharmacogenomics and systems biology in transporters is necessary to connect individuals' genetic profiles with systematic drug responses in the human body. Understanding of gene-diet interactions and the effects of epigenetic changes on transporter gene expression may help improve clinical drug efficacy. The integration of pharmacogenomics, nutrigenomics, epigenetics, and systems biology may enable us to move from disease treatment to disease prevention and optimal health. The key issues in such integrative understanding include the correlations between structure and function, genotype and phenotype, and systematic interactions among transporters, other proteins, nutrients, drugs, and the environment. The exploration in these key issues may ultimately contribute to personalized medicine with high efficacy but less toxicity.

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.

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

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

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

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

Sequence variation database for the Wilson disease copper transporter, ATP7B

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

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.

Wilson disease--a practical approach to diagnosis, treatment and follow-up

Wilson disease is an inherited, autosomal recessive, copper accumulation and toxicity disorder that affects about 30 individuals per million. This rare disease is caused by mutations in the gene encoding a copper-transporting P-type ATPase, which is important for copper excretion into bile, leading to copper accumulation in the liver. Toxic copper concentrations can also be found in the brain and kidney, and clinical phenotypes include hepatic, haemolytic, neurologic and psychiatric diseases. Diagnosis is based on the combination of clinical features and findings such as increased urinary copper excretion, reduced levels of serum ceruloplasmin, high concentrations of copper in liver tissues and Kayser-Fleischer rings. Genetic studies are also becoming available for clinical use, but the utility of direct mutation analysis is limited. Wilson disease can be treated, and early diagnosis is essential: the goal of therapy is to reduce copper accumulation either by enhancing its urinary excretion or by decreasing its intestinal absorption. Medical therapies include penicillamine, trientine, zinc and tetrathiomolibdate. Liver transplantation is a relatively successful treatment option when medical therapy fails or in case of acute liver failure, even though it is also characterized by short- and long-term complications.

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.

Wilson's disease: an update

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

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

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

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.