Diseases of the retina include a wide spectrum of photoreceptor-affecting phenotypes that have been mapped to 1120 loci on the human genome (RetNet Retinal Information Network). Currently, less than half of the causal genes have been identified (RetNet Retinal Information Network), although substantial progress has been made in determining the genetic basis of monogenic eye disorders. Mutations in new genes that are responsible for some form of retinal degeneration are identified on a regular basis. The vast majority of these genes are involved in rare phenotypes in a limited numbers of patients.

When the ATP-binding cassette (ABC)–transporter gene, ABCR, was cloned and characterized in 1997 as the causal gene for autosomal recessive Stargardt disease (Allikmets et al. 1997b), it seemed as if just another missing link had been added to the extensive table of genetic determinants of rare monogenic retinal dystrophies. Now, 13 years later, mutations in the ABCR gene (also called “ABCA4”) continue to emerge as one of the predominant determinants of a wide variety of retinaldegeneration phenotypes. ABCR has caused exciting and sometimes intense discussions among ophthalmic geneticists, resulting in 150 publications during this brief period of time. Now, in the current issue of the Journal, two more studies report interesting new data on ABCR genetics (Maugeri et al. 2000 [in this issue]; Rivera et al. 2000 [in this issue]).