ATP-binding cassette (ABC) transporter genes are involved in the regulation of the amount of dietary cholesterol retained in the body. ABCG8, expressed at high levels in the liver and intestine, normally cooperates with ABCG5 to limit intestinal absorption and promote biliary excretion of sterols. The mutated form of this transporter can lead to sterol accumulation and atherosclerosis or sitosterolemia, a rare autosomal recessive disorder, characterized by hyperabsorption of sterols and the inability to excrete sterols into bile.