Heritability of plasma leptin levels: a twin study.

To examine the influence of genetic factors on plasma leptin levels. We measured plasma leptin levels, body mass index and body fat distribution in healthy young female monozygotic (n = 19) and dizygotic (n = 14) twins. The twin zygosity was verified by determination of short tandem repeat and amplified fragment length polymorphism systems. The genetic analysis included analysis of variance-based and maximum likelihood-based methods. Plasma leptin levels were correlated significantly with body mass index (r = 0.59, P < 0.001), waist circumference (r = 0.54, P < 0.001) and hip circumference (r = 0.63, P < 0.001), but not with age (r = -0.17) or the waist:hip ratio (r = 0.02). The heritability estimates derived from intraclass correlations were significant for body mass index (P = 0.001), waist circumference (P = 0.004), hip circumference (P = 0.01) and plasma leptin levels (P = 0.005), but not for the waist:hip ratio (P = 0.22). In the maximum likelihood-based path analysis, heritability was estimated at 79% for body mass index and at 73% for plasma leptin levels. After adjustment for body mass index, the heritability estimate for leptin levels from the model-fitting approach was 55%. Genetic factors are major determinants of plasma leptin levels in humans and may account for as much as half of the variance in leptin levels.