Identification of novel cis-mutations in the GJA8 gene in a 3-generation Iranian family with autosomal dominant congenital nuclear cataract

Cataract is mainly due to the presence of high molecular weight protein, which disrupts the normal function of the lens. Pathogenic variants in Gap Junction protein alpha-8 (GJA8) have been associated with autosomal dominant congenital nuclear cataract. In general, mutations in those genes that have important functions in lens development lead to congenital cataract.We conducted whole-exome sequencing (WES) in a four-year-old male patient referred to the genetic center for genetic analysis. He had developed cataract at an early age. DNAs were extracted from the blood samples of all family members and subjected to PCR-Sanger sequencing to confirm the WES results.WES analysis on the proband revealed two mutations in the GJA8 gene (c.G12C, c.G58A). His mother, alongside several other members of the third-generation family, had developed cataract. Sanger sequencing of the interested regions showed that these two mutations were co-segregated in all affected members. However, none of the healthy individuals carried these mutations confirming that these two mutations are located in the same allele (complex allele). Bioinformatics analysis of the mutated GJA8 RNA and protein structure confirmed the pathogenicity of the cis-mutations.Genetic segregation analysis in a three-generation family and also bioinformatics analysis showed that the complex-allele containing c.G12C+c.G58A mutations in the GJA8 gene is a pathogenic variant that causes autosomal-dominant congenital nuclear cataract.