ATP8A2 and aceruloplasminemia: For instance, mutations in ATP8B1 cause progressive familial intrahepatic cholestasis type I and benign recurrent intrahepatic cholestasis11, and mutations in ATP8A2 cause axonal degeneration in mice and a severe neurological disorder that is characterized by cerebellar ataxia, mental retardation and disequilibrium syndrome12, 14–16.