ATP-binding cassette transporter A1 (ABCA1) is a membrane integral protein which plays a vital role in High Density Lipoprotein (HDL) metabolism and exerts a protective effect against Hypoalphalipoproteinemia (HA) by mediation of rate-limiting step in HDL biogenesis. The gene discussed is ABCA1; the disease is apolipoprotein A-I deficiency.