Self-reported zygosity and the equal-environments assumption for psychiatric disorders in the Vietnam Era Twin Registry

Hong Xian, Jeffrey F. Scherrer, Seth A. Eisen, William R. True, Andrew C. Heath, Jack Goldberg, Michael J. Lyons, Ming T. Tsuang

Research output: Contribution to journalArticle

55 Scopus citations

Abstract

The equal-environments assumption (EEA) in twin studies of psychiatric disorders assumes that the family environment which contributes to risk for a disorder is equally correlated between monozygotic (MZ) and dizygotic (DZ) twin pairs. In a study of psychiatric disorders in female twins, Kendler and colleagues (1993) have demonstrated the utility of a test of the EEA which includes a specified family environmental factor defined by using measures of perceived zygosity. We tested the EEA assumption among 3155 male-male twin pair members of the Vietnam Era Twin Registry for the following DSM-III-R lifetime disorders: alcohol dependence, marijuana dependence, any illicit drug dependence, nicotine dependence, major depression, and posttraumatic stress disorder. The majority of MZ (81.6%; n = 1593) and DZ (90.2%; n = 1086) twin pairs agreed with the investigator's assigned zygosity. The best-fitting model for each of these disorders did not allow for a specified family environmental influence. These results support the usefulness of perceived zygosity in tests of the EEA. In male twin pairs, perceived zygosity has little impact on twin similarity for common psychiatric disorders.

Original languageEnglish
Pages (from-to)303-310
Number of pages8
JournalBehavior genetics
Volume30
Issue number4
DOIs
StatePublished - Dec 1 2000

Keywords

  • Equal-environments assumption
  • Males
  • Psychiatric disorders
  • Twins
  • Veterans

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