Biology of Transgender Persons

admin April 10, 2024 Understanding Identity Orientation Expression and Characteristics No Comment

Transgender people are those who feel like their gender doesn’t match the sex they were said to be when they were born. Sometimes, there’s confusion about the words used to talk about transgender people, which can make things tricky for doctors and others who help them. 

A long time ago in 1910s, a person named Magnus Hirschfeld came up with the word “transvestite” to describe people who like wearing clothes of the opposite sex. Then, in the 1940s, another US Psychiatrist named David Cauldwell used the word “transsexual” to talk about people who’ve had medical treatments to change their sex. Later, in 1967, an individual who is pioneer in transgender medicine named Harry Benjamin published about transsexual people, which made the word more well-known (Meyerowitz, 2009; Benjamin, 1967).

Before, being transgender was seen as a mental health issue, and the World Health Organization labeled it that way in a book called the International Classification of Diseases-10. But now, we understand more about the biological reasons behind why people feel like they’re a different gender. This has led to a big change in how we think about it. In the newest version of the book, called the International Classification of Diseases-11, released in 2018, WHO started using the term “gender incongruence” instead, and they put it in a different part of the book that deals with sexual health (WHO, 2018).

The term “gender dysphoria” is used to describe the distress someone feels when their gender doesn’t match the sex they were assigned at birth. Gender isn’t always just male or female. Some people feel like they’re in between or neither. A survey done in Netherlands found that around 3.2% to 4.6% of people felt this way (Kuyper & Wijsen, 2014). This can be challenging for healthcare providers because there isn’t a standard of care for “non-binary” population. At Ally Heart, we have LGBTQIA+ affirmative healthcare providers and clinical psychologists who helps you navigate your distress and confusion and embrace your true gender identity.

Many things can influence how someone’s gender identity develops. Some of these factors are biological. This includes things like prenatal (before birth) exposure to certain hormones (androgens) and how the brain is structured (neuroanatomy).

Exposure to androgens before birth:

Evidence from studies in animals, like guinea pigs, showed that when pregnant females were exposed to testosterone, their female offspring showed more male-like behavior when they grew up (Arnold & McCarthy, 2016; Phoenix et al., 1959). In humans, females with a condition called congenital adrenal hyperplasia, which exposes them to high levels of male hormones before birth, often prefer activities typically associated with boys when they are kids. These girls also have a higher chance of experiencing gender dysphoria, which means feeling uncomfortable with their assigned sex at birth (Hines et al., 2004; Dessens et al., 2005).

On the other hand, individuals with a condition called complete androgen insensitivity syndrome (CAIS), who are genetically male but don’t respond to male hormones, usually identify as female. However, there have been some rare cases where females with CAIS raised as girls identify as male (Wisniewski et al., 2000; Hines et al., 2003; Kulshreshtha et al., 2009, T’Sjoen et al., 2011).

Another condition, 5-alpha-reductase deficiency, causes ambiguous genitalia at birth due to a lack of a hormone called dihydrotestosterone. Some individuals with this condition are raised as girls but later transition to living as males during puberty. A study found that most of these individuals eventually identified as male during puberty, even though they were raised as female. However, it’s not clear if their gender identity changed or just their outward expression of gender (Cohen-Kettenis, 2005; Imperato-McGinley et al., 1979).

Brain Structure:

Some parts of the brain may be different between men and women. For instance, studies show that men tend to have larger total brain volume and amygdala, while women have a bigger cortical brain and hippocampus (Luders & Toga, 2010).

There’s a part of the brain called the bed nucleus of the stria terminalis (BST) in the limbic system, which is involved in sexual behavior in animals (Zhou et al., 1995). Researchers think there might be a link between gender identity and the size of this area. One post-mortem study found that transgender women had fewer neurons in the BST, similar to non-transgender women, while transgender men had more neurons in the BST. These differences were not because of hormone changes in adulthood but were established early in brain development (Zhou et al., 1995; Kruijver, 2000)

Another brain area called the interstitial nucleus of the anterior hypothalamus 3 (INAH3) also shows some differences between men and women. This area is linked to the BST and other brain regions related to gender identity and sexual behavior. Some studies suggest that the volume of INAH3 in transgender individuals matches their gender identity (Garcia-Falgueras & Swaab, 2008).

Endogenous Biology:

Gender identity isn’t determined by chromosomes. For example, people with XY chromosomes, like those with Complete Androgen Insensitivity Syndrome (CAIS), often identify as female (Wisniewski et al., 2000; Hines et al., 2003). However, there’s strong evidence that biological factors play a significant role in gender identity.

Studies with twins show that genetics can influence gender identity. One study with female twins suggested that genes might account for 11% of gender identity (Burri et al., 2011). Another study with both male and female twins estimated that family factors could affect gender identity by 24% to 31% (Bailey et al., 2007).

Research on transgender individuals and twins showed that 39% of identical twins shared transgender identity, while none of the non-identical twins did (Heylens et al., 2012). Although some studies have flaws, others suggest there might be genetic elements linked to gender identity or gender dysphoria (Coolidge et al., 2002; Sasaki et al., 2016).

Scientists have tried to find specific genes related to transgender identity. Some genes, like CYP17 (encoding for 17- a-hydroxylase) and RYR3 (related to calcium homeostasis), have been suggested to be associated with identifying as transmasculine (Ferna´ndez et al., 2008; Yang et al., 2017).

If you are also feeling gender dysphoria, you can book your first appointment at Ally Heart here.

REFERENCES:

  • Arnold AP, McCarthy MM. Sexual differentiation of the brain and behavior: a primer. In: Pfaff DW, Volkow ND, editors. Neuroscience in the 21st century. New York: Springer; 2016. p. 2139–68.
  • Benjamin H. The transsexual phenomenon. Trans N Y Acad Sci 1967;29(4): 428–30.
  • Burri A, Cherkas L, Spector T, et al. Genetic and environmental influences on fe male sexual orientation, childhood gender typicality and adult gender identity. PLoS One 2011;6(7):e21982. 
  • Cohen-Kettenis PT. Gender change in 46,XY persons with 5alpha-reductase-2 deficiency and 17beta-hydroxysteroid dehydrogenase-3 deficiency. Arch Sex Behav 2005;34(4):399–410. 
  • Coolidge FL, Thede LL, Young SE. The heritability of gender identity disorder in a child and adolescent twin sample. Behav Genet 2002;32(4):251–7. 
  • Dessens AB, Slijper FME, Drop SLS. Gender dysphoria and gender change in chromosomal females with congenital adrenal hyperplasia. Arch Sex Behav 2005;34(4):389–97.
  • Ferna´ndez R, Corte´s-Corte ´s J, Esteva I, et al. The CYP17 MspA1 polymorphism and the gender dysphoria. J Sex Med 2015;12(6):1329–33. 25. Bentz E-K, Hefler LA, Kaufmann U, et al. A polymorphism of the CYP17 gene related to sex steroid metabolism is associated with female-to-male but not male-to-female transsexualism. Fertil Steril 2008;90(1):56–9. 
  • Garcia-Falgueras A, Swaab DF. A sex difference in the hypothalamic uncinate nucleus: relationship to gender identity. Brain 2008;131(Pt 12):3132–46.
  • Heylens G, De Cuypere G, Zucker KJ, et al. Gender identity disorder in twins: a review of the case report literature. J Sex Med 2012;9(3):751–7. 
  • Hines M, Ahmed SF, Hughes IA. Psychological outcomes and gender-related development in complete androgen insensitivity syndrome. Arch Sex Behav 2003;32(2):93–101.
  • Hines M, Brook C, Conway GS. Androgen and psychosexual development: core gender identity, sexual orientation and recalled childhood gender role behavior in women and men with congenital adrenal hyperplasia (CAH). J Sex Res 2004; 41(1):75–81.
  • Imperato-McGinley J, Peterson RE, Gautier T, et al. Androgens and the evolution of male-gender identity among male pseudohermaphrodites with 5alpha-reduc tase deficiency. N Engl J Med 1979;300(22):1233–7.
  • Kruijver FP, Zhou JN, Pool CW, et al. Male-to-female transsexuals have female neuron numbers in a limbic nucleus. J Clin Endocrinol Metab 2000;85(5): 2034–41. 
  • Kulshreshtha B, Philibert P, Eunice M, et al. Apparent male gender identity in a patient with complete androgen insensitivity syndrome. Arch Sex Behav 2009; 38(6):873–5. 
  • Kuyper L, Wijsen C. Gender identities and gender dysphoria in the Netherlands. Arch Sex Behav 2014;43(2):377–85.
  • Luders E, Toga AW. Sex differences in brain anatomy. Prog Brain Res 2010;186: 3–12.
  • Meyerowitz JJ. How sex changed: A history of transsexuality in the United States. Cambridge (MA): Harvard University Press; 2009.
  • Phoenix CH, Goy RW, Gerall AA, et al. Organizing action of prenatally adminis tered testosterone propionate on the tissues mediating mating behavior in the female guinea pig. Endocrinology 1959;65:369–82. 9. 
  • Sasaki S, Ozaki K, Yamagata S, et al. Genetic and environmental influences on traits of gender identity disorder: a study of Japanese twins across develop mental stages. Arch Sex Behav 2016;45(7):1681–95. 
  • T’Sjoen G, De Cuypere G, Monstrey S, et al. Male gender identity in complete androgen insensitivity syndrome. Arch Sex Behav 2011;40(3):635–8.
  • Wisniewski AB, Migeon CJ, Meyer-Bahlburg HF, et al. Complete androgen insen sitivity syndrome: long-term medical, surgical, and psychosexual outcome. J Clin Endocrinol Metab 2000;85(8):2664–9. 
  • World Health Organization. WHO releases new International Classification of Diseases (ICD 11). Available at: http://www.who.int/news-room/detail/18-06-2018who-releases-new-international-classification-of-diseases-(icd-11).
  • Yang F, Zhu X-H, Zhang Q, et al. Genomic characteristics of gender dysphoria patients and identification of rare mutations in RYR3 gene. Sci Rep 2017;7(1): 8339.
  • Zhou JN, Hofman MA, Gooren LJ, et al. A sex difference in the human brain and its relation to transsexuality. Nature 1995;378(6552):68–70.