People suffering from androgen insensitivity syndrome (AIS) are male from a genetic point of view but feel profoundly female. Mental rotation tests have shown that these people activate the same areas of the brain as women to solve these tasks.  This research, led by Julie Bakker, FNRS senior research fellow and project leader at the University of Liège’s GIGA Neurosciences, suggests that sex hormones are more influential than genetics on the sexual differentiation of the brain.

Changing sex in the space of a day? Many people have already expressed this wish at least once... To satisfy their curiosity, and just to feel and understand what it's like to be in the skin of a girl or a boy... However, you don’t choose to be born a girl or a boy. Genetics are the deciding factor! However, the latter isn’t infallible and can, in certain cases, lead to situations where the border between male and female isn’t clearly distinguished.

This means that some people are born with male and female genital organs. This is referred to as intersex. This anatomical ambiguity almost inevitably leads to sexual identity issues. Furthermore, the definition of gender isn’t limited to an individual’s genital organs. People with all the physical characteristics of a man can feel deeply female. That’s because the differences between men and women are also located in the brain. This is what is known as the sexual differentiation of the brain. This begins when the embryo develops until puberty. FNRS senior research fellow and project leader of the GIGA-Neurosciences’ Research Group in Behavioural Neuroendocrinology at the University of Liège, Julie Bakker studies the mechanisms underpinning the sexual differentiation of the brain in order to better understand gender identity problems.

Puberty,  a moment of truth that is difficult to accept

To study the sexual differentiation of the brain, Julie Bakker and her team work not only on transgenic mouse models (see the article “A male or female brain? A question of oestradiol!") but also on human models. Within the framework of a recently published study in the journal Cerebral Cortex (1), the researcher focused on complete androgen insensitivity syndrome (CAIS). People with the latter are genetically male but have a female sexual identity.  “They have an X chromosome and a Y chromosome like men but don’t have androgen receptors and are therefore insensitive to these hormones that play a key role in the masculinisation of tissues and the brain”, explains Julie Bakker. Consequently, CAIS leads to a female appearance. “In general, we become aware of the problem quite late, during puberty if a girl hasn’t started menstruating yet”, the researcher points out. “We discover at this point that these women don't have a uterus or ovaries but have testicles in the abdominal position. In the majority of cases, it is recommended that the testicles are removed and that they follow an oestrogen treatment, i.e. female sex hormones”. While this helps them to decide on their sexual identity, these women without any female genital organs can’t have any children... A fact that is very difficult to accept by those who had always imagined becoming a mother one day. The work of Julie Bakker aims to better understand the mechanisms underlying the sexual differentiation of the brain in order to be better able to prevent the appearance of such problems and/or better support and orient those in question.  

(1) Van Hemmen J, Veltman DJ, Hoekzema E, Cohen-Kettenis PT, Dessens AB, Bakker J. Neural Activation During Mental Rotation in Complete Androgen Insensitivity Syndrome: the Influence of Sex Hormones and Sex Chromosomes. Cereb Cortex. 2014 Dec 1. pii: bhu280.