American Journal of Epidemiology Vol. 155, No. 2 : 132-139
Copyright © 2002 by The Johns Hopkins University School of Hygiene and Public Health
ORIGINAL CONTRIBUTIONS |
Genetic Contribution to Rate of Change in Functional Abilities among Danish Twins Aged 75 Years or More
1 Danish Twin Registry, Institute of Public Health, University of Southern Denmark, DK-5000 Odense, Denmark.
2 Danish Center for Demographic Research, Odense University, DK-5000 Odense, Denmark.
3 Max Planck Institute for Demographic Research, Rostock D-18057, Germany.
4 Department of Psychology, University of Minnesota, Minneapolis, MN.
In a previous cross-sectional study of twins, the authors found evidence of a substantial genetic influence on functional abilities among elderly women. It has been suggested that rate of change in functional abilities over time could underlie such findings and that rate-of-change phenotypes may have an even larger genetic component than "level" phenotypes (e.g., functional abilities per se). If so, rate-of-change phenotypes could be more powerful than level phenotypes in studies aimed at identifying specific polymorphisms of importance for aging. In 1995, the authors assessed a population-based sample of 2,401 Danish twins aged 75 years or more. The survivors were recontacted after 2 years and again after 4 years. Consistent mean-level declines, high within-person correlations over time, and substantial heritability in the female sample were observed for functional abilities. Nonetheless, structural-equation analyses revealed only a very modest and nonsignificant heritability for rate of change in functional abilities: 16% (95% confidence interval: 0, 35) for women and 9% (95% confidence interval: 0, 44) for men. This study had a large initial sample size, high participation rates, and a valid and reliable measure of rate of change in a phenotype that had previously shown substantial heritability in cross-sectional analyses in the same twin population. Still, the present study revealed only a modest and nonsignificant genetic influence on rate of change, which suggests that detection of polymorphisms influencing rate of change in functional abilities among the elderly may prove to be difficult.
activities of daily living; aging; genetics; twin studies; twins; variation (genetics)
Abbreviations: LSADT, Longitudinal Study of Aging Danish Twins
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