Genetic findings in over 600 individuals with inherited retinal disorders in Finland

Abstract

AbstractPurpose: To report genetic findings in patients with suspected inherited retinal disorders (IRD) in a large Finnish cohort.Methods: The study was conducted retrospectively on IRD‐patients treated at the Department of Ophthalmology, Helsinki University Hospital between January 1, 2012, and December 31, 2020. Eligibility criteria were met by 786 patients. Clinical diagnosis, genetic testing method and result, relevant family history, and mode of inheritance were drawn from the electronic health registries.Results: Of the 638 patients who underwent genetic testing, 79% received a genetic diagnosis. The genetic findings corresponded to autosomal recessive (AR) inheritance in 242 patients, X‐linked in 158, and autosomal dominant (AD) in 94, whereas pathogenic variants in mitochondrial genes were found in 22 patients. The most common genetic diagnosis was a pathogenic variant in RS1 causing X‐linked retinoschisis (n = 86, 17% of all patients with a positive genetic finding). Of retinitis pigmentosa ‐associated genes, causative variants were most commonly found in CERKL (n = 43, 8.5%), RPGR (n = 31, 6.1%), and EYS (n = 25, 5.0%). CERKL variant c.375C > G, p.(Cys125Trp) and EYS variant c.1155 T > A, p.(Cys385Ter), both with known founder effects in the Finnish population, were frequently discovered (n = 69 and 53, respectively). Variants in the ABCA4 gene explained IRD in 24 patients. Pathogenic variants were also found in CHM (n = 26), OPA1 (n = 16), and CLRN1 (n = 16).Conclusions: The genetic causes of IRDs in Finland differ from other countries because of its isolated population history. Compared to similar studies in other countries, the percentage of patients with a positive genetic finding was higher (79%), which can partly be explained by the enriched founder mutations in the population. About 20% of the patients still lack a genetic diagnosis. These patients might have causative variants that are difficult to detect with current testing methods (such as complex structural variants) or the variants are in genes not yet associated with IRD.