 Mutations in either genes result in a lipid disorder, sitosterolemia.The molecular mechanisms regulating the absorption of dietary sterols in the body are poorly understood, and as sitosterolemia is a rare autosomal recessively inherited lipid metabolic disorder characterized by hyperabsorption and decreased biliary excretion of dietary sterols, studies have focused on the molecular basis of sitosterolemia to shed light on important principles concerning intestinal sterol absorption as well as cholesterol secretion into bile.In 1998, sitosterolemia (STSL) locus has been mapped to the short arm of human chromosome 2 (2p21) after studying 10 well-characterized families with this disorder.