Kinga M Bujakowska
Massachusetts Eye and Ear Infirmary- Harvard Medical School, USA
Posters & Accepted Abstracts: J Clin Exp Ophthalmol
Statement of the Problem: Inherited retinal degenerations (IRDs) are an important cause of blindness affecting over two million people worldwide. Even though IRDs are mostly monogenic, they are genetically heterogeneous, with mutations in over 200 genes leading to disease. Despite substantial progress in sequencing and new disease gene discovery, current strategies can genetically solve only about 60% of IRD cases. The high number of unsolved cases can be attributed to the yet-unidentified genes, large insertion/ deletions also called copy number variations (CNVs), and deep intronic mutations, which are not easily detected by targeted nextgeneration sequencing (NGS) approaches. This presentation will give an overview of the methodology and the challenges related to genetic diagnostic testing, based on the genetic results from a cohort of 500 IRD patients. Methodology: The patients included in the study were recruited and clinically examined at the Massachusetts Eye and Ear Infirmary. Patients underwent a full ophthalmic examination and their DNA samples were studied by Genetic Eye Disease (GEDi) diagnostic testing, SNP genotyping array, quantitative real-time PCR (qRT-PCR), PCR and Sanger sequencing. The read-depth NGS analysis was performed with two methods (Exome-Depth and an in-house algorithm). The study protocol adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board. All subjects signed informed consent. Findings: GEDi testing with the initial analysis of rare single nucleotide variants (SNVs) and small insertion/deletions solves 55% of IRD patients. Mutations in USH2A (10%), ABCA4 (3%), EYS (3%), RPGR (3%) and RHO (3%) were the most frequent cause of disease. Further analysis of NGS read-depth predicts likely causal CNVs in 11% of IRD patients, where deletions in USH2A were the most common (22%). Conclusion & Significance: Analysis of a large IRD cohort indicates that CNVs are important contributors to the etiology of IRDs, being responsible for approximately 11% of genetic cases.
