12/7/2023 0 Comments Higher 2d 4d ratio women![]() ![]() In 2020, a more recent meta-analysis 6 reported significantly feminized 2D:4D in MtF individuals (d = 0.24). This short systematic review included only few studies with rather small sample sizes or data retrieved from abstracts (which can be influenced by reporting bias), and it did not provide extensive meta-regression and subgroup analyses or distinguish between case–control and cohort studies. Concerning gender dysphoria and 2D:4D, contradictory evidence exists, which has been summarized in a meta-analytical commentary conducted in 2017 19 where the authors report a small effect size indicating feminized 2D:4D of the right hand (but not the left hand) in MtF individuals and no associations at all in FtM individuals. ![]() It is frequently used to examine the link between prenatal androgen exposure and postnatal phenotypes including diseases, mental disorders, and behaviors reflecting gender bias or being influenced by first trimester organizational changes induced by testosterone/estrogen ratios 12, such as alcohol addiction 13, autism spectrum disorders 14, 15, sexual orientation 16, the risk for different forms of cancer 17, and physical prowess 18. A lower 2D:4D reflects higher prenatal androgen exposure 9 and hence, the 2D:4D is lower in males than in females 10, 11. Thus, this research area relies on proxies such as the second-to-fourth digit length ratio (2D:4D), a biomarker determined by the balance of prenatal testosterone to estrogen 7, and therefore indicating the prenatal androgen load 8. In humans, however, it is not possible to directly investigate the effects of prenatal androgens owing to ethical reasons and the long time period between the intrauterine window and the establishment of gender identity. For a more detailed description of gender dysphoria in patients with disorders of sex development and possible confounding variables, see Sadr et al. Additionally, studies examining subjects with congenital adrenal hyperplasia (CAH) or subjects with partial or complete androgen insensitivity syndrome (AIS/CAIS) suggest that (1) levels of gender dysphoria are higher when brain androgenization mismatches gender of upbringing and (2) that levels of gender dysphoria are lower when brain androgenization matches gender of upbringing 6. The theory of early organizational testosterone effects on gender identity is further supported by review evidence that transgender individuals’ brains show changes away from their natal sex and toward their perceived gender 5. Animal studies show an association between perinatal testosterone and the size of the bed nucleus of the stria terminalis (BNST) 3, a region linked to gender identity in humans 4. Despite the growing amount of research in this area, causal mechanisms are still unclear. This growth in prevalence is possibly due to greater social acceptance, de-pathologization, and greater awareness of therapeutic options 2. Evidence suggests that the prevalence has increased over the last decades to up to 5–14 male-to-female transgender (MtF) individuals per 1000 adult males and 2–3 female-to-male transgender (FtM) individuals per 1000 adult females 2. Transgender identity or gender dysphoria are defined as experiencing an inconsistency between physical phenotype and one’s perceived gender 1. This original investigation and the updated meta-analysis clarify the association between transgender identity and 2D:4D indicating the influence of prenatal androgen on the development of gender identity in subjects born as males. In both studies, no significant results were revealed for female-to-male transgender individuals versus female controls. Concordantly, the meta-analytic results suggest a significant difference in 2D:4D among MtF individuals compared to male controls, which was even more pronounced when individuals had been diagnosed by a clinician instead of self-identified as transgender. feminized) left-hand 2D:4D in the male-to-female transgender (MtF) identity than in the male control group with a Cohen’s d = 0.271. In our study providing new original data, we found a significantly higher (i.e. A random-effects meta-analysis of the literature (17 samples, n = 3674) also quantifies the overall magnitude of the difference in 2D:4D between transgender individuals and controls. Patients were recruited at a specialized psychiatrist’s medical office, whereas controls were hired via flyers, advertisements, and as convenience sample. In a study of 464 participants, we compared the 2D:4D of transgender individuals with age- and sex-matched controls. The objectives of the present study were to provide additional original data and an updated meta-analysis concerning this association. Previously reported associations between second-to-fourth digit length ratio (2D:4D), a proxy for prenatal androgen load, and transgender identity have been inconsistent. ![]()
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