AQP1, typically localized to portal venules, hepatic arterioles, and bile ducts in normal liver and early-stage primary biliary cirrhosis (PBC), is aberrantly overexpressed in proliferating bile ductules and arterial capillaries in advanced PBC, potentially contributing to angiogenesis, fibrosis, and the progression of portal hypertension (86). The gene discussed is AQP1; the disease is primary biliary cholangitis.