Serum Lipids and Serum Uric Acid in Human Twins.

This report describes a study of serum total cholesterol, free cholesterol, glyceride glycerol, total phospholipids, and uric acid in human twins and is presented in three sections. Section 1 presents evidence that interpair variance of free cholesterol, total cholesterol, total phospholipids, glyceride glycerol, and uric acid are significantly greater in dizygotic than monozygotic twins. Twins living apart have greater variance than twins living together ; interpair variance is greater than intrapair variance for all variates. These results provide more conclusive evidence for genetic control of blood lipids and uric acid in normal man than has been available previously. Section 2 presents interrelations of total cholesterol, glyceride glycerol, and uric acid. Glyceride glycerol and total cholesterol show significant regression coefficients in women but not in men. Section 3 presents evidence that monozygotic twins show significant evidence of heterogeneity with respect to intrapair differences of total cholesterol, free cholesterol, glyceride glycerol, and uric acid. This argument is supported by two parallel lines of reasoning; a new apprcach to twin data which we have devised, and a method for studying the concept of zygosity in twins developed by Fisher before the introduction of blood typing for determination of zygosity. Demonstration that monozygotic twins do not form a homogeneous population focuses attention upon an unanswered question regarding the resemblance between twins which is deeply ingrained in twin studies but has received little recent attention.