Whole Genome Sequencing Revealed Mutations in Two Independent Genes as the Underlying Cause of Retinal Degeneration in an Ashkenazi Jewish Pedigree

Abstract

Retinitis pigmentosa (RP) causes progressive photoreceptor loss resulting from mutations in over 80 genes. This study identified the genetic cause of RP in three members of a non-consanguineous pedigree. Detailed ophthalmic evaluation was performed in the three affected family members. Whole exome sequencing (WES) and whole genome sequencing (WGS) were performed in the three affected and the two unaffected family members and variants were filtered to detect rare, potentially deleterious variants segregating with disease. WES and WGS did not identify potentially pathogenic variants shared by all three affected members. However, WES identified a previously reported homozygous nonsense mutation in <i>KIZ</i> (c.226C>T, p.Arg76*) in two affected sisters, but not in their affected second cousin. WGS revealed a novel 1.135 kb homozygous deletion in a retina transcript of <i>C21orf2</i> and a novel 30.651 kb heterozygous deletion in <i>CACNA2D4</i> in the affected second cousin. The sisters with the <i>KIZ</i> mutation carried no copies of the <i>C21orf2</i> or <i>CACNA2D4</i> deletions, while the second cousin with the <i>C21orf2</i> and <i>CACNA2D4</i> deletions carried no copies of the <i>KIZ</i> mutation. This study identified two independent, homozygous mutations in genes previously reported in autosomal recessive RP in a non-consanguineous family, and demonstrated the value of WGS when WES fails to identify likely disease-causing mutations.