Wilson disease

Abstract

In the spring of 1912, Samuel Alexander Kinnier Wilson, a young registrar at the National Hospital, Queen’s Square, London, described the detailed clinical and pathologic findings of 4 patients, all of whom, he believed, had the same disease. He also included careful descriptions of 8 similar patients from the literature, in each case pointing out the clinical features of progressive lenticular degeneration in association with the pathologic findings of hepatic cirrhosis.1Wilson S.A.K. Progressive lenticular degeneration a familial nervous disease associated with cirrhosis of the liver.Lancet. 1912; 1: 1115-1119Abstract Scopus (36) Google Scholar, 2Wilson S.A.K. Progressive lenticular degeneration a familial nervous disease associated with cirrhosis of the liver.Brain. 1912; 34: 295-507Crossref Scopus (747) Google Scholar Although Wilson believed that hepatic involvement was not a significant factor in the evolution of the disease, the prominent role of hepatic cirrhosis in the clinical presentation was soon readily apparent.3Bramwell B. Familial cirrhosis of the liver four cases of acute fatal cirrhosis of the liver in the same family, the patients being respectively nine, ten, fourteen and fourteen years of age—suggested relationship to Wilson’s progressive degeneration of the lenticular nucleus.Edinb Med J. 1916; 17: 90-99Google Scholar In 1948, Cummings4Cummings J.N. The copper and iron content of the liver and brain in the normal and hepatolenticular degeneration.Brain. 1948; 71: 410-417Crossref PubMed Scopus (227) Google Scholar showed the presence of excess copper in the tissues of affected individuals, and soon thereafter Scheinberg and Gitlin5Scheinberg I.H. Gitlin D. Deficiency of ceruloplasmin in patients with hepatolenticular degeneration.Science. 1952; 116 (484-450)Crossref PubMed Scopus (202) Google Scholar showed a deficiency of ceruloplasmin in the serum of patients with Wilson disease. A simple and effective treatment for many patients became available when Walshe6Walshe J.M. Penicillamine, a new oral therapy for Wilson’s disease.Am J Med. 1956; 21: 487-492Abstract Full Text PDF PubMed Scopus (512) Google Scholar introduced penicillamine as an oral copper chelator. The recognition that Wilson disease is a disorder of copper homeostasis gave rise to the hypothesis that specific cellular mechanisms govern the metabolism of this metal and led to a pursuit to define the molecular basis of this disease. Detailed family studies indicated that Wilson disease is inherited as an autosomal recessive disorder, and linkage analysis with a multisibship inbred pedigree established that the affected gene was localized7Bearn A. A genetical analysis of 30 families with Wilson disease.Ann Hum Genet. 1960; 24: 33-39Crossref PubMed Scopus (82) Google Scholar, 8Frydman M. Bonne-Tamir B. Farrer L.A. Conneally P.M. Magazanik A. Ashbel S. Goldwitch Z. Assignment of the gene for Wilson disease to chromosome 13 linkage to the esterase D locus.Proc Natl Acad Sci U S A. 1985; 82: 1819-1821Crossref PubMed Scopus (262) Google Scholar on chromosome 13. Subsequent identification of the Wilson disease gene showed that this locus encodes a copper-transporting P-type adenosine triphosphatase (ATPase) that is highly evolutionarily conserved and permits the efficient excretion of copper into the bile.9Tanzi R.E. Petrukhin K. Chernov I. Pellequer J.L. Wasco W. Ross B. Romano D.M. Parano E. Pavone L. Brzustowicz L.M. Devoto M. Peppercorn J. Bush A.I. Sternlieb I. Pirastu M. Gusella J.F. Evgrafov O. Penchaszadeh G.K. Honig B. Edelman I.S. Soares M.B. Scheinberg I.H. Gilliam T.C. The Wilson disease gene is a copper transporting ATPase with homology to the Menkes disease gene.Nat Genet. 1993; 5: 344-350Crossref PubMed Scopus (1164) Google Scholar, 10Bull P.C. Thomas G.R. Rommens J.M. Forbes J.R. Cox D.W. The Wilson disease gene is a putative copper transporting P-type ATPase similar to the Menkes gene.Nat Genet. 1993; 5: 327-337Crossref PubMed Scopus (1676) Google Scholar, 11Yamaguchi Y. Heiny M.E. Gitlin J.D. Isolation and characterization of a human liver cDNA as a candidate gene for Wilson disease.Biochem Biophys Res Commun. 1993; 197: 271-277Crossref PubMed Scopus (471) Google Scholar Elucidation of the molecular genetic basis of Wilson disease has provided fundamental insights into the mechanisms of cellular inorganic biochemistry and permitted the development of novel diagnostic and therapeutic approaches in a number of human diseases.12Culotta V.C. Gitlin J.D. Disorders of copper transport.in: Scriver C.R. Beaudet A.L. Sly W.S. Valle D. The molecular and metabolic basis of inherited disease. 3. McGraw-Hill, New York2001: 3105-3136Google Scholar Copper is an essential trace element that permits the facile transfer of electrons in a diverse, yet essential, group of cuproenzymes required for cellular respiration, iron oxidation, pigment formation, neurotransmitter biosynthesis, antioxidant defense, peptide amidation, and connective tissue formation.12Culotta V.C. Gitlin J.D. Disorders of copper transport.in: Scriver C.R. Beaudet A.L. Sly W.S. Valle D. The molecular and metabolic basis of inherited disease. 3. McGraw-Hill, New York2001: 3105-3136Google Scholar Numerous dietary foods are rich in copper that is absorbed primarily through the stomach and duodenum. Biliary excretion is the only physiological route for copper elimination, and each day an amount of copper is excreted in the bile that is equivalent to that absorbed. The liver plays a critical role in copper metabolism, serving as the site of storage for this metal and the primary determinant regulating biliary excretion.13Tao T.Y. Gitlin J.D. Hepatic copper metabolism insights from genetic disease.Hepatology. 2003; 37: 1241-1247Crossref PubMed Scopus (128) Google Scholar Studies using copper isotopes show rapid clearance of this metal from the portal circulation, with 10% of the isotope reappearing in the serum bound to the plasma protein ceruloplasmin within 24 hours after a single dose.14Sternlieb I. Scheinberg I.H. Radiocopper in diagnosing liver disease.Semin Nucl Med. 1972; 2: 176-188Abstract Full Text PDF PubMed Scopus (29) Google Scholar Ceruloplasmin is a ferroxidase that has an essential role in iron metabolism and contains greater than 95% of the plasma copper.15Hellman N.E. Gitlin J.D. Ceruloplasmin metabolism and function.Annu Rev Nutr. 2002; 22: 439-458Crossref PubMed Scopus (642) Google Scholar The remaining copper present in the plasma is bound to amino acids, and it is believed that these complexes provide the mechanism for transport of this metal to various tissues. Renal filtration plays a role in copper excretion only under rare circumstances when tubular reabsorption is exceeded. The uptake and storage of copper in the liver occurs in hepatocytes, and it is these cells that determine the rate of biliary excretion of this metal. The essential role of hepatocytes in copper metabolism is shown by the normalization of copper homeostasis in copper-overloaded individuals with Wilson disease after liver transplantation.16Emre S. Atillasoy E.O. Ozdemir S. Schilsky M. Rathna Varma C.V. Thung S.N. Sternlieb I. Guy S.R. Sheiner P.A. Schwartz M.E. Miller C.M. Orthotopic liver transplantation for Wilson’s disease a single-center experience.Transplantation. 2001; 72: 1232-1236Crossref PubMed Scopus (108) Google Scholar At steady state, the amount of copper excreted in the bile is directly proportional to the size of the hepatic copper pool. The hepatocyte is capable of rapidly increasing biliary copper excretion in response to increases in systemic copper, and, therefore, hepatic copper overload is an unusual occurrence under physiological conditions.17Gollan J.L. Deller D.J. Studies on the nature and excretion of biliary copper in man.Clin Sci. 1973; 44: 9-15PubMed Google Scholar There is no enterohepatic circulation of copper, and once excreted into the bile, this metal exists as an unabsorbable complex that is excreted in the stool. Ceruloplasmin is synthesized in hepatocytes and secreted into the plasma after the incorporation of copper late in the secretory pathway.15Hellman N.E. Gitlin J.D. Ceruloplasmin metabolism and function.Annu Rev Nutr. 2002; 22: 439-458Crossref PubMed Scopus (642) Google Scholar Failure to incorporate copper during ceruloplasmin biosynthesis results in the secretion of an apoprotein that is devoid of enzymatic activity and rapidly degraded. For this reason, the serum ceruloplasmin concentration can be a useful indicator of copper status. In copper deficiency, as hepatic copper stores decrease, there is minimal copper available for transport into the hepatocyte secretory pathway, and the biliary copper content and serum ceruloplasmin concentration are diminished.18Olivares M. Araya M. Uauy R. Copper homeostasis in infant nutrition deficit and excess.J Pediatr Gastroenterol Nutr. 2000; 31: 102-111Crossref PubMed Scopus (33) Google Scholar The human fetus acquires copper by placental transport and subsequently stores this metal in the developing liver. The hepatic copper content at birth is increased relative to later in life because of a developmental decrease in biliary excretion in utero.19Arrese M. Ananthananarayanan M. Suchy F.J. Hepatobiliary transport molecular mechanisms of development and cholestasis.Pediatr Res. 1998; 44: 141-147Crossref PubMed Scopus (58) Google Scholar As a consequence, copper is unavailable to the hepatocyte secretory pathway, and the newborn liver predominantly secretes apoceruloplasmin that is devoid of copper and is turned over rapidly in the serum. This developmental physiology abrogates the use of serum ceruloplasmin for newborn screening to identify asymptomatic individuals with Wilson disease. As bile flow increases after birth, copper is transported into the secretory pathway of the hepatocyte, with a resultant increase in the serum ceruloplasmin concentration and the biliary copper content.20Gitlin J.D. Aceruloplasminemia.Pediatr Res. 1998; 44: 271-276Crossref PubMed Scopus (151) Google Scholar Although ceruloplasmin contains almost all the copper present in serum, this protein has no essential role in copper transport or metabolism or biliary copper excretion at any stage of human development, as evidenced by normal copper homeostasis in humans and mice with aceruloplasminemia.15Hellman N.E. Gitlin J.D. Ceruloplasmin metabolism and function.Annu Rev Nutr. 2002; 22: 439-458Crossref PubMed Scopus (642) Google Scholar Cellular copper uptake occurs via a polytopic membrane protein termed Ctr1 that is essential for early embryonic development.21Lee J. Prohaska J.R. Thiele D.J. Essential role for mammalian copper transporter Ctr1 in copper homeostasis and embryonic development.Proc Natl Acad Sci U S A. 2001; 98: 6842-6847Crossref PubMed Scopus (357) Google Scholar, 22Kuo Y.M. Zhou B. Cosco D. Gitschier J. The copper transporter CTR1 provides an essential function in mammalian embryonic development.Proc Natl Acad Sci U S A. 2001; 98: 6836-6841Crossref PubMed Scopus (295) Google Scholar Ctr1 transports copper across the hepatocyte basolateral membrane in a high-affinity, metal-specific fashion that is dependent on multimerization and endocytosis of this protein23Klomp A.E. Juijn J.A. Van Der Gun L.T. Van Den Berg I.E. Berger R. Klomp L.W. The N-terminus of the human copper transporter 1 (hCTR1) is localized extracellularly, and interacts with itself.Biochem J. 2003; 370: 881-889Crossref PubMed Scopus (73) Google Scholar, 24Petris M.J. Smith K. Lee J. Thiele D.J. Copper-stimulated endocytosis and degradation of the human copper transporter, hCtr1.J Biol Chem. 2003; 278: 9639-9646Crossref PubMed Scopus (244) Google Scholar (Figure 1). Although uptake is a critical step in the supply of copper to the liver, the continuous accumulation of copper in Wilson disease, despite massive increases in total hepatic copper content, suggests that copper homeostasis is not regulated at this step. Under physiological circumstances, the availability of free intracellular copper is restricted.25Rae T.D. Torres A.S. Pufahl R.A. O’Halloran T.V. Mechanism of Cu,Zn-superoxide dismutase activation by the human metallochaperone hCCS.J Biol Chem. 2001; 276: 5166-5176Crossref PubMed Scopus (94) Google Scholar Therefore, after hepatocyte uptake, copper is bound to a family of proteins termed metallochaperones that function to deliver this metal to specific pathways, protecting against intracellular copper chelation.26O’Halloran T.V. Culotta V.C. Metallochaperones, an intracellular shuttle service for metal ions.J Biol Chem. 2000; 275: 25057-25060Crossref PubMed Scopus (654) Google Scholar, 27Huffman D.L. O’Halloran T.V. Function, structure, and mechanism of intracellular copper trafficking proteins.Annu Rev Biochem. 2001; 70: 677-701Crossref PubMed Scopus (411) Google Scholar The copper chaperone Atox1 is essential for the trafficking of copper to the hepatocyte secretory pathway through direct interaction with the Wilson disease P-type ATPase, ATP7b.28Wernimont A.K. Huffman D.L. Lamb A.L. O’Halloran T.V. Rosenzweig A.C. Structural basis for copper transfer by the metallochaperone for the Menkes/Wilson disease proteins.Nat Struct Biol. 2000; 7: 766-771Crossref PubMed Scopus (346) Google Scholar, 29Larin D. Mekios C. Das K. Ross B. Yang A.S. Gilliam T.C. Characterization of the interaction between the Wilson and Menkes disease proteins and the cytoplasmic copper chaperone, HAH1p.J Biol Chem. 1999; 274: 28497-28504Crossref PubMed Scopus (147) Google Scholar, 30Hamza I. Schaefer M. Klomp L.W. Gitlin J.D. Interaction of the copper chaperone HAH1 with the Wilson disease protein is essential for copper homeostasis.Proc Natl Acad Sci U S A. 1999; 96: 13363-13368Crossref PubMed Scopus (239) Google Scholar Atox1 contains a single copy of the copper-binding motif MXCXXC, which is also present in the amino-terminus of ATP7b (Figure 2). The binding of Atox1 in this amino-terminal region is required for normal hepatic copper metabolism, as shown by analysis of specific ATP7b mutations in patients with Wilson disease.30Hamza I. Schaefer M. Klomp L.W. Gitlin J.D. Interaction of the copper chaperone HAH1 with the Wilson disease protein is essential for copper homeostasis.Proc Natl Acad Sci U S A. 1999; 96: 13363-13368Crossref PubMed Scopus (239) Google Scholar Within the hepatocyte cytoplasm, copper is also found complexed with cysteine-rich proteins termed metallothioneins.31Palmiter R.D. The elusive function of metallothioneins.Proc Natl Acad Sci U S A. 1998; 95: 8428-8430Crossref PubMed Scopus (591) Google Scholar Although they serve no direct role in copper trafficking or homeostasis, metallothioneins may function to protect against the toxicity of this metal under circumstances of copper overload31Palmiter R.D. The elusive function of metallothioneins.Proc Natl Acad Sci U S A. 1998; 95: 8428-8430Crossref PubMed Scopus (591) Google Scholar, 32Kelly E.J. Palmiter R.D. A murine model of Menkes disease reveals a physiological function of metallothionein.Nat Genet. 1996; 13: 219-222Crossref PubMed Scopus (105) Google Scholar (Figure 1).Figure 2Structural model of the Wilson disease copper-transporting ATPase, ATP7b, illustrating adenosine triphosphate (ATP)-dependent copper transport across the lipid bilayer. Highlighted amino acids regions include MXCXXC copper-binding regions, the DKTGT-containing site of the aspartyl phosphate, the GDGVND ATP-binding site, and the CPC copper-binding region in the sixth transmembrane domain. The site of the most common missense mutation (H1069Q) is shown within a SEHPL sequence. Reprinted with permission from the American Society for Biochemistry and Molecular Biology.38View Large Image Figure ViewerDownload (PPT) ATP7b is a copper-transporting P-type ATPase expressed within the secretory pathway of hepatocytes, and inherited loss-of-function mutations in the gene that encodes this ATPase result in Wilson disease.33Schaefer M. Gitlin J.D. Genetic disorders of membrane transport. IV. Wilson’s disease and Menkes disease.Am J Physiol. 1999; 276: G311-G314PubMed Google Scholar ATP7b is predominantly located at the trans-Golgi network and functions to transfer copper into the secretory pathway for both incorporation into apoceruloplasmin and excretion into the bile33Schaefer M. Gitlin J.D. Genetic disorders of membrane transport. IV. Wilson’s disease and Menkes disease.Am J Physiol. 1999; 276: G311-G314PubMed Google Scholar, 34Lutsenko S. Petris M.J. Function and regulation of the mammalian copper-transporting ATPases insights from biochemical and cell biological approaches.J Membr Biol. 2003; 191: 1-12Crossref PubMed Scopus (170) Google Scholar (Figure 1). As the hepatocyte copper content increases, ATP7b cycles to a cytoplasmic compartment near the canalicular membrane, where copper is accumulated in vesicles before biliary excretion.35Hung I.H. Suzuki M. Yamaguchi Y. Yuan D.S. Klausner R.D. Gitlin J.D. Biochemical characterization of the Wilson disease protein and functional expression in the yeast Saccharomyces cerevisiae.J Biol Chem. 1997; 272: 21461-21466Crossref PubMed Scopus (287) Google Scholar, 36Schaefer M. Hopkins R.G. Failla M.L. Gitlin J.D. Hepatocyte-specific localization and copper-dependent trafficking of the Wilson’s disease protein in the liver.Am J Physiol. 1999; 276: G639-G646PubMed Google Scholar In patients with Wilson disease, the lack of functional ATP7b limits the copper available for incorporation into ceruloplasmin, resulting in secretion of a rapidly degraded apoprotein. The resulting decrease in serum ceruloplasmin concentration is a diagnostic hallmark of this disorder (Figure 1). Although the cell biological mechanisms of vesicular copper movement and excretion at the canalicular membrane of hepatocytes are unknown, recent studies in Bedlington terrier copper toxicosis have identified a small cytosolic protein termed Murr1 that is required for this process37van De Sluis B. Rothuizen J. Pearson P.L. van Oost B.A. Wijmenga C. Identification of a new copper metabolism gene by positional cloning in a purebred dog population.Hum Mol Genet. 2002; 11: 165-173Crossref PubMed Scopus (303) Google Scholar (Figure 1). A homologous protein has been detected in human liver, suggesting that further analysis of Murr1 function will provide useful insights into this pathway of hepatic copper metabolism. Several motifs found in all P-type ATPases are present in ATP7b, including an invariant aspartate reside that is the site of the β-aspartyl phosphoryl intermediate required for adenosine triphosphate-dependent copper transport across the lipid bilayer38Payne A.S. Gitlin J.D. Functional expression of the Menkes disease protein reveals common biochemical mechanisms among the copper-transporting P-type ATPases.J Biol Chem. 1998; 273: 3765-3770Crossref PubMed Scopus (134) Google Scholar (Figure 2). Copper transport requires metal transfer from the amino-terminus to a high-affinity site in the transmembrane channel, accompanied by adenosine triphosphate binding and aspartate phosphorylation.34Lutsenko S. Petris M.J. Function and regulation of the mammalian copper-transporting ATPases insights from biochemical and cell biological approaches.J Membr Biol. 2003; 191: 1-12Crossref PubMed Scopus (170) Google Scholar, 39Moller J.V. Juul B. le Maire M. Structural organization, ion transport, and energy transduction of P-type ATPases.Biochim Biophys Acta. 1996; 1286: 1-51Crossref PubMed Scopus (654) Google Scholar The MXCXXC motifs in the amino-terminus of ATP7b are the site of Atox1 interaction and subsequent copper binding. The most common disease allele found in Northern European populations with Wilson disease is an H1069Q missense mutation found within a conserved SEHPL motif in the cytoplasmic loop between the fifth and sixth transmembrane domains40Petrukhin K. Lutsenko S. Chernov I. Ross B.M. Kaplan J.H. Gilliam T.C. Characterization of the Wilson disease gene encoding a P-type copper transporting ATPase genomic organization, alternative splicing, and structure/function predictions.Hum Mol Genet. 1994; 3: 1647-1656Crossref PubMed Scopus (300) Google Scholar, 41Thomas G.R. Forbes J.R. Roberts E.A. Walshe J.M. Cox D.W. The Wilson disease gene spectrum of mutations and their consequences.Nat Genet. 1995; 9: 210-217Crossref PubMed Scopus (485) Google Scholar (Figure 2). This mutation results in a temperature-sensitive defect in ATP7b folding and copper-dependent trafficking, suggesting a potential role for this motif in the intracellular localization of ATP7b.42Payne A.S. Kelly E.J. Gitlin J.D. Functional expression of the Wilson disease protein reveals mislocalization and impaired copper-dependent trafficking of the common H1069Q mutation.Proc Natl Acad Sci U S A. 1998; 95: 10854-10859Crossref PubMed Scopus (184) Google Scholar, 43Huster D. Hoppert M. Lutsenko S. Zinke J. Lehmann C. Mossner J. Berr F. Caca K. Defective cellular localization of mutant ATP7B in Wilson’s disease patients and hepatoma cell lines.Gastroenterology. 2003; 124: 335-345Abstract Full Text PDF PubMed Scopus (121) Google Scholar Wilson disease is observed with a prevalence of approximately 1:30,000, and this is equivalent among all ethnic groups. Although the gene frequency is increased in specific consanguineous populations in which haplotype studies provide evidence for a founder effect, worldwide the heterozygous carrier rate is approximately 1:100, with a disease incidence of 15–25 per million.44Gollan J.L. Gollan T.J. Wilson disease in 1998 genetic, diagnostic and therapeutic aspects.J Hepatol. 1998; 28: 28-36Abstract Full Text PDF PubMed Google Scholar, 45Schilsky M.L. Wilson disease genetic basis of copper toxicity and natural history.Semin Liver Dis. 1996; 16: 83-95Crossref PubMed Scopus (129) Google Scholar Molecular analysis of the ATP7b gene in affected patients and families has detected more than 200 distinct mutations, approximately half of which are missense, largely confined to transmembrane domains or well-defined consensus motifs.46Loudianos G. Gitlin J.D. Wilson’s disease.Semin Liver Dis. 2000; 20: 353-364Crossref PubMed Scopus (138) Google Scholar, 47Cox D.W. Moore S.D. Copper transporting P-type ATPases and human disease.J Bioenerg Biomembr. 2002; 34: 333-338Crossref PubMed Scopus (99) Google Scholar Databases containing identified mutations are maintained by the University of Alberta (http://www.uofa-medical-genetics.org/wilson/index.php) and the Sackler School of Medicine (http://life2.tau.ac.il/GeneDis/Tables/Wilson/wilson.html). In populations of Northern European descent, the H1069Q mutation accounts for 40% of the disease alleles, whereas in Asian populations, an A778L mutation within the fourth transmembrane domain occurs in approximately 30% of affected individuals. This degree of allelic heterogeneity means that most affected individuals will be compound heterozygotes, therefore complicating phenotype-genotype analysis. Nevertheless, consistent with the marked clinical variability often observed between affected siblings with Wilson disease, studies in patients homozygous for specific alleles show little correlation between a given mutation and the age of onset, clinical features, biochemical parameters, or disease severity.48Riordan S.M. Williams R. The Wilson’s disease gene and phenotypic diversity.J Hepatol. 2001; 34: 165-171Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar Taken together, these data suggest that additional genetic and environmental factors significantly influence the phenotypic outcome of specific mutations in individuals with Wilson disease. For this reason, clinical studies in patients with defined mutations may not be useful in elucidating the physiological details of copper homeostasis. In contrast to these clinical studies, analysis of patient mutations has begun to clarify the molecular pathogenesis of Wilson disease. These studies show specific abnormalities in ATP7b-dependent copper transport, subcellular localization, copper-induced trafficking, and interaction with Atox1.30Hamza I. Schaefer M. Klomp L.W. Gitlin J.D. Interaction of the copper chaperone HAH1 with the Wilson disease protein is essential for copper homeostasis.Proc Natl Acad Sci U S A. 1999; 96: 13363-13368Crossref PubMed Scopus (239) Google Scholar, 35Hung I.H. Suzuki M. Yamaguchi Y. Yuan D.S. Klausner R.D. Gitlin J.D. Biochemical characterization of the Wilson disease protein and functional expression in the yeast Saccharomyces cerevisiae.J Biol Chem. 1997; 272: 21461-21466Crossref PubMed Scopus (287) Google Scholar, 42Payne A.S. Kelly E.J. Gitlin J.D. Functional expression of the Wilson disease protein reveals mislocalization and impaired copper-dependent trafficking of the common H1069Q mutation.Proc Natl Acad Sci U S A. 1998; 95: 10854-10859Crossref PubMed Scopus (184) Google Scholar, 43Huster D. Hoppert M. Lutsenko S. Zinke J. Lehmann C. Mossner J. Berr F. Caca K. Defective cellular localization of mutant ATP7B in Wilson’s disease patients and hepatoma cell lines.Gastroenterology. 2003; 124: 335-345Abstract Full Text PDF PubMed Scopus (121) Google Scholar, 49Forbes J.R. Cox D.W. Functional characterization of missense mutations in ATP7B Wilson disease mutation or normal variant?.Am J Hum Genet. 1998; 63: 1663-1674Abstract Full Text Full Text PDF PubMed Scopus (147) Google Scholar, 50Forbes J.R. Cox D.W. Copper-dependent trafficking of Wilson disease mutant ATP7B proteins.Hum Mol Genet. 2000; 9: 1927-1935Crossref PubMed Scopus (136) Google Scholar, 51Tsivkovskii R. Efremov R.G. Lutsenko S. The role of the invariant His-1069 in folding and function of the Wilson’s disease protein, the human copper-transporting ATPase ATP7B.J Biol Chem. 2003; 278: 13302-13308Crossref PubMed Scopus (69) Google Scholar This analysis has resulted in a model of disease pathogenesis consistent with the concept that loss of ATP7b function impairs holoceruloplasmin biosynthesis and biliary copper excretion, with resultant copper-mediated oxidative damage, activation of cell-death pathways, leakage of copper into the plasma, and eventual copper overload in most tissues52Sokol R.J. Antioxidant defenses in metal-induced liver damage.Semin Liver Dis. 1996; 16: 39-46Crossref PubMed Scopus (39) Google Scholar, 53Strand S. Hofmann W.J. Grambihler A. Hug H. Volkmann M. Otto G. Wesch H. Mariani S.M. Hack V. Stremmel W. Krammer P.H. Galle P.R. Hepatic failure and liver cell damage in acute Wilson’s disease involve CD95 (APO-1/Fas) mediated apoptosis.Nat Med. 1998; 4: 588-593Crossref PubMed Scopus (226) Google Scholar (Figure 1). Although ATP7b is expressed in many tissues, including the central nervous system, widespread copper accumulation is likely the result of a loss of hepatocyte ATP7b function, because this is reversed after liver transplantation in affected patients.54Schilsky M.L. Diagnosis and treatment of Wilson’s disease.Pediatr Transplant. 2002; 6: 15-19Crossref PubMed Scopus (60) Google Scholar In this model, the phenotypic heterogeneity observed in patients with Wilson disease could result from genetic and environmental factors that influence copper sequestration by metallothionein, copper delivery to the secretory pathway by Atox1, or copper excretion into bile by Murr1 or homologs of the V-ATPase and Gef1 chloride channel, which play a role in this process in yeast.55Eide D.J. Bridgham J.T. Zhao Z. Mattoon J.R. The vacuolar H(+)-ATPase of Saccharomyces cerevisiae is required for efficient copper detoxification, mitochondrial function, and iron metabolism.Mol Gen Genet. 1993; 241: 447-456Crossref PubMed Scopus (81) Google Scholar, 56Gaxiola R.A. Yuan D.S. Klausner R.D. Fink G.R. The yeast CLC chloride channel functions in cation homeostasis.Proc Natl Acad Sci U S A. 1998; 95: 4046-4050Crossref PubMed Scopus (148) Google Scholar, 57Davis-Kaplan S.R. Askwith C.C. Bengtzen A.C. Radisky D. Kaplan J. Chloride is an allosteric effector of copper assembly for the yeast multicopper oxidase Fet3p an unexpected role for intracellular chloride channels.Proc Natl Acad Sci U S A. 1998; 95: 13641-13645Crossref PubMed Scopus (111) Google Scholar This model also allows for the possibility that a single mutant ATP7b allele might serve as a risk factor for copper-mediated hepatocyte injury in individuals with more common liver disorders, such as alcoholic cirrhosis.58Pyeritz R.E. Genetic heterogeneity in Wilson disease lessons from rare alleles.Ann Intern Med. 1997; 127: 70-72Crossref PubMed Scopus (14) Google Scholar There are 3 animal models of Wilson disease, including the Long-Evans Cinnamon rat, the toxic milk mouse, and a murine ATP7b gene deletion.59Li Y. Togashi Y. Sato S. Emoto T. Kang J.H. Takeichi N. Kobayashi H. Kojima Y. Une Y. Uchino J. Spontaneous hepatic copper accumulation in Long-Evans Cinnamon rats with hereditary hepatitis. A model of Wilson’s disease.J Clin Invest. 1991; 87: 1858-1861Crossref PubMed Scopus (287) Google Scholar, 60Wu J. Forbes J.R. Chen H.S. Cox D.W. The LEC rat has a deletion in the copper transporting ATPase gene homologous to the Wilson disease gene.Nat Genet. 1994; 7: 541-545Crossref PubMed Scopus (347) Google Scholar, 61Theophilos M.B. Cox D.W. Mercer J.F. The toxic milk mouse is a murine model of Wilson disease.Hum Mol Genet. 1996; 5: 1619-1624Crossref PubMed Scopus (154) Google Scholar, 62Coronado V. Nanji M. 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