ClinVar

Description

The c.35delG (p.G12Vfs*2) alteration, located in exon 2 (coding exon 1) of the GJB2 gene, consists of a deletion of one nucleotide at position 35, causing a translational frameshift with a predicted alternate stop codon after 2 amino acids. The GJB2 gene has a single coding exon, so while the alteration is truncating, the mRNA is not predicted to undergo nonsense mediated decay (NMD) and a truncated mutant protein could still be expressed. Premature termination codons located either in the last exon or within 50-55 nucleotides upstream of the 3’-most exon-exon junction usually fail to elicit NMD (Maquat, 2004). The exact functional impact of these altered amino acids is unknown at this time; however, this alteration and additional truncating alterations downstream of this alteration have been reported in the literature as disease-causing (Roux, 2004). Based on data from gnomAD, the - allele has an overall frequency of 0.619% (1737/280696) total alleles studied. The highest observed frequency was 0.958% (1217/127068) of European (non-Finnish) alleles. The c.35delG variant is the most common GJB2 pathogenic variant among Caucasians individuals, and has been reported in patients with mild to profound hearing loss of multiple ethnicities (Denoyelle, 1997; Gasparini, 2000; Gualandi, 2002; Roux, 2004; Hilgert, 2009; Mahdieh, 2016; Zytsar, 2018). Additionally, this variant was observed in trans with p.N176D in multiple families with syndromic hearing loss with ectodermal involvement (Youssefian, 2018; Youssefian, 2022). Functional studies show an absence of protein expression and reduced intercellular diffusion of dye in vitro (D'Andrea, 2002). Based on the available evidence, this alteration is classified as pathogenic.