Identification of the RP31 Gene, Mutated in Retinal Degeneration Patients Associated With Perivascular RPE Atrophy

Abstract

Purpose:: To identify the disease-causing mutation in a large French-Canadian family with an autosomal dominant retinal degeneration and perivascular RPE atrophy which maps to 9p (RP31). To explain the molecular basis for photoreceptor cell death due to mutations in the RP31 gene.

Methods:: Linkage analysis was used on twenty-six individuals from the French-Canadian family after standard ophthalmological evaluations. To identify the disease causing mutation, 53 genes within the critical interval of 14 Mb underwent direct genomic sequencing. A variety of molecular and cell biological techniques were used (bioinformatics, cloning into expression vectors, site-directed mutagenesis, Western blot, RNA in situ, immunocytochemistry on patient lymphocytes and MDCK cell lines, immunohistochemistry on retinas from different animal species and co-immunoprecipitation analysis) in order to explore the disease mechanism involved in this particular retinal degeneration.

Results:: Here we report the identification of the gene causing RP31. It is found to be mutated in two families of different origins (French and German). Both mutations cause frameshift leading to premature stop codon and are thus predicted to result in truncated proteins. RNA expression studies indicate the gene to be ubiquitously expressed. Functional studies show a specific cellular localization of the protein in the inner-outer segment boundary of the photoreceptor cells in the retina. Immunoprecipitation studies show co-localization and possible interaction with proteins known to cause retinal degeneration with the newly described RP31 protein.

Conclusions:: This is the first report of a ubiquitous and multifunctional gene causing only retinal degeneration. Mutations in RP31 gene suggest haploinsufficiency as the cause of the disease mechanism and makes rescue of the phenotype amenable to somatic gene therapy by sub-retinal injection.

Keywords: retinal degenerations: cell biology • positional cloning • photoreceptors