Genetic influences on F cells and other hematologic variables: a twin heritability study

To assess the relative contribution of genetic factors in the variation of F cells (FC) and other hematologic variables, we conducted a classical twin study in unselected twins. The sample included 264 identical (monozygotic [MZ]) twin pairs and 511 nonidentical (dizygotic [DZ]) same-sex twin pairs (aged 20 to 80 years) from the St. Thomas' UK Adult Twin Register. The FC v alues were distributed continuously and positively skewed, with values rang ing from 0.6% to 22%, FC values were higher in women than in men and decrea sed with age, with the variables accounting for 2% of the total FC variance . The intraclass correlations of FC values were higher in MZ (rMZ = 0.89) t han in DZ (rDZ = 0.49) twins. The Xmnl-(G)gamma polymorphism in the beta-gl obin gene cluster had a significant effect on FC levels, accounting for app roximately 13% of the total FC variance. Variance components analysis showe d that the FC values were accounted for predominantly by additive genetic a nd nonshared environmental influences, with an estimate of heritability of 0.89, Hemoglobin levels and red blood cell, white blood cell, and platelet numbers were also substantially heritable, with heritability estimates of 0 .37, 0.42, 0.62, and 0.57, respectively. Previously, studies of sib pairs w ith sickle cell disease and isolated family studies showed that high levels of Hb F and FC tend to be inherited. Here, our classical twin study demons trated that the variance of FC levels in healthy adults Is largely genetica lly determined, (C) 2000 by The American Society of Hematology.