Acta Genet Med Gemellol 36:541-548 (1987) ©1987 by The Mendel Institute, Rome Genetic and Environmental Variation in Menstrual Cycle: Histories of Two British Twin Samples O.B.A. van den Akker 1 , G.S. Stein 2 , M.C. Neale 1 , R.M. Murray 1 1 Institute of Psychiatry, University of London, and 2 Farnborough Hospital, Kent, UK Abstract. Information about menstrual cycle variables was obtained by questionnaire using 462 female twin pairs. The twins were either members of the Institute of Psychiatry Volunteer Twin Register, or of the Birmingham Population-based Register. The two samples were analysed separately using univariate and multivariate methods so that an independent replication was obtained. Maximum likelihood estimation was used to fit simple models of genetic and environmental variation to these data. The results suggest that age of menarche, menstrual cycle regularity and premenstrual symptom reporting may be heritable, whereas menstrual cycle length is not. The results should be interpreted with caution as not ali variables were replicated in the smaller sample, and the method of retrospective menstrual cycle data collection has been questioned. Key words: Menarche, Menstrual cycle, Twin register, Model fitting procedures, Genetic analysis INTRODUCTION This study examined the extent to which genetic factors are important in the timing and expression of menstrual cycle variables. Premenstrual tension, menstrual cycle length and regularity, as well as age of menarche, are ali subject to biological and psychological influences. By examining the concordance rates of these variables in identical and non- identical twins, an indication of the importance of the genetic contribution can be obtai- ned. Variations in the age of menarche have been studied in different parts of the world, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0001566000006929 Downloaded from https://www.cambridge.org/core. IP address: 54.90.122.156, on 15 Oct 2021 at 14:44:58, subject to the Cambridge Core terms of use,