Mutation Analysis of Ocular Genes

The RHO gene, which encodes rhodopsin, was the first gene in which mutations were found that were associated with an inherited retinal disease (1 ). RHO was examined by exon screening in a large population of patients with autosomal dominant retinitis pigmentosa (adRP), because a linkage study in an Irish family showed one locus of adRP to be on human chromosome 3q (2 )-where RHO had been previously mapped (3 ). Since that time, over 100 different diseasecausing mutations have been found in RHO, and many other mutations in at least 55 additional genes. Also, there are at least 120 other retinal disease loci for which the defective genes have not yet been identified (for reviews, see refs. 4-6 ; RetNet<http://www.sph. uth.tmc.edu/retnet/>). In short, there is much mutation hunting yet to be done.