Genetic and epidemiological investigations on pigmentary degeneration of the retina and allied disorders in Switzerland

Abstract

The authors describe the results of a genetic and epidemiological investigation of pigmentary degeneration of the retina and allied diseases (Bardet-Biedl syndrome, congenital tapeto-retinal amaurosis of Leber, retinitis punctata albescens, fundus albipunctatus cum hemeralopia, etc.) in Switzerland. About 90% of all cases of pigmentary degeneration of the retina are transmitted by the recessive mode, and 9% by the dominant mode of inheritance. One family alone presents a recessive sex-linked transmission of retinitis pigmentosa. In this family, the female heterozygotes show the typical tapetal reflex as described by Falls and Cotterman in 1948. The frequency of pigmentary degeneration of the retina in Switzerland can be estimated at 1 : 7000, the gene frequency at 1 : 84, and the frequency of heterozygotes at 1 : 42. About 10% of all cases are offspring of marriages between first cousins. There are some isolates in Switzerland with a high incidence of retinitis pigmentosa. One isolate, in particular, in the Canton of Valais, allowed us to demonstrate a phenotypical alternation between different types of pigmentary degeneration within several branches of a large family originating from a common ancestor. Among the hereditary affections associated with tapeto-retinal degenerations, congenital deafness is the most frequent (being associated with retinitis pigmentosa in 13%). The Bardet-Biedl syndrome was observed in 4 patients out of a population of 700,000 inhabitants (1 : 175,000). Finally, the authors stress the importance of an investigation of isolates, since they permit a more satisfactory classification of abiotrophic diseases.