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