ROM1 and retinitis pigmentosa 1: To date, 45 known genes/loci have been identified in non syndromic RP, including 15 for autosomal dominant- (14 cloned, one mapped), 24 for autosomal recessive- (18 cloned, six mapped), five for X-linked- inheritance (two cloned, three mapped), and one, ROM1, which has been found mutated only in digenism with RDS. It has been estimated that the cloned genes account for about 50% of dominant RP, 40% of recessive RP and approximately 80% of X-linked RP, indicating that many genes remain to be identified [26].