Identification of novel RPGR (retinitis pigmentosa GTPase regulator) mutations in a subset of X-linked retinitis pigmentosa families segregating with the RP3 locus

The X-linked form of retinitis pigmentosa (XLRP) is a severe disease of the retina, characterised by night blindness and visual field constriction in a degenerative process, culminating with complete loss of sight within the third decade of life. Genetic mapping studies have identified two major loci for XLRP: RP3 (70%-75% of XLRP) and RP2 (20%-25% of XLRP). The RPGR (retinitis pigmentosa GTPase regulator) gene has been cloned within the RP3 genomic interval and it has been shown that 10%-20% of XLRP families have mutations in this gene. Here, we describe a single-strand conformational polymorphism-based mutation screening of RPGR in a pool of 29 XLRP families for which the disease segregates with the RP3 locus, in order to investigate the proportion of RP3 families with RPGR mutations and to relate the results to previous reports. Five different new mutations have been identified: two splice site mutations for exon 1 and three frameshift mutations in exons 7, 10 and 11. The percentage of RPGR mutations identified is 17% (5/29) in our genetically well-defined population. This figure is comparable to the percentage of RP2 gene mutations that we have detected in our entire XLRP patient pool (10%-15%). A correlation of RPGR mutations with phenotype in the families described in this study and the biochemical characterisation of reported mutations may provide insights into the function of the protein.