A Novel Homozygous R764H Mutation in CRB1 Causes Autosomal Recessive Retinitis Pigmentosa in a Consanguineous Family

Purpose: Retinitis pigmentosa (RP; MIM 268000) is a hereditary disease characterized by poor night vision and progressive loss of photoreceptors, eventually leading to blindness. This degenerative process primarily affects peripheral vision due to the loss of rods. Autosomal recessive RP (arRP) is clinically and genetically heterogeneous. It has been associated with mutations in different genes, including CRB1 (Crumbs homolog 1). The aim of this study was to determine the causative gene in a Tunisian patient with arRP born to non consanguineous parents.Methods: Four accessible family members were included. They underwent full ophthalmic examination with best corrected Snellen visual acuity, fundus photography and fluoroangiography. Haplotype analyses were used to test linkage in the family to 20 arRP loci, including ABCA4, LRAT, USH2A, RP29, CERKL, CNGA1, CNGB1, CRB1, EYS, RP28, MERTK, NR2E3, PDE6A, PDE6B, RGR, RHO, RLBP1, TULP1. All exons and intron-exon junctions of candidate genes not excluded by haplotype analysis were PCR amplified and directly sequenced.Results: A 39 aged affected member was individualized. Best corrected visual acuity was OR: 20/63, OS: 20/80. Visual loss began at the third decade. Funduscopic examination and FA revealed typical advanced RP changes with bone spicule-shaped pigment deposits in the posterior pole and the mild periphery along with retinal atrophy, narrowing of the vessels and waxy optic discs. Haplotypes analysis revealed homozygosity with microsatellites markers D1S412 and D1S413 on chromosome 1q31.3. These markers flanked the CRB1 gene. Our results excluded linkage of all the other arRP loci/ genes tested. Sequencing of the 12 coding exons and splice sites of CRB1 gene disclosed a homozygous missense mutation in exon 7 at nucleotide c.(2291 G>A), resulting in an Arg to Hist substitution (p.R764H).Conclusions: R764H is a novel mutation associated with CRB1-related arRP. Previously, an R764C mutation was observed. Extending the mutation spectrum of CRB1 with additional families is important for genotype-phenotype correlations