Archives of Sexual Behavior

, Volume 35, Issue 3, pp 346–357 | Cite as

Two Monozygotic Twin Pairs Discordant for Female-to-Male Transsexualism

  • Nancy L. SegalEmail author
Clinical Case Report Series

Two monozygotic female twin pairs discordant for transsexualism are described. These reports double the number of such case studies in the current scientific literature. Interviews with the twins and their families indicated that unusual medical and life history factors did not play causal roles. However, inspection of medical records for one transsexual twin suggested that some early life experiences may have exacerbated tendencies toward male gender identification. In both pairs, the twins' gender identity differences emerged early, consistent with, but not proof of, co-twin differences in prenatal hormonal influences. The identification of additional discordant MZ female twin pairs can advance biological and psychological understanding of transsexualism. Suggestions for future research, based upon findings from these two twin pairs and from studies of female-to-male transsexuals, are provided.


Twins monozygotic gender identity disorder transsexualism 



The cooperation of the twins and their families is gratefully acknowledged. Scott L. Hershberger, Ph.D., and Richard A. Lippa, Ph.D., reviewed earlier versions of this manuscript. This work was completed, in part, by a fellowship from the American Association for University Women.


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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  1. 1.Department of PsychologyCalifornia State UniversityFullertonUSA
  2. 2.Department of PsychologyCalifornia State UniversityFullertonUSA

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