ABCA4 (ATP-binding cassette, sub-family A (ABC1), member 4, Rim Protein) is a member of the superfamily of ATP-binding cassette (ABC) transporters (Illing et al., 1997). ABC proteins transport various molecules across extra- and intracellular membranes. This protein is a retina-specific ABC transporter with N-retinylidene-PE as a substrate. It is expressed exclusively in retina photoreceptor cells, indicating the gene product mediates transport of an essential molecule across the photoreceptor cell membrane. Mutations in this gene are found in patients diagnosed with Stargardt disease and are associated with retinitis pigmentosa-19 and age-related macular degeneration (Wiszniewski et al., 2003). Defects in ABCA4 are the cause of Stargardt disease type 1 (STGD1) (Molday et al., 2000). STGD is one of the most frequent causes of macular degeneration in childhood. Defects in ABCA4 are also known to cause fundus flavimaculatus (FFM), age-related macular degeneration type 2 (ARMD2) and cone-rod dystrophy type 3 (CORD3) (Klevering et al., 2005).
