ABCA4 and Stargardt disease: Recessive Stargardt disease (STGD1), a form of juvenile macular degeneration, is caused by more than 1000 mutations in the photoreceptor-specific ABCA4 gene, which encodes the ATP-binding cassette transporter in photoreceptors.1,2 The transporter facilitates the clearance of all-trans–retinaldehyde,3 which is generated by photon-mediated cis-trans isomerization of retinaldehyde in the photoreceptor cell.