Acta Genet Med Gemellol 29:143-149 (1980) The Mendel Institute/Alan R. Liss, Inc. ^^ Received 9 October 1979 Final 29 January 1980 Heritability of Systolic Blood Pressure Analysis of Variance in MZ Twin Parents and Their Children R. J. Rose 1 , D. W. Fulker 2 , J. Z. Miller 1 , C. E. Grim 3 , J. C. Christian 4 1 Department of Psychology, Indiana University, Bloomington; 2 Institute of Psychiatry, University of London; 3 Department of Medicine and' 4 Department of Medical Genetics, Indiana University School of Medicine, Indianapolis Systolic blood pressure, standardized for age and sex, was measured in 76 MZ twin pairs and their 341 children. Maximum likelihood estimation of genetical and environmental parameters from the independent parental and offspring ANOVAs indicated a complete absence of both maternal and shared environmental effects, together with a heritability of 63%. These results are shown to be reasonably consistent with those from previous studies. Key words: Systolic blood pressure, Maximum likelihood genetic analysis, Twin model INTRODUCTION Estimation of genetic and environmental sources of human variation is the raison d'etre of traditional twin studies. Partioned variances of monozygotic (MZ) and dizygotic (DZ) twins are compared, and estimates of genetic variance are derived. This approach, simple, yet sound, has formed the cornerstone of quantitative human genetics. In the past decade, however, advances have been made both in methodological designs employing twin subjects and in analytic methods for estimating sources of variation. The purpose of this report is to illustrate a maximum likelihood procedure [5] for estimating genetic and environmental parameters. The application is to standardized systolic blood pressures measured in MZ twin parents and their children [13]. Familial aggregation of blood pressure is well established, and recent evidence docu- ments sibling resemblance early in life [16]. Twin studies have revealed significant genetic variance in blood pressure levels at different ages [2, 6, 9]. Uncertainty remains, however, over the nature and magnitude of maternal effects and the influences of common family 0001-5660/80/2902-0143S01.70 © 1980 Alan R. Liss, Inc. https://doi.org/10.1017/S000156600000862X Published online by Cambridge University Press