A LINKAGE SURVEY OF 20 DOMINANT RETINITIS-PIGMENTOSA FAMILIES - FREQUENCIES OF THE 9 KNOWN LOCI AND EVIDENCE FOR FURTHER HETEROGENEITY

Autosomal dominant retinitis pigmentosa (ADRP) is caused by mutations in two known genes, rhodopsin and peripherin/Rds, and seven loci ident ified only by linkage analysis. Rhodopsin and peripherin/Rds have been estimated to account for 20-31% and less than 5% of ADRP, respectivel y. No estimate of frequency has previously been possible for the remai ning loci, since these can only be implicated when families are large enough for linkage analysis. We have carried out such analyses on 20 u nrelated pedigrees with 11 or more meioses. Frequency estimates based on such a small sample provide only broad approximations, while the ab ove estimations are based on mutation detection in much larger clinic based patient series. However, when markers are informative, linkage a nalysis cannot fail to detect disease causation at a locus, whereas mu tation detection techniques might miss some mutations. Also diagnosing dominant RP from a family history taken in a genetic clinic may not b e reliable. It is therefore interesting that 10 (50%) of the families tested have rhodopsin-RP, suggesting that, in large clearly dominant R P pedigrees, rhodopsin may account for a higher proportion of disease than had previously been suspected. Four (20%) map to chromosome 19q, implying that this is the second most common ADRP locus. One maps to c hromosome 7p, one to 17p, and one to 17q, while none maps to 1cen, per ipherin/Rds, 8q, or 7q. Three give exclusion of all of these loci, sho wing that while the majority of dominant RP maps to the known loci, a small proportion derives from loci yet to be identified.