ABCA (ABC1)
The human ABCA subfamily contains 12 full transporters. These transporters separate into two subgroups based primarily on phylogenetic analysis and intron structure (Arnould et al., 2001). The first group of transporters contains seven genes distributed among six chromosomes (ABCA1, ABCA2, ABCA3, ABCA4, ABCA7, ABCA12, and ABCA13), whereas the second group comprises five genes (ABCA5, ABCA6, ABCA8, ABCA9, and ABCA10) on chromosome 17q24.3 (Broccardo et al., 2001). Several ABCA sub-family genes are associated with human disease. The ABCA1 protein is definitively involved in disorders of cholesterol transport and HDL biosynthesis. Tangier Disease (TD), a rare genetic disorder of lipoprotein metabolism, is caused by mutations in the ABCA1 gene (Remaley et al., 1999; Rust et al., 1999). This disease presents with deficient levels of HDL cholesterol and apoprotein A-I causing a myriad of symptoms, including orange-yellow tonsils, anemia, thrombocytopenia, peripheral neuropathy, hepatosplenomegaly, lymphadenopathy, and corneal opacity. Tangier Disease can also be associated with an increased risk of coronary artery disease (Maranghi et al., 2019). The ABCA4 protein performs critical steps in the visual cycle by transporting vitamin A derivatives in the outer segments of rod photoreceptor cells. Pathogenic variants in ABCA4 cause Stargardt disease (STGD1), which is a common early-onset maculopathy.