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Genetic and environmental influences on self-reported reduced hearing in the old and oldest old
K Christensen1, H Frederiksen, H J Hoffman
1Danish Twin Registry, Institute of Public Health, and the Danish Center for Demographic Research, Odense.
Objectives:
The aim of the present twin study was to estimate the relative importance of genetic and environmental factors in variation in self-reported reduced hearing among the old and the oldest old.
Design:
Self-reported hearing abilities of older twins assessed at intake interview in a population-based longitudinal survey.
Setting:
Denmark.
Participants:
Twins age 75 and older identified in the population-based Danish Twin Registry in 1995. An interview was conducted with 77% of 3,099 individuals in the study population. In 1997 and 1999, a follow-up contact to the survivors was made and an additional 2,778 twins, age 70-76, were included in the study.
Measurements:
Reduced hearing was assessed by the same question in all interview waves. Heritability (proportion of the population variance attributable to genetic variation) was estimated using structural-equation analyses.
Results:
The prevalence of self-reported reduced hearing corresponded to previous studies and showed the expected age and sex dependence. Concordance rates, odds ratios, and correlations were consistently higher for monozygotic twin pairs than for dizygotic twin pairs in all age and sex categories, indicating heritable effects. Structural-equation analyses revealed a substantial heritability for self-reported reduced hearing of 40% (95% CI = 19-53%). The remaining variation could be attributed to individuals' nonfamilial environments.
Conclusion:
We found that genetic factors play an important role in self-reported reduced hearing in both men and women age 70 and older. Because self-reports of reduced hearing involve misclassification, this estimate of the genetic influence on hearing disabilities is probably conservative. Hence, genetic and environmental factors play a substantial role in reduced hearing among the old and oldest old. This suggests that clinical epidemiological studies of age-related hearing loss should include not only information on environmental exposures but also on family history of hearing loss and, if possible, biological samples for future studies of candidate genes for hearing loss.