Gray matter volume differences between transgender men and cisgender women: A voxel-based morphometry study.

Abstract

Gender dysphoria (GD) is characterized by distress due to inconsistency between gender identity and biological sex. Individuals with GD often desire to be the other gender, which is called transgender. Although altered brain volumes in transgender people, particularly transgender women, have been reported, the particular brain regions have been inconsistent among studies. This study aimed to investigate neuroanatomical differences in transgender men without physical interventions. T1-weighted magnetic resonance images (MRIs) were acquired in 21 transgender men and 21 cisgender women matched for biological sex and age. Whole-brain comparisons using voxel-based morphometry (VBM) were performed to identify gray matter volume (GMV) differences between transgender men and cisgender women. Transgender men showed greater GMV in the right posterior cingulate gyrus (PFWE-corr = 3.06×10-6) and the left occipital pole (PFWE-corr = 0.017) and lower GMV in the left middle temporal gyrus (PFWE-corr = 0.017) than cisgender women. Even after including serum sex hormone levels as covariates, the posterior cingulate gyrus was still significant (PFWE-corr < 0.05). In contrast, the occipital pole and the middle temporal gyrus were not significant after controlling for the sex hormone levels (PFWE-corr > 0.05), especially affected by testosterone but not estradiol. These findings suggest that transgender men have altered brain structure. We suggest that larger posterior midline structures may contribute to sensitivity to self-referential processing through altered visual perception in transgender people.