Novel mutations of the ATP7B gene in Japanese patients with Wilson disease

Retinoids rescue ceruloplasmin secretion and alleviate oxidative stress in Wilson's disease-specific hepatocytes

Wilson’s disease (WD) is a copper metabolic disorder caused by a defective ATP7B function. Conventional therapies cause severe side effects and significant variation in efficacy, according to cohort studies. Thus, exploring new therapeutic approaches to prevent progression to liver failure is urgent. To study the physiology and pathology of WD, immortalized cell lines and rodent WD models have been used conventionally; however, a large gap remains among different species as well as in genetic backgrounds among individuals. We generated induced pluripotent stem cells (iPSCs) from four WD patients carrying compound heterozygous mutations in the ATP7B gene. ATP7B loss- and gain-of-functions were further manifested with ATP7B-deficient iPSCs and heterozygously corrected R778L WD patient-derived iPSCs using CRISPR-Cas9-based gene editing. Although the expression of ATP7B protein varied among WD-specific hepatocytes differentiated from these iPSCs, the expression and secretion of ceruloplasmin (Cp), a downstream copper carrier in plasma, were consistently decreased in WD patient-derived and ATP7B-deficient hepatocytes. A transcriptome analysis detected abnormalities in the retinoid signaling pathway and lipid metabolism in WD-specific hepatocytes. Drug screening using WD patient-derived hepatocytes identified retinoids as promising candidates for rescuing Cp secretion. All-trans retinoic acid also alleviates reactive oxygen species production induced by lipid accumulation in WD-specific hepatocytes treated with oleic acid. These patient-derived iPSC-based hepatic models function as effective platforms for the development of potential therapeutics for hepatic steatosis in WD and other fatty liver diseases.

Identification and characterization of a novel 43-bp deletion mutation of the ATP7B gene in a Chinese patient with Wilson's disease: a case report

Background

Wilson’s disease (WD) is an autosomal recessive disorder characterized by copper accumulation. ATP7B gene mutations lead to ATP7B protein dysfunction, which in turn causes Wilson’s disease.

Case presentation

We describe a male case of Wilson’s disease diagnosed at 10 years after routine biochemical test that showed low serum ceruloplasmin levels and Kayser–Fleischer rings in both corneas. Analysis of the ATP7B gene revealed compound heterozygous mutations in the proband, including the reported c.3517G > A mutation and a novel c.532_574del mutation. The c.532_574del mutation covered a 43-bp region in exon 2, and resulted in a frameshift mutation (p.Leu178PhefsX10). By base sequence analysis, two microhomologies (TCTCA) were observed on both deletion breakpoints in the ATP7B gene. Meanwhile, the presence of some sequence motifs associated with DNA breakage near the deletion region promoted DNA strand break.

Conclusions

By comparison, a replication-based mechanism named fork stalling and template switching/ microhomology-mediated break-induced replication (FoSTeS/MMBIR) was used to explain the formation of this novel deletion mutation.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0567-z) contains supplementary material, which is available to authorized users.

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.

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.

Carrier frequency of the GJB2 mutations that cause hereditary hearing loss in the Japanese population

Hearing impairment is one of the most common sensory disorders that affect ~1 in 1000 children, and half of them are considered to be hereditary. Information about the carrier frequencies of mutations that underlie autosomal recessive disorders is indispensable for accurate genetic counseling to predict the probability of patients' children's disease. However, there have been few reports specific to the Japanese population. GJB2 mutations are reported to be the most frequent cause of hereditary hearing loss, and the mutation spectrum and frequency of GJB2 mutations were reported to vary among different ethnic groups. In this study, we investigated the carrier frequency of GJB2 mutations and the mutation spectrum in 509 individuals randomly selected from the general Japanese population. We show that the carrier frequencies of the two most common pathogenic mutations are 1.57% (8/509) for c.235delC and 1.77% (9/509) for p.Val37Ile. In addition to these mutations, we found two pathogenic variants (p.[Gly45Glu;Tyr136*] and p.Arg143Trp), and the total carrier frequency was estimated to be around 3.73% (19/509). We also detected six unclassified variants, including two novel variants (p.Cys60Tyr and p.Phe106Leu), with the former predicted to be pathogenic. These findings will provide indispensable information for genetic counseling in the Japanese 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.

Homozygosity for Non-H1069Q Missense Mutations in ATP7B Gene and Early Severe Liver Disease: Report of Two Families and a Meta-analysis

Most patients with Wilson's disease (WD) are compound heterozygote, which complicates establishing genotype-phenotype correlations. We identified five patients who presented with early and/or severe hepatic disease who are homozygous for W939C missense mutation on exon 12 of ATP7B. We therefore conducted a meta-analysis to determine the phenotype of patients homozygous for missense or nonsense mutations in all ATP7B exons.The meta-analysis showed that 69% and 31% of patients are homozygous for H1069Q and non-H1069Q mutations, respectively. Compared to patients with H1069Q, those with non-H1069Q mutations were significantly more likely to have a hepatic phenotype, severe liver disease, a mixed phenotype, and less likely to have a neurologic phenotype. Compared to patients with nonsense mutations, those with non-H1069Q ones were equally likely to present with a hepatic phenotype and to have severe liver disease. Mean age at symptom onset in the non-H1069Q versus the H1069Q group was 15.5 versus 20.5years (p<0.001).Our data suggest that mutation W939C and other non-H1069Q missense mutations are associated with early disease onset, a hepatic phenotype, and a high risk of hepatic failure in homozygous patients. Early identification of such patients by genetic screening is important for timely initiation of treatment and prevention of complications.

Systems biology approach to Wilson's disease

Wilson's disease (WD) is a severe disorder of copper misbalance, which manifests with a wide spectrum of liver pathology and/or neurologic and psychiatric symptoms. WD is caused by mutations in a gene encoding a copper-transporting ATPase ATP7B and is accompanied by accumulation of copper in tissues, especially in the liver. Copper-chelation therapy is available for treatment of WD symptoms and is often successful, however, significant challenges remain with respect to timely diagnostics and treatment of the disease. The lack of genotype-phenotype correlation remains unexplained, the causes of fulminant liver failure are not known, and the treatment of neurologic symptoms is only partially successful, underscoring the need for better understanding of WD mechanisms and factors that influence disease manifestations. Recent gene and protein profiling studies in animal models of WD began to uncover cellular processes that are primarily affected by copper accumulation in the liver. The results of such studies, summarized in this review, revealed new molecular players and pathways (cell cycle and cholesterol metabolism, mRNA splicing and nuclear receptor signaling) linked to copper misbalance. A systems biology approach promises to generate a comprehensive view of WD onset and progression, thus helping with a more fine-tune treatment and monitoring of the disorder.

Homozygous mutations in the conserved ATP hinge region of the Wilson disease gene: association with liver disease

OBJECTIVE

To determine whether any correlation exists between the phenotype and genotype of 2 Lebanese families with members affected with Wilson disease (WD).

BACKGROUND

WD is an autosomal-recessive disorder of copper transport with significant phenotypic diversity. Most patients are compound heterozygous making it difficult to establish a clear link between phenotype and genotype.

STUDY

We investigated 14 members from 2 Lebanese families (H and Z) with 5 members affected with WD. Mutation analysis of the ATP7B gene, and clinical assessments were carried out for both families. We also performed a literature search retrieving reported phenotypes of all patients homozygous to mutations in any of the 21 exons of the ATP7B.

RESULTS

Patients of the H and Z-families were found homozygous for the respective Asn1270Ser and Pro1273Leu mutations in the adenosine triphosphate (ATP) hinge region of exon 18. Of the healthy members, 6 were heterozygous and 3 had normal sequences. Clinically, 4 patients had liver cirrhosis and 1 had asymptomatic transaminitis. One of the patients also had neurologic symptoms. Screening the literature for patients homozygous for mutations in the ATP hinge region identified 25 patients including ours. The overall prevalence of the hepatic phenotype among patients homozygous for mutation in exon 18 was 80% and was significantly higher than those in exons 7, 14, and 21.

CONCLUSIONS

We hereby report the association of liver disease with homozygous mutations in the conserved ATP hinge region of exon 18 of the ATP7B gene.

Dietary supplement implicated in fulminant hepatic failure in a well-controlled Wilson disease patient

We encountered a patient with previously well-controlled Wilson disease who experienced fulminant hepatic failure with hemolytic anemia, possibly caused by the dietary supplement Health Proportion(®) (Jubilant Co., Ltd., Ehime, Japan). A 21-year-old woman was admitted to our hospital with marked liver dysfunction and severe hemolytic anemia. Free serum copper level was elevated at 101 μg/dl, and urinary copper excretion was extremely increased (25,600 μg/day). Plasma exchange and continuous hemodiafiltration were performed to remove serum copper and to treat the hemolytic anemia. However, liver function did not improve, and she underwent liver transplantation on 28th day after admission. Copper and iron contents in the resected liver were high at 851.9 μg and 551.7 μg/dry liver weight (g), respectively, despite the patient having regularly taken D-penicillamine since diagnosis and having a well-controlled copper level 1 year before her admission. Two months before admission, the patient had taken a dietary supplement made from soybeans for 1 month. This supplement was labeled as containing large amounts of copper and iron, and we assume that this caused fulminant hepatic failure with hemolytic crisis in this patient. It is important to be mindful of the micronutrient content of dietary supplements, especially for metabolic disorder patients.

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.

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

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

Wilson disease: pathophysiology, diagnosis, treatment, and screening

Wilson disease is an autosomal recessive condition of copper metabolism that was once considered fatal. The identification of the gene for Wilson disease has led to a better understanding of the molecular defect underlying this disorder and has impacted on disease diagnosis for some individuals. Medical therapy with chelating agents or zinc salts remains the mainstay of therapy for most patients, and liver transplant is lifesaving for those with advanced disease refractory to medical therapy or with fulminant hepatic failure. Future cell-based and genetic therapies may provide a cure for this disorder.

Wilson's Disease and Its Pharmacological Treatment

Wilson's disease is an inherited copper toxicosis caused by defective putative copper transporting ATPase in the liver. Because of impaired biliary secretion, copper remains in the liver, resulting in chronic hepatic lesions including fatty metamorphosis, chronic hepatitis and cirrhosis. In the latter stage, extrapyramidal syndromes may develop with and without symptomatic hepatic lesions. Acute liver damage associated with hemolysis and deep jaundice may be the first manifestation. The majority of patients show hypoceruloplasminemia, which has been used as a screening test for the disease. A large number of mutations in the ATP7B gene have been reported. Thus, genetic diagnosis might be limitedly used to presymptomatic diagnosis of siblings when mutations are identified in an index patient. Introduction of penicillamine caused a revolution in the treatment of patients. Another chelater, trientine, is now available for those intolerant of penicillamine. Tetrathiomolibdate and zinc acetate are additional alternatives currently being tested. Hypoceruloplasminemia and further reduction after chelation therapy may be associated with iron overload. This complication is closely related with impaired transport of ferrous ion due to ferroxidase deficiency. Noncompliance and teratogenicity are other major concerns because any treatment with the agents listed above is a life long regimen. Despite various side effects of penicillamine, its teratogenicity is negligible. These data indicate that penicillamine is the first choice of drug for this disease.

Mutation spectrum and polymorphisms in ATP7B identified on direct sequencing of all exons in Chinese Han and Hui ethnic patients with Wilson's disease

Wilson's disease (WD), an autosomal recessive copper transport disorder, usually presents with symptoms involving the liver or central nervous system. The disease is caused by a large number of mutations in the ATP7B gene comprising 21 expressed exons. Some of the mutations appear to be population specific, whereas others are found in probands from a variety of different ethnic backgrounds. This paper presents the results of screening of the ATP7B gene by means of the direct sequencing of all exons in the gene in 39 Han and one Hui ethnic Chinese patients. Nineteen novel mutations were revealed along with nine others that have been previously described; 57.5% of the mutations were located in exons 8, 13, and 12. In particular, the Arg778Leu mutation in exon 8 was found in 55% of these Chinese patients in at least one allele. Five patients were homozygotes and 17 patients were heterozygotes for Arg778Leu. The detection rate on direct sequencing of the polymerase chain reaction products of all exons of the ATP7B gene in 40 unrelated patients was 83.8% of alleles. Seventeen polymorphisms were also identified in patients and healthy controls. We first reported the presence of ATP7B mutations in Chinese Hui ethnic patients and summarize our results here along with the previously reported findings. A significant correlation between genotype and phenotype was not found in 37 homozygotes and 52 heterozygotes for Arg778Leu.

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.