Orv Hetil. 2008 Aug 17;149(33):1555-60.
[Overview of the biological etiology of transsexualism]
[Article in Hungarian]
Kórász K, Simon L.
Semmelweis Egyetem, Altalános Orvostudományi Kar, Budapest, Hungary.
Gender identity disorder, or transsexualism as it is more commonly known, is a highly complex clinical entity. The general belief among behavioural scientists and physicians is that transsexualism is an identifiable and incapacitating disease which can be diagnosed and successfully treated by reassignment surgery. Although the exact etiology of gender identity disorder is unknown, several environmental, genetic and anatomical theories have been described. The reviewers draw attention to the possible genetic, hormonal, immunological and anatomical causes. An attempt is made to point out the future trends in research, highlighting their progressive features.
PMID: 18687574 [PubMed - indexed for MEDLINE]
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J Sex Med. 2009 Feb;6(2):449-55. Epub 2008 Jul 15.
Genetic factors increase fecundity in female maternal relatives of bisexual men as in homosexuals.
Ciani AC, Iemmola F, Blecher SR.
University of Padova, General Psychology, Padova, Italy.
andrea.camperio@unipd.it
INTRODUCTION: Recent studies on male homosexuals showed increased fecundity of maternal female relatives of homosexual probands, compared to those of heterosexual controls. We have suggested that these data could be explained by the transmission, in the maternal line, of an X-linked genetic factor that promotes androphilic behavior in females and homosexuality in males. AIM: Our original studies were on relatives of male subjects who declared themselves to be exclusively homosexual. However, the relationship between homosexuality and bisexuality, including the possibility of shared genetic factors, is complex and largely unexplored. To cast light on this issue, in the present study we examined whether relatives of bisexuals show the same indirect fitness advantage as previously demonstrated for homosexuals. MAIN OUTCOME MEASURES: Subjects completed a questionnaire on their sexual orientation, sexual behavior, and their own and their relatives' fecundity. METHODS: We studied 239 male subjects, comprising 88 who were exclusively or almost exclusively heterosexual (pooled to comprise our "heterosexual" group), 86 who were bisexual, and 65 exclusively or almost exclusively homosexual individuals (pooled in our "homosexual" group). Bisexuals were here defined on the basis of self-identification, lifetime sexual behavior, marital status, and fecundity. RESULTS: We show that fecundity of female relatives of the maternal line does not differ between bisexuals and homosexuals. As in the previous study on homosexuals, mothers of bisexuals show significantly higher fecundity, as do females in the maternal line (cumulated fecundity of mothers, maternal grandparents, and maternal aunts), compared to the corresponding relatives of heterosexual controls.This study also shows that both bisexuals and homosexuals were more frequently second and third born. However, only homosexuals had an excess of older male siblings, compared to heterosexuals. CONCLUSIONS: We present evidence of an X-chromosomal genetic factor that is associated with bisexuality in men and promotes fecundity in female carriers.
PMID: 18637994 [PubMed - indexed for MEDLINE]
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PLoS One. 2008 Jun 18;3(6):e2282.
Sexually antagonistic selection in human male homosexuality.
Camperio Ciani A, Cermelli P, Zanzotto G.
Dipartimento di Psicologia Generale, Università di Padova, Padova, Italy.
andrea.camperio@unipd.it
Several lines of evidence indicate the existence of genetic factors influencing male homosexuality and bisexuality. In spite of its relatively low frequency, the stable permanence in all human populations of this apparently detrimental trait constitutes a puzzling 'Darwinian paradox'. Furthermore, several studies have pointed out relevant asymmetries in the distribution of both male homosexuality and of female fecundity in the parental lines of homosexual vs. heterosexual males. A number of hypotheses have attempted to give an evolutionary explanation for the long-standing persistence of this trait, and for its asymmetric distribution in family lines; however a satisfactory understanding of the population genetics of male homosexuality is lacking at present. We perform a systematic mathematical analysis of the propagation and equilibrium of the putative genetic factors for male homosexuality in the population, based on the selection equation for one or two diallelic loci and Bayesian statistics for pedigree investigation. We show that only the two-locus genetic model with at least one locus on the X chromosome, and in which gene expression is sexually antagonistic (increasing female fitness but decreasing male fitness), accounts for all known empirical data. Our results help clarify the basic evolutionary dynamics of male homosexuality, establishing this as a clearly ascertained sexually antagonistic human trait.
PMID: 18560521 [PubMed - indexed for MEDLINE]
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Arch Sex Behav. 2008 Feb;37(1):85-99.
Sexual orientation in women with classical or non-classical congenital adrenal hyperplasia as a function of degree of prenatal androgen excess.
Meyer-Bahlburg HF, Dolezal C, Baker SW, New MI.
New York State Psychiatric Institute & Department of Psychiatry, Columbia University, 1051 Riverside Drive, New York, NY 10032, USA.
meyerb@childpsych.columbia.edu
46,XX individuals with classical congenital adrenal hyperplasia (CAH) due to deficiency of the enzyme, 21-hydroxylase, show variable degrees of masculinization of body and behavior due to excess adrenal androgen production. Increased bisexuality and homosexuality have also been reported. This article provides a review of existing reports of the latter and presents a new study aimed at replicating the previous findings with detailed assessments of sexual orientation on relatively large samples, and at extending the investigation to the mildest form, non-classical (NC) CAH. Also, this is the first study to relate sexual orientation to the specific molecular genotypes of CAH. In the present study, 40 salt-wasters (SW), 21 SV (simple-virilizing), 82 NC, and 24 non-CAH control women (sisters and female cousins of CAH women) were blindly administered the Sexual Behavior Assessment Schedule (SEBAS-A, 1983 ed.; H. F. L. Meyer-Bahlburg & A. A. Ehrhardt, Privately printed). Most women were heterosexual, but the rates of bisexual and homosexual orientation were increased above controls not only in women with classical CAH, but also in NC women, and correlated with the degree of prenatal androgenization. Classifying women by molecular genotypes did not further increase the correlation. Diverse aspects of sexual orientation were highly intercorrelated, and principal components analysis yielded one general factor. Bisexual/homosexual orientation was (modestly) correlated with global measures of masculinization of non-sexual behavior and predicted independently by the degree of both prenatal androgenization and masculinization of childhood behavior. We conclude that the findings support a sexual-differentiation perspective involving prenatal androgens on the development of sexual orientation.
PMID: 18157628 [PubMed - indexed for MEDLINE]
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Arch Sex Behav. 2008 Feb;37(1):145-9.
Eye color, hair color, blood type, and the rhesus factor: exploring possible genetic links to sexual orientation.
Ellis L, Ficek C, Burke D, Das S.
Department of Sociology, Minot State University, Minot, ND 58707, USA.
lee.ellis@minotstateu.edu
The present study sought to expand the limited evidence that sexual orientation is influenced by genetic factors. This was accomplished by seeking statistical differences between heterosexuals and homosexuals for four traits that are known to be genetically determined: eye color, natural hair color, blood type, and the Rhesus factor. Using a sample of over 7,000 U.S. and Canadian college students supplemented with additional homosexual subjects obtained through internet contacts, we found no significant differences between heterosexuals and homosexuals regarding eye color or hair color. In the case of blood type and the Rh factor, however, interesting patterns emerged. Heterosexual males and females exhibited statistically identical frequencies of the A blood type, while gay men exhibited a relatively low incidence and lesbians had a relatively high incidence (p < .05). In the case of the Rh factor, unusually high proportions of homosexuals of both sexes were Rh- when compared to heterosexuals (p < .06). The findings suggest that a connection may exist between sexual orientation and genes both on chromosome 9 (where blood type is determined) and on chromosome 1 (where the Rh factor is regulated).
PMID: 18074215 [PubMed - indexed for MEDLINE]
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