Editor—Retinitis pigmentosa (RP) is the term given to a group of inherited retinal degenerations affecting approximately 1 in every 4000 people.1 Clinical presentation includes night blindness, a peripheral bone spicule appearance to the retina, constriction of retinal arterioles, and visual field loss. RP can be inherited in an autosomal dominant, autosomal recessive, or X linked fashion, with autosomal dominant RP (ADRP) accounting for around 20%.2 Within the autosomal dominant category there is both clinical and genetic heterogeneity. Nine ADRP loci have been reported to date. Mutations in rhodopsin account for between 20 and 50% of ADRP3-6 and those in peripherin/RDS for less than 5%,7 8 while around 20% of large families are linked to a major locus on chromosome 19q.9 The remaining six loci, for which genes have not yet been identified, are relatively rare and approximately 15% of families do not map to any known locus, indicating yet further genetic heterogeneity.6 10

The RP1 locus on 8q was first identified by linkage analysis in a large pedigree known as UCLA-RP01, originating in the Appalachian mountains of Kentucky in eastern USA.11The phenotype in UCLA-RP01 is described as type 2 or R type ADRP, with regional and combined loss of both rod and cone photoreceptor sensitivities. A second unrelated family of Australian origin has also been linked to RP1.12 Crossovers in these families place the locus in a 4 cM interval between markers D8S601 and D8S285. The phenotype in both families is reported as showing wide variation in severity and age of onset, and subjects in both were found to carry the gene yet manifest no symptoms. …