Cholestasis is a condition in which bile is not properly transported from the liver to the small intestine. Cholestasis can be caused by an array of childhood diseases, including the genetic diseases Alagille syndrome (ALGS), alpha-1 antitrypsin (a-1AT) deficiency, bile acid synthesis and metabolism defects, and progressive familial intrahepatic cholestasis (PFIC) or benign recurrent intrahepatic cholestasis(BRIC). This study will investigate the natural history and progression of the four previously mentioned cholestatic liver diseases to provide a better understanding of the causes and effects of the diseases.