Magnetic Resonance Spectroscopy in Gender Dysphoria

Background: Much research has been conducted on sexual dimorphisms of the human brain to determine whether and to what extent a brain gender exists. Consequently, a variety of studies using different neuroimaging techniques attempted to identify the existence of a brain phenotype in people with gender dysphoria (GD). However, to date, brain sexual dimorphisms at the metabolite level in transgender people have not been explored using magnetic resonance spectroscopy ((1)H-MRS). Methods: In this study, 29 transgender men, 30 cisgender men and 35 cisgender women underwent (1)H-MRS at 3 Tesla MRI to characterize common brain metabolites. Specifically, absolute levels of N –acetyl aspartate (NAA), choline (Cho), creatine (Cr), glutamate (Glu), myo-inositol (mI) and their respective ratios were assessed in two brain regions, i.e. the amygdala-anterior hippocampus and the lateral parietal cortex. Influences of nicotine consumption, physical activity, education and psychopathology were considered. Results: The results indicated a sex-assigned at birth pattern for choline and glutamate ratios in the amygdala-anterior hippocampus of trans men. In the lateral parietal cortex cis men and cis women differed in the majority of metabolites (i.e. mI; Cr; NAA/Cr; Cho/Cr; mI/Cr; NAA/mI). Moreover, except for mI, trans men did not differ from either cisgender group, showing a pattern subtly moving towards the experienced gender identity. Post-hoc, careful exploration of the age of onset of GD in transgender men demonstrated the possibility of a developmental trend in absolute NAA levels, as a measure of neuronal function. Conclusion: We found sex-typical (1)H-MRS spectra and they appear to be brain region specific. While the brain metabolite levels in trans men mostly resembled that of cis women, interesting findings such as modulation by age of onset warrant future enquiry to address potential neurobiological underpinnings of GD.