Macular Degeneration: Genetics of 4 Distrinct Phenotypes

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The focus of this proposal is to study the biological basis of macular degeneration as will be seen through four large independent pedigrees with distinct forms of macular degeneration segregating in Mendelian fashion. We are in the process of positional cloning and candidate gene analysis of these pedigrees, with current emphasis on early onset atrophic macular degeneration. Currently no treatment is available for these debilitating diseases. Cloning of these genes will provide an opportunity to look at the process of degeneration of macula from four biological genetic perspectives. The four forms of macular degeneration we are studying are: (1). Early onset autosomal dominant atrophic macular degeneration (adMD), (2). X-linked cone-rod dystrophy (COD1), (3). Late onset atrophic macular degeneration (adMD) and (4). Hemorrhagic macular atrophy. We mapped the disease locus for early onset adMD to a 4.9 cM interval on chromosome 6q (6q-adMD) and for COD1 to about 1 cM at Xpll. We have excluded most of the known macular degeneration loci for late onset adMD and hemorrhagic macular degeneration, and a genome wide scan to localize the disease genes is in progress. We have constructed physical and transcript maps of the 6q-adMD interval. Characterization of genes corresponding to candidate ESTs in the critical region is currently in progress. We will work toward positional cloning by: (a) localizing the disease gene to a small interval by ascertaining additional members of the pedigrees and analyzing new markers, (b) Characterizing candidate genes, and (c) Screening candidate genes for mutations. Once the gene(s) for above macular degeneration(s) (MD) is cloned, we will study the possible association between the macular degeneration gene and other phenotypic forms of macular diseases including AMD. Because we can not work on all four pedigrees simultaneously, some of the work is planned for sequential analysis. This study will result in identification of gene mutations causing selective degeneration of macula. These genes will help in understanding the mechanism underlying the variable age of onset and variable rate of progression of the above degenerations and will assist in developing effective treatments either to slow the rate of progression or to delay the age of onset of the disease.