A Missense Mutation in GJA8 Encoding Connexin 50 in a Chinese Pedigree with Autosomal Dominant Congenital Cataract

Abstract

Congenital cataract is leading cause of visual impairment and blindness in children worldwide. Approximately one-third of congenital cataract cases are familial, whose genetic etiology can be distinguished by targeted exome sequencing. Here, a three-generation congenital cataract pedigree was recruited, and physical and ophthalmologic examinations were taken. Targeted exome sequencing of 139 cataract-related genes was performed on the proband III:1. Sanger sequencing was used to validate the presence of variation identified via exome sequencing in family members and 200 controls. Conservative and functional prediction was performed with bioinformatic tools. We, thus, found a heterozygous missense mutation c.10T>A (p.W4R) in gap junction protein alpha 8 (GJA8) in the patients. However, this mutation was not present in normal family members and 200 unrelated controls. The GJA8 gene encodes a gap junction protein, connexin 50 (Cx50), in lens fibers that provide channels for exchange of ions and small molecules between adjacent cells. Conservative and functional prediction suggests that the W-to-R substitution at codon 4 may impair the function of the human Cx50 protein. Accordingly, we analyzed the distribution of Flag-tagged mutant Cx50 protein in HeLa cervical cancer cells. Immunofluorescent staining showed that the W-to-R substitution impaired Cx50 trafficking to the plasma membrane to form the gap junction. In conclusion, c.10T>A (p.W4R) in GJA8 is the newly identified genetic cause of familial congenital cataract. The W-to-R substitution near the amino-terminus may alter the localization of mutant Cx50, thereby impairing gap junction formation, which is the molecular pathogenic mechanism of this mutation.

Keywords: GJA8; congenital cataract; connexin 50; gap junction; targeted exome sequencing.