A homozygous deletion in RPE65 in a small Sardinian family with autosomal recessive retinal dystrophy

PURPOSE: We have been engaged in an ongoing study to screen candidate genes for mutations in small families with various forms of autosomal recessive retinal dystrophy. Here we report the screening of a cohort of 14 families from Sardinia for mutations in the genes encoding the alpha- and beta-subun its of cGMP-phosphodiesterase and RPE65 (PDE6A, PDE6B, and RPE65). METHODS: Haplotype analysis was performed on each family using simple seque nce repeat markers closely flanking or within each of the three gene candid ates. For families in which a gene could not be ruled out from segregating with disease, exons of the gene from proband DNAs were screened for mutatio ns by SSCPE (single strand conformation polymorphism electrophoresis). All variants found by SSCPE were sequenced directly. RESULTS: By haplotype analysis, 6/14, 11/14, and 4/13 families were ruled o ut for PDE6A, PDE6B, and RPE65, respectively. A few variants were found in the proband DNAs of the remaining families, but only one was significant: a 20 bp deletion in exon 4 of RPE65. The deletion co-segregated with disease in one family and caused a frame shift that produces a stop codon downstre am. It was absent from the other Sardinian families that we tested, and fro m Sardinian and North American controls. Results of studies of phenotype in homozygotes and heterozygotes in this Sardinian family are compared with t hose from a non-Sardinian family recently reported to have the same RPE65 m utation. CONCLUSIONS: This RPE65 mutation, which appears to be quite restricted in i ts occurrence in Sardinia, leads to childhood onset severe retinal dystroph y or Leber congenital amaurosis. Affecteds of the other 13 plus two additio nal families were diagnosed with arRP. This family lived in an area of Sard inia where none of the others lived suggesting different ancestral origins.