Wilson disease is a copper metabolism disorder caused by mutations in ATP7B, a coppertransporting adenosine triphosphatase. A molecular diagnosis was performed on 135 patients with Wilson disease in Taiwan. We identified 36 different mutations, eight of which were novel: five missense mutations (Ser986Phe, Ile1348Asn, Gly1355Asp, Met1392Lys, and Ala1445Pro), one deletion (2810delT) in the coding region, and two nucleotide substitutions (2133AfiC and 2215AfiT) in the promoter region. These mutations were not observed in 100 control subjects and reduced the activity of the mutated protein by at least 50% when compared with wild-type ATP7B. In addition to exon 8, our data indicate another mutation hotspot in exon 12 where 9.62% of all mutations occurred. An alternative splice variant of ATP7B lacking exon 12 was observed in one patient who had a homozygous 2810delT mutation and very mild clinical symptoms. Clinical examination and functional characterization of alternative splice variants of ATP7B lacking exon 12 showed that they retained 80% of their biological activity. The 2810delT mutation increased the expression of these variants, which may have explained the mild symptoms in the patient with the 2810delT mutation. We also discovered that treating liver cancer cells with a Na 1 /H 1 exchanger inhibitor, 5-(N-ethyl-Nisopropyl)-amiloride, significantly enhanced the expression of the alternative splice variant of ATP7B lacking exon 12. Conclusion: This study suggests a novel therapeutic strategy for patients with mutations in exon 12. (HEPATOLOGY 2010;52:1662-1670) W ilson disease (WD) is an autosomal recessive copper metabolism disorder with a prevalence of 1 in 35,000 to 100,000 live births. [1][2][3] It is characterized by impaired biliary excretion and deficient incorporation of copper into ceruloplasmin, leading to toxic accumulation of copper in the liver, brain, cornea, and kidney. The resulting liver cirrhosis and neurological damage are fatal if not treated with copper-chelating agents such as penicillamine. Prompt and appropriate treatment depends on correctly diagnosing WD in the patient and any affected siblings. 4,5 Patients with WD most often exhibit progressive liver degeneration, neuropsychiatric symptoms, or both. The diagnosis of WD is determined by signs and symptoms in conjunction with laboratory tests that indicate impaired hepatic copper metabolism. However, these standard tests may yield false positive or false negative results. Failure to correctly diagnose a patient with WD can result in lost opportunities for prophylactic therapy or inappropriate administration of potentially toxic drugs. [4][5][6] Furthermore, standard tests cannot detect heterozygous carriers or be used for presymptomatic diagnosis. Molecular diagnosis is a Abbreviations: 5 0 UTR, 5 0