The filtering allele frequency (the lower threshold of the 95% CI of 143/1558, including 8 homozygous observations) of the c.109G>A (p.Val37Ile) variant in the GJB2 gene is 7.9% for East Asian genomes in gnomAD.This is a high enough frequency that, in the absence of conflicting data, might warrant a benign classification based on the thresholds defined by the ClinGen Hearing Loss Expert Panel for autosomal recessive hearing loss variants (BA1). However, based on the evidence outlined below, the ClinGen Hearing Loss Expert Panel believes that the evidence for the pathogenicity of this variant for nonsyndromic hearing loss outweighs its high allele frequency in population databases. Therefore, the BA1 code will not contribute to the overall classification. The homozygous genotype and compound heterozygous genotype with another variant in GJB2 have shown to be statistically enriched in patients with nonsyndromic sensorineural hearing loss compared to individuals representative of the general population in gnomAD and/or those who underwent carrier screening at Counsyl. (PS4; PMID: 31160754). This study also reported the variant in 139 homozygous affected probands, 17 affected probands with the p.Met34Thr variant in trans, 131 affected probands with a variant asserted to be P/LP in ClinVar, and 78 affected probands with a premature GJB2 termination codon in trans. However, because the variant is also very frequent in the general population, this criteria has been applied at the strength of Moderate. (PM3; PMID: 31160754). The p.Val37Ile variant in GJB2 has been reported to segregate with hearing loss in at least 21 family members (PP1_Strong; PMID: 31160754). Although homozygous or compound heterozygous observations have been identified in individuals with normal hearing, it has been suggested that individuals with the p.Val37Ile variant lose hearing at ~1dB/year, suggesting an age-related penetrance (PMID: 27308839). Furthermore, in dye transfer and electrical coupling assays, both functional studies have shown that the variant impacts protein function (PMID: 26088551, 12505163, 16300957) and knock-in mouse model demonstrated that the p.Val37Ile variant leads to the phenotype. However, because the codon for p.Val37 in mouse (GTG) was different from that in human (GTT), c.109G>A in mouse would translate into p.Val37Met, and the dye transfer and coupling assays have limited validation and correlation with pathogenicity, neither was not counted as functional evidence. (PMID: 27623246). Of note, the severity of hearing loss is known to be mild on average and there have been multiple accounts of incomplete penetrance of the variant in families/individuals with p.Val37Ile in a biallelic genotype. In summary, this variant meets criteria to be classified as pathogenic for autosomal recessive nonsyndromic genetic hearing loss based on the ACMG/AMP criteria applied, as specified by the Hearing Loss Expert Panel: PS4, PP1_Strong, PM3.

The GJB2 c.109G>A (p.Val37Ile) missense variant is widely reported in the literature. The variant was first identified in a compound heterozygous state with a second variant in a single individual with hearing loss (Abe et al. 2000). Pollak et al. (2007) found the variant was significantly overrepresented in individuals with hearing loss as compared to controls (5.2% compared to 0.43%) and suggested that this variant might cause a late onset, mild form of hearing loss with reduced penetrance when found in combination with other variants in the GJB2 gene. In an evaluation of over 1000 newborns, Wu et al. (2011) identified several homozygotes and compound heterozygotes for the p.Val37Ile variant, with both normal hearing and varying degrees of hearing loss. Expression studies have demonstrated that the p.Val37Ile variant results in a complete loss of homotypic gap junction channel activity (Snoeckx et al. 2005). The p.Val37Ile variant is reported at a frequency of 0.08586 in the Kinh in Ho Chi Minh City, Vietnam, population of the 1000 Genomes Project. This frequency is high but may be consistent with the prevalence of mild hearing loss in the population. Based on the collective evidence, the p.Val37Ile variant is classified as pathogenic for autosomal recessive nonsyndromic hearing loss, though is associated with a mild phenotype and reduced penetrance. This variant was observed by ICSL as part of a predisposition screen in an ostensibly healthy population.

This variant is classified as Pathogenic. Evidence in support of pathogenic classification: This variant has strong previous evidence of pathogenicity in unrelated individuals. This variant has been classified as pathogenic by an expert panel for autosomal recessive deafness (ClinVar); Other missense variants comparable to the one identified in this case have moderate previous evidence for pathogenicity. Alternative changes, p.(Val37Phe) and p.(Val37Ala), have been reported several times as likely pathogenic and once as a VUS in patients with recessive hearing loss (ClinVar). Additional information: Variant is predicted to result in a missense amino acid change from Val to Ile; This variant is heterozygous; This gene is associated with both recessive and dominant disease. The autosomal dominant disease is commonly associated with pathogenic missense variants. The autosomal recessive disease is associated with bi-allelic loss-of-function variants and includes both missense and protein truncating variants (NIH Genetics Home Reference, PMID: 12792423); Variant is present in gnomAD (v4) at a frequency >=0.05 in the East Asian subpopulation (3869 heterozygotes, 101 homozygotes); An alternative amino acid change at the same position has been observed in gnomAD (v4) (54 heterozygotes, 0 homozygotes); Variant is located in the annotated connexin domain (DECIPHER); Missense variant with inconclusive in silico prediction and/or uninformative conservation; Loss of function is a known mechanism of disease in this gene and is associated with both deafness and skin conditions (OMIM). Dominant negative is also a suggested mechanism (PMID: 28428247); The condition associated with this gene has incomplete penetrance. This variant is well known to result in incomplete penetrance in patients with recessive deafness (PMID: 31160754); This variant in known to have variable expressivity (PMID: 31160754). Severity can range from mild to profound with intrafamilial variability also commonly seen. Commonly, truncating variants are associated to a more severe hearing loss (PMID: 20301449); Heterozygous variant detected in trans with a second PATHOGENIC heterozygous variant ( NM_004004.6(GJB2):c.101T>C; p.(Met34Thr)) in a recessive disease; Inheritance information for this variant is not currently available in this individual.

PP1_strong, PM3, PS4

GJB2: PM3:Very Strong, PM2:Supporting, PS3:Supporting

Variant summary: GJB2 c.109G>A (p.Val37Ile) results in a conservative amino acid change located in the Connexin, N-terminal of the encoded protein sequence. Three of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 0.0074 in 280234 control chromosomes in the gnomAD database, including 91 homozygotes. This frequency is not significantly higher than expected for a pathogenic variant in GJB2 causing Autosomal Recessive Non-Syndromic Hearing Loss (0.0074 vs 0.025), allowing no conclusion about variant significance. This variant was first listed as a polymorphism by Kelley_1998 due to finding of one heterozygote of this variant in 96 control persons. However, all following studies on genotype-phenotype in patients and gene function suggest that this variant is pathogenic. In hearing loss patients with this variant, clinical severity ranges from mild to moderate. In a Chinese study (Chai_2015), the variant was strongly associated with both mild-to-moderate (p=2.01011) and severe-to-profound (p=0.001) HI, but was estimated to have a rather low penetrance (17%). Huang_2015 showed that among the 3,864 Chinese patients, 106 (2.74%) had a homozygous p.V37I variation or a compound p.V37I plus other GJB2 pathogenic mutation, a frequency that was significantly higher than that in the control group (600 individuals, 0%). Homozygotes of this variant or compound heterozygotes of this variant and a pathogenic variant in GJB2 were reported in patients with hearing loss in populations other than East Asian (Robionet_2000, Wilcox_2000, Snoeckx_2005). In vitro junctional conductance and biochemical permeability study on mutant Cx26 V37I showed the function of Cx26 V37I was significantly decreased (Bruzzone_2003 and Kim_2015). Nine clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 without evidence for independent evaluation. Eight of these have reported a classification as pathogenic (n=7) or likely pathogenic (n =1). This is consistent with the results of the "Clingen hearing loss variant curation expert panel" that has settled upon a classification for this variant as "Pathogenic" based on compelling statistical and supporting functional evidence (personal correspondence, manuscript in preparation at this time of classification) . Based on the evidence outlined above, the variant was classified as pathogenic.

This GJB2 variant has been vetted by the ClinGen Hearing Loss Expert Panel and is predicted to be associated with autosomal recessive sensorineural hearing loss that is typically mild to moderate and bilateral. GJB2 c.109G>A (rs72474224) reaches polymorphic frequency (>1%) within the East Asian subpopulation in a large population dataset6 (gnomAD: 1665/19952 alleles; 8.3%, 96 homozygotes), however, it was found to be significantly overrepresented in hearing loss patients compared to population controls. This variant was found to segregate with hearing loss in a large number of families. Functional studies suggest that GJB2 c.109G>A impacts connexin 26 function, however, this has not been confimed to reflect the biologic process in human cochlea. We consider this variant to be pathogenic.

PS1_Very strong, PM3_Supporting, PM5_Moderate, PP3_Supporting

A Heterozygous Missense variant c.109G>A in Exon 2 of the GJB2 gene that results in the amino acid substitution p.Val37Ile was identified. The observed variant has a minor allele frequency of 0.00772/0.00624% in gnomAD exomes and genomes, respectively. The severity of the impact of this variant on the protein is medium, based on the effect of the protein and REVEL score . Rare Exome Variant Ensemble Learner (REVEL) is an ensembl method for predicting the pathogenicity of missense variants based on a combination of scores from 13 individual tools: MutPred, FATHMM v2.3, VEST 3.0, PolyPhen-2, SIFT, PROVEAN, MutationAssessor, MutationTaster, LRT, GERP++, SiPhy, phyloP, and phastCons. The REVEL score for an individual missense variant can range from 0 to 1, with higher scores reflecting greater likelihood that the variant is disease-causing. ClinVar has also classified this variant as Pathogenic [Variant ID : 17023]. The variant has previously been reported for deafness by Shen, Jun, et al., 2019. Experimental studies have shown that this missense change disrupts the formation of homotypic junctional channels in vitro by Chen, Ying, et al., 2016. For these reasons this variant has been classified as Pathogenic.

The p.Val37Ile variant in GJB2 is a well established allele that is known to be pathogenic in the homozygous state or in the compound heterozygous state with another pathogenic GJB2 variant and typically results in a mild to moderate hearing loss (Snoeckx 2005 PMID: 16380907, Huculak 2006 PMID: 17036313, Pollak 2007 PMID: 17935238). In rare cases, it may even be associated with normal hearing. Additionally, it has been reported as pathogenic in ClinVar by the ClinGen Hearing Loss Expert panel (Variation ID 17023; Shen 2019 PMID: 31160754). In summary, this variant meets criteria to be classified as pathogenic for autosomal recessive non-syndromic hearing loss. ACMG/AMP Criteria applied: PP1_Strong, PM3_VeryStrong.

The prevalence of the variant in affected individuals is significantly increased compared to the prevalence in controls.;For recessive disorders, detected in trans with a pathogenic variant.;Co-segregation with disease in multiple affected family members in a gene definitively known to cause the disease.

This is a nonsynonymous variant in the GJB2 gene (OMIM: 121011). Pathogenic variants in this gene have been associated with autosomal recessive hearing loss 1A. This variant has been reported in the homozygous or compound heterozygous state in many unrelated affected individuals (PMID: 31160754) (PM3_Very_Strong) and it segregated with disease in at least 21 individuals from multiple families (PMID: 31160754, 28489599, 24945352, 26088551) (PP1_Strong). This variant is associated with variable expressivity and incomplete penetrance. The penetrance of this variant is estimated to be lower than other pathogenic alleles in the GJB2 gene, with an estimation of less than 20%. Hearing loss, when observed, is usually mild to moderate in severity, bilateral and progresses slowly (PMID: 31160754, 17935238, 24654934). Multiple computational algorithms predict a deleterious effect for this variant (REVEL score: 0.656) (PP3). Other reputable laboratories have reported this variant as pathogenic or likely pathogenic, and this classification has been validated by an expert panel in ClinVar (PP5). This variant has a 4.4881% maximum allele frequency in non-founder control populations (https://gnomad.broadinstitute.org/). Based on the current evidence, this variant is classified as pathogenic for autosomal recessive hearing loss 1A.

The c.109G>A variant in GJB2 is a missense variant predicted to cause substitution of valine to isoleucine at amino acid 37. This variant has been observed in one or more individuals affected with the associated recessive disease, as either homozygous or compound heterozygous with a second variant (PMID: 28489599, 34032567, 16380907, 12081719). Computational prediction algorithms indicate this variant is likely to affect gene or protein function. Given the available evidence, this variant is classified as Pathogenic.

PS4_strong, PP1_strong, PM3_moderate

A homozygous pathogenic variant was detected in the GJB2 gene. The GJB2 c.109G>A p.(Val37Ile) is a missense variant classified as pathogenic for autosomal recessive nonsyndromic genetic hearing loss by the ClinGen Hearing Loss Variant Curation Expert Panel (ClinVar accession: VCV000017023.129). Individuals who are homozygous for GJB2 c.109G>A p.(Val37Ile) typically manifest mild to moderate hearing loss affecting high to mid-sound frequencies (PMID: 31160754).

The variant is observed in the gnomAD v4.1.0 dataset (total allele frequency: 0.252%). Predicted Consequence/Location: Missense variant In silico tool predictions suggest damaging effect of the variant on gene or gene product [REVEL: 0.66 (>=0.6, sensitivity 0.68 and specificity 0.92); 3Cnet: 0.88 (> 0.75, sensitivity 0.96 and precision 0.92)]. The same nucleotide change resulting in the same amino acid change has been previously reported as pathogenic/likely pathogenic with strong evidence (ClinVar ID: VCV000017023 /PMID: 10633133 /3billion dataset). The variant has been observed in multiple (>3) similarly affected unrelated individuals (PMID: 31160754). The variant has been reported to be in trans with a pathogenic variant as either compound heterozygous or homozygous in at least one similarly affected unrelated individual (PMID: 31160754 /3billion dataset). The variant has been reported to co-segregate with the disease in at least 5 similarly affected relatives/individuals in the same family or similarly affected unrelated families (PMID: 12505163, 16300957, 26088551, 27308859, 27623246, 31160754). Different missense changes at the same codon (p.Val37Ala, p.Val37Leu, p.Val37Phe) have been reported as pathogenic/likely pathogenic with strong evidence (ClinVar ID: VCV000179256, VCV000449490 /PMID: 15365987, 17666888, 37108562 /3billion dataset). Therefore, this variant is classified as Pathogenic according to the recommendation of ACMG/AMP guideline.

NM_004004.5(GJB2):c.109G>A(V37I) is classified as pathogenic in the context of GJB2-related DFNB1 nonsyndromic hearing loss and deafness and is typically associated with slowly progressive bilateral mild to moderate hearing loss. Sources cited for classification include the following: PMID 12121355, 16840571, 16300957, 17935238, 10633133 and 15479191. Classification of NM_004004.5(GJB2):c.109G>A(V37I) is based on the following criteria: This is a well-established pathogenic variant in the literature that has been observed more frequently in patients with clinical diagnoses than in healthy populations. Please note: this variant was assessed in the context of healthy population screening.

ACMG classification criteria: PS4 strong, PM3 moderated, PP1 strong

This sequence change is predicted to replace valine with isoleucine at codon 371 of the GJB2 protein, p.(Val37Ile). The valine residue is highly conserved (100 vertebrates, Multiz alignments), and located in the connexin domain. There is a small physicochemical difference between valine and isoleucine. The highest population minor allele frequency in the population database gnomAD v4.0 is 4.5% (2,013/44,852 alleles, 90 homozygotes) in the East Asian population, which is higher than expected for a recessive disease. The prevalence of the variant in individuals with nonsyndromic deafness is significantly increased compared with the prevalence in controls (PMID: 31160754). The variant has been identified as compound heterozygous with a second pathogenic allele in more than a hundred individuals and homozygous in more than a hundred individuals, typically manifesting with mild to moderate hearing loss (PMID: 31160754). The variant segregates in at least 21 affected siblings over multiple families (PMID: 31160754). Additionally, in vitro functional studies of the variant demonstrate impaired function (PMID: 12505163, 16300957, 26088551). Computational evidence predicts a deleterious effect for the missense substitution (REVEL = 0.656). Based on the classification scheme RMH ACMG Guidelines v1.6.1, this variant is classified as PATHOGENIC, with reduced penetrance. Following criteria are met: PP1_Strong, PM3_VeryStrong, PS3_Supporting, PP3, BS1.

Case control studies suggest this variant is associated with hearing loss; homozygous and compound heterozygous genotypes are statistically enriched in individuals with autosomal recessive nonsyndromic hearing loss compared to the general population (PMID: 31160754); Classified as pathogenic by the ClinGen Hearing Loss Expert Panel, and noted to show variable expressivity and incomplete penetrance (PMID: 31160754, 26582918); In silico analysis indicates that this missense variant does not alter protein structure/function; This variant is associated with the following publications: (PMID: 16380907, 15070423, 15479191, 22975760, 22995991, 12792423, 10830906, 19586875, 30473554, 17036313, 25087612, 30609409, 34416374, 30311386, 34943631, 23638949, 24645897, 9529365, 25262649, 17935238, 23873582, 24654934, 12505163, 22613756, 24158611, 22106692, 24212883, 16300957, 19707039, 24945352, 22574200, 23637863, 26088551, 16840571, 17041943, 10633133, 12121355, 22567861, 27623246, 27792752, 19043807, 26885124, 26061099, 27153395, 26896187, 27308839, 26104599, 25388846, 28012523, 28901477, 28786104, 26990548, 26119842, 16952406, 29921236, 29287868, 28489599, 30094485, 30693673, 31195736, 31370293, 30733538, 31180159, 30344259, 30146550, 31914302, 31541171, 31827275, 31980526, 32386258, 30896630, 33724713, 32645618, 30872718, 34062854, 33597575, 33638616, 30828346, 34426522, 34192699, 33096615, 32067424, 33095980, 31078570, 35861108, 37248651, 36190904, 34515852, 37838930, 35853923, 37070846, 35939872, 36597107, 36515421, 34519870, 38069086, 35734583, 36453950, 35982127, 36048236, 37271870, 38254107, 35816303, 35314707, 34403091, 35478332, 36147510, 35611242, 34599368, 35016843, 35114279, 34032567, 31160754, 27535533, 26582918)

This variant is one of the most common variants associated with nonsyndromic hearing loss and is reported to have reduced penetrance in some families (PMID: 31160754, 30311386, 28489599). Therefore, the apparently high frequency of this variant in the general population is consistent with pathogenicity (Genome Aggregation Database (gnomAD), Cambridge, MA (URL: http://gnomad.broadinstitute.org)). This variant has been reported in individuals with autosomal recessive nonsyndromic hearing loss and deafness. Heterozygous individuals with hearing loss have also been reported. Assessment of experimental evidence suggests this variant results in abnormal protein function. (PMID: 12505163, 16300957)

PS4, PM3, PP1_Strong

The c.109G>A (p.Val37Ile) variant affects a highly conserved amino acid and is predicted by multiple in silico tools to have a deleterious effect on protein function. This is a known Pathogenic variant and it has been previously reported as homozygous and compound heterozygous change in individuals with nonsyndromic hearing loss (PMID: 31160754, 9529365, 10982180, 12121355, 16380907, 16840571, 17036313, 17041943, 17935238). Functional studies have shown that this variant may have a damaging effect on intercellular biochemical permeability and conductance of the connexin 26 channel (PMID: 12505163). This variant has been classified as Pathogenic by ClinGen Expert Panel (PMID: 31160754; ClinVar). The c.109G>A (p.Val37Ile) variant is present in the gnomAD v4 population database at a frequency of 0.2% (3869/1613686) in the heterozygous state and reported in 101 individuals in the homozygous state. Based on the available evidence, the c.109G>A (p.Val37Ile) variant is classified as Pathogenic.

Based on ACMG/AMP guidelines and Hearing Loss Expert Panel specific criteria: PS4, PP1_Strong, PM3

The c.109G>A;p.(Val37Ile) missense variant has been observed in affected individual(s) and ClinVar contains an entry for this variant (Clinvar ID: 17023: PMID: 31160754; 23637863; 29926981) - PS4. Well-established in vitro or in vivo functional studies support a damaging effect on the gene or gene product (PMID: 26088551, 12505163, 16300957; 26088551; 31562289) - PS3_moderate. The variant is located in a mutational hot spot and/or critical and well-established functional domain (Connexin) - PM1. The p.(Val37Ile) was detected in trans with a pathogenic variant (PMID: 31160754; 26088551; 24654934; 23637863; 29926981) - PM3_very strong Pathogenic missense variant in this residue have been reported (Clinvar ID: 179256; 449490) - PM5. The variant co-segregated with disease in multiple affected family members (PMID: 31160754; 26088551; 23637863) - PP1_strong. Multiple lines of computational evidence support a deleterious effect on the gene or gene product - PP3. and allele frequency is greater than expected for disorder -BS1. In summary, the currently available evidence indicates that the variant is pathogenic.

Criteria applied: PS3_MOD,PM3_VSTR,PM5_STRPP1_VSTR,PP3

The c.109G>A (p.V37I) alteration is located in coding exon 1 of the GJB2 gene. This alteration results from a G to A substitution at nucleotide position 109, causing the valine (V) at amino acid position 37 to be replaced by an isoleucine (I). for autosomal recessive GJB2-related nonsyndromic hearing loss; however, it is unlikely to be causative of autosomal dominant GJB2-related nonsyndromic hearing loss or autosomal dominant GJB2-related syndromic hearing loss with ectodermal involvement. Based on data from gnomAD, the A allele has an overall frequency of 0.756% (2132/282164) total alleles studied. The highest observed frequency was 8.345% (1665/19952) of East Asian alleles. This alteration has been more commonly reported in individuals of Asian ancestry (both affected and controls) (Huculak, 2006; Tang, 2006; Li, 2012). Although rare, homozygous and compound heterozygous observations have been identified in individuals with normal hearing; however presentation is typically associated with childhood onset bilateral sensorineural hearing loss (Shen, 2019; Tang, 2006). A more recent study has reported the p.V37I variant as pathogenic with variable expressivity and incomplete penetrance with progressive hearing loss over time when detected in homozygous or compound heterozygous forms (Chen, 2020). This variant has been detected as a homozygous finding in multiple families with sensorineural hearing loss (Ambry internal data). This amino acid position is highly conserved in available vertebrate species. Functional studies demonstrate an inability to induce formation of homotypic gap-junction channels, leading to a complete loss of channel activity (Bruzzone, 2003). However, large cohort studies have reported that hearing loss is typically in the mild to moderate range suggesting that the phenotypic presentation may not reflect the functional data (Snoeckx, 2005; Huculak, 2006). The in silico prediction for this alteration is inconclusive. Based on the available evidence, this alteration is classified as pathogenic.

NM_004004.6(GJB2):c.109G>A is a missense mutation predicted to affect gene function. Literature reports indicate that the frequency of this variant is significantly higher in the affected population compared to the control population (OR=20) [PMID: 31160754] (PS4); literature reports demonstrate co-segregation of this variant with the disease in multiple affected family members [PMID: 31160754] (PP1_Strong); literature reports have detected homozygous variants at this locus in multiple patients [PMID: 31160754] (PM3); the frequencies of this variant in the 1000 Genomes Project (1000G), the China Genome Database, the Exome Aggregation Consortium (ExAC), and the Genome Aggregation Database (gnomAD) are 0.0153754, 0.03411398, 0.00658697444352844, and 0.0706543, respectively; this known variant is classified as Pathogenic (P) in the ClinVar database and as DM in the HGMD database [PMID: 10633133; 10830906; 12121355; 12505163; 12792423]. In summary, based on the ACMG Guidelines, 2015 (PMID: 25741868), the above evidence supports this variant as Pathogenic for autosomal dominant 3A, classified as PS4, PP1_Strong, and PM3.

The GJB2 c.109G>A; p.Val37Ile variant (rs72474224) is reported in the literature in multiple individuals affected with hearing loss (Baux 2017, Kecskemeti 2018, Posukh 2019, Putcha 2007, Zhou 2019). However, homozygosity for p.Val37Ile has been associated with normal hearing (Tang 2006) as well as with slight, mild or moderate hearing loss, primarily in individuals of Asian background (Bason 2002, Dahl 2006, Kim 2015, Kim 2013, Pollak 2007, Rabionet 2000). The p.Val37Ile variant is reported as pathogenic by several laboratories in ClinVar (Variation ID: 17023) and has been shown to disrupt protein function using a Xenopus oocyte-based gap junction formation assay (Bruzzone 2003) and a gap junction permeability assay in HEK293 cells (Kim 2015). This variant is found predominantly in the East Asian population with an allele frequency of 8.3% (1665/19952 alleles, including 96 homozygotes) in the Genome Aggregation Database (v2.1.1). Additionally, other variants at this codon (c.110T>C; p.Val37Ala and c.109G>C; p.Val37Leu) have been reported in individuals with sensorineural hearing loss (Azaiez 2004, Putcha 2007). Based on available information, this variant is considered to be mildly pathogenic. References: Azaiez H et al. GJB2: the spectrum of deafness-causing allele variants and their phenotype. Hum Mutat. 2004 24:305-311. PMID: 15365987. Bason L et al. Homozygosity for the V37I Connexin 26 mutation in three unrelated children with sensorineural hearing loss. Clin Genet. 2002 61:459-464. PMID: 12121355. Baux D et al. Combined genetic approaches yield a 48% diagnostic rate in a large cohort of French hearing-impaired patients. Sci Rep. 2017 7:16783. PMID: 29196752. Bruzzone R et al. Loss-of-function and residual channel activity of connexin26 mutations associated with non-syndromic deafness. FEBS Lett. 2003 533:79-88. PMID: 12505163. Dahl HH et al. The contribution of GJB2 mutations to slight or mild hearing loss in Australian elementary school children. J Med Genet. 2006 43:850-855. PMID: 16840571. Kecskemeti N et al. Analysis of GJB2 mutations and the clinical manifestation in a large Hungarian cohort. Eur Arch Otorhinolaryngol. 2018 275:2441-2448. PMID: 30094485. Kim J et al. Non-syndromic hearing loss caused by the dominant cis mutation R75Q with the recessive mutation V37I of the GJB2 (Connexin 26) gene. Exp Mol Med. 2015 47:e169. PMID: 26088551. Kim SY et al. Prevalence of p.V37I variant of GJB2 in mild or moderate hearing loss in a pediatric population and the interpretation of its pathogenicity. PLoS One. 2013 8:e61592. PMID: 23637863. Pollak A et al. M34T and V37I mutations in GJB2 associated hearing impairment: evidence for pathogenicity and reduced penetrance. Am J Med Genet A. 2007 143A:2534-2543. PMID: 17935238. Posukh OL et al. Unique Mutational Spectrum of the GJB2 Gene and its Pathogenic Contribution to Deafness in Tuvinians (Southern Siberia, Russia): A High Prevalence of Rare Variant c.516G>C (p.Trp172Cys). Genes (Basel). 2019 Jun 5;10(6):429. PMID: 31195736. Putcha GV et al. A multicenter study of the frequency and distribution of GJB2 and GJB6 mutations in a large North American cohort. Genet Med. 2007 9:413-426. PMID: 17666888. Rabionet R et al. Molecular basis of childhood deafness resulting from mutations in the GJB2 (connexin 26) gene. Hum Genet. 2000 106:40-44. PMID: 10982180. Tang HY et al. DNA sequence analysis of GJB2, encoding connexin 26: observations from a population of hearing impaired cases and variable carrier rates, complex genotypes, and ethnic stratification of alleles among controls. Am J Med Genet A. 2006 140:2401-2415. PMID: 17041943. Zhou Y et al. Mutation analysis of common deafness genes among 1,201 patients with non-syndromic hearing loss in Shanxi Province. Mol Genet Genomic Med. 2019 7:e537. PMID: 30693673.

The GJB2 c.109G>A (p.Val37Ile) variant is classified as Pathogenic for autosomal recessive nonsyndromic hearing loss(Accession:VCV000017023.156). According to the ClinGen Hearing Loss Expert Panel, this variant meets criteria PS4, PP1_Strong, and PM3 (Shen 2019). It is the most prevalent GJB2 variant in the Chinese population, with an overall carrier rate of 11.6% and significant regional variation (higher in southern China) (Zhang 2025). In our cohort from Hainan (Li ethnic group), individuals with biallelic genotypes have confirmed hearing loss during clinical follow-up, predominantly presenting with mild-to-moderate, symmetric, high-frequency sloping hearing loss, consistent with recent pediatric studies (Zheng 2025). Heterozygous carriers are asymptomatic, supporting autosomal recessive inheritance. Functional studies and a knock-in mouse model have demonstrated that this variant impacts protein function and exhibits age-related penetrance (Chen 2016, Bruzzone 2003).

This sequence change replaces valine, which is neutral and non-polar, with isoleucine, which is neutral and non-polar, at codon 37 of the GJB2 protein (p.Val37Ile). This variant is present in population databases (rs72474224, gnomAD 8%), and has an allele count higher than expected for a pathogenic variant. This variant has been reported in the literature in a large meta-analysis involving several thousand cases and controls (PMID: 28489599). This variant has been reported frequently in individuals affected with mild to moderate deafness particularly among populations in eastern Asia (PMID: 23637863, 26885124, 26061099, 17036313, 16952406, 21488715). It has been shown to segregate with autosomal recessive deafness in families (PMID: 28489599, 24945352, 26088551). Although this variant is more common in the population than expected for a pathogenic variant, the penetrance of this variant is estimated to be less than 20% of other disease-causing variants in GJB2 (PMID: 17935238, 24654934). ClinVar contains an entry for this variant (Variation ID: 17023). Invitae Evidence Modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) has been performed for this missense variant. However, the output from this modeling did not meet the statistical confidence thresholds required to predict the impact of this variant on GJB2 protein function. Experimental studies have shown that this missense change disrupts the formation of homotypic junctional channels in vitro (PMID: 12505163). Furthermore in vivo knock-in and knock-out mouse models recapitulate the deafness phenotype observed in humans (PMID: 27623246). In summary, this variant is reported to cause sensorineural deafness. However, as this variant is associated with a lower penetrance than other pathogenic alleles in the GJB2 gene, it has been classified as Pathogenic (low penetrance).

As part of Carrier Screening testing performed at First Genomix, this variant was identified in a heterozygous state in a patient who is not affected with this condition.

This patient is a carrier of a heterozygous pathogenic variant in the GJB2 gene associated with autosomal recessive deafness 1A. The GJB2 variant (c.109G>A; p.V37I) identified in this patient is a missense variant reported to be a common pathogenic variant in individuals with Asian ancestry and is associated with mild to moderate, sometimes progressive hearing impairment in individuals with various ages. (Gallant et al. 2013, PMID: 23873582; Huculak et al. 2006, PMID: 17036313; Bruzzone et al. 2003, PMID: 12505163; Li et al. 2012, PMID: 22574200)

The GJB2 c.109G>A variant is predicted to result in the amino acid substitution p.Val37Ile. This variant in the homozygous state has been reported to be strongly associated with both mild-to-moderate (P=2.0×10-11) and severe-to-profound (P=0.001) hearing impairment, but was estimated to have a low penetrance (17%). Onset of hearing loss was 65% congenital and 35% delayed in individuals that were homozygous for c.109G>A (Chai et al. 2015. PubMed ID: 24654934). This variant has also been reported to cause nonsyndromic hearing loss in the compound heterozygous state with a second disease causing GJB2 variant (Abe et al. 2000. PubMed ID: 10633133). The c.109G>A variant has been reported at a subpopulation frequency of up to 8.2% in a database of individuals with unknown phenotype, which is unusually high for a pathogenic variant. However, a ClinGen Hearing Loss expert panel has classified this variant as pathogenic for autosomal recessive nonsyndromic hearing loss, noting hearing loss is typically mild with incomplete and possibly age-related penetrance (https://www.ncbi.nlm.nih.gov/clinvar/variation/17023/; Shen et al. 2019. PubMed ID: 31160754). This variant is interpreted as pathogenic.