Search for the identification of new genes causing autosomal recessive retinitis pigmentosa

Purpose The molecular diagnosis of autosomal recessive Retinitis Pigmentosa (arRP) is challenging because of the large genetic and clinical heterogeneity of this disease: to date, 36 arRP genes as well as 3 loci have been identified accounting for approximately 60 % of arRP families. Two major genes, USH2A and EYS, are responsible for 13 to 19 % of the cases, the other genes being minority. Here, we developed a strategy to search for new genes/loci causing arRP in a series of consanguineous families. Methods Inbred families were genotyped using microsatellite markers specific for USH2A and EYS genes. Families resulting from this first screening were analyzed using 250K SNP microarrays with TASE software (Transmitted Allele Search Engine). Known genes in homozygous regions were PCR/sequenced. Whole Exome Sequencing is running for a few families. Results A total of 44 inbred families were analyzed. Among them, 14 (32 %) were fully or partly homozygous for EYS or USH2A markers. We selected 16/30 of the remaining families for SNPs genotyping and homozygosity mapping. We found the causative mutation in 7 families (43 %) in a known gene (RP1, RLBP1, NR2E3, CNGB1, IMPG2, PDE6A) while in 6 others sequencing of known genes in homozygous regions is still ongoing. For the 3 remaining families, potentially new loci were found (in chromosomes 3, 10 and 21) for which the results of whole exome sequencing is being analysed. Conclusion About 43 % of the tested consanguineous families had a positive molecular diagnosis and a candidate gene approach is ongoing for the 3 loci.