Genetics or environment? Type A behavior and cardiovascular risk factors in twin children

The heritability of Type A behavior and other cardiovascular risk factors was investigated in twin school-age children. The purpose was to differentiate those risk factors that have the potential to respond to environmental and life-style changes. The sample consisted of 71 monozygotic and 34 same-sex, dizygotic twin pairs 6 to 11 years old residing in the Philadelphia metropolitan area. Systolic and diastolic blood pressure, triceps skinfold thickness, body mass, and fasting blood specimens for lipid profiles were collected during home visits. Teachers rated the children's Type A behavior and two of its subcomponents, impatience-aggression and competitive achievement-striving, using the Matthews Youth Test for Health. Statistically significant heritability estimates were found for Type A behavior and its subcomponents, triglycerides, systolic blood pressure, and body mass. Nevertheless, there was substantial environmental influence on these risk factors. The greatest environmental influence was observed for HDL-cholesterol, LDL-cholesterol, apolipoprotein-B and diastolic blood pressure.