Defective ABCG5 causes sitosterolemia

ATP-binding cassette sub-family G member 5 (ABCG5 aka sterolin-1), is a "half transporter", that forms a complex with another half transporter ABCG8 (aka sterolin-2) in the endoplasmic reticulum. This complex translocates to the plasma membrane to mediate the ATP-dependent intestinal absorption and facilitation of biliary secretion of cholesterol and phytosterols (e.g. sitosterol). Defects in either of these half transporters result in loss of enterocyte discrimination between cholesterol and sitosterol causing sterol accumulation and predisposition for atherosclerosis. Defects in ABCG5 are the cause of sitosterolemia (MIM:210250), characterised by unrestricted intestinal absorption of both cholesterol and plant-derived sterols causing hypercholesterolemia and premature coronary atherosclerosis. Patients with sitosterolemia absorb between 15 and 60% of ingested sitosterol and excrete only a fraction of this into the bile.

Summary from Reactome (R-HSA-5679096), read 2026-09-23.