ATP-binding cassette sub-family G member 8 is a protein that in humans is encoded by the ABCG8 gene.
The protein encoded by this gene is a member of the superfamily of ATP-binding cassette (ABC) transporters. ABC proteins transport various molecules across extra- and intra-cellular membranes. ABC genes are divided into seven distinct subfamilies (ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, White). This protein is a member of the White subfamily. The protein encoded by this gene functions as a half-transporter to limit intestinal absorption and promote biliary excretion of sterols. It is expressed in a tissue-specific manner in the liver, colon, and intestine. This gene is tandemly arrayed on chromosome 2, in a head-to-head orientation with family member ABCG5. Mutations in this gene may contribute to sterol accumulation and atherosclerosis, and have been observed in patients with sitosterolemia.
A loss-of-function mutation in ABCG8 impairs the removal of sterols from cells and, in the homozygous case, leads to sitosterolemia. Heterozygous individuals show slightly increased sterol absoption, normal cholesterol levels, and slightly elevated phytosterol levels.
A gain-of-function SNP rs11887534 increases the likelihood of gallbladder disease, especially cholesterol gallstones. This is probably because more cholesterol is pumped into the bile lumen.
