The National Heart and Lung Institute twin study of cardiovascular disease risk factors: Organization and methodology

The National Heart and Lung Institute undertook a twin study on the etiology of coronary heart disease and genetic relations underlying differential levels of coronary risk. Between 1969 and 1974, 250 MZ and 264 DZ male twin pairs aged 42-56 were examined. The examination featured a medical and family history, a dietary interview, ECG, blood pressure, weight and height measurement, a variety of blood chemistry tests, including complete lipoprotein analyses, and lung function tests. Zygosity was determined through 22 red cell antigens. A detailed interview dealing with the twins' relationships to each other was also obtained. Each of the quantitative variables was tested for the presence of genetic variance using the method of Christian. This method first tests the equality of the total variances of MZ and DZ twins by a two tailed F' test. When the hypothesis of equality of these two variances is rejected, use of the among-component estimate of genetic variance is indicated. The current report discusses the organization and methodology of the study while accompanying reports focus on the genetic variance in blood lipids, blood pressure, and coronary prone behavior patterns.