A homozygosity-based search for mutations in patients with autosomal recessive retinitis pigmentosa, using microsatellite markers.

PURPOSE To identify possible mutations in known candidate genes in patients with autosomal recessive (ar) and simplex retinitis pigmentosa (RP), by using an established strategy of flexible, multiplexed, microsatellite-based homozygosity mapping. METHODS A total of 78 microsatellite markers corresponding to 16 genes known to be responsible for arRP were selected and used in 18 multiplex amplifications, followed by genotyping. Twelve consanguineous probands and 47 nonconsanguineous probands (59 patients with arRP or simplex RP) agreed to the screening. RESULTS Of the 59 probands examined, 24 had a mean of 1.4 genes showing homozygosity for all markers within the corresponding gene region. Subsequent direct sequencing revealed three homozygous mutations. Two of them were novel mutations in the genes TULP1 (c.1145T-->C, F382S) and CNGB1 (c.3444 + 1G-->A). The other was a mutation in RPE65 (c.1543C-->T, R515W), which is known to cause Leber's congenital amaurosis. The clinical features of each patient, together with the cosegregation analysis, strongly support the pathogenicity of these mutations. CONCLUSIONS This systematic approach facilitated the identification of genes that cause arRP, and the results provide a widened spectrum of the mutation severity associated with a broader range of phenotypic manifestations of arRP.