Comprehensive molecular diagnosis of 160 Leber congenital amaurosis or Early Onset Severe Retinal Dystrophy by targeted next generation sequencing.

Abstract

Purpose: The incidence of Leber congenital amaurosis (LCA) and other early-onset severe retinal dystrophies (EOSRD) is estimated to 7:10 000 births in France. The visual outcome of affected infants is variable, ranging from stationary cone-rod dystrophy with -at best -light perception (Type I), to severe, yet progressive, rod-cone dystrophy with low, but measurable, visual acuity in the first two decades of life (Type II) . In addition, these blind infants are at risk of developing skeletal, neurologic and renal dysfunctions later in their life. Hitherto, 45 genes have been identified which mutations underlie these diseases. Recent advances have demonstrated that both the visual outcome and the extraocular involvement are strongly correlated to the disease-gene. The aim of this work was to demonstrate the importance of targeted next generation sequencing to improve the care and follow-up of patients.

Methods: 55 known retinal disease genes were captured, including the 45 genes known to cause isolated and syndromic LCA/EOSRD and 10 genes of differential diagnoses. Targeted next-generation sequencing (TNGS) was performed for a cohort of 154 unrelated cases. The presence of candidate variants was confirmed by Sanger sequencing and the segregation with the disease was confirmed by analysis of patients’ relatives.

Results: We successfully identified causative mutations, including 6 copy number variations, in 98/154 index cases. Mutations were identified in a gene known to cause isolated LCA in 80/98 individuals, 49/80 and 31/80 of whom carried mutations in type I and type II genes, respectively. Mutations in genes for syndromic LCA were detected in 13/98 index cases with no overt extraocular symptoms at the time of diagnosis. Finally, differential diagnosis were demonstrated in 5/98 individuals.

Conclusions: Molecular screening of genes responsible for early-onset blindness using TNGS has allowed confirming the diagnosis of type I or type II LCA/EOSRD in 60% of the cases. It has allowed showing that extraocular follow-up was irrelevant in more than 50% of the cases, whereas it was required in 8.5% of the individuals included in the study. In addition, exhaustive screening of all genes known to cause isolated and syndromic LCA and EOSRD using TNGS has allowed rapid and efficient selection of patients available for the identification of novel genes.