Exploring copy number variations in Lebanese families with rod-cone dystrophy reveals a novel deletion in PRPF31 with haploinsufficiency

Rod-cone dystrophy (RCD), also known as retinitis pigmentosa, is the most common group of retinal dystrophies, affecting around 1:4,000 individuals worldwide. In the present work, we performed a copy number variation (CNV) analysis on next-generation sequencing (NGS) data from two Lebanese families with RCD, since no disease-causing mutations were identified through the analysis of single nucleotide variants (SNVs) and insertions/deletions (Indels). NGS, real-time PCR (qPCR), and chromosomal microarray were performed to identify, validate, and delineate the causative CNVs identified in both families involved in this study. Additionally, expression analysis using qPCR and western blotting was conducted to assess the effect of the PRPF31 variant on gene and protein expression levels. A novel heterozygous deletion (701 bp) spanning exons 6 and 7 of PRPF31 was identified in the first family (F11), resulting in autosomal dominant RCD due to haploinsufficiency. This was confirmed by reduced mRNA levels and the complete absence of protein expression in the affected individuals (F11:III.2 and F11:II.2). In the second family (F26), we identified a previously documented homozygous deletion in the exons 3-19 of MERTK gene, which is responsible for causing severe autosomal recessive RCD. The current study expands the mutational spectrum of PRPF31 and MERTK genes, underscoring the importance of CNVs and haploinsufficiency in RCD etiology. These findings serve as a foundation for future analyses concerning gene augmentation therapies.