Clinical and molecular characterization of Wilson's disease in China: identification of 14 novel mutations

Research progress in stem cell therapy for Wilson disease

Wilson disease (WD), also known as hepatolenticular degeneration, is an autosomal recessive disorder characterized by disorganized copper metabolism caused by mutations in the ATP7B gene. Currently, the main treatment options for WD involve medications such as d-penicillamine, trientine hydrochloride, zinc acetate, and liver transplantation. However, there are challenges that encompass issues of poor compliance, adverse effects, and limited availability of liver sources that persist. Stem cell therapy for WD is currently a promising area of research. Due to the advancement in stem cell directed differentiation technology in vitro and the availability of sufficient stem cell donors, it is expected to be a potential treatment option for the permanent correction of abnormal copper metabolism. This article discusses the research progress of stem cell therapy for WD from various sources, as well as the challenges and future prospects of the clinical application of stem cell therapy for WD.

Phenotype and molecular characterization of Wilson's disease in Morocco

BACKGROUND AND STUDY AIMS

In Morocco the prevalence of Wilson disease (WD) and the spectrum of mutations are not known. The aim of the present study was to estimate the prevalence of WD in Morocco, to evaluate the phenotype among a large cohort of WD patients, and to characterize ATP7B variants in a subgroup of WD patients.

PATIENTS AND METHODS

We collected data from 226 patients admitted to five university hospital centers in Morocco between 2008 and 2020. The diagnosis was based on clinical manifestations, function tests and biochemical parameters. The genotype was characterized in 18 families diagnosed at the University Hospital Center of Marrakesh, by next generation sequencing.

RESULTS

The mean annual prevalence in Morocco was 3.88 per 100,000 and the allele frequency was 0.15 %. Among the 226 patients included (121 males and 105 females), 196 were referred for a hepatic or neurological involvement and 30 were asymptomatic. The mean age at diagnosis was 13 ± 5.1 years (range: 5 - 42 years). Consanguinity was found in 63.3 % of patients. The mean duration of illness was 2.8 ± 1.9 years. Kayser-Fleischer rings were found in 131 (67.9 %) of 193 patients. Among the 196 symptomatic patients, 141/159 (88.7 %) had low serum ceruloplasmin (<0.2 g/L) and a high 24-hours urinary copper (>100 μg/day) was found in 173/182 (95.1 %) patients. The initial treatment was D-penicillamine in 207 patients, zinc acetate in five, zinc sulfate in five, and nine patients were not treated; 60/207 (29 %) patients have stopped treatment. A total of 72 patients died; the mortality rate was 31.9 %. Eight different ATP7B variants were identified among the 18 patients studied, of which two were novel (p.Cys1104Arg and p.Gln1277Hisfs*52), and six previously published (p.Gln289Ter, p.Cys305Ter, p.Thr1232Pro, p.Lys1020Arg, p.Glu583ArgfsTer25 and c.51+4A>T). All informative patients were homozygous for the disease-causing mutation.

CONCLUSION

In Morocco, a high prevalence due to consanguinity and a high mortality rate due to the difficulty of diagnosis and lack of treatment were observed in WD patients. NGS sequencing identified new ATP7B variants in WD patients from Morocco.

The diagnostic yield of exome sequencing in liver diseases from a curated gene panel

Exome sequencing (ES) has been used in a variety of clinical settings but there are limited data on its utility for diagnosis and/or prediction of monogenic liver diseases. We developed a curated list of 502 genes for monogenic disorders associated with liver phenotypes and analyzed ES data for these genes in 758 patients with chronic liver diseases (CLD). For comparison, we examined ES data in 7856 self-declared healthy controls (HC), and 2187 patients with chronic kidney disease (CKD). Candidate pathogenic (P) or likely pathogenic (LP) variants were initially identified in 19.9% of participants, most of which were attributable to previously reported pathogenic variants with implausibly high allele frequencies. After variant annotation and filtering based on population minor allele frequency (MAF ≤ 10-4 for dominant disorders and MAF ≤ 10-3 for recessive disorders), we detected a significant enrichment of P/LP variants in the CLD cohort compared to the HC cohort (X2 test OR 5.00, 95% CI 3.06-8.18, p value = 4.5e-12). A second-level manual annotation was necessary to capture true pathogenic variants that were removed by stringent allele frequency and quality filters. After these sequential steps, the diagnostic rate of monogenic disorders was 5.7% in the CLD cohort, attributable to P/LP variants in 25 genes. We also identified concordant liver disease phenotypes for 15/22 kidney disease patients with P/LP variants in liver genes, mostly associated with cystic liver disease phenotypes. Sequencing results had many implications for clinical management, including familial testing for early diagnosis and management, preventative screening for associated comorbidities, and in some cases for therapy. Exome sequencing provided a 5.7% diagnostic rate in CLD patients and required multiple rounds of review to reduce both false positive and false negative findings. The identification of concordant phenotypes in many patients with P/LP variants and no known liver disease also indicates a potential for predictive testing for selected monogenic liver disorders.

Clinical, biochemical and molecular characterization of Wilson's disease in Moroccan patients

Background

Wilson Disease (WD) is an autosomal recessive inherited metabolic disease caused by mutations in the ATP7B gene. WD is characterized by heterogeneous clinical presentations expressed by hepatic and neuropsychiatric phenotypes. The disease is difficult to diagnose, and misdiagnosed cases are commonly seen.

Methods

In this study, the presented symptoms of WD, the biochemical parameters as well as its natural history are described based on cases collected in Mohammed VI Hospital University of Marrakech (Morocco). We screened and sequenced 21 exons of ATP7B gene from 12 WD patients that confirmed through biochemical diagnosis.

Results

Mutational assessment of the ATP7B gene showed six homozygous mutations in 12 individuals however, 2 patients had no evidence of any mutation in promoter and exonic regions. All mutations are pathogenic and most were missense mutations. c.2507G > A (p.G836E), c.3694A > C (p.T1232P) and c.3310 T > C (p.C1104R) that were identified in 4 patients. The other mutations were a non-sense mutation (c.865C > T (p.C1104R)) detected in 2 patients, a splice mutation (c.51 + 4A > T) detected in 2 patients and a frameshift mutation (c.1746 dup (p.E583Rfs*25) detected in 2 patients.

Conclusion

Our study is the first molecular analysis in Moroccan patients with Wilson's disease, the ATP7B mutational spectrum in the Moroccan population is diverse and still unexplored.

Genomic Variations in ATP7B Gene in Indian Patients with Wilson Disease

OBJECTIVE

To report genotype data of the patients with Wilson disease (WD) hailing from across several parts of India to add to the available spectrum of causative variants in ATP7B gene (ATPase copper transporting beta polypeptide gene) and associated phenotypes in the Indian population.

METHODS

The entire ATP7B gene was sequenced in 58 patients with WD and additional testing was also done by MLPA to look for intragenic deletions duplications and exome sequencing to rule out genetic variations with similar phenotypic overlap.

RESULTS

Of all patients, 37 patients had a total of 33 distinct pathogenic variations, including 29 in the exonic regions and 4 at intronic splice sites. Of the variations identified, six were novel. The underlying genomic variations could be identified in nearly two-thirds of the patients by sequencing the entire gene.

CONCLUSIONS

This study reports the genotype-phenotype data to add to the available spectrum of causative variants in ATP7B gene. The inability to detect a pathogenic variation in some patients and the existence of phenotypic variations in individuals with the same variation suggest that additional factors or genes may play a role in causation of the disease. Further, a marked genetic heterogeneity was found in the study patients, indicating ethnic diversity of the Indian population.

Nomogram-based prediction of portal vein system thrombosis formation after splenectomy in patients with hepatolenticular degeneration

Objective

Splenectomy is a vital treatment method for hypersplenism with portal hypertension. However, portal venous system thrombosis (PVST) is a serious problem after splenectomy. Therefore, constructing an effective visual risk prediction model is important for preventing, diagnosing, and treating early PVST in hepatolenticular degeneration (HLD) surgical patients.

Methods

Between January 2016 and December 2021, 309 HLD patients were selected. The data were split into a development set (215 cases from January 2016 to December 2019) and a validation set (94 cases from January 2019 to December 2021). Patients' clinical characteristics and laboratory examinations were obtained from electronic medical record system, and PVST was diagnosed using Doppler ultrasound. Univariate and multivariate logistic regression analyses were used to establish the prediction model by variables filtered by LASSO regression, and a nomogram was drawn. The area under the curve (AUC) of receiver operating characteristic (ROC) curve and Hosmer-Lemeshow goodness-of-fit test were used to evaluate the differentiation and calibration of the model. Clinical net benefit was evaluated by using decision curve analysis (DCA). The 36-month survival of PVST was studied as well.

Results

Seven predictive variables were screened out using LASSO regression analysis, including grade, POD14D-dimer (Postoperative day 14 D-dimer), POD7PLT (Postoperative day 7 platelet), PVD (portal vein diameter), PVV (portal vein velocity), PVF (portal vein flow), and SVD (splenic vein diameter). Multivariate logistic regression analysis revealed that all seven predictive variables had predictive values (P < 0.05). According to the prediction variables, the diagnosis model and predictive nomogram of PVST cases were constructed. The AUC under the ROC curve obtained from the prediction model was 0.812 (95% CI: 0.756-0.869) in the development set and 0.839 (95% CI: 0.756-0.921) in the validation set. Hosmer-Lemeshow goodness-of-fit test fitted well (P = 0.858 for development set; P = 0.137 for validation set). The nomogram model was found to be clinically useful by DCA. The 36-month survival rate of three sites of PVST was significantly different from that of one (P = 0.047) and two sites (P = 0.023).

Conclusion

The proposed nomogram-based prediction model can predict postoperative PVST. Meanwhile, an earlier intervention should be performed on three sites of PVST.

Mutational analysis of exon 8 and exon 14 of ATP7B gene in Bangladeshi children with Wilson disease

BACKGROUND : Wilson disease (WD) is an autosomal recessive disorder caused by mutation in the Adenosine Triphosphate 7B (ATP7B) gene. The spectrum of ATP7B mutation varies in different populations. The objective of this study was to identify the mutation in exon 8 and exon 14 of ATP7B gene in Bangladeshi children clinically diagnosed as WD. We also aimed to explore the phenotypic presentation.

METHODS

It was a cross sectional observational study. The study was conducted at the Department of Paediatric Gastroenterology, Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh from January 2017 to June 2018. A total of 37 patients diagnosed with WD were enrolled for the study. Venous blood (about 3 mL) was drawn aseptically from each patient into tube containing ethyline diamine tetraacetic acid (EDTA) and preserved at -30°C for long-term preservation. The peripheral blood leukocytes of the patients and genomic DNAs were extracted. Exons 14 and 8 of ATP7B and their associated splice-site junctions were amplified by the polymerase chain reaction (PCR). The size and quantity of PCR products were verified by electrophoresis in 1.5% (w/v) agarose gel. 74 (37 × 2) PCR products were sent for Sanger Sequencing. The sequences were analyzed by Chromas version 2.6.6 software and the nucleotide blast was done by National Center for Biotechnology Information (NCBI) nucleoblast. Finally, the sequences were analyzed using AB Applied Bio systems and were matched with the reference sequences using MEGA software.

RESULTS

In this study, a single novel homozygous mutation pLeu.1071Val in the exon 14 was found in every (100%) studied child clinically diagnosed with WD. Heterozygous mutation p.Gly1061Glu in exon14 was also found in 6 patients (11%) with WD, which is one of the common mutations in this disease. In exon 8, p.Arg778Leu mutation was detected in one patient (2.7%), which is common in the Chinese and the South Asian populations and was heterozygous. Two novel heterozygous missense mutations p.K785R (2.7%) and p.S744F (2.7%) were also found in two other children in the exon 8.

CONCLUSION

We found three novel mutations in Bangladeshi children with WD, one of which may be tagged as founder mutation for Bangladeshi population. This finding indicates the necessity to study the mutation profiles of the whole ATP7B gene in our population for risk prediction. A further large-scale study will help in the development of a Mutational Data Base of Bangladeshi population with WD.

Mutation spectrum of ATP7B gene in pediatric patients with Wilson disease in Vietnam

Background

Wilson disease (WD) is caused by mutations in the copper-transporting P-type adenosine triphosphatase encoded by the ATP7B gene. In this study, we screened and identified the ATP7B mutations among unrelated Vietnamese pediatric patients.

Methods

One-hundred-thirteen pediatric patients with clinically diagnosed WD were recruited. DNA samples were extracted from peripheral blood. Mutations in the ATP7B gene were identified by Sanger sequencing.

Results

Approximately 98% of the clinically diagnosed WD patients carried ATP7B mutations. A total of 35 different ATP7B variants were detected, including five novel mutations (L658P, L792P, T977K, IVS4 + 1G > A and IVS20 + 4A > G). Remarkably, this study revealed that S105* was the most prevalent variant (32.27%), followed by L1371P (9.09%), I1148T (7.27%), R778L (6.36%), T850I (5.45%), V176Sfs*28 and IVS14-2A > G (4.55%). Most ATP7B mutations were located in the exon 2 (37.73%), exon 16 (10.00%), exon 8 (9.55%), exon 20 (9.09%), exon 10 and exon 18 (5.45%), exon 14 (5.00%), exon 13 and intron 14 (4.55%). We developed a streamlined procedure to quickly characterize mutations in the ATP7B gene in the Vietnamese children, starting with sequencing exon 2 and subsequently to exons 8,10,13-16,18, and 20 to allow quick diagnosis of clinically suspected patients.

Conclusion

The mutational spectrum and hotspots of ATP7B gene in the Vietnamese population were fairly different from other East Asian populations. A streamlined procedure was developed to screen exon 2 in ATP7B gene among suspected WD patients to reduce genetically diagnostic cost, to facilitate early detection and intervention in countries with limited resources.

Genetic studies discover novel coding and non-coding mutations in patients with Wilson's disease in China

OBJECTIVES

Wilson disease (WD) is a rare autosomal recessive genetic disorder associated with various mutations in the ATP7B gene and leads to significant disability or death if untreated. Early diagnosis and proper therapy usually predict a good prognosis, especially in pre-symptomatic WD. Genetic testing provides an accurate and effective diagnostic method for the early diagnosis of WD.

METHODS

We recruited 18 clinically diagnosed WD patients from 16 unrelated families and two independent individuals. The next-generation sequencing of the ATP7B gene was performed. The 293T cell lines were divided into wild-type (WT) ATP7B and mutated ATP7B groups. Cell proliferation was determined by Cell Counting Kit-8 (CCK-8) assay and apoptosis was detected by Annexin V/propidium iodide (PI) assays.

RESULTS

Pedigree analysis showed that compound heterozygous variants (17/18, 94.44%) were present in the majority of WD patients. A total of 33 ATP7B gene variants were identified, including three variants with uncertain significance (VUS) [two splice mutations (c.51+2T>G, c.1543+40G>A) and one frameshift mutation (c.3532_3535del)]. The CCK-8 and apoptosis assays demonstrated that the VUS of ATP7B could significantly affect the transportation of copper.

CONCLUSIONS

The study revealed genetic defects of 16 Chinese families and two independent individuals with WD, which enriched the mutation spectrum of the ATP7B gene worldwide and provided valuable information for studying the mutation types of ATP7B in the Chinese populations. Genetic testing in WD patients is necessary to shorten the time to initiate therapy, reduce damage to the liver and improve the prognosis.

Mutation analysis of the ATP7B gene and genotype-phenotype correlation in Chinese patients with Wilson disease

AIM

To discover the novel ATP7B mutations in 103 southern Chinese patients with Wilson disease (WD), and to determine the spectrum and frequency of mutations in the ATP7B gene and genotype-phenotype correlation in a large-scale sample of Chinese WD patients.

METHODS

One hundred three WD patients from 101 unrelated families in southern China were enrolled in this study. Genomic DNA was extracted from the peripheral blood. Direct sequencing of all 21 exons within ATP7B was performed. Subsequently, an extensive study of the overall spectrum and frequency of ATP7B mutations and genotype-phenotype correlation was performed in all Chinese patients eligible from the literature, combined with the current southern group.

RESULTS

In 103 patients with WD, we identified 48 different mutations (42 missense mutations, 4 nonsense mutations and 2 frameshifts). Of these, 3 mutations had not been previously reported: c.1510_1511insA, c.2233C>A (p.Leu745Met) and c.3824T>C (p.Leu1275Ser). The c.2333G>T (p.Arg778 Leu) at exon 8, was the most common mutation with an allelic frequency of 18.8%, followed by c.2975C>T (p.Pro992Leu) at exon 13, with an allelic frequency of 13.4%. In the comprehensive study, 233 distinct mutations were identified, including 154 missense mutations, 23 nonsense mutations and 56 frameshifts. Eighty-five variants were identified as novel mutations. The c.2333G>T (p.Arg778 Leu) and c.2975C>T (p.Pro992Leu) were the most common mutations, with allelic frequencies of 28.6% and 13.0%, respectively. Exons 8, 12, 13, 16 and 18 were recognised as hotspot exons. Phenotype-genotype correlation analysis suggested that c.2333G>T (p.Arg778 Leu) was significantly associated with lower levels of serum ceruloplasmin (P = 0.034). c.2975C>T (p.Pro992Leu) was correlated with earlier age of disease onset (P = 0.002). Additionally, we found that the c.3809A>G (p.Asn1270Ser) mutation significantly indicated younger onset age (P = 0.012), and the c.3884C>T (p.Ala1295Val) mutation at exon 18 was significantly associated with hepatic presentation (P = 0.048). Moreover, the patients with mixed presentation displayed the initial WD features at an older onset age than the groups with either liver disease or neurological presentation (P = 0.039, P = 0.015, respectively). No significant difference was observed in the presence of KF rings among the three groups with different clinical manifestations.

CONCLUSION

In this study, we identified three novel mutations in 103 WD patients from the southern part of China, which could enrich the previously established mutational spectrum of the ATP7B gene. Moreover, we tapped into a large-scale study of a Chinese WD cohort to characterise the overall phenotypic and genotypic spectra and assess the association between genotype and phenotype, which enhances the current knowledge about the population genetics of WD in China.

Molecular analysis of 53 Chinese families with Wilson's disease: Six novel mutations identified

Background

Wilson's disease (WD) is a rare autosomal recessive inherited disorder that is induced by defects of the ATP7B gene and characterized by damage to the liver and nervous system caused by aberrant copper metabolism. The identification of pathogenic mutations on two homologous chromosomes has become the gold standard for the diagnosis of WD.

Methods

Sanger sequencing and multiplex ligation‐dependent probe amplification (MLPA) were combined to establish a genetic diagnosis for patients from 53 unrelated Chinese WD families.

Results

Biallelic mutations were detected by Sanger sequencing in 50 of the probands, while single heterozygous mutations were detected in the remaining three probands. A total of 45 diverse pathogenic mutations were detected, and 6 previously unreported mutations were involved. Five asymptomatic patients were screened from 85 family members of 38 probands participating in the study.

Conclusion

This study contributes to the enlargement of the mutational spectrum of the ATP7B gene among the population of China and highlights the significance of genetic testing for asymptomatic patients.

A novel heterozygous carrier of ATP7B mutation with muscle weakness and tremor: A Chinese Case Report

Wilson's disease (WD) is an autosomal recessive genetic disease linked to ATP7B, which is located on the chromosome 13q14.3. We presently report a hepatolenticular degeneration carrier whose clinical phenotype mainly included limb weakness and tremor with a novel WD mutation. The mutation in Exon 10 of ATP7B Gene [c.2480G>A p. (Arg827Gln)] was identified after gene sequencing. We have provided diagnostic analyses, such as muscle biopsy and electrophysiology, which would be helpful to deepen the understanding of the pathogenesis underneath nerve damage in WD heterozygote carriers (Hzc).

Complex ATP7B mutation patterns in Wilson disease and evaluation of a yeast model for functional analysis of variants

Wilson disease (WD) is a rare autosomal recessive genetic disorder that is associated with various mutations in the ATP7B gene. Although ATP7B variants are frequently identified, the exact mutation patterns remain unknown because of the absence of pedigree studies, and the functional consequences of individual ATP7B variants remain to be clarified. In this study, we recruited 65 clinically diagnosed WD patients from 60 unrelated families. Pedigree analysis showed that besides several ATP7B homozygous variants (8/65, 12.3%), compound heterozygous variants (43/65, 66.2%) were present in the majority of WD patients. There were 20% of the patients had one (12/65, 18.5%) or multiple (1/65, 1.5%) variants in only a single allele, characterized by a high ratio of splicing or frameshift variants. Nine ATP7B variants were cloned into the pAG426GPD yeast expression vector to evaluate their functional consequences, and the results suggested different degrees of functional disruption from mild or uncertain to severe, consistent with the corresponding phenotypes. Our study revealed the complex ATP7B mutation patterns in WD patients and the applicability of a yeast model system to the evaluation of the functional consequences of ATP7B variants, which is essential for WD cases that are difficult to interpret.

High genetic carrier frequency of Wilson's disease in France: discrepancies with clinical prevalence

Background

Wilson’s disease (WD) is a rare autosomal recessive metabolic disease caused by ATP7B gene mutations tat cause excessively high copper levels, particularly in the liver and brain. The WD phenotype varies in terms of its clinical presentation and intensity. Diagnosing this metabolic disorder is important as a lifelong treatment, based on the use of copper chelating agents or zinc salts, is more effective if it’s started early. Worldwide prevalence of WD is variable, with an average of 1/30,000. In France, a recent study based on French health insurance data estimated the clinical prevalence of the disease to be around 3/200,000.

Methods

To estimate the genetic prevalence of WD in France, we analysed the ATP7B gene by Next Generation Sequencing from a large French cohort of indiscriminate subjects.

Results

We observed a high heterozygous carrier frequency of ATP7B in France. Among the 697 subjects studied, 18 variants classified as pathogenic or probably pathogenic were found at heterozygous level in 22 subjects (22 alleles/1394 alleles), yielding a prevalence of 0.032 or 1/31 subjects.

Conclusions

This considerable and unexplained discrepancy between the heterozygous carrier frequency and the clinical prevalence of WD may be explained by the clinical variability, the incomplete penetrance and the existence of modifiers genes. It suggests that the molecular analysis of ATP7B should be interpreted with caution, always alongside copper assays (ceruloplasmin, relative exchangeable copper, 24 h-urinary copper excretion) with particular respect to exome sequencing.

Presumed missense and synonymous mutations in ATP7B gene cause exon skipping in Wilson disease

BACKGROUND & AIMS

Wilson disease is an inborn error of metabolism caused by abnormalities of the copper-transporting protein-encoding gene ATP7B. Recently, the phenomenon of exon skipping, in which exonic mutations result in abnormal splicing, has been associated with various diseases. The present study investigated the splicing defects of the ATP7B exonic variants identified in a cohort of 44 patients with Wilson disease.

METHOD

All patients were analysed for ATP7B gene by direct sequencing or multiplex ligation-dependent probe amplification analysis. To identify the potential pathogenicity of the candidate mutations that may induce exon skipping, both in vivo RT-PCR analysis using RNA from peripheral leukocytes and in vitro functional splicing by minigene construction were conducted.

RESULTS

The patterns of inheritance of the mutations in ATP7B identified in 44 patients exhibited homozygotes (7 patients), compound heterozygotes (32 patients) and heterozygotes (5 patients). In all patients, we detected 25 different ATP7B mutations, including 17 missenses, 1 frameshift, 3 nonsenses, 2 exonic deletions and 2 splicing alteration. In these mutations, 4 mutations have not been previously described in the literature or entered in human genome mutation database. Furthermore, we identified synonymous mutation c.4014T>A and missense mutation R919G caused exon skipping in the ATP7B mRNA transcript.

CONCLUSION

Our results suggest that aberrant exon skipping associated to putative splicing enhancer disruption and silencer creation is one previously unrecognized mechanism in Wilson disease. What is more, the multiplex ligation-dependent probe amplification assay for the detection of exon deletions may be valuable in individuals with clinical Wilson disease diagnosis where one or no mutation has been identified by sequencing.

Biochemical and molecular characterisation of neurological Wilson disease

Background

To identify biochemical and genetic features that characterise neurological Wilson disease as a distinct disease subgroup.

Methods

Detailed biochemical profiles and genotypic characteristics of neurological (86 patients) and hepatic subgroups (233 patients) from 368 unrelated Korean families were analysed.

Results

Compared with patients in the hepatic subgroup, patients in the neurological subgroup had a later age at onset, a higher proportion with Kayser-Fleischer rings and higher serum creatinine levels, and a lower proportion with favourable outcome (62% vs 80%, P<0.016). At diagnosis, the neurological subgroup had lower serum ceruloplasmin (3.1±2.1 mg/dL vs 4.2±3.2 mg/dL, P<0.001), total copper (26.4±13.8 µg/dL vs 35.8±42.4 µg/dL, P=0.005), free copper (17.2±12.5 µg/dL vs 23.5±38.2 µg/dL, P=0.038) and urinary copper (280.9±162.9 µg/day vs 611.1±1124.2 µg/day, P<0.001) levels. Serum aspartate aminotransferase, alanine aminotransferase, gamma glutamyltransferase and total bilirubin levels, as well as prothrombin time, were also lower in the neurological subgroup. Liver cirrhosis was more common but mostly compensated in the neurological subgroup. Frameshift, nonsense or splice-site ATP7B mutations and mutations in transduction or ATP hinge domains (2.4% vs 23.1%, P=0.006) were less common in the neurological subgroup.

Conclusion

The neurological subgroup had distinct clinical, biochemical and genetic profiles. Further studies are required to identify the factors, with or without association with copper metabolism, underlying the neurological presentation for which treatment needs to be targeted to improve the clinical outcome of this subgroup.

Epidemiology, diagnosis, and treatment of Wilson's disease

Wilson's disease (WD) is an autosomal recessive disease caused by a mutation of the ATP7B gene, resulting in abnormal copper metabolism. The major clinical features of WD include liver disease, neurological disorders, K-F rings, and osteoporosis. The prevalence of WD in China is higher than that in Western countries. Early diagnosis and lifelong treatment will lead to better outcomes. Drugs such as sodium dimercaptosuccinate (Na-DMPS), Zn, and Gandou Decoction can be used to treat WD. Some studies have shown that the combination of traditional Chinese medicine and Western medicine is the best approach to treating WD. In order to identify better treatments, this article describes the specific clinical symptoms of Wilson's disease, its diagnosis, and treatment options.

Wilson's Disease in China

Wilson's disease (WD) is an autosomal recessive disorder of copper metabolism. Its incidence is higher in China than in western countries. ATP7B is the causative gene and encodes a P-type ATPase, which participates in the synthesis of holoceruloplasmin and copper excretion. Disease-causing variants of ATP7B disrupt the normal structure or function of the enzyme and cause copper deposition in multiple organs, leading to diverse clinical manifestations. Given the variety of presentations, misdiagnosis is not rare. Genetic diagnosis plays an important role and has gradually become a routine test in China. The first Chinese spectrum of disease-causing mutations of ATP7B has been established. As a remediable hereditary disorder, most WD patients have a good prognosis with an early diagnosis and chelation treatment. However, clinical trials are relatively few in China, and most treatments are based on the experience of experts and evidences from other countries. It is necessary to study and develop appropriate regimens specific for Chinese WD patients.

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.

Development and evaluation of an unlabeled probe high-resolution melting assay for detection of ATP7B mutations in Wilson's disease

BACKGROUND

Wilson's disease (WD) is a rare autosomal recessive disorder characterized by the deposition of copper mainly in the liver or nerve system that leads to their dysfunction. Mutations in the gene encoding ATPase, Cu+ transporting, beta polypeptide (ATP7B) are causative for WD. The aim of this study was to develop a rapid and convenient assay for detection of the three most common causative ATP7B mutations, p.R778L, p.P992L, and p.V1106I.

METHODS

Plasmids containing DNA fragments harboring each of the three ATP7B mutations were constructed. High-resolution melting (HRM) analysis was conducted by asymmetric polymerase chain reaction (PCR) amplification with paired primer and unlabeled probe, performed in a 96-well plate formatted LightCycler 480 Real-Time PCR System. The assay was evaluated for accuracy and reproducibility by genotyping of 41 WD cases.

RESULTS

The unlabeled probe HRM assays performed on constructs with the p.R778L, p.P992L, and p.V1106I mutations in the ATP7B gene resulted in additional melting peaks. According to the unlabeled probe HRM molecular signature, we could differentiate homozygous mutations from wild-type with the ΔTm (difference between melting temperatures) >4°C, and the coefficient of variation in repeatability tests was <5%. In the validation assay using our method to examine clinical samples, a 100% accuracy rate was achieved.

CONCLUSIONS

The newly developed assay to rapidly genotype the ATP7B mutations is convenient, accurate, and reproducible, and represents a favorable alternative to Sanger sequencing in the identification of specific ATP7B mutations.

Recent advance in the molecular genetics of Wilson disease and hereditary hemochromatosis

Metabolic liver diseases such as Wilson disease (WD) and hereditary hemochromatosis (HH) possess complicated pathogenesis and typical hereditary characteristics with the hallmarks of a deficiency in metal metabolism. Mutations in genes encoding ATPase, Cu + transporting, beta polypeptide (ATP7B) and hemochromatosis (HFE) or several non-HFE genes are considered to be causative for WD and HH, respectively. Although the identification of novel mutations in ATP7B for WD and HFE or the non-HFE genes for HH has increased, especially with the application of whole genome sequencing technology in recent years, the biological function of the identified mutations, as well as genotype-phenotype correlations remain to be explored. Further analysis of the causative gene mutation would be critical to clarify the mechanisms underlying specific disease phenotypes. In this review, we therefore summarize the recent advances in the molecular genetics of WD and HH including the updated mutation spectrums and the correlation between genotype and phenotype, with an emphasis on biological functional studies of the individual mutations identified in WD and HH. The weakness of the current functional studies and analysis for the clinical association of the individual mutation was also discussed. These works are essential for the understanding of the association between genotypes and phenotypes of these inherited metabolic liver diseases.

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

AIM: To study the effect of anti-copper treatment for survival of hepatic cells expressing different ATP7B mutations in cell culture.

METHODS: The most common Wilson disease (WD) mutations p.H1069Q, p.R778L and p.C271*, found in the ATP7B gene encoding a liver copper transporter, were studied. The mutations represent major genotypes of the United States and Europe, China, and India, respectively. A human hepatoma cell line previously established to carry a knockout of ATP7B was used to stably express WD mutants. mRNA and protein expression of mutant ATP7B, survival of cells, apoptosis, and protein trafficking were determined.

RESULTS: Low temperature increased ATP7B protein expression in several mutants. Intracellular ATP7B localization was significantly impaired in the mutants. Mutants were classified as high, moderate, and no survival based on their viability on exposure to toxic copper. Survival of mutant p.H1069Q and to a lesser extent p.C271* improved by D-penicillamine (DPA) treatment, while mutant p.R778L showed a pronounced response to zinc (Zn) treatment. Overall, DPA treatment resulted in higher cell survival as compared to Zn treatment; however, only combined Zn + DPA treatment fully restored cell viability.

CONCLUSION: The data indicate that the basic impact of a genotype might be characterized by analysis of mutant hepatic cell lines.

Targeted next-generation sequencing of the ATP7B gene for molecular diagnosis of Wilson disease

OBJECTIVES

In recent years, next-generation sequencing (NGS) technologies, which enable high throughput sample processing at relatively lower costs, are adopted in both research and clinical settings. A multiplex PCR-based NGS assay to identify mutations in the ATP7B gene for routine molecular diagnosis of Wilson disease was evaluated in comparison with the gold standard direct Sanger sequencing.

DESIGN AND METHODS

Five multiplex PCRs to amplify the partial promoter, 5' untranslated and the entire coding regions of the ATP7B gene were designed. Indexed paired-end libraries were generated from the pooled amplicons using Nextera XT DNA Sample Preparation Kit and subjected to NGS on the MiSeq platform. DNA from the peripheral blood of 12 patients with Wilson disease, 2 B-lymphocyte cell lines and 3 external quality assurance samples were sequenced by the MiSeq and Sanger sequencing.

RESULTS

Complete coverage was achieved across the targeted bases without any drop-out sequences. The observed read depth in a single run with 20 samples was >100X. Comparison of the NGS results against Sanger sequencing data on a panel of clinical specimens, cell lines and European Molecular Genetics Quality Networks (EMQN) quality assurance samples showed 100% concordance in identifying pathogenic mutations.

CONCLUSION

With the capability of generating relatively higher throughput in a short time period, the NGS assay is a viable alternative to Sanger sequencing for detecting ATP7B mutations causally linked to Wilson disease in the clinical diagnostic laboratory.

Novel mutations of the ATP7B gene in Han Chinese families with pre-symptomatic Wilson's disease

BACKGROUND

Wilson's disease (WD) is an autosomal recessive genetic disorder of copper metabolism, caused by mutations in the ATP7B gene, resulting in copper accumulation in the liver, brain, kidney, and cornea and leading to significant disability or death if untreated. Early diagnosis and proper therapy usually predict a good prognosis, especially in pre-symptomatic WD. Genetic testing is the most accurate and effective diagnostic method for early diagnosis.

METHODS

The clinical and biochemical features of three unrelated Han Chinese families with pre-symptomatic WD were reported. The molecular defects in these families were investigated by polymerase chain reaction and DNA sequencing. Hundred healthy children with the same ethnic background served as controls. Bioinformatic tools (polymorphism phenotyping-2, sorting intolerant from tolerant, protein analysis through evolutionary relationships, and predictor of human deleterious single nucleotide polymorphisms) were combined and used to predict the functional effects of mutations.

RESULTS

We identified 2 novel ATP7B mutations (p.Leu692Pro and p.Asn728Ser) and 3 known mutations (p.Met769fs, p.Arg778Leu and p.Val1216Met) in these Chinese WD families. These mutations were not observed in the 100 normal controls. The bioinformatic method showed that p.Leu692Pro and p.Asn728Ser mutations are pathogenic.

CONCLUSIONS

Our research enriches the mutation spectrum of the ATP7B gene worldwide and provides valuable information for studying the mutation types and mode of inheritance of ATP7B in the Chinese population. Liver function analysis and genetic testing in young children with WD are necessary to shorten the time to the initiation of therapy, reduce damage to the liver and brain, and improve prognosis.

Geographic distribution of ATP7B mutations in Wilson disease

CONTEXT

Geographic distribution of ATP7B mutations in different populations.

OBJECTIVE

To summarise common mutations in the ATP7B gene and graphically illustrate their prevalence in different populations.

METHODS

A literature search was done using PubMed and the Wilson Disease Mutation Database (http://www.wilsondisease.med.ualberta.ca/database).

RESULTS

p.His1069Gln is the most prevalent mutation seen in Europe. In the Mediterranean countries, the array of prevalent mutations is different from the rest of Europe. In Far East Asian countries, the mutation p.Arg778Leu is the most common. In India, no single mutation seems to be dominant, owing to the vast ethnic diversity of the country. The p.Cys271* mutation is dominant in the east, west and south, but not reported in the north. In the Middle East, data from Saudi Arabia shows the p.Gln1399Arg mutation as the most prevalent. In the US, the p.His1069Gln is dominant, whereas in Brazil the mutation c.3402delC dominates.

CONCLUSION

Clinical features in WD patients can be misleading and often absent. Genetic testing is used to confirm the diagnosis. However, owing to the large gene size and vast diversity in the mutations, genetic testing can be time-consuming and tedious. This study reviews ATP7B mutations seen in different populations and can help develop time-saving methods and expediate the process of genetic analysis of WD.

Genetic and Clinical Analysis in a Cohort of Patients with Wilson's Disease in Southwestern China

BACKGROUND AND AIMS

Wilson's disease (WD), characterized by a disorder of copper metabolism, is an inherited autosomal recessive disease caused by mutations in the ATP7B gene.

METHODS

To explore genotype-phenotype correlations in Chinese WD patients and to evaluate the frequency of the ATP7B mutations, we described 77 clinically and biochemically confirmed WD patients and detected mutations in ten WD families from southwestern China. Clinical features were presented and all the exons of the ATP7B gene were screened.

RESULTS

The appearance of Kayser-Fleischer (K-F) rings was closely related to onset age, particularly before 10 years old. For those patients with predominantly neurological symptoms, MRI was the most sensitive and preferred examination. Eight mutations of the ATP7B gene were detected including seven reported mutations (c.2302dup, c.2304delC, c.2333 G>T, c.2621 C>T, c.2755 C>G, c.2975 C>T and c.1366 G>C) and four novel mutations (c.3446 G>A, c.3767insCA, c.3406 G>A and c.3700delG). c.2333 G>T was detected in 6/20 alleles (30%), accounting for the largest proportion, which could be regarded as a mutation hotspot in this region.

CONCLUSIONS

Our study extends the mutation spectrum of ATP7B and analyzes the relationship between mutations in the ATP7B gene and clinical findings of WD.

Mutational characterization of ATP7B gene in 103 Wilson's disease patients from Southern China: identification of three novel mutations

Wilson's disease (WD) is an autosomal recessive inheritance disorder of copper metabolism due to mutations in the ATP7B gene. The distribution of ATP7B gene mutations is diverse in different population. This study aimed to examine the genotypes of the ATP7B mutant alleles in WD patients from Southern China. Genomic DNA was extracted from 103 WD patients and 60 healthy patients. Mutations were screened and detected by DNA sequencing. A total of 51 different ATP7B mutations were identified in WD patients, including six homozygous, 51 compound heterozygous, and 39 single heterozygotes. Three mutations were found to be novel, including one missense mutation (c.2549C>T) and two frameshift mutations (c.3851_3876del and c.1057delC). The most frequent mutations are Arg778Leu (18.93%), Ile1148Thr (8.74%), and Pro992Leu (4.37%). Different from the published results of early studies, Ile1148Thr was found to be the second common mutation in our cohort. The highest mutation detection rate was on exon 8 (43.69%), followed by exon 16 (24.27%), and exon 12 (17.48%). The total mutation detection rate on exon 8, 12, and 16 was 85.44%. No ATP7B gene mutation was found in healthy patients. In conclusion, we identified three novel mutations and Ile1148Thr as another hotspot mutation in WD patients from Southern China. Most of the mutations can be detected by screening exon 8, 12, and 16. Our research has further enriched the mutation spectrum of the ATP7B gene in Chinese and may help to develop genetic screening strategies of WD.

A novel ATP7B gene mutation in a liver failure patient with normal ceruloplasmin and low serum alkaline phosphatase

Wilson's disease (WD) is a rare disorder of copper metabolism resulting in accumulation of copper in liver and other organs. We present a liver failure patient, who was misdiagnosed for two years, with normal ceruloplasmin and low serum alkaline phosphatase. Molecular testing revealed a novel p.Ala982Thr mutation within ATP7B gene. The pathology of liver sample showed a large amount of copper deposition in the hepatocytes and confirmed the diagnosis of WD. Our data highlighted the importance of molecular testing in the early diagnosis of atypical WD.

Comprehensive analysis on clinical features of Wilson's disease: an experience over 28 years with 133 cases

OBJECTIVES

Here, we reported our experience over 28 years with 133 cases of patients with Wilson's disease (WD) in order to illustrate the diverse clinical presentation and to improve understanding and early diagnosis of WD.

METHODS

We reviewed the medical records of patients with WD at Shengjing Hospital of China Medical University from 1993 to 2011. The clinical manifestations and laboratory findings were analyzed. The diagnosis was based on the presence of Kayser-Fleisher (K-F) rings, low serum copper levels, low serum ceruloplasmin levels, increased urinary copper concentrations before or after penicillamine challenge.

RESULTS

Among them, 93 patients mainly presented with hepatic manifestations, 27 with neural abnormalities, and 13 presented with others. Age range at diagnosis was wide (3-74 years, average 13·2 years), and five patients were over 40 years. The oldest one was aged 74 years and presented with neuropsychiatric disorder. The positive rate of K-F rings was 93·0%. The serum ceruloplasmin decreased in 83·6% patients, 24-hour urinary copper increased in 88·1% patients, and serum copper decreased in 68·9% patients. About 79·7% of patients were diagnosed within 6 months, but only 33·1% were diagnosed at their initial medical consultation. There was a substantial delay of up to 15 years.

CONCLUSIONS

The clinical manifestation of WD is very diverse and no one feature is completely reliable. Doctors in many fields have opportunities to encounter this disease, and the most important thing is to be aware of the possibility of WD.

EGFP tags affect cellular localization of ATP7B mutants

AIMS

Wilson's disease is an autosomal recessive disorder of copper metabolism due to mutations within ATP7B gene. Clinical investigations indicate that ATP7B truncations are associated with an early age of onset when compared to its missense mutations. In vitro studies show that mislocalization of ATP7B mutants is involved in disease-causing mechanisms. Enhanced green fluorescent protein (EGFP) tags are commonly used in in vitro studies of cellular localization of ATP7B mutants. However, there is still much unknown about cellular localization of ATP7B truncations.

METHODS

Here, we subcloned full-length human wild-type, a missense mutation (T935M), and four truncating mutants (E332X, Q511X, Q547X, Q819X) of ATP7B into pEGFP-C1, pEGFP-N2 and pCMV-myc, and transfected Chinese hamster ovary (CHO) and SH-SY5Y cells with them, respectively.

RESULTS

ATP7B truncations all showed a diffuse and homogenous distribution pattern within the cytosol of CHO and SH-SY5Y cells, whereas its wild-type proteins and T935M mutation were clustered in the Golgi apparatus. Furthermore, we found that EGFP tags at N- or C-terminal would severely affect cellular localization of ATP7B truncations, and EGFP tags at N-terminal also have an influence on T935M localization.

CONCLUSION

EGFP tags may not be suitable for the detection of cellular localization of ATP7B mutants.

Mutational analysis of ATP7B in north Chinese patients with Wilson disease

Wilson disease (WD) is an autosomal recessive inherited disease caused by abnormalities of the copper-transporting protein encoding gene ATP7B. In this study, we examined ATP7B for mutations in 114 individuals of Chinese Han population living in north China who were diagnosed as WD. Totally, we identified 36 mutations and 11 single-nucleotide polymorphisms (SNPs), of which 14 mutations have never been reported previously and 5 were firstly described in Chinese. Among these, p.R778L (21.5%), p.A874V (7.5%) and p.P992L (6.1%) were the most frequent mutations. A genotype of p.L770L+p.R778L+p.P992L was the most frequent triple mutations and two pairs of mutations, p.L770L/p.R778L and p.A874V/p.I929V, were closely related. In addition, a database was established to summarize all ATP7B mutations, including those reported previously and those identified in this study. Popular algorithms were used to predict the functional effects of these mutations, and finally, by comparative genomics approaches, we predicted a group of mutation hot spots for ATP7B. Our study will broaden our knowledge about ATP7B mutations in WD patients in north China, and be helpful for clinical genetic testing.