High density lipoprotein cholesterol. A 16-year longitudinal study in aging male twins

The National Heart, Lung, and Blood Institute Twin Study is a collaborative, longitudinal study of white, male twins who were veterans of World War II and were born between 1917 and 1927. The twins were selected from the National Academy of Sciences/National Research Council Twin Panel and were examined three times (1969-73, 1981-82, and 1986-87). At all three exams, the dizygotic (DZ) twins were found to have a greater total variance for high density lipoprotein cholesterol (HDL-C) than the monozygotic (MZ) twins (p less than 0.05). DZ variance estimates were also larger than the variance of singletons from the second National Health and Nutrition Examination Survey. At the third exam, HDL-C was divided by precipitation into HDL2 and HDL3 fractions, and HDL2 was found to be the primary cause of the greater DZ total variance (DZ/MZ HDL2 variance = 2.22). The DZ/MZ variance ratio decreased 9% after adjustment of HDL2 for correlations with plasma triglycerides, alcohol consumption, smoking, exercise, and body mass index measured at the third exam. Postulated causes of the difference between MZ and DZ total variances include World War II induction screening, environmental influences unique to one zygosity, and genetic factors related to twinning. Further understanding of the etiology of this striking difference between MZ and DZ twin variance for HDL-C fractions could lead to more effective methods of decreasing the complications of arteriosclerosis.