Identification of LCA9, a New Locus for Leber's Congenital Amaurosis on Chromosome 1p36

Abstract

Abstract: : Purpose:To identify a new locus for Leber's congenital amaurosis (LCA) in a large consanguineous pedigree in which the known loci for LCA had been excluded. Methods:A single large consanguineous Pakistani pedigree in which there were six affected individuals was examined. All reported a typical history of LCA, with severe non-progressive visual impairment since birth. Examination revealed best corrected visual acuity was perception of light, the presence of nystagmus and posterior sub-capsular lens opacities was universally found, and keratoconus was evident in one family member. Fundoscopy showed optic nerve head pallor, retinal vascular attenuation, macular staphylomata, varying degrees of pigmentary disturbance and white spots, all features recognised to lie within the clinical spectrum of LCA. Genomic DNA was extracted from peripheral blood leucocytes, and family members were typed with microsatellite markers spanning the known loci for LCA. Haplotype analysis of the data generated clearly excluded these loci, as heterozygosity was evident. Hence, a whole genome wide linkage search was performed. Results:The data generated from genotyping the family with 407 microsatellite markers was analysed, using Genehunter. A multipoint lod score of 3.5 was observed between D1S1612 and D1S3699, much of the remaining genome was excluded by negative lod scores. Typing of additional markers, led to a final refinement of the locus to an autozygous region of 10cM extending over 5.7Mb of DNA, between D1S2667 and D1S1597, generating a lod score of 4.4. Using the UCSC human genome browser, 46 fully annotated candidate genes were found to lie within this region, including retinoid binding protein 7 (RBP7), however no mutations were identified in the coding sequence of this gene by SSCP or sequence analysis. Conclusions:This report demonstrates further evidence of locus heterogeneity regarding LCA. Currently the critical disease interval is large and contains gaps in the sequence assembly. Further progress will be made on completion of sequence data, sampling further members of this pedigree, and identifying new pedigrees linking to this locus.

Keywords: retinal degenerations: hereditary • linkage analysis • candidate gene analysis