Objective: To study the contribution of genes and environment to the variation of insulin sensitivity, and the effect of body mass index (BMI), age and sex.
Methods: A total of 296 healthy same-sex twin pairs were studied, including 223 monozygotic (MZ) and 73 dizygotic (DZ) twin pairs aged 5-18(mean age, 12+/-4 years). Microsatellite polymorphism (STR) was used to diagnose zygosity of twins. Model-fitting method using Mx package was performed to analyze the genetic and environmental variance of homeostasis model assessment insulin resistance index (HOMA IR) and HOMA beta cell function index (HBCI), before and after adjusting BMI. The effect of age and sex on the model was tested.
Results: HOMA IR was correlated with age, sex and BMI, while HBCI was correlated with age. Genetic analysis showed in ACE model, heritability of HOMA IR in boys and girls was different before and after BMI adjustment; heritability of HBCI was not different significantly. Heritability of HOMA IR and HBCI were 0.25, 0.24, respectively, after adjusting BMI.
Conclusion: Gene and environment influence insulin sensitivity of children and adolescents together, whereas environment seems to play a more important role. The effect of BMI on estimating heritability of insulin sensitivity is considerable, differing from sex or age.