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

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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.

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ACKNOWLEDGMENTS

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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Authors and Affiliations

  1. Department of Psychology, California State University, Fullerton, California, USA

    Nancy L. Segal Ph.D.

  2. Department of Psychology, California State University, 800 N. State College Blvd., Fullerton, California, 92834, USA

    Nancy L. Segal Ph.D.

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  1. Nancy L. Segal Ph.D.
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Correspondence to Nancy L. Segal Ph.D..

APPENDIX: QUESTIONS SENT BY E-MAIL TO J AND L'S PARENTS

APPENDIX: QUESTIONS SENT BY E-MAIL TO J AND L'S PARENTS

Mother:

  1. 1.

    How old were you when you delivered the twins? How old was your husband?

  2. 2.

    Was there one placenta or two?

  3. 3.

    At what stage of the pregnancy did you experience the car accident? Please explain exactly what happened.

  4. 4.

    At what stage of the pregnancy did you develop a kidney infection. How severe was it?

  5. 5.

    Were there other stressful events linked to this pregnancy? Marital issues? Weight gain?

  6. 6.

    Were your other (three) pregnancies s stressful as this one?

  7. 7.

    Can you provide details about both twins' early heath?

  8. 8.

    Was your husband hoping for boys or for girls?

Father:

  1. 1.

    Please describe the twins' early behavioral differences and similarities.

  2. 2.

    When did it appear that J preferred boys' games, clothing etc?

  3. 3.

    The twins indicated that there was one placenta and two sacs–is this what the doctors told you?

  4. 4.

    Did you try to treat both twins the same, as girls, as they were growing up? That is, did you discourage J from doing boy's things?

  5. 5.

    Please feel free to comment on anything else of importance.

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Segal, N.L. Two Monozygotic Twin Pairs Discordant for Female-to-Male Transsexualism. Arch Sex Behav 35, 346–357 (2006). https://doi.org/10.1007/s10508-006-9037-3

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