| The influence of insulin-like growth factor-2 (IGF2) genotype on total body fat-free mass (FFM), muscle strength, and sustained power (SP) was evaluated repeatedly at approximately 2-year intervals across the adult age span in two cohorts from the Baltimore Longitudinal Study of Aging (BLSA). The first cohort consisted of 94 men who were tested for isometric grip strength and SP between 1960--1985 (cohort 1). The second cohort consisted of 246 men and 239 women who were tested for total body FFM and isokinetic peak torque between 1992--2002 (cohort 2). An average of 5.3 +/- 2.5 (range 2--10) and 1.9 +/- 0.8 (range 1--5) of follow-up tests per subject were performed in cohort 1 and 2, respectively. Subjects were retrospectively genotyped for the IGF2 gene's ApaI polymorphism. Each gender group was analyzed separately. Differences between genotype groups for total FFM, strength, and SP at first visit, at peak age (35 yr), at age 65, and across the adult age span were analyzed using either two-sample t-tests or mixed effects models, depending on the specific comparisons made and the cohort used for the analysis. Due to imprinting of the IGF2 gene, only A/A (cohort 1, n = 13; cohort 2, n = 57) and G/G (cohort 1, n = 49; cohort 2, n = 338) subjects were analyzed. Isokinetic arm strength (arm PTCon) at time of first visit was lower in A/A men than in G/G men (P < 0.05). Compared to G/G women, A/A women had lower total body FFM, lower isokinetic arm (PTCon and PTEcc) and leg (PTCon) strength than G/G women at the time of first visit, and lower model-predicted mean values at age 35 (all P < 0.05) for these muscle phenotypes. Furthermore, this difference between the genotype groups was maintained for model-predicted age-65 values and across the adult age span (P < 0.05). No genotype-associated differences in rates of loss of isometric grip strength and SP were found. These results support the hypothesis that variation within a gene known to influence developing muscle (IGF2) may also affect muscle mass and muscle function in later life. |
