Boys don’t cry. They climb trees, fight, and play with trains. Girls are different. They prefer horseback riding, pinky glitter clothes, and playing with dolls. Of course there are exceptions and not all kids fit within these stereotypes. But a few children are more extreme. They strongly identify and behave as the other gender, and express the wish or conviction tobe the other gender. These children fulfill the criteria for the diagnosis

Gender Dysphoria (GD), the extreme feeling of incongruence between one’s experienced gender and one’s natal sex.
The goal of my PhD thesis was to answer the question whether children with GD, next to their gender-variant behavior, may actually have the brain characteristics of the opposite gender. There are subtle sex differences in the brain in terms of functions and structure, which already develop before a child is born, and then get accentuated during puberty. Using magnetic resonance imaging, we tested two age groups, prepubertal children and 16 year old adolescents, in order to investigate the contribution of sex hormones, during these two developmental phases, on brain sex differences. Our findings indeed suggest that children with GD show certain brain sex characteristics that better match and reflect their experienced gender, rather than their natal sex. However, this was not equally seen in both the gender dysphoric boys and girls, and also depended on the type of measure. Besides, the sex-atypical brain characteristics were more clearly observed in the older, gender dysphoric adolescent groups, suggesting an important role for puberty.