Molecular genetics of macular degeneration

Macular degeneration is a leading cause of blindness that affects the aged population. The complexity of the molecular basis of macular disease is now beginning to be elucidated with the identification of disease-causing genes. For example, mutations in the ABCR gene, (recently identified in cones as well) which codes for retinal rod-specific ABCR protein is responsible for Stargardt macular dystrophy/fundus flavimaculatus, an autosomal recessive macular dystrophy with juvenile onset, which accounts for 7% of human retinal degenerative diseases. The gene mutant in X-linked juvenile retinoschisis, XLRS1, is the first macular dystrophy gene to be isolated by positional cloning. Mutations in the peripherin/RDS gene have been shown to be associated with a variety of distinct forms of macular degenerations. The tissue inhibitor of metalloproteinase 3 (TIMP3) is implicated in autosomal dominant Sorsby fundus dystrophy. Best vitelliform macular dystrophy was mapped to 11q12-q13. The cloned gene product is the protein bestrophin, which is a retinal specific gene expressed in the RPE and possibly involved in the metabolism and transport of polyunsaturated fatty acids. The cloning of genes for rare heritable forms of macular degeneration will increase our understanding of the basic pathogenesis of the disease process. In the future this should also allow us to test the hypothesis that the coincidence of subclinical mutations in a number of genes involved in the formation and function of the macula can be responsible for cases of age-related macula-degeneration which is by far the most common form of these macular disorders.