[From gene to disease; hepatocystin and autosomal dominant polycystic liver disease]

Polycystic liver disease (PCLD, MIM 174050) is a dominantly inherited condition characterised by the presence in the liver of multiple cysts of biliary epithelial origin. It must be distinguished from autosomal dominant polycystic kidney disease type 1 (ADPKD-1, MIM 173900) and type 2 (ADPKD-2). Both disorders may be complicated by polycystic liver disease, but renal involvement is absent in PCLD. PCLD is often asymptomatic, but if symptoms arise, they are usually due to the mass effect of cysts. The phenotype is more severe in females and correlates with the number of pregnancies or estrogen use. The gene for PCLD has been assigned to chromosome 19p13.2-13.1. Two separate large-scale positional cloning efforts have managed to identify PRKCSH as the gene underlying PCLD. Up to now, all mutations found in PRKCSH introduce stopcodons in the m-RNA, resulting in premature termination of translation to protein. This suggests a loss of function of the encoding protein. The protein, designated by us as hepatocystin, is predicted to be localised in the endoplasmic reticulum. Multiple biological roles have been suggested for hepatocystin, such as a substrate for phosphorylation by protein kinase C, binding to advanced glycation endproducts, and a function as the non-catalytic beta-subunit of glucosidase-II. The role of hepatocystin in PCLD, however, remains to be elucidated.