Genetic determinants of plasma ACE and renin activity in young normotensive twins.

OBJECTIVE: We investigated the determinants of plasma renin activity (PRA) and plasma levels of angiotensin-converting enzyme (pACE), including the effect of the D/I polymorphism of the angiotensin-converting enzyme (ACE) gene, in monozygotic (MZ) and dizygotic (DZ) twins. METHODS: Sixty-nine pairs of twins underwent measurements of blood pressure, pACE and ACE D/I genotyping. In addition, in 30 pairs ambulatory blood pressure (ABP) monitoring was carried out. To ascertain twin's zygosity, some highly discriminating variable number of tandem repeats micro- and mini-satellite systems were analysed by polymerase chain reaction (PCR) followed by polyacrylamide gel electrophoresis and silver staining. The D/I polymorphism was assessed by PCR; pACE was measured in triplicate with a colorimetric assay, and PRA by a commercial kit. In DZ twins, identity by descent of the D/I alleles was examined by PCR amplification of a highly polymorphic simple sequence repeat at the human growth hormone gene. RESULTS: pACE levels were significantly (P < 0.01) higher in DD (9.27 +/- 2.60 IU/l, mean +/-SD) than in II (6.68 +/- 3.0), with DI having intermediate levels (7.93 +/- 2.7). No difference of PRA between different D/I genotypes was found. Twin data analysis showed a statistically significant heritability of pACE, but not of PRA. No differences between MZ and DZ twins in PRA, pACE and the relationship of the D/I genotype with pACE was found. Besides showing that the D/I genotype was the most important predictor of pACE, a multivariate analysis demonstrated that identity by descent of the D/I allele, as assessed by growth hormone (GH) genotyping, also significantly affected pACE. CONCLUSIONS: In this study of normotensive twins, pACE and not PRA showed significant heritability, the former being tightly associated with the D/I ACE gene polymorphism, and/or with a quantitative trait locus in linkage disequilibrium with it.

Heritability of plasma leptin levels: a twin study.

OBJECTIVE: To examine the influence of genetic factors on plasma leptin levels. SUBJECTS AND METHODS: 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. RESULTS: 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%. CONCLUSIONS: 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.

No effect of genetic variation at the angiotensinogen locus on ambulatory blood pressure level in normotensive subjects.

The aim of the study was to evaluate the potential association between ambulatory blood pressure and the molecular variants T174M and M235T of the angiotensinogen gene in a random sample of young normotensive men (n = 145). The two point mutations were detected using restriction digests of a mispairing polymerase chain reaction product. Twenty-four-hour ambulatory blood pressure monitoring was performed with a SpaceLabs 90207 device. Ambulatory blood pressure levels did not vary according to T174M and M235T genotypes. When the subjects were grouped according to their blood pressure level (as indicated by tertiles of their 24-h ambulatory blood pressure), no significant differences in allele frequencies between the three groups were found. Our results indicate that the T174M and M235T molecular variants of the angiotensinogen gene have no major influence on ambulatory blood pressure in young normotensive subjects.

Genetic influences on insulinemia in normotensive twins.

The aim of this study was to establish the contribution of genetic factors to the variance of plasma insulin concentration in healthy, normotensive twins. Seventeen pairs of monozygotic (MZ) and 17 pairs of dizygotic (DZ) twins were investigated. The test of genetic variance revealed a significantly larger within-pair variance of fasting plasma insulin (FPI) and a relative insulin resistance (RIR) in the DZ twins, in comparison with the MZ twins. Both FPI and RIR had a higher intraclass correlation coefficient in the MZ twins than in the DZ twins; the corresponding heritability estimates were 0.54 for FPI and 0.66 for RIR. Adjusting for age, gender, and body mass index did not affect heritability 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.