Autosomal recessive retinitis pigmentosa is associated with missense mutation in CRB1 in a consanguineous Pakistani family

Retinitis pigmentosa (RP) causes severe visual impairment early in life. The purpose of this study was to identify families with autosomal recessive RP (arRP), their exclusion analysis and identification of novel loci/genes/mutations in affected individuals. Twenty five consanguineous Pakistani families suffering from non syndromic Retinitis pigmentosa (RP) were ascertained from different areas of Pakistan to participate in this study. 85 affected and 210 normal individuals of selected families and from the healthy population took part in this research work. The clinical records of affected family members were retrospectively analyzed and ophthalmological examinations were performed in selected families. Genomic DNA was extracted from peripheral blood samples of phenotypically healthy and affected individuals. Exclusion analysis was done initially for the screening of the causative gene using highly polymorphic microsatellite markers. Genetic investigations using polymorphic microsatellite markers revealed homozygosity with CRB1 gene on chromosome 1 in affected individuals of family RP1. All other families and 210 healthy or control samples showed exclusion with the selected loci/genes. Haplotypes were constructed to appraise the results statistically. For further confirmation of linkage, sequence analysis of the linked gene (CRB1) was done. Sequence analysis revealed a novel missense mutation (c.1459T>C) in exon 6 of the CRB1 gene segregating with disease phenotype. This mutation resulted in a substitution of proline for serine at amino acid 487 (p.Ser487Pro). These findings suggest a founder effect of the p.Ser487Pro mutation in the Pakistani population and extend the spectrum of known CRB1 mutations. It was therefore concluded that the missense mutation in CRB1, leading to premature termination of the protein, is responsible for RP phenotype in the affected individuals of RP1.