Finger Length Ratio (2D:4D) in Adults with Gender Identity Disorder

Abstract

From early childhood, gender identity and the 2nd to 4th finger length ratio (2D:4D) are discriminative characteristics between sexes. Both the human brain and 2D:4D may be influenced by prenatal testosterone levels. This calls for an examination of 2D:4D in patients with gender identity disorder (GID) to study the possible influence of prenatal testosterone on gender identity. Until now, the only study carried out on this issue suggests lower prenatal testosterone levels in right-handed male-to-female GID patients (MtF). We compared 2D:4D of 56 GID patients (39 MtF; 17 female-to-male GID patients, FtM) with data from a control sample of 176 men and 190 women. Bivariate group comparisons showed that right hand 2D:4D in MtF was significantly higher (feminized) than in male controls, but similar to female controls. The comparison of 2D:4D ratios of biological women revealed significantly higher (feminized) values for right hands of right handed FtM. Analysis of variance confirmed significant effects for sex and for gender identity on 2D:4D ratios but not for sexual orientation or for the interaction among variables. Our results indirectly point to the possibility of a weak influence of reduced prenatal testosterone as an etiological factor in the multifactorially influenced development of MtF GID. The development of FtM GID seems even more unlikely to be notably influenced by prenatal testosterone. Analysis of variance confirmed significant effects for sex and for gender identity on 2D:4D ratios but not for sexual orientation or for the interaction among variables. Our results indirectly point to the possibility of a weak influence of reduced prenatal testosterone as an etiological factor in the multifactorially influenced development of MtF GID. The development of FtM GID seems even more unlikely to be notably influenced by prenatal testosterone.

Click-Evoked Otoacoustic Emissions in Children and Adolescents with Gender Identity Disorder

“…In accordance with the present results, Schneider, Pickel, and Stalla (2006) as well as Kraemer et al (2009) found evidence for more female-typical 2D:4D ratios in a group of 63 adult males diagnosed with GID, especially when restricting the analysis to right-handed subjects. This finding supports the hypothesis that men with GID might have been exposed to lower levels of androgen during early development.…”

The transsexual brain – A review of findings on the neural basis of transsexualism

“…The digit ratio also has been studied in transsexuals, yielding a higher digit ratio in MtF transsexuals than in control males, similar to control females. By contrast, the digit ratio of FtM transsexuals was found to be in the range of control females (Kraemer et al, 2009;Schneider, Pickel, & Stalla, 2006). The findings support the assumption of prenatal testosterone exposure as etiological factor of transsexualism, at least for MtF transsexualism.…”

The Relationship Between Digit Ratio (2D:4D) and Sexual Orientation in Men from China

“…Among studies using a 7-point Kinsey-like scale (which ranges from 0 to 6) to assess sexual orientation, homosexuals have been categorized as those with a score of 6 (e.g., Hall & Schaeff, 2008), with a score of 5 and 6 (e.g., Rahman, 2005), or with a score equal to or higher than 2 (e.g., Kangassalo et al, 2011;Rahman & Wilson, 2003a, b). Studies using the 9-point Kinsey-like scale (which ranges from 1 to 9) to assess sexual orientation have classified individuals with a total score of 11 or less on three items as homosexuals (Kraemer et al, 2006(Kraemer et al, , 2009. Additionally, some studies categorized individuals according to participants' own choice of descriptor: heterosexual, homosexual, or bisexual (e.g., Lippa, 2003;Manning et al, 2007).…”