Association of the ACTN3 genotype and physical functioning with age in older adults

Objective. The purpose of this study was to examine the association of the alpha-actinin-3 (ACTN3) R577X polymorphism on muscle function and physical performance in older adults. Methods. We measured knee extensor torque, midthigh muscle cross-sectional area, muscle quality, short physical performance battery score, and 400-meter walk time at baseline and after 5 years in white older adults aged 70-79 years in the Health, Aging and Body Composition Study cohort (n = 1367). Incident persistent lower extremity limitation (PLL) over 5 years was additionally assessed. We also examined white men in the Osteoporotic Fractures in Men Study, a longitudinal, observational cohort (n = 1152) of men 65 years old or older as a validation cohort for certain phenotypes. Results. There were no significant differences between genotype groups in men or women for adjusted baseline phenotypes. Male X-homozygotes had a significantly greater adjusted 5-year increase in their 400-meter walk time compared to R-homozygotes and heterozygotes (p = .03). In women, X-homozygotes had a ~35% greater risk of incident PLL compared to R-homozygotes (hazard ratio = 0.65, 95% confidence interval = 0.44-0.94). There were no other significant associations between any of the phenotypes and ACTN3 genotype with aging in either cohort. Conclusions. The ACTN3 polymorphism may influence declines in certain measures of physical performance with aging in older white adults, based on longitudinal assessments. However, the influence of the ACTN3 R577X polymorphism does not appear to have a strong effect on skeletal muscle-related phenotypes based on the strength and consistency of the associations and lack of replication with regard to specific phenotypes. Key Words: Genetics--Elderly--Sarcopenia--Skeletal muscle.