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

Segal, Nancy L.

doi:10.1007/s10508-006-9037-3

Cited by 33 publications

(27 citation statements)

References 52 publications

(43 reference statements)

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“…Ten MZ pairs have been reported as discordant for premature ovarian failure, with inter-twin transplantation, resulting in pregnancies in eight cases [Silber et al, 2008]. Two MZ twin pairs have been reported who were discordant for female-to-male transsexualism [Segal, 2006]. In a study of seven pairs of MZ twins discordant for sexual orientation (lesbian/heterosexual), the lesbian twins had significantly lower 2nd/4th digit length ratios on both hands.…”

Section: Other Examples Of Discordancementioning

confidence: 99%

Non‐identical monozygotic twins, intermediate twin types, zygosity testing, and the non‐random nature of monozygotic twinning: A review

Machin

2009

American J of Med Genetics Pt C

137

102

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Monozygotic twins (MZ) are rarely absolutely “identical.” This review discusses the types of genetic/epigenetic and prenatal environmental post‐zygotic mechanisms that cause discordance within such twin pairs. Some of these mechanisms—ranging from heterokaryotypia to skewed X‐chromosome inactivation—may cause extreme discordance, but these extremes are merely the more emphatic examples of discordance that, to some degree, underlies the majority of MZ twin pairs. Because of the entrenched misconception that MZ twins are necessarily identical, many MZ twin pairs are mistakenly designated as dizygotic (DZ). Clinical benefits to accurate zygosity determination include correct solid organ transplantation matching, if one twin requires donation for a non‐genetically mediated disease; the opportunity of preventive management for disorders that do not manifest synchronously; and better counseling to parents regarding their individually unique, and often psychologically puzzling, twin offspring. In twin pairs with complex and confusing biological origins, more detailed zygosity testing may be required. For example, intermediate trigametic and tetragametic chimeric dizygotic twins are reviewed, some of whom are, nevertheless, monochorionic (MC). Because of inter‐fetal vascular anastomoses in MC twins, genetic results from blood samples may not accurately reflect discordance in solid organs. Previously, it was thought that MZ twinning was some sort of embryological fluke. However, familial monozygotic twinning is more common than suggested by the literature. Seven new families are presented in an accompanying paper. Despite the difficulties and dangers of twin pregnancy (especially so for MC twins), human twinning persists, and continues to both challenge and fascinate parents, clinicians and geneticists. © 2009 Wiley‐Liss, Inc.

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Section: Other Examples Of Discordancementioning

confidence: 99%

Non‐identical monozygotic twins, intermediate twin types, zygosity testing, and the non‐random nature of monozygotic twinning: A review

Machin

2009

American J of Med Genetics Pt C

137

102

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“…In MF transsexualism, there are reports of six monozygotic (MZ) twin pairs concordant for transsexualism (Anchersen, 1956;Gooren, Frantz, Eriksson, & Rao, 1989;Green, 2000;Hyde & Kenna, 1977;Tsur, Borenstein, & Seidman, 1991;Zucker & Bradley, 1995), five MZ twin pairs discordant for transsexualism (Gooren et al, 1989;Green & Stoller, 1971;Hepp, Milos, & Braun-Sharm, 2004;Zucker & Bradley, 1995), and one report of two dizygotic (DZ) transsexual male triplets with a nontranssexual female co-triplet (McKee, Roback, & Hollender, 1976). In FM transsexual twins, one concordant (Sadeghi & Fakhrai, 2000) and four discordant MZ pairs (Garden & Rothery, 1992;Green & Stoller, 1971;Segal, 2006) have been reported. Moreover, most of the MZ and DZ twin case reports share not only genes but also many environmental factors.…”

Section: Introductionmentioning

confidence: 99%

Familiality of Gender Identity Disorder in Non-Twin Siblings

et al. 2009

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Familial studies and reports of co-occurrence of gender identity disorder (GID) within a family may help to clarify the question of whether transsexualism is a familial phenomenon. In a sample of 995 consecutive transsexual probands (677 male-to-female [MF] and 318 female-to-male [FM]), we report 12 pairs of transsexual non-twin siblings (nine pairs of MF siblings, two pairs of MF-FM siblings, and one pair of FM siblings). The present study doubles the number of case reports of co-occurrence of transsexualism in non-twin siblings available in the literature. According to our data, the probability that a sibling of a transsexual will also be transsexual was 4.48 times higher for siblings of MF than for siblings of FM transsexual probands, and 3.88 times higher for the brothers than for the sisters of transsexual probands. Moreover, the prevalence of transsexualism in siblings of transsexuals (1/211 siblings) was much higher than the range expected according to the prevalence data of transsexualism in Spain. The study suggests that siblings of transsexuals may have a higher risk of being transsexual than the general population, and that the risk is higher for brothers than sisters of transsexuals, and for siblings of MF than FM transsexuals. Nevertheless, the risk is low.

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“…Only five pairs represent FTM MZ twins. Four pairs were discordant (Garden & Rothery, 1992;Green & Stoller, 1971;Segal, 2006) and only one was concordant for transsexualism (Sadeghi & Fakhrai, 2000). Seven additional MZ FTM transsexual twin pairs (two concordant and five discordant) were reported by Diamond and Hawk (2004).…”

mentioning

confidence: 89%

“…Several MZ twin pairs and one triplet (FTM and MTF) concordant or discordant for transsexualism have been reported (Anchersen, 1956;Buhrich, Bailey, & Martin, 1991;Garden & Rothery, 1992;Green, 2000;Green & Stoller, 1971;Hyde & Kenna, 1977;McKee, Roback, & Hollander, 1976;Sadeghi & Fakhrai, 2000;Segal, 2006;Zucker & Bradley, 1995). Only five pairs represent FTM MZ twins.…”

mentioning

confidence: 99%

“…Concordant MZ twins only allow estimation of the genetic contribution, but do not allow the estimation of shared environmental factors as a second potential source for similarity. MZ twins discordant for a trait may shed light on relevant environmental influences as they share the same genetic background (Segal, 2006). Therefore, the relative influence of genetic and environmental factors of transsexualism could only be estimated analyzing a set of MZ and DZ twins, optimally derived from a population-based registry.…”

mentioning

confidence: 99%

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