Aetiology

The causes of gender incongruence/gender dysphoria are unknown. At first, hypotheses about causation addressed psychological factors and came mostly from a psychoanalytic perspective. Over the decades, however, available evidence has suggested a multifactorial aetiology, with biological and social factors rising in importance.[16][17]

There is known to be a slightly elevated rate of gender incongruence and dysphoria among people with Klinefelter's syndrome and congenital adrenal hyperplasia.[18][19][20][21][22]​ It is also known that birth-assigned males with gender incongruence and dysphoria are more likely than the general population to be left-handed.[23] A genetic association has been postulated as one possible cause of gender incongruence and gender dysphoria; a review of case report studies suggests higher rates in monozygotic twins versus dizygotic twins.[24] There is some evidence to suggest that CYP17 is a gene associated with the development of gender incongruence and gender dysphoria in birth-assigned females.[25]

Some observations suggest children and adults with gender incongruence and gender dysphoria show more features of autism spectrum disorder (ASD) than the general population.[12][13][26]​​ At one gender clinic prevalence of autistic traits consistent with a clinical diagnosis of ASD among individuals undertaking treatment was 5.5%, compared with reports of 0.5% to 2.0% ASD diagnoses in the general population.[26] Transgender people with ASD sometimes have an atypical presentation of gender dysphoria/incongruence, which makes a correct diagnosis and determination of treatment options for gender dysphoria/incongruence more difficult.[12][27]

Pathophysiology

As a general rule, neurological and physiological function in transgender people appear to be the same as in the general population.

However some small differences in brain structure have been suggested.​ One small study showed that the size of the bed nucleus of the brain's stria terminalis was in keeping with the person’s sense of gender rather than their birth-assigned sex.[28] Another study showed white matter changes in birth-assigned female transgender people prior to hormone treatment that were akin to those seen in non-transgender males.[29] Magnetic resonance imaging of transgender women suggests the presence of a larger, female-like putamen compared to that found in controls (non-transgender males).[30]

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