Prevalence and audiological features in carriers of GJB2 mutations, c.35delG and c.101T>C (p.M34T), in a UK population study

Objectives To determine the carrier rate of the GJB2 mutation c.35delG and c.101T>C in a UK population study; to determine whether carriers of the mutation had worse hearing or otoacoustic emissions compared to non-carriers. Design Prospective cohort study. Setting University of Bristol, UK. Participants Children in the Avon Longitudinal Study of Parents and Children. 9202 were successfully genotyped for the c.35delG mutation and c.101>T and classified as either carriers or non-carriers. Outcome measures Hearing thresholds at age 7, 9 and 11？years and otoacoustic emissions at age 9 and 11. Results The carrier frequency of the c.35delG mutation was 1.36% (95% CI 1.13 to 1.62) and c.101T>C was 2.69% (95% CI 2.37 to 3.05). Carriers of c.35delG and c.101T>C had worse hearing than non-carriers at the extra-high frequency of 16？kHz. The mean difference in hearing at age 7 for the c.35delG mutation was 8.53？dB (95% CI 2.99, 14.07) and 12.57？dB at age 9 (95% CI 8.10, 17.04). The mean difference for c.101T>C at age 7 was 3.25？dB (95% CI ？0.25 to 6.75) and 7.61？dB (95% CI 4.26 to 10.96) at age 9. Otoacoustic emissions were smaller in the c.35delG mutation carrier group: at 4？kHz the mean difference was ？4.95？dB (95% CI ？6.70 to ？3.21) at age 9 and ？3.94？dB (95% CI ？5.78 to ？2.10) at age 11. There was weak evidence for differences in otoacoustic emissions amplitude for c.101T>C carriers. Conclusion Carriers of the c.35delG mutation and c.101T>C have worse extra-high-frequency hearing than non-carriers. This may be a predictor for changes in lower-frequency hearing in adulthood. The milder effects observed in carriers of c.101T>C are in keeping with its classification as a mutation causing mild/moderate hearing loss in homozygosity or compound heterozygosity