ATP7B and Wilson disease: Genetic mutations in the copper transporter ATP7B disrupt biliary copper excretionresulting in a massive hepatic copper accumulation and Wilson's disease (WD).Using Atp7b−/− mice, an animal model for WD,we demonstrate that Atp7b inactivation also up-regulates anavailable but underutilized secondary pathway for copper removal from the body,which produces a clinically well-known phenomenon of high urinary copper in WDpatients.