Abstract
Purpose: :
The Israeli population includes sub-populations of different ethnic backgrounds in which founder mutations and autosomal recessive disease become highly prevalent because of a high rate of consanguineous marriages. The purpose of this long-term, on-going study is to characterize the clinical features and identify the genetic cause of disease in Israeli patients with hereditary retinal degenerations.
Methods: :
Clinical analyses included family history, ocular examination, full-field electroretinography, electro-oculography, color vision testing, perimetry, and retinal imaging. Molecular genetic techniques included linkage analysis, homozygosity mapping, candidate gene screening, and mutation analysis.
Results: :
Over the last 8 years, 913 families that include over 1800 patients with hereditary retinal and macular diseases were recruited. In 60% of families the pattern of inheritance was autosomal recessive, in 8% autosomal dominant, in 8% X-linked and the remainder were isolate cases in which the mode of transmission could not be determined. The most common phenotype is retinitis pigmentosa (39% of families), followed by Leber congenital amaurosis (9%), cone-rod dystrophy (9%), Stargardt disease (6%), Usher syndrome (7%), CSNB (5%), maculopathy (4%), and achromatopsia (4%). Rarer disease phenotypes include Bardet-Bidell syndrome, enhanced S-cone syndrome, Best disease, choroideremia, and others. The genetic cause of disease was identified in 259 (28%) of families up to now. In many cases, the mutations were novel ones in known genes, and were prevalent in specific sub-populations sharing the same ethnic background. The homozygosity mapping technique has allowed the recent identification of three novel RP-causing genes, FAM161A, IMPG2, and DHDDS.
Conclusions: :
A decade ago, only a small fraction of Israeli patients with hereditary retinal degenerations carried a genetic diagnosis. The establishment of a number of molecular genetic laboratories focusing on these diseases has significantly improved this situation. As the number of recruited patients is growing, the rate of molecular genetic diagnosis is increasing, and the high prevalence of specific mutations in sub-populations of defined ethnic backgrounds greatly improves efficacy of diagnosis. The high rate of consanguineous marriages in the population we serve allows effective use of the homozygosity mapping technique, facilitating the identification of novel disease-causing genes.
Keywords: retinal degenerations: hereditary • genetics • electrophysiology: clinical