As part of our ongoing linkage studies of degenerative retinal diseases, we tested seven DNA markers and two classical genetic markers from chromosome 4 in two extended families with autosomal dominant retinitis pigmentosa (ADRP). Our goals were (1) to detect or exclude linkage of ADRP to markers spanning most of chromosome 4 and (2) to contribute useful new information regarding the linkage map of this chromosome. Our results exclude linkage of ADRP from more than 82% of chro mosome 4. We detected four new linkage relationships: loose linkage of K082 (D4S10) and G1E5 (D4S21) at a distance of 21 cM; loose linkage of 4F2 (D4S18) and GC protein at a distance of 19 cM; tight linkage (i.e., no recombinants) between B3D (D4S44), B5A (D4S40), and the MNS blood group; and tight linkage between 4F2 and GDS5 (D4S23). These data, combined with previously reported data, exclude ADRP from approximately 35% of the human genome.

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