Heritability of impaired balance: a nationwide cohort study in twins.

SUMMARY: In this large population-based twin study, a self-estimated impaired balance, an important risk factor for osteoporotic fractures, had a modest heritability of 0.27. Individual-specific environmental influences seem to be the dominating cause for impaired balance.
INTRODUCTION: The principal causal components of an osteoporotic fracture are falls and weakened bone strength. While bone strength has a strong genetic origin, the heritable influences on impaired balance that contribute to the risk of injurious falls at older age are uncertain.
METHODS: To evaluate the heritability and environmental influence on self-reported impaired balance in older men and women, we used data from a sample of 22,998 Swedish twins, 55 to 99 years of age.
RESULTS: An impaired balance was reported by 2,890 (12.3%) of the twins. The tetrachoric correlation for impaired balance was only slightly lower for like-sex dizygotic twins (0.31) compared to monozygotic twins (0.36). These correlations indicate a modest familial (genetic and shared environmental) influence. Model fitting results indicate that the age- and sex-adjusted heritability for impaired balance was 0.27 (95%CI = 0.01-0.45). Individual-specific environmental influences differed only slightly by sex and age.
CONCLUSION: These results imply that a self-reported impaired balance, an independent risk factor for osteoporotic fractures, has a modestly heritable etiology in older subjects. Our observation can partly explain the previously observed modest heritability for osteoporotic fractures even though there is a high heritability for bone mineral density.