Identification of a Major Gene (RP25) for Autosomal Recessive Retinitis Pigmentosa

Abstract

Purpose: : To identify the disease gene in 6 Spanish families with autosomal recessive retinitis pigmentosa (arRP) linked to the RP25 locus on chromosome 6p12.1-q15.

Methods: : Extensive bioinformatics analysis of the RP25 interval was carried out. Sixty genes within the RP25 critical interval were screened for mutations using an ABI 3730 automated sequencer. A comparative genome hybridisation (CGH) based array was undertaken to investigate if copy number variations (CNVs) exist within RP25. Different molecular techniques including RNA expression analysis, RT-PCR and 5` and 3` rapid amplification of cDNA ends (RACE) were also used to characterize the causative gene.

Results: : The RP25 locus spans ~34 Mb and bioinformatics analysis of the region indicated in excess of 110 genes of which 60 (55%) were excluded as disease causing genes. Herein we report the identification of the RP25 gene using the positional cloning technique in parallel with the CGH approach. Mutations that include small and large deletions have been identified in three unrelated RP25-linked families (two consanguineous and one non-consanguineous). All mutations led to premature stop codons and are thus predicted to result in a truncated protein. RNA expression studies indicate that RP25 is a retina specific gene. RT-PCR and 5` and 3` RACE experiments supported by bioinformatics revealed RP25 to be the largest gene discovered in the human eye so far.

Conclusions: : This is the first report of a major gene for recessive RP. The nature of mutations identified in the RP25 gene suggests loss of function as the mechanism for the RP phenotype. This could make rescuing this phenotype amenable to somatic gene therapy by sub-retinal injection.

Keywords: gene screening • retina • candidate gene analysis