A novel locus for Leber congenital amaurosis (LCA4) with anterior keratoconus mapping to chromosome 17p13

Purpose. A two-generation consanguineous Pakistani family with autosomal re cessive Leber congenital amaurosis (LCA, MIM 204,000) and keratoconus was i dentified. All affected individuals have bilateral keratoconus and congenit al pigmentary retinopathy. The goal of this study was to link the disease p henotype in this family. METHODS. Genomic DNA was amplified across the polymorphic microsatellite po ly-CA regions identified by markers. Polymerase chain reaction (PCR) produc ts were separated by nondenaturing polyacrylamide gel electrophoresis. Alle les were assigned to individuals, which allowed calculation of LOD scores u sing the Cyrillic and MLINK software program. The retinal guanylate cyclase (RETGC-1, GDB symbol GUC2D) and pigment epithelium-derived factor (PEDF) g enes were analyzed by heteroduplex analysis and direct sequencing for mutat ions in diseased individuals. RESULTS. Based on a whole genome linkage analysis the first locus for this combined phenotype has been mapped to chromosome 17p13. Linkage analysis ga ve a two point LOD score of 3.21 for marker D17S829. Surrounding this marke r is a region of homozygosity of 15.77 cM, between the markers D17S1866 and D17S960; however, the crossover for the marker D17S1529 refines the region to 10.77 cM within which the disease gene is predicted to lie. Mutation sc reening of the nearby RETGC-1 gene, which has been shown to be associated w ith LCA1, revealed no mutations in the affected individuals of this family. Similarly, another prime candidate in the region PEDF;was also screened fo r mutations. The factor has been shown to be involved in the photoreceptor differentiation and neuronal survival. No mutations were found in this gene either. Furthermore, RETGC-1 was physically excluded from the critical dis ease region based on the existing physical map. CONCLUSIONS. It is therefore suggested that this combined phenotype maps to a new locus and is due to an as yet uncharacterized gene within the 17p13 chromosomal region.