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We examined whether recalled childhood gender nonconformity and self-reported adult gender nonconformity is familial, using data from 1154 families selected for having at least two homosexual brothers. Specifically, we examined the extent to which homosexual men's variation in gender nonconformity runs in families by examining pairs of genetic brothers who were both homosexual (N = 672-697 full sibling concordant pairs). We also examined similarity between homosexual and heterosexual brothers (N = 79-82 full sibling discordant pairs). Consistent with past studies, concordant pairs yielded modest positive correlations consistent with moderate genetic and/or familial environmental effects on gender nonconformity. Unlike results of smaller past studies, discordant pairs also yielded modest positive, though nonsignificant, correlations. Our results support the feasibility of supplementing genetic studies of male sexual orientation with analyses of gender nonconformity variation.

Family and twin studies suggest that genes play a role in male sexual orientation. We conducted a genome-wide association study (GWAS) of male sexual orientation on a primarily European ancestry sample of 1,077 homosexual men and 1,231 heterosexual men using Affymetrix single nucleotide polymorphism (SNP) arrays. We identified several SNPs with p < 10 -5 , including regions of multiple supporting SNPs on chromosomes 13 (minimum p = 7.5 × 10 -7 ) and 14 (p = 4.7 × 10 -7 ). The genes nearest to these peaks have functions plausibly relevant to the development of sexual orientation. On chromosome 13, SLITRK6 is a neurodevelopmental gene mostly expressed in the diencephalon, which contains a region previously reported as differing in size in men by sexual orientation. On chromosome 14, TSHR genetic variants in intron 1 could conceivably help explain past findings relating familial atypical thyroid function and male homosexuality. Furthermore, skewed X chromosome inactivation has been found in the thyroid condition, Graves' disease, as well as in mothers of homosexual men. On pericentromeric chromosome 8 within our previously reported linkage peak, we found support (p = 4.1 × 10 -3 ) for a SNP association previously reported (rs77013977, p = 7.1 × 10 -8 ), with the combined analysis yielding p = 6.7 × 10 -9 , i.e., a genome-wide significant association.

Studies of subjective and genital sexual arousal in monosexual (i.e. heterosexual and homosexual) men have repeatedly found that erotic stimuli depicting men's preferred sex produce strong responses, whereas erotic stimuli depicting the other sex produce much weaker responses. Inconsistent results have previously been obtained in bisexual men, who have sometimes demonstrated distinctly bisexual responses, but other times demonstrated patterns more similar to those observed in monosexual men. We used fMRI to investigate neural correlates of responses to erotic pictures and videos in heterosexual, bisexual, and homosexual men, ages 25-50. Sixty participants were included in video analyses, and 62 were included in picture analyses. We focused on the ventral striatum (VS), due to its association with incentive motivation. Patterns were consistent with sexual orientation, with heterosexual and homosexual men showing female-favoring and male-favoring responses, respectively. Bisexual men tended to show less differentiation between male and female stimuli. Consistent patterns were observed in the whole brain, including the VS, and also in additional regions such as occipitotemporal, anterior cingulate, and orbitofrontal cortices. This study extends previous findings of gender-specific neural responses in monosexual men, and provides initial evidence for distinct brain activity patterns in bisexual men., Competing Interests: The authors declare no competing financial interests.

A high proportion of self-identified gay men exhibit aspects of bisexuality during their lives. Some identify as bisexual before later identifying as gay; this has been called transitional bisexuality. Although many gay men report no attraction to women-or even sexual disgust toward them-others report some slight attraction to women. The latter have been studied as mostly homosexual men. We studied men with and without a history of transitional bisexuality, as well as mostly homosexual (i.e., those with Kinsey scores of 5) and completely homosexual (i.e., those with Kinsey scores of 6) men with respect to their sexual history with women, their current self-reported sexual arousal and disgust toward women and men, and their patterns of genital sexual arousal to female and male stimuli. Gay men with a history of transitional bisexuality generally lacked current sexual attraction and sexual arousal to women, compared with other gay men. Thus, transitional bisexuality among future gay men is mostly a matter of transitional bisexual identification. In contrast, mostly homosexual men showed statistically significant increases in genital arousal to female stimuli, compared with completely homosexual men.

Background: Gynandromorphophilia (GAMP) is sexual interest in gynandromorphs (GAMs; colloquially, shemales). GAMs possess a combination of male and female physical characteristics. Thus, GAMP presents a challenge to conventional understandings of sexual orientation as sexual attraction to the male v. female form. Speculation about GAMP men has included the ideas that they are homosexual, heterosexual, or especially, bisexual., Method: We compared genital and subjective sexual arousal patterns of GAMP men with those of heterosexual and homosexual men. We also compared these groups on their self-ratings of sexual orientation and sexual interests., Results: GAMP men had arousal patterns similar to those of heterosexual men and different from those of homosexual men. However, compared to heterosexual men, GAMP men were relatively more aroused by GAM erotic stimuli than by female erotic stimuli. GAMP men also scored higher than both heterosexual and homosexual men on a measure of autogynephilia., Conclusions: Results provide clear evidence that GAMP men are not homosexual. They also indicate that GAMP men are especially likely to eroticize the idea of being a woman.

Background: Findings from family and twin studies support a genetic contribution to the development of sexual orientation in men. However, previous studies have yielded conflicting evidence for linkage to chromosome Xq28., Method: We conducted a genome-wide linkage scan on 409 independent pairs of homosexual brothers (908 analyzed individuals in 384 families), by far the largest study of its kind to date., Results: We identified two regions of linkage: the pericentromeric region on chromosome 8 (maximum two-point LOD = 4.08, maximum multipoint LOD = 2.59), which overlaps with the second strongest region from a previous separate linkage scan of 155 brother pairs; and Xq28 (maximum two-point LOD = 2.99, maximum multipoint LOD = 2.76), which was also implicated in prior research., Conclusions: Results, especially in the context of past studies, support the existence of genes on pericentromeric chromosome 8 and chromosome Xq28 influencing development of male sexual orientation.

Prior research suggests that sex typicality (especially femininity of females, but also masculinity of males) relates to perceptions of attractiveness, for both heterosexual and homosexual individuals. Using videos from childhood and adulthood, we investigated how different components of sex typicality contributed to this effect, whether the sex of the evaluator or of the target moderated the effect, and how the relationship of attractiveness with sex typicality varied across the lifespan. In Study 1, videos of 45 female and 50 male heterosexual and homosexual adult targets (ages 18-30 years) were judged by 56 female and 65 male heterosexual and homosexual raters (ages 18-30 years). Results suggested that both heterosexual men and lesbians viewed more feminine women as more attractive. Femininity of appearance was a primary contributor to this relationship. Masculinity was not related to men's attractiveness. Study 2 used similar methodology (44 male and 46 female heterosexual and homosexual targets and 22 male and 20 female heterosexual raters). Study 2 replicated results of Study 1. In addition, Study 2 included ratings of childhood videos of targets (ages 0-15). Results suggested that childhood femininity related to attractiveness of both young girls and young boys and that the relationship became stronger for girls as they got older. The impact of femininity on attractiveness may, therefore, depend on both targets' sex and their maturity.

Sex-atypical behaviors may be used to identify a person as homosexual. To shield themselves from prejudice, homosexual people may attempt to conceal these behaviors. It is not clear how effectively they can do so. In Study 1, we asked homosexual participants to conceal their sex-atypical behaviors while talking about the weather. Raters watched videos of the participants and judged the likelihood that each participant was homosexual. Homosexual participants were able to partially conceal signs of their orientation, but they remained distinguishable from heterosexual participants. In Study 2, we tested the ability to conceal signs of one's sexual orientation in a more demanding situation: a mock job interview. In this scenario, homosexual men were even less effective at concealing their orientation. Higher cognitive demands in this new situation may have interfered with their ability to conceal.

In this issue, P. Hegarty (see record 2009-09998-015) comments on an article by G. Rieger, J. A. W. Linsenmeier, L. Gygax, and J. M. Bailey (see record 2007-19851-006) that compared videos of homosexual and heterosexual people from childhood and adulthood. The current authors claim it is reasonable to treat masculinity-femininity as a bipolar scale and present justification for the approach used in the earlier study. Measures used by Rieger et al. (2008) yielded large differences between homosexual and heterosexual participants, and these differences are likely to be more meaningful than the low and nonsignificant within-group correlations on which Hegarty chose to focus. The authors address his suggestion that they are working within a paradigm detrimental to the well-being of homosexual and gender-nonconforming individuals and suggest that greater openness to research such as theirs could have beneficial consequences.

Currently the predominant cultural understanding of male-to-female transsexualism is that all male-to-female (MtF) transsexuals are, essentially, women trapped in men's bodies. This understanding has little scientific basis, however, and is inconsistent with clinical observations. Ray Blanchard has shown that there are two distinct subtypes of MtF transsexuals. Members of one subtype, homosexual transsexuals, are best understood as a type of homosexual male. The other subtype, autogynephilic transsexuals, are motivated by the erotic desire to become women. The persistence of the predominant cultural understanding, while explicable, is damaging to science and to many transsexuals.

Some lesbians and gay men tend to be more gender nonconforming, on average and for certain traits, than their heterosexual counterparts. Gender nonconformity in childhood has also been linked to adult homosexuality. Studies of both lesbians and gay men also find elevated rates of psychological distress. We hypothesized that these facts may be related. Individuals who violate social norms for gender-appropriate behavior may suffer from stigmatization by both heterosexual and homosexual people, leading to higher levels of psychological distress. We examined whether several measures of gender nonconformity were related to psychological distress in a community-based sample of gay men and lesbians. These included self-reports of childhood and adulthood gender nonconformity, as well as observer ratings of current behavior. Several measures of gender nonconformity were related to each other for both lesbians and gay men. In addition, gender nonconformity was related to psychological distress, but only for gay men. Finally, both lesbian and gay male participants reported more positive attitudes towards gender conformity than nonconformity, although the pattern was somewhat different for each group. We discuss the implications of these results for future studies of gender nonconformity and for the promotion of psychological health in lesbians and gay men.

Homosexual and nonhomosexual (relative to genetic sex) female-to-male transsexuals (FTMs) were compared on a number of theoretically or empirically derived variables. Compared to nonhomosexual FTMs, homosexual FTMs reported greater childhood gender nonconformity, preferred more feminine partners, experienced greater sexual rather than emotional jealousy, were more sexually assertive, had more sexual partners, had a greater desire for phalloplasty, and had more interest in visual sexual stimuli. Homosexual and nonhomosexual FTMs did not differ in their overall desire for masculinizing body modifications, adult gender identity, or importance of partner social status, attractiveness, or youth. These findings indicate that FTMs are not a homogeneous group and vary in ways that may be useful in understanding the relation between sexual orientation and gender identity.

Research has generally supported the existence of familial-genetic factors for male sexual orientation, but has not shed much light on the specific nature of those influences. Gay men with gay brothers provide the opportunity to examine several hypotheses. Sixty-six men, representing 37 gay male sibling pairs, completed questionnaires assessing behavior on various measures including childhood and adult gender nonconformity, timing of awareness of homosexual feelings, self-acceptance, and the quality of family relationships. Consistent with prior findings using twins, gay brothers were similar in their degree of childhood gender non-conformity, suggesting that this variable may distinguish etiologically (e.g., genetically) heterogeneous subtypes. The large majority of gay men with brothers knew about their own homosexual feelings before they learned about their brothers' homosexual feelings, suggesting that discovery of brothers' homosexuality is not an important cause of male homosexuality.

We recruited twins systematically from the Australian Twin Registry and assessed their sexual orientation and 2 related traits: childhood gender nonconformity and continuous gender identity. Men and women differed in their distributions of sexual orientation, with women more likely to have slight-to-moderate degrees of homosexual attraction, and men more likely to have high degrees of homosexual attraction. Twin concordances for nonheterosexual orientation were lower than in prior studies. Univariate analyses showed that familial factors were important for all traits, but were less successful in distinguishing genetic from shared environmental influences. Only childhood gender nonconformity was significantly heritable for both men and women. Multivariate analyses suggested that the causal architecture differed between men and women, and, for women, provided significant evidence for the importance of genetic factors to the traits' covariation.

Available evidence suggests that male homosexuality is both familial and somewhat heritable and that some cases may be caused by an X-linked gene. However, most studies have recruited subjects in a relatively unsystematic manner, typically via advertisements, and hence suffer from the potential methodological flaw of ascertainment bias due to volunteer self-selection. In the present study we assessed the familiality of male homosexuality using two carefully ascertained samples and attempted to replicate findings consistent with X-linkage in three samples. The percentage of siblings of the probands rated as either homosexual or bisexual, with a high degree of certainty, ranged from 7 to 10% for brothers and 3 to 4% for sisters. These estimates are higher than recent comparable population-based estimates of homosexuality, supporting the importance of familial factors for male homosexuality. Estimates of lambda s for male homosexuality ranged from 3.0 to 4.0. None of the samples showed a significantly greater proportion of maternal than paternal homosexual uncles or homosexual male maternal first cousins. Although our results differed significantly with those of some prior studies, they do not exclude the possibility of moderate X-linkage for male sexual orientation.

On average, gay men are somewhat feminine and lesbians somewhat masculine, but there is variation within each group. The authors examined the consequences of this variation for gay men's and lesbians' desirability as romantic partners. In 2 studies the authors analyzed personal advertisements. Homosexual people were more likely than heterosexual people to mention traits related to sex typicality and more likely to request sex-typical than sex-atypical partners. In 2 studies the authors assessed partner preferences directly. On average, gay men preferred men who described themselves as masculine rather than feminine, but this preference was weaker among men who rated themselves as relatively feminine. Lesbians preferred women who described themselves as feminine looking but did not discriminate against women calling themselves masculine acting. The authors discuss implications of the results for theories of sexual orientation and the adjustment of sex-atypical homosexual people.

Two studies were undertaken to confirm the previous findings that homosexual men in general tend to have a later than expected birth order and that extremely feminine homosexual men also tend to have a higher than expected proportion of brothers (i.e., a higher sibling sex ratio). Subjects in Study 1 were Dutch, adult and adolescent, biological male patients with gender dysphoria (persistent and recurrent desires to belong to the opposite sex), who were undergoing treatment with feminizing hormones. These comprised 83 patients who reported sexual attraction to other males (the homosexual group) and 58 who reported sexual attraction to females or equal attraction to males and females (the non-homosexual group). Subjects in Study 2 were Dutch adolescent male patients at another hospital. The homosexual group consisted of 21 gender-dysphoric homosexual teenagers referred to a gender identity clinic for children and adolescents. The control group were 21 adolescent males referred to the child psychiatry department of the same hospital for reasons other than gender identity disorder, homosexuality, or transvestism. These were individually matched to the homosexual subjects on age and sibship size. In both studies, the homosexual group had a significantly later average birth order than the comparison group. In Study 1, the homosexual group had a significantly elevated sibling sex ratio; this was not tested in Study 2 because of its small sample size. These studies add to the mounting evidence that late birth orders are common to all homosexual samples and that elevated sibling sex ratios are an additional characteristic of extremely feminine ones.

Male sexual orientation is strongly associated with childhood sex-typed behavior, but there are also marked within-orientation differences. Gay men show increased variance compared to heterosexual men on retrospective measures of childhood sex-typed behavior. Individual differences among gay men for their degree of sex-typed behavior may have important implications. However, there has been little attention given to the reliability or validity of retrospective measures of such differences that are most common. Gay men and their mothers completed questionnaires assessing the men's sex-typicality during childhood. Results of structural modeling analyses found that mothers' and sons' reports were significantly associated, both regarding the general level of sex-typed behavior and the specific behaviors, supporting the validity of retrospectively measured individual differences for those characteristics.