[Audiological characterization of the GJB2 gene c.109G>A (p.V37I) hotspot variant during childhood and comparison between family members].

OBJECTIVE

To determine the prevalence of GJB2 gene c.109G>A (p.V37I) variant among infants with congenital hearing loss and analyze the initial audiological characteristics of children harboring the variant, compare the audiometric difference among individuals with various genotypes, and explore genetic and audiological manifestations of the affected families.

METHODS

One hundred twenty six infants diagnosed with congenital hearing loss at the Neonate Screening Center of Ningbo City from June 2021 to December 2024 were selected as the study subjects. The neonates, in addition with members from 16 of their families, had undergone genetic screening for variants of 208 hotspot sites within 24 deafness-associated genes. For cases identified with monoallelic variants and concurrent hearing loss, the full GJB2 gene was sequenced. Meanwhile, a retrospective analysis was carried out on 23 children whom were confirmed to have hearing loss and the c.109G>A variant by whole exome sequencing from March 2022 to December 2024. And 102 children who were excluded to have hearing loss and pathogenic variants by whole exome sequencing were selected as normal controls. Audiological features of individuals harboring the c.109G>A variant were compared. This study has been approved by the Medical Ethics Committee of The Affiliated Women and Children's Hospital of Ningbo University (Ethics No.: EC2023-009).

RESULTS

For the 126 infants with congenital hearing loss, prospective screening has identified 58 (46.03%) to harbor the c.109G>A variant. These included 38 homozygotes and 16 compound heterozygotes. Retrospective review of the 23 c.109G>A positive children has identified 15 as homozygotes and 8 as compound heterozygotes. Genetic testing of the 16 pedigrees has identified 7 homozygotes and 1 compound heterozygote. For the homozygotes combined (n = 53), 96.2% exhibited bilateral symmetric hearing loss, with 78.3% showing high-frequency sloping patterns, and 98.1% having a hearing threshold ranging from 20 to 65 dB. For the compound heterozygotes combined (n = 24), 95.8% showed symmetric loss, with 59.4% having high-frequency sloping, and 97.9% had a hearing threshold ranging from 20 to 65 dB. Both groups showed significantly elevated ABR/PTA thresholds compared with the normal controls (P = 0.000). The compound heterozygous group had higher ABR thresholds (43.3 ± 15.0 dB nHL) compared with the homozygous group (39.1 ± 12.0 dB nHL, P = 0.005).

CONCLUSION

Infants harboring the GJB2 c.109G>A variant primarily manifest as mild-to-moderate, symmetric, high-frequency sloping hearing loss. Nearly one-third of affected children have thresholds between 20 to 35 dB nHL, suggesting that ABR > 35 dB nHL alone may underestimate the hearing impairment in this population. Compared with homozygotes, compound heterozygotes with the the GJB2 c.109G>A variant can confer a more severe hearing loss.