To evaluate the clinical phenotype of ten Tunisian families with non-syndromic retinitis pigmentosa (RP), to characterize genes and mutations causing these conditions, and to elaborate phenotype-genotype correlations.
Descriptive clinical genetic study of 114 individuals, of whom 27 are affected by non-syndromic RP. Ophthalmic examination and various visual tests were performed. DNA was analyzed using single nucleotide polymorphism, microsatellite genotyping and direct sequencing to determine the genes and mutations involved.
We identified seven mutated genes: RPE65, RDH12, USHER 2A, PDE6a, PDE6b, CRB1, and NR2E3. Analysis of phenotype-genotype correlation indicated that some genes were associated with specific phenotypes. In RPE65 mutations, we found early onset dystrophy, nystagmus, keratoconus, white dot deposits in earlier stages and clumped pigment in later stages. The RDH12-associated phenotype (juvenile RP) showed severe and early-onset dystrophy, diffuse spicule pigmentation, macular edema and thickening, and tomographic re-organization of retinal layers. The CRB1 mutation was characterized by preserved para-arteriolar retinal pigment epithelium and no hemeralopia.
RP is clinically and genetically heterogeneous. The two ultimate goals of research are to provide efficient clinical diagnostic of affected gene by phenotype-genotype correlation and to design novel treatment regimens. Our goal is to create a specific chip for our population, and then future research will focus on the identification of the remaining causal genes, the elucidation of the molecular mechanisms of disease in the retina and the development of gene therapy approaches.