Whole Exome Sequencing Reveals Novel and Recurrent Disease-Causing Variants in Lens Specific Gap Junctional Protein Encoding Genes Causing Congenital Cataract

Abstract

Pediatric cataract is clinically and genetically heterogeneous and is the most common cause of childhood blindness worldwide. In this study, we aimed to identify disease-causing variants in three large British families and one isolated case with autosomal dominant congenital cataract, using whole exome sequencing. We identified four different heterozygous variants, three in the large families and one in the isolated case. Family A, with a novel missense variant (c.178G>C, p.Gly60Arg) in GJA8 with lamellar cataract; family B, with a recurrent variant in GJA8 (c.262C>T, p.Pro88Ser) associated with nuclear cataract; and family C, with a novel variant in GJA3 (c.771dupC, p.Ser258GlnfsTer68) causing a lamellar phenotype. Individual D had a novel variant in GJA3 (c.82G>T, p.Val28Leu) associated with congenital cataract. Each sequence variant was found to co-segregate with disease. Here, we report three novel and one recurrent disease-causing sequence variant in the gap junctional protein encoding genes causing autosomal dominant congenital cataract. Our study further extends the mutation spectrum of these genes and further facilitates clinical diagnosis. A recurrent p.P88S variant in GJA8 causing isolated nuclear cataract provides evidence of further phenotypic heterogeneity associated with this variant.

Identification of a New Mutation p.P88L in Connexin 50 Associated with Dominant Congenital Cataract

“…The P88 residue does not form the channel wall directly; however, it is highly conserved evolutionarily and most likely plays an essential role in the protein structure and function. A few mutations of the residue, P88T, P88S and P88Q, have been reported previously to cause various types of congenital cataracts ( Shiels et al, 1998 ; Arora et al, 2006 ; Vanita et al, 2008a ; Ge et al, 2014 ; Berry et al, 2020 ). Consistent with these reports, there was no microphthalmia or microcornea symptom associated with the P88L mutation, implying that P88 mutations probably do not perturb the LECs proliferation in vivo .…”

“…With the advances of next generation sequencing technologies, more and more new genetic mutations are identified. For example, some new mutations in Cx46, Cx50 and other genes were recently found to be associated with cataract and other visual impairments ( Berry et al, 2020 ; Fan et al, 2020 ). Despite all the mutations identified thus far, the known mutations can explain only a small fraction of hereditary diseases.…”

Beyond the Channels: Adhesion Functions of Aquaporin 0 and Connexin 50 in Lens Development

“…Thus, like AQP0, Cx50 is capable of mediating both homotypic interaction and heterotypic protein-membrane interaction ( Hu et al, 2017 ). Furthermore, a Cx50 mutant, P88S, a site mutation that impairs the ability of Cx50 to form functional gap junction channels and hemichannels ( Berry et al, 2020 ), exhibits comparable cell adhesive capability as WT Cx50 ( Hu et al, 2017 ). Thus, this experimental evidence suggests that Cx50, but not the other lens Cxs, acts as a cell adhesive molecule, and this adhesive function is independent of its role in forming Cx channels.…”

Evaluating gap junction variants for a role in pediatric cataract: an overview of the genetic landscape and clinical classification of variants in the GJA3 and GJA8 genes

“…The GJA3 gene contained seven frame-shift variants, all of which are in the N-terminal cytoplasmic tail. Six of these seven frame-shift variants were reported to have AD inheritance [12,[114][115][116][117][118][119] with the most proximal of these being the p.(Ser256Glnfs*68) [114] and the most distal the p.(Thr400Hisfs*68) [119] change.…”

“…Subsequently, a second report of this variant was observed in a multigenerational Danish family, where it segregated in all seven affected and one unaffected individual [16]. The only other AD-rp variant reported in GJA3 was c.82G>A p.(Val28Met) observed in five affected and two unaffected individuals in an Indian family [121], and a different variant at the same residue p.(Val28Leu) reported in a singleton [114]. Interestingly, with the p.(Val28Met) variant, variable age of onset was observed in the family with three of the five affected individuals receiving a cataract diagnosis after 20 years of age and the two unaffected variant carriers in the youngest generation of the family.…”