Cholestasis is a rare condition that involves a reduction or obstruction of bile flow from the liver to the small intestine. When bile flow is hindered, a waste product pigment called bilirubin can escape into the bloodstream and build up to harmful levels. This may lead to the easily recognizable cholestatic symptoms of jaundice, itching, and impaired growth and eventually to more serious health problems. Four rare genetic liver disorders— ALGS, a-1AT, bile acid synthesis and metabolism defects, and PFIC—account for about 20% to 30% of all infant cases of cholestasis. These four disorders compose a group of related diseases that can cause significant growth problems during childhood, serious liver problems, the need for liver transplantation, and potentially death. More research on these rare liver diseases is necessary to develop a scientific basis for improvement in diagnostic techniques and treatments. Current diagnostic procedures are complex, and the development of simpler diagnostic tests would facilitate early diagnosis and treatment. 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.