Deviations from the mendelian inheritance of retinitis pigmentosa

Abstract

Retinitis pigmentosa (RP) is a heterogeneous group of hereditary disorders causing progressive retinal degeneration. Dominant, recessive, and X-linked forms are well established, but studies invariably reveal a high proportion of simplex cases inconsistent with the assumptions of simple monogenic inheritance. Segregation analysis of data ascertained in the RP National Survey showed that distribution of cases in families could be accounted for only by invoking assumptions of reduced penetrance and a proportion of sporadic cases.For proband sibships with normal parents, the hypothesis that all cases were recessive was rejected (X2 = 33.6), and the proportion of sporadic cases estimated to be 21%. RP and hearing loss are characteristic features of several monogenic syndromes, and even in the absence of a specific syndrome diagnosis, hearing impairment was the most commonly reported extraocular symptom in the survey, with 20.1% of probands having mild loss, and an additional 7.4% severe impairment. For the re...