Because expanded tracts of (CAG)n had been found in certain genes as the cause of neurodegenerative disease, Keen et al. (1997) sought evidence of (CAG)n expansions as the cause of disease in a panel of 8 autosomal dominant ... Because expanded tracts of (CAG)n had been found in certain genes as the cause of neurodegenerative disease, Keen et al. (1997) sought evidence of (CAG)n expansions as the cause of disease in a panel of 8 autosomal dominant retinitis pigmentosa pedigrees, including families known to map to the RP9, RP11 (600138), and RP13 (600059) loci, using the technique known as repeat expansion detection (RED). In the family studies no evidence of such expanded repeats was uncovered. Keen et al. (2002) described a previously uncharacterized human gene (RP9; 607331) mapping to the RP9 critical interval at 7p14.2. A missense mutation (607331.0001) was identified in affected members and obligate carriers in the British family with linkage to 7p originally described by Inglehearn et al. (1993). Another missense mutation (607331.0002) in the RP9 gene was identified in a single retinitis pigmentosa patient by screening a panel of 300 dominant, recessive, and genetically undefined retinitis pigmentosa patients. The phenotype of this patient was consistent with that described for the RP9 family. The function of the RP9 gene was unknown and the pathogenic mechanism remained to be determined.