Genetic factors that regulate cytosolic epoxide hydrolase activity in normal human lymphocytes.

To determine whether genetic mechanisms control large variations in cytosolic epoxide hydrolase (cEH) activity of unstimulated lymphocytes from normal human subjects, cEH activity was measured in: a) 6 sets of monozygotic (MZ) twins and 6 sets of dizygotic (DZ) twins; b) 100 unrelated male subjects and c) 6 families. The twin study revealed predominantly genetic control (H2/1 = 0.95). Variability was markedly less within MZ (intrapair variance = 0.25) than DZ twins (intrapair variance = 6.33). In 100 unrelated male subjects the extent of interindividual variation was 11-fold. Unimodal distribution of values among 99 subjects encompassed a six-fold range. One outlier with very high activity clearly stood apart. Using the whole distribution curve we phenotyped members of 6 families. In the outlier's family, analysis of 3 generations suggested autosomal dominant transmission of high cEH activity. Analysis of the other 5 families and 12 sets of twins, all from the large unimodal distribution, was consistent with either monogenic or polygenic control of variations within this mode.