The aim of this study was to establish the contribution of genetic fac
tors to the variance of plasma insulin concentration in healthy, normo
tensive twins. Seventeen pairs of monozygotic (MZ) and 17 pairs of diz
ygotic (DZ) twins were investigated. The test of genetic variance reve
aled a significantly larger within-pair variance of fasting plasma ins
ulin (FPI) and a relative insulin resistance (RIR) in the DZ twins, in
comparison with the MZ twins. Both FPI and RIR had a higher intraclas
s correlation coefficient in the MZ twins than in the DZ twins; the co
rresponding heritability estimates were 0.54 for FPI and 0.66 for RIR.
Adjusting for age, gender, and body mass index did not affect heritab
ility estimates for either FPI or RIR. Our data indicate that genetic
factors are important determinants of insulinemia in normal subjects,
independent of body mass index. (C) 1997 American Journal of Hypertens
ion, Ltd.