Mitochondrial DNA haplogroups and age-related hearing loss

Objective: To determine whether variants of the mitochondrial genome influence the risk of developing age-related hearing loss (ARHL). Design: Cross-sectional study. Setting: Eligible participants were noninstitutionalized permanent residents 49 years or older identified in a door-to-door census of 2 suburban postcode areas, west of Sydney, Australia. Participants: The Blue Mountains Hearing Study (BMHS) was a population-based survey of hearing loss, conducted during 1997 to 1999, among the participants of the Blue Mountains Eye Study cohort. Main Outcome Measures: We defined hearing impairment as the pure-tone average of audiometric hearing thresholds at 500, 1000, 2000, and 4000 Hz (> 25-but <= 40-dB hearing level [HL] [mild hearing loss], > 40- but <= 60-dB HL [moderate hearing loss], or > 60-dB HL [severe hearing loss]) in the better of the 2 ears. Results: Of the 2765 BMHS participants, 912 (33%) were found to have ARHL. After adjusting for other hearing loss risk factors, mitochondrial DNA (mtDNA) haplogroups U and K were independently associated with a higher prevalence of ARHL compared with subjects with other haplogroups. Haplogroup U was significantly associated with moderate to severe ARHL (multivariable-adjusted odds ratio, 1.63; 95% confidence interval, 1.10-2.41). Haplogroup K was associated with severity types of ARHL in persons aged 50 to 59 years (odds ratio, 3.02; 95% confidence interval, 1.30-6.99). There was also a joint effect between mtDNA haplogroups U and K and other known hearing loss risk factors such as diabetes and past noise exposure. Conclusion: Findings from this older Australian population demonstrate an association between certain mtDNA haplogroups and ARHL, as well as a link to the susceptibility of other known risk factors for ARHL.