EYS mutations and implementation of minigene assay for variant classification in EYS-associated retinitis pigmentosa in northern Sweden

Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous group of inherited retinal degenerations. The ortholog of Drosophila eyes shut/spacemaker, EYS on chromosome 6q12 is a major genetic cause of recessive RP worldwide, with prevalence of 5 to 30%. In this study, by using targeted NGS, MLPA and Sanger sequencing we uncovered the EYS gene as one of the most common genetic cause of autosomal recessive RP in northern Sweden accounting for at least 16%. The most frequent pathogenic variant was c.8648_8655del that in some patients was identified in cis with c.1155T>A, indicating Finnish ancestry. We also showed that two novel EYS variants, c.2992_2992+6delinsTG and c.3877+1G>A caused exon skipping in human embryonic kidney cells, HEK293T and in retinal pigment epithelium cells, ARPE-19 demonstrating that in vitro minigene assay is a straightforward tool for the analysis of intronic variants. We conclude, that whenever it is possible, functional testing is of great value for classification of intronic EYS variants and the following molecular testing of family members, their genetic counselling, and inclusion of RP patients to future treatment studies.