Heritability of leptin levels and the shared genetic effects on body mass index and leptin in adult Finnish twins

OBJECTIVES: Leptin is involved in the regulation of body weight, but the relative role of genetic and environmental influences on inter-individual variation in leptin levels is unknown. DESIGN AND SUBJECTS: To investigate the genetic and environmental contributions to the association of body mass index (BMI) with serum leptin levels, 58 monozygotic (MZ, 27M, 31F), and 74 like-sexed dizygotic (DZ, 32M, 42F) Finnish twin pairs aged 50 - 76 y were studied. MEASUREMENTS: Serum leptin levels, weight, height, hip and waist measurements. RESULTS: Women had higher mean leptin levels (16.8 +/- 9.5 ng/ml), and more overall variability in leptin levels than men (6.4 +/- 3.5 ng/ml; P < 0.0001). Leptin levels correlated highly with BMI in men and women. Among women, the MZ and DZ pairwise correlations for leptin were 0.41 (P = 0.009) and 0.07 (P = 0.32), respectively. Among men the MZ and DZ pairwise correlations for leptin were 0.47 (P = 0.006) and 0.23 (P = 0.10). Univariate twin analysis indicated that, among women, 34% and, among men, 45% of the variance in leptin can be attributed to additive genetic effects, and the remainder to unique environmental effects. Significant non-additive genetic or shared familial effects could not be demonstrated. A bivariate twin analysis of leptin and BMI indicated that the correlation between additive genetic effects on leptin and BMI was 0.79 (95% CI 0.68 - 0.86) in women, and 0.68 (0.51 - 0.80) in men. The correlation between environmental effects on leptin and BMI was 0.77 (95% CI 0.66 - 0.85) in women, and 0.48 (0.26 - 0.66) in men. CONCLUSION: Leptin levels are moderately heritable in older adults, and a substantial proportion of genetic effects are in common on leptin levels and obesity in both women and men.