A twin-study of genetic contributions to hearing acuity in late middle age

Background. Declines in hearing acuity, especially in the high frequency range, often appear in middle age. The objective of this study was to characterize genetic and environmental influences that may underlie this pattern. Methods. One hundred seventy-nine monozygotic and 150 dizygotic twin pairs, ranging in age from 52 to 60 years, were selected from the Vietnam Era Twin Registry and individually tested for hearing acuity in the frequency range from 500 to 8000 Hz. Biometrical modeling was used to quantify genetic and environmental influences. Results. For individuals' better ears, approximately two-thirds (65%-70%, 95% confidence interval [CI], 46%-75%) of the variance in hearing acuity in the middle and high frequency ranges could be accounted for by genetic factors. For the individuals' poorer ear, which would be expected to show lower heritability, approximately one-half (41%-54%, 95% CI, 11%-67%) of the variance in the middle and high frequency ranges could be accounted for by genetic influences. Within a given frequency range, the same genetic factors influenced both the better and poorer ears. In contrast, although there was some overlap of genetic influences on the middle and high frequencies within a given ear, there were also some genetic influences that were specific to each frequency. Conclusions. Results suggest that genetic effects play an important role in the level of hearing loss that often appears in late middle age. These data have important implications for identifying persons who may be especially vulnerable to environmental risk factors such as noise exposure and medications with ototoxic properties.