Copper toxicosis gene MURR1 is not changed in Wilson disease patients with normal blood ceruloplasmin levels

Therapeutic implications of impaired nuclear receptor function and dysregulated metabolism in Wilson's disease

Copper is an essential trace element that is required for the activity of many enzymes and cellular processes, including energy homeostasis and neurotransmitter biosynthesis; however, excess copper accumulation results in significant cellular toxicity. The liver is the major organ for maintaining copper homeostasis. Inactivating mutations of the copper-transporting P-type ATPase, ATP7B, result in Wilson's disease, an autosomal recessive disorder that requires life-long medicinal therapy or liver transplantation. Current treatment protocols are limited to either sequestration of copper via chelation or reduction of copper absorption in the gut (zinc therapy). The goal of these strategies is to reduce free copper, redox stress, and cellular toxicity. Several lines of evidence in Wilson's disease animal models and patients have revealed altered hepatic metabolism and impaired hepatic nuclear receptor activity. Nuclear receptors are transcription factors that coordinate hepatic metabolism in normal and diseased livers, and several hepatic nuclear receptors have decreased activity in Wilson's disease and Atp7b-/- models. In this review, we summarize the basic physiology that underlies Wilson's disease pathology, Wilson's disease animal models, and the possibility of targeting nuclear receptor activity in Wilson's disease patients.

A Century of Progress on Wilson Disease and the Enduring Challenges of Genetics, Diagnosis, and Treatment

Wilson disease (WD) is a rare, inherited metabolic disorder manifested with varying clinical presentations including hepatic, neurological, psychiatric, and ophthalmological features, often in combination. Causative mutations in the ATP7B gene result in copper accumulation in hepatocytes and/or neurons, but clinical diagnosis remains challenging. Diagnosis is complicated by mild, non-specific presentations, mutations exerting no clear effect on protein function, and inconclusive laboratory tests, particularly regarding serum ceruloplasmin levels. As early diagnosis and effective treatment are crucial to prevent progressive damage, we report here on the establishment of a global collaboration of researchers, clinicians, and patient advocacy groups to identify and address the outstanding challenges posed by WD.

Wilson's Disease: Facing the Challenge of Diagnosing a Rare Disease

Wilson disease (WD) is a rare disorder caused by mutations in ATP7B, which leads to the defective biliary excretion of copper. The subsequent gradual accumulation of copper in different organs produces an extremely variable clinical picture, which comprises hepatic, neurological psychiatric, ophthalmological, and other disturbances. WD has a specific treatment, so that early diagnosis is crucial to avoid disease progression and its devastating consequences. The clinical diagnosis is based on the Leipzig score, which considers clinical, histological, biochemical, and genetic data. However, even patients with an initial WD diagnosis based on a high Leipzig score may harbor other conditions that mimic the WD's phenotype (Wilson-like). Many patients are diagnosed using current available methods, but others remain in an uncertain area because of bordering ceruloplasmin levels, inconclusive genetic findings and unclear phenotypes. Currently, the available biomarkers for WD are ceruloplasmin and copper in the liver or in 24 h urine, but they are not solid enough. Therefore, the characterization of biomarkers that allow us to anticipate the evolution of the disease and the monitoring of new drugs is essential to improve its diagnosis and prognosis.

COMMD1, a multi-potent intracellular protein involved in copper homeostasis, protein trafficking, inflammation, and cancer

Copper is a trace element indispensable for life, but at the same time it is implicated in reactive oxygen species formation. Several inherited copper storage diseases are described of which Wilson disease (copper overload, mutations in ATP7B gene) and Menkes disease (copper deficiency, mutations in ATP7A gene) are the most prominent ones. After the discovery in 2002 of a novel gene product (i.e. COMMD1) involved in hepatic copper handling in Bedlington terriers, studies on the mechanism of action of COMMD1 revealed numerous non-copper related functions. Effects on hepatic copper handling are likely mediated via interactions with ATP7B. In addition, COMMD1 has many more interacting partners which guide their routing to either the plasma membrane or, often in an ubiquitination-dependent fashion, trigger their proteolysis via the S26 proteasome. By stimulating NF-κB ubiquitination, COMMD1 dampens an inflammatory reaction. Finally, targeting COMMD1 function can be a novel approach in the treatment of tumors.

The macrophage activation marker soluble CD163 is elevated and associated with liver disease phenotype in patients with Wilson's disease

BACKGROUND

Macrophages play a significant role in liver disease development and progression. The macrophage activation marker soluble (s)CD163 is associated with severity and prognosis in a number of different acute and chronic liver diseases but has been only sparsely examined in Wilson's disease (WD). We investigated sCD163 levels in patients with acute and chronic WD and hypothesized associations with liver disease phenotype and biochemical markers of liver injury.

METHODS

We investigated sCD163 in two independent cohorts of WD patients: 28 patients with fulminant WD from the US Acute Liver Failure (ALF) Study Group registry and 147 patients with chronic disease from a German WD registry. We included a control group of 19 healthy individuals. Serum sCD163 levels were measured by ELISA. Liver CD163 expression was determined by immunohistochemistry.

RESULTS

In the ALF cohort, median sCD163 was 10-fold higher than in healthy controls (14.6(2.5-30.9) vs. 1.5(1.0-2.7) mg/L, p < 0.001). In the chronic cohort, median sCD163 was 2.6(0.9-24.9) mg/L. There was no difference in sCD163 according to subgroups based on initial clinical presentation, i.e. asymptomatic, neurologic, hepatic, or mixed. Patients with cirrhosis at the time of diagnosis had higher sCD163 compared with those without cirrhosis (3.0(1.2-24.9) vs. 2.3(0.9-8.0) mg/L, p < 0.001); and both cohorts significantly lower than the ALF patients. Further, sCD163 correlated positively with ALT, AST, GGT and INR (rho = 0.27-0.53); and negatively with albumin (rho = - 0.37), (p ≤ 0.001, all). We observed immunohistochemical CD163 expression in liver tissue from ALF patients.

CONCLUSIONS

Although sCD163 is not specific for WD, it was elevated in WD patients, especially in those with ALF. Further, sCD163 was higher in patients with cirrhosis compared to patients without cirrhosis and associated with biochemical markers of liver injury and hepatocellular function. Thus, macrophage activation is evident in WD and associates with liver disease phenotype and biochemical parameters of liver disease. Our findings suggest that sCD163 may be used as a marker of liver disease severity in WD patients.

Association of Variants in the CP, ATOX1 and COMMD1 Genes with Wilson Disease Symptoms in Latvia

Wilson's disease (WD) is a copper metabolism disorder, caused by allelic variants in the ATP7B gene. Wilson's disease can be diagnosed by clinical symptoms, increased copper and decreased cerulopasmin levels, which could all also be by other genetic variants beyond the ATP7B gene, e.g., disturbed ceruloplasmin biosynthesis can be caused by pathogenic allelic variants of the CP gene. Copper metabolism in the organism is affected by several molecules, but pathogenic variants and related phenotypes are described with COMMD1 and ATOX1 genes. The aim of the study was to test other genes, CP, ATOX1 and COMMD1, for possible influence to the manifestation of WD. Patients were enrolled on the basis of Leipzig's diagnostic criteria, 64 unrelated patients with confirmed WD. Direct sequencing of promoter region of the CP gene and ATOX1 and COMMD1 gene exons was conducted. Statistically significant differences were found between the two variants in the CP gene and the ATP7B genotype (rs66508328 variant AA genotype and the rs11708215 variant GG genotype) were more common in WD patients with an unconfirmed ATP7B genotype. One allelic (intronic) variant was found in the ATOX1 gene without causing the functional changes of the gene. Three allelic variants were identified in the COMMD1 gene. No statistically significant differences were found between allele and genotype frequencies and the first clinical manifestations of WD. Different variants of the CP gene contributed to a WD-like phenotype in clinically confirmed WD patients with neurological symptoms and without identified pathogenic variants in the ATP7B gene. Allelic variants in the ATOX1 and COMMD1 genes do not modify the clinical manifestation of WD in Latvian patients. (266 words).

Genetics and epigenetic factors of Wilson disease

Wilson disease (WD) is a complex condition due to copper accumulation mainly in the liver and brain. The genetic base of WD is represented by pathogenic mutations of the copper-transporting gene ATP7B with consequent lack of copper excretion through the biliary tract. ATP7B is the only gene so far identified and known to be responsible for the development of the disease. Our understanding of the disease has been evolving as functional studies have associated specific disease-causing mutations with specific copper-transporter impairments. The most frequent variant in patients of European descent is the H1069Q missense mutation and it has been associated with protein misfolding, aberrant phosphorylation of the P-domain, and altered ATP binding orientation and affinity. Conversely, there is much less understanding of the relation between the genotype and the clinical manifestations of WD. WD is characterized by a highly varied and unpredictable presentation with different combined hepatic, neurological, and psychiatric symptoms. Several studies have attempted to correlate genotype and phenotype but the most recent evidences on larger populations failed to identify a relation between genotype and clinical presentations. Given that so far also modifier genes have not shown convincing association with WD, there is growing interest to identify epigenetic mechanisms of gene expression regulation as underlying the onset and progression of WD phenotype. Evidence from animal models indicated changes in methionine metabolism regulation with possible effects on DNA methylation. Mouse models of WD have indicated transcript level changes of genes related to DNA methylation in fetal and adult livers. And finally, evidence is accumulating regarding DNA methylation changes in patients with WD. It is unexplored how ATP7B genetic mutations combine with epigenetic changes to affect the phenotype. In conclusion, WD is a genetic disease with a complex regulation of its phenotype that includes molecular genetics and epigenetic mechanisms.

Wilson disease: At the crossroads between genetics and epigenetics-A review of the evidence

Environmental factors, including diet, exercise, stress, and toxins, profoundly impact disease phenotypes. This review examines how Wilson disease (WD), an autosomal recessive genetic disorder, is influenced by genetic and environmental inputs. WD is caused by mutations in the copper-transporter gene ATP7B, leading to the accumulation of copper in the liver and brain, resulting in hepatic, neurological, and psychiatric symptoms. These symptoms range in severity and can first appear anytime between early childhood and old age. Over 300 disease-causing mutations in ATP7B have been identified, but attempts to link genotype to the phenotypic presentation have yielded little insight, prompting investigators to identify alternative mechanisms, such as epigenetics, to explain the highly varied clinical presentation. Further, WD is accompanied by structural and functional abnormalities in mitochondria, potentially altering the production of metabolites that are required for epigenetic regulation of gene expression. Notably, environmental exposure affects the regulation of gene expression and mitochondrial function. We present the "multi-hit" hypothesis of WD progression, which posits that the initial hit is an environmental factor that affects fetal gene expression and epigenetic mechanisms and subsequent "hits" are environmental exposures that occur in the offspring after birth. These environmental hits and subsequent changes in epigenetic regulation may impact copper accumulation and ultimately WD phenotype. Lifestyle changes, including diet, increased physical activity, stress reduction, and toxin avoidance, might influence the presentation and course of WD, and therefore may serve as potential adjunctive or replacement therapies.

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.

Outcome and development of symptoms after orthotopic liver transplantation for Wilson disease

BACKGROUND

Wilson disease (WD) is an autosomal recessive copper storage disease resulting in hepatic and neurologic dysfunction. Liver transplantation is an effective treatment for fulminant cases for patients with chronic liver disease. Reports on the outcome of neuropsychiatric symptoms after orthotopic liver transplantation (OLT) are limited.

AIM

To assess the course of neuropsychiatric and hepatic symptoms after liver transplantation for Wilson disease

METHODS

Nineteen patients with Wilson disease received liver transplantation and were followed prospectively from 2005 to 2010 for the development of hepatic, neurological and psychiatric symptoms.

RESULTS

Eight patients (all female) were transplanted for acute liver failure and eleven patients for chronic liver failure. Patient survival rates one and five yr after transplantation were 78% and 65%, respectively. Of the surviving patients, hepatic symptom scores improved in all patients and neurological symptom scores improved in all but one patient after OLT compared to the time of initial diagnosis and compared to pre-OLT status. Psychiatric symptoms showed moderate improvements.

CONCLUSION

Survival after OLT for Wilson disease with end-stage liver disease is excellent. Overall, neuropsychiatric symptoms improved after transplantation, substantiating arguments for widening of the indication for liver transplantation in symptomatic neurologic Wilson disease patients with stable liver function.

Efficacy and safety of oral chelators in treatment of patients with Wilson disease

BACKGROUND & AIMS

Wilson disease is a genetic copper storage disorder that causes hepatic and neurologic symptoms. Chelating agents (D-penicillamine, trientine) are used as first-line therapies for symptomatic patients, but there are few data from large cohorts. We assessed the safety of D-penicillamine and trientine therapy and outcomes of patients with Wilson disease.

METHODS

We performed a retrospective analysis of data on 380 patients with Wilson disease from tertiary care centers in Germany and Austria, and 25 additional patients from the EUROWILSON registry. Chelator-based treatment regimens were analyzed for their effect on neurologic and hepatic symptoms and for adverse events that led to discontinuation of therapy (Kaplan-Meier estimation; data were collected for a mean of 13.3 y after therapy began).

RESULTS

Changes in medication were common, resulting in analysis of 471 chelator monotherapies (326 patients receiving D-penicillamine and 141 receiving trientine). Nine of 326 patients treated with D-penicillamine and 3 of 141 patients given trientine underwent liver transplantation. Adverse events leading to discontinuation of treatment were more frequent among those receiving D-penicillamine than trientine (P = .039). Forty-eight months after therapy, hepatic deterioration was reported in only 4 of 333 patients treated initially with a chelating agent. Hepatic improvements were observed in more than 90%, and neurologic improvements were observed in more than 55%, of therapy-naive patients, and values did not differ significantly between treatments. However, neurologic deterioration was observed less frequently in patients given D-penicillamine first (6 of 295) than those given trientine first (4 of 38; P = .018).

CONCLUSIONS

Chelating agents are effective therapies for most patients with Wilson disease; D-penicillamine and trientine produce comparable outcomes, although D-penicillamine had a higher rate of adverse events. Few patients receiving chelation therapy had neurologic deterioration, which occurred more frequently in patients who received trientine.

Association of dopamine receptor gene polymorphisms with the clinical course of Wilson disease

BACKGROUND

Dopamine receptor D2 (DRD2) polymorphisms are proposed to be important factors in the presentation of neuropsychiatric symptoms in many disorders, including decreased striatum levels of dopamine D2 receptors in Wilson disease. The present study investigated the association between DRD2 gene polymorphisms and clinical manifestation of Wilson disease.

METHODS

Analyzing data from 97 symptomatic Wilson disease patients, we investigated the DRD2 gene polymorphisms rs1800497, rs1799732, and rs12364283. We assessed the polymorphisms impact on the phenotypic presentation of the disease.

RESULTS

Generally, the DRD2 gene polymorphisms had no impact on the hepatic or neuropsychiatric clinical presentation of Wilson disease. However, rs1799732 deletion allele carriers with neuropsychiatric symptoms had earlier onset of WD symptoms by almost 6 years compared with individuals without this allele (22.5 vs. 28.3 years; P < 0.05). This unfavorable effect of the rs1799732 polymorphism was even more pronounced among adenosine triphosphatase 7B gene (ATP7B) p.H1069Q homozygous patients, in whom carriership of the deletion allele was related to earlier initial neuropsychiatric manifestation by 14 years (18.4 vs. 32.2 years; P < 0.01).

CONCLUSIONS

Genetic variation of DRD2, specifically the rs1799732 polymorphism, may produce an earlier clinical presentation of Wilson disease neuropsychiatric symptoms and signs that occur in the course of dopaminergic system impairment due to copper accumulation in the brain. We speculate that this effect may be due to the impact of DRD2 polymorphism on dopamine D2 receptor density, but further studies are needed to understand the mechanisms of such phenotypic effects.

Canine models of copper toxicosis for understanding mammalian copper metabolism

Hereditary forms of copper toxicosis exist in man and dogs. In man, Wilson's disease is the best studied disorder of copper overload, resulting from mutations in the gene coding for the copper transporter ATP7B. Forms of copper toxicosis for which no causal gene is known yet are recognized as well, often in young children. Although advances have been made in unraveling the genetic background of disorders of copper metabolism in man, many questions regarding disease mechanisms and copper homeostasis remain unanswered. Genetic studies in the Bedlington terrier, a dog breed affected with copper toxicosis, identified COMMD1, a gene that was previously unknown to be involved in copper metabolism. Besides the Bedlington terrier, a number of other dog breeds suffer from hereditary copper toxicosis and show similar phenotypes to humans with copper storage disorders. Unlike the heterogeneity of most human populations, the genetic structure within a purebred dog population is homogeneous, which is advantageous for unraveling the molecular genetics of complex diseases. This article reviews the work that has been done on the Bedlington terrier, summarizes what was learned from studies into COMMD1 function, describes hereditary copper toxicosis phenotypes in other dog breeds, and discusses the opportunities for genome-wide association studies on copper toxicosis in the dog to contribute to the understanding of mammalian copper metabolism and copper metabolism disorders in man.

Evolving perspectives in Wilson disease: diagnosis, treatment and monitoring

Wilson disease (WD), the autosomal recessively inherited copper overload disorder, remains a diagnostic and therapeutic challenge. In the last decade, direct sequencing of the affected gene ATP7B became commercially available, but interpretation of the results still requires careful attention. Thus, a combination of tests reflecting the disturbed copper metabolism is needed to make the final diagnosis. Because of the low disease frequency, the existing treatment concepts are not based on controlled trails. Here, recent outcome reports of larger cohort studies challenge the recommended therapies and call for individualized treatment strategies. The notion, that certain medical regimens may either be insufficient to upkeep copper homeostasis or may lead to a clinically relevant overtreatment, demand a continuous monitoring of patients even after decades of therapy. In this article, we review current diagnostic and therapeutic approaches in WD.

Genetic variability in the methylenetetrahydrofolate reductase gene (MTHFR) affects clinical expression of Wilson's disease

BACKGROUND & AIMS

Wilson's disease (WND) is an autosomal recessive disorder of copper (Cu) transport, resulting from pathogenic mutations in the ATP7B gene. The reason for the high variability in phenotypic expressions of WND is unknown. Hepatotoxic and neurotoxic effects of homocysteine (Hcy), as well as interrelationships between Hcy and Cu toxicity, were documented.

METHODS

We genotyped the two 5,10-methylenetetrahydrofolate reductase (one of the key folate/Hcy pathway enzymes) gene (MTHFR) polymorphisms: C677T and A1298C in 245 WND patients. Next, we tested the modulation of WND phenotypes by genotypes of MTHFR.

RESULTS

MTHFR C677T genotype distribution deviated from that expected from a population in Hardy-Weinberg equilibrium (C677T, χ(2) = 12.14, p = 0.0005). Patients with the MTHFR 1298C allele were younger at symptoms' onset than those without this allele (median (IQR) age, 24.9 (14.0) years vs. 28.5 (12.0) years, p = 0.006). Carriers of MTHFR "high activity" diplotype (double wild-type homozygotes 677CC/1298AA) manifested WND at older age, than non-carriers (median (IQR) age, 33.5 (9.0) years vs. 25.0 (13.0) years, p = 0.0009). Patients with the MTHFR 677T allele less frequently exhibited the neurological WND phenotype (31 (29.5%) vs. 36 (48.0%)), and more frequently presented with hepatic WND (44 (41.9%) vs. 22 (29.3%)), compared with subjects MTHFR 677T(-).

CONCLUSIONS

We postulate that MTHFR polymorphism contributes to the phenotypic variability of WND.

Zinc monotherapy is not as effective as chelating agents in treatment of Wilson disease

BACKGROUND & AIMS

Wilson disease is a genetic disorder that affects copper storage, leading to liver failure and neurologic deterioration. Patients are treated with copper chelators and zinc salts, but it is not clear what approach is optimal because there have been few studies of large cohorts. We assessed long-term outcomes of different treatments.

METHODS

Patients in tertiary care centers were retrospectively analyzed (n = 288; median follow-up time, 17.1 years) for adherence to therapy, survival, treatment failure, and adverse events from different treatment regimens (chelators, zinc, or a combination). Hepatic treatment failure was defined as an increase in activity of liver enzymes (aspartate aminotransferase, alanine aminotransferase, and γ-glutamyltransferase) >2-fold the upper limit of normal or >100% of baseline with an increase in urinary copper excretion.

RESULTS

The median age at onset of Wilson disease was 17.5 years. Hepatic and neuropsychiatric symptoms occurred in 196 (68.1%) and 99 (34.4%) patients, respectively. Hepatic treatment failure occurred more often from zinc therapy (14/88 treatments) than from chelator therapy (4/313 treatments; P < .001). Actuarial survival, without transplantation, showed an advantage for chelating agents (P < .001 vs zinc). Changes in treatment resulted mostly from adverse events, but the frequency did not differ between groups. Patients who did not respond to zinc therapy showed hepatic improvement after reintroduction of a chelating agent.

CONCLUSIONS

Treatments with chelating agents or zinc salt are effective in most patients with Wilson disease; chelating agents are better at preventing hepatic deterioration. It is important to identify patients who do not respond to zinc therapy and have increased activities of liver enzymes, indicating that a chelating agent should be added to the therapeutic regimen.

Genetic analysis of BIRC4/XIAP as a putative modifier gene of Wilson disease

Wilson disease (WD) is an autosomal-recessive copper overload disorder caused by mutations in the copper-transporting adenosine triphosphatase (ATPase) ATP7B. It presents with a highly variable clinical phenotype ranging from asymptomatic to fulminant hepatic failure or progressive neurological involvement. No clear genotype-phenotype correlation has been established. Thus, variants in modifier genes could have an impact on WD manifestation and severity. Recently, the antiapoptotic protein baculoviral IAP repeat-containing protein 4 BIRC4/XIAP has been suggested as a regulator of copper-induced cell death. With the aim of investigating a putative role of BIRC4/XIAP as modifier gene in individuals with copper overload, we analyzed a WD patient cohort (n = 98) for sequence variants at the BIRC4/XIAP locus. When compared with clinical data, the previously described coding single nucleotide polymorphisms (SNPs) at the BRIC4/XIAP locus (rs28382721, rs28382722, rs28382723, rs5956583, rs28382740, rs12838858, rs28382741) did not correlate with age of onset or clinical presentation in our collective. However, three previously unreported variants in the BIRC4/XIAP gene were identified (c.1-26 T > G; c.1408A > T; p.T470S; c.1019A > G; p.N340S). The two patients with variants leading to amino acid exchanges in the BIRC4/XIAP protein showed a remarkably early disease onset at the age of 5 years. Furthermore, one of these patients was only heterozygous for disease-causing mutations in the ATP7B gene. In summary, these data emphasize the need to further elucidate a role of BIRC4/XIAP variants as putative pathogenetic factors in copper overload disorders.

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.

A novel COMMD1 mutation Thr174Met associated with elevated urinary copper and signs of enhanced apoptotic cell death in a Wilson Disease patient

Wilson disease (WD) results from accumulation of copper and caused due to mutations in ATP7B, a copper transporting ATPase. Besides regular hepatic and neurological symptoms, WD patients occasionally manifest atypical symptoms due to unknown cause. To understand the molecular etiology of atypical WD manifestations, we screened COMMD1, a gene implicated in canine copper toxicosis, in 109 WD patients including those with atypical symptoms. In a patient showing apoptotic symptoms and high urinary copper surpassing normal WD levels, we identified a novel, putative mutation in COMMD1. Two other changes were also identified in the gene. We have examined genotype-phenotype correlation between the detected changes and the atypical presentation of the WD patient.

Relevance of animal models for understanding mammalian copper homeostasis

As a trace element, copper has a crucial role in mammalian metabolism, but it can be toxic in excess. The importance of a balanced copper homeostasis is illustrated by several copper-associated disorders in man, such as Menkes and Wilson disease, and in a wide variety of animal models (eg, mice, dogs, and sheep). Proteins involved in controlling copper metabolism have been well studied in yeast and in vitro. Recently, naturally occurring mutants and transgenic mouse models have been used to study the physiologic role of copper transporters in copper homeostasis. We discuss the most common mammalian animal models used to study copper-related diseases, evaluate what these model systems have recently shown about copper metabolism, and discuss the importance of these models for identifying specific and sensitive biomarkers associated with copper status in the near future.

Developmental expression of Commd1 in the liver of the Jackson toxic milk mouse

Wilson disease (WD) is due to mutations in ATP7B, which encodes an intracellular metal-transporting P-type ATPase. In WD holoceruloplasmin production and biliary excretion of copper are decreased, leading to copper overload, oxidative stress and apoptotic cell death. Other copper-binding proteins include COMMD1, which is inactive in the Bedlington terrier hereditary copper toxicosis, and XIAP, which regulates apoptosis. We examined developmental expression of Commd1 and Xiap in the Jackson toxic milk mouse (Atp7b(tx-J), G712D missense mutation in Atp7b). Expression of Commd1 mRNA appeared unchanged by PCR but real-time PCR demonstrated 3- to 4-fold increase over the first 6 months of life. Immunodetectable Xiap dropped over the first 8 months of life and was nearly undetectable from 6 months onward. Cytosolic NF-kappaB rose then dropped precipitously at 5-6 months. In tx-j mice hepatic copper accumulation leads to decreased Xiap, increased Commd1; these responses ultimately fail to prevent progressive apoptotic cell damage.

Distinct Wilson's disease mutations in ATP7B are associated with enhanced binding to COMMD1 and reduced stability of ATP7B

BACKGROUND & AIMS

Wilson's disease (WD) is characterized by hepatic copper overload and caused by mutations in the gene encoding the copper-transporting P-type adenosine triphosphatase (ATPase) ATP7B. ATP7B interacts with COMMD1, a protein that is deleted in Bedlington terriers with hereditary copper toxicosis. Here we characterized the implications of the interaction between COMMD1 and ATP7B in relation to the pathogenesis of WD.

METHODS

Glutathione-S-transferase pull-down experiments, co-immunoprecipitations, immunofluorescence microscopy, site-directed mutagenesis, and biosynthetic labeling experiments were performed to characterize the interaction between COMMD1 and ATP7B and the effects of WD causing mutations.

RESULTS

COMMD1 specifically interacted with the amino-terminal region of ATP7B. This interaction was independent of intracellular copper levels and of the expression of the copper chaperone ATOX1. Four WD patient-derived mutations in this region of ATP7B significantly increased its binding to COMMD1. Two of these mutations also resulted in mislocalization and increased degradation rate of ATP7B. Although COMMD1 did not affect copper-induced trafficking of ATP7B, it markedly decreased the stability of newly synthesized ATP7B.

CONCLUSIONS

Our data implicate COMMD1 in the pathogenesis of WD and indicate that COMMD1 exerts its regulatory role in copper homeostasis through the regulation of ATP7B stability.

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.

COMMD proteins: COMMing to the scene

COMM Domain-containing or COMMD proteins are a recently discovered group of factors defined by the presence of a unique motif in their extreme carboxy termini (Copper metabolism MURR1, or COMM domain). This protein family is comprised of ten members which are widely conserved throughout evolution and share certain functional properties. At the present time, a number of seemingly discrete functions have been ascribed to these factors. These include the regulation of such events as the activity of the transcription factor NF-kappaB, copper homeostasis, the function of the epithelial sodium channel, and cell proliferation. A unifying mechanism that would explain all these events is lacking at the moment, but recent studies suggest that regulation of the ubiquitin pathway may be the basis of many of the functions of the COMMD protein family.

Inherited metabolic disease of the liver

PURPOSE OF REVIEW

The past decade has seen extraordinary growth in our understanding of the pathophysiology of Wilson disease, genetic hemochromatosis and alpha-1 antitrypsin deficiency as we continue to elucidate the molecular and cellular machinery involved in their pathogenesis. The continued progress in the elaboration of the molecular biology, genetics, epidemiology, and management of these prototypical inherited metabolic diseases will be the focus of this review.

RECENT FINDINGS

Wilson disease and genetic hemochromatosis involve defects in metal transport with copper and iron accumulation in hepatocytes, respectively. In alpha-1 antitrypsin deficiency, hepatocytes accumulate defective alpha-1 antitrypsin that misfolds. As a more complete picture of the molecular biology of the proteins and genes involved in transport has evolved, so has our understanding of the etiopathogenesis of these disorders and the variety of phenotypes observed. Finally, new ideas regarding the clinical management of these disorders will emerge with elucidation of the cellular basis for these diseases.

SUMMARY

The recent developments detailed in this article have important implications for the future diagnosis and treatment of these diseases. Recent discoveries link molecular defects with alterations in the functional machinery of the cell, and provide new avenues for advancing the diagnosis and treatment of these disorders.