Genetics of plasma cholesterol and triglycerides. A study of adult male twins

White male twins born between 1917 and 1927 (514 sets, 250 MZ and 264 DZ) were studied in 5 U.S. centers as a part of the National Heart and Lung Institute Twin Study. Fasting plasma triglycerides and cholesterol, as well as cholesterol in very low density and high density lipoproteins (HDL), were measured. Analysis of variance of the five lipids revealed no significant differences between the means of MZ and DZ twins and only DHL cholesterol was significantly variable among the 5 centers. A new method was used to choose an estimate of genetic variance. This method includes an estimate of genetic variance for use when the total variances of MZ and DZ twins are unequal. DZ twins had greater total variance for triglycerides. When genetic variance was estimated by subtracting the within MZ sets mean square from the within DZ sets mean square, all of the lipids had significant estimates of genetic variance; however when genetic variance was estimated by a method designed to correct bias due to unequal total variances of MZ and DZ twins, only triglycerides had significant genetic variance. The heritability of plasma triglycerides was calculated to be 0.6. Differential within twin pair environmental effects on MZ and DZ twins have been postulated to cause differences in total variance. If this is true, previous reports of twins showing significant estimates of genetic variance for plasma cholesterol may be due to environmental bias.