Ocular Findings in Patients with Autosomal Dominant Retinitis Pigmentosa Due to a 3-Base Pair Deletion at Codon 255/256 of the Human Rhodopsin Gene

Abstract

Retinitis pigmentosa (RP) is a genetically heterogeneous group of progressive hereditary retinal dystrophies. All three modes of Mendelian inheritance, autosomal dominant, autosomal recessive, and X-linked have been described. Even within the same mode of inheritance further genetic heterogeneity has been proven during the last three years as different genes/loci on different chromosomes have been identified for autosomal dominant retinitis pigmentosa (adRP) (for review see ref.1, and Farrar et al., this volume). The gene for rhodopsin which is localized on the long arm of chromosome 3 was the first adRP gene identified². Since then an ever increasing number of allelic rhodopsin mutations have been described³. Different types and methods of subgrouping of adRP had been suggested on the basis of clinical observations^4–8. The most widely accepted classification is that of Massof and Finkelstein who divided adRP in two types⁵. Type I is characterized with a diffuse loss of rod function and with an onset of night blindness usually during the first decade of life. The cone function is relatively well preserved throughout life. In contrast, type II (“sector”) of adRP shows a regional loss of both rod and cone function, and a much later onset of night blindness. Type I is identical to type “D”, and type II to type “R” according to Lyness and coworkers⁸. As this classification is based solely on phenotypic features, identification of the primary genetic defect may allow a more appropriate subtyping.