Search for mutations in patients with autosomal recessive retinitis pigmentosa using homozygosity–based screening with multiple locus–specific microsatellite markers

Abstract

Abstract: : Purpose: To establish a rapid and systematic screening method for detection of genes responsible for the autosomal recessive retinitis pigmentosa (arRP). Methods: Fifty–eight Japanese patients with simplex RP or arRP (twelve with consanguinity) were examined for "homozygosity by decent", using microsatellite markers in the sixteen known candidate genes of arRP (Am J Hum Genet 2003;73:suppl.578). Results: Homozygosity of examined markers reached an average of 7% and 2% in patients with and without consanguinity, respectively. Thirty–five patients revealed heterozygosity for all the genes tested and were excluded from further screening. For remaining 23 patients, one to three genes showed homozygosity and were further screened for responsible mutations. Subsequent direct sequencing revealed two novel homozygous mutations in two genes: RPE65 (R515W) in a simplex RP patient with consanguinity and TULP1 (F382S) in a patient with arRP without consanguinity. The mutation in RPE65 co–segregated with the disease and F382S in TULP1 is being searched for segregation. None of these sequence changes was found among 318 chromosomes from normal subjects. Clinical features of the two patients matched well with previously reported features of the patients carrying mutations in the respective genes. Conclusions: This systematic approach facilitates the molecular diagnosis of arRP if homozygous mutation in RP–causative gene is anticipated.

Keywords: mutations • retinal degenerations: hereditary • gene mapping