ABCA1 (ATP Binding Cassette Subfamily A Member 1) is a protein encoded by the ABCA1 gene, located on chromosome 9q31.1. It is a member of the ATP-binding cassette (ABC) transporter family, which uses energy from ATP hydrolysis to transport various substrates across cell membranes. ABCA1 specifically facilitates the efflux of cholesterol and phospholipids from cells to extracellular acceptors such as apolipoprotein A-I (APOA1), playing a crucial role in the formation of high-density lipoprotein (HDL) particles. This process is essential for reverse cholesterol transport (RCT), which helps remove excess cholesterol from tissues and prevents atherosclerosis. Mutations in the ABCA1 gene can lead to Tangier disease, a rare genetic disorder characterized by extremely low levels of HDL cholesterol and cholesterol accumulation in tissues.