Background: Gender dysphoria is characterised by an incongruency between the perceived gender identity and the biological sex. The cause of gender dysphoria is unclear and environmental as well as genetic factors may be important. It is well known that during sexual differentiation sex steroids control not only the differentiation of the internal and external genitalia but also the sexual differentiation of the brain. Structural as well as functional differences have been shown between the male and female brain.
Objective and Hypotheses: We hypothesised that this sexual differentiation of the brain may be atypical in children and adolescents with gender dysphoria.
Method: We analysed brain MRI scans of 91 gender dysphoric adolescents (54 female-to-male and 37 male-to-female) for differences in gray matter volume using voxel based morphometry. Data of gender dysphoric individuals were compared to controls (44 boys and 52 girls). In addition fMRI scans were acquired of gender dysphoric adolescents and controls while performing cognitive tasks (mental rotation and tower of London).
Results: Voxel based morphometry showed six sexually dimorphic areas, three male and three female dominant. The gray matter volume in these areas in gender dysphoric individuals was in between male and female values, showing a pattern of volumes being larger in females than female-to-males than males-to-females than males, or vice versa. Performance on the cognitive tasks was similar in males and females. fMRI scans did however show sexually dimorphic activity levels in certain brain areas. Again, activity levels in these brain areas in gender dysphoric individuals were in between those of males and females.
Conclusion: Structural and functional differences between the male and female brain are already obvious in adolescence. In individuals with gender dysphoria subtle differences in brain structure and function were identified compared to controls of the biological sex.
20 - 22 Sep 2014
European Society for Paediatric Endocrinology