The atypical brain development of transsexuals

Transsexuals are convinced that they were born in the body of the opposite gender and would do almost anything to change that fact. This transformation occurs step by step, by first taking on the social role of the other gender, then taking hormones and then undergoing a series of major operations, after which just 0.4 percent express regret later.

The gender team of the Vrije Universiteit Medical Centre in Amsterdam has been a pioneer in this field for many years, initially under the leadership of professor Louis Gooren and now of professor Peggy Cohen-Kettenis. This is unusual because the Bible, on which the VU is founded, states in Deuteronomy 22:5-6: “A woman must not wear men’s clothing, nor a man wear women’s clothing, for the Lord your God detests anyone who does this.”

 

In the womb

Male-to-female (M2F) transsexuality occurs in 1 in 10,000 men, and female-to-male (F2M) transsexuality in 1 in 30,000 women. Gender problems are often expressed early in development. Mothers describe how from the moment their son could talk, he would wear his mother’s clothes and shoes, he was exclusively interested in girls’ toys and mostly played with girls. But not all children with gender problems want to change gender later. If necessary, puberty can be delayed for a while with a hormone inhibitor to gain additional time to make a decision about whether to undergo treatment or not.

All of the data indicate that gender problems develop in the womb. Small changes have been found in genes involved in the effect of hormones on brain development, which increase the chance of transsexuality developing. Abnormal hormone levels in the fetus in the womb and medicines that the mother takes during pregnancy that disturb the breakdown of sex hormones can increase the chance of transsexuality developing.

Sexual differentiation of our genitalia occurs in the first few months of pregnancy while sexual differentiation of the brain takes place in the second half of pregnancy. As these two processes occur at different times, it is theorised that in transsexuality these processes are influenced independently of each other. If that hypothesis is true, then we would expect female structures in the male brains of M2F transsexuals and vice versa in F2M transsexuals.

Brain and hormones

In 1995 such a reversal of the gender difference was published by us inNature. It involved the bed nucleus of the stria terminalis (BSTc), a brain structure implicated in sexual behaviour. The BSTc was found to be  twice as large in men and contained double the number of neurons than in women. In M2F transsexuals we found a female BSTc. The only F2M transsexual we  could study did indeed have a male BSTc.

We could exclude the possibility that the reversal of the gender difference in transsexuals was caused by changed hormone levels in adulthood. Reversal must therefore have taken place during development. When a researcher finally does publish something interesting, the nicest comment that colleagues can come up with is: “This must first be confirmed by an independent group.” That can take a while, as it took me 20 years to collect the brain material for this study.

Thus, I was delighted to hear that Ivanka Savic’s research group the Karolinska Institute in Stockholm published a study last year of functional brain scanning of living M2F transsexuals. They had not yet been surgically altered nor had they started taking hormones. They were stimulated with male and female pheromones, scents that you pick up unconsciously. These scents produce different stimulation patterns in the hypothalamus and other brain regions in control men and women. The stimulation pattern in M2F transsexuals lay between that of men and women.

Last year Ramachandran, a psychologist and  neurologist in the United States presented an interesting hypothesis and preliminary results on transsexuality. His idea is that in M2F transsexuals the representation of the penis is lacking in the cerebral cortex and in F2M transsexuals the region for breasts during development is not mapped onto the cerebral cortex, which is why the brain does not consider the organs as its “own” and wants to get rid of them.

Everything indicates that during the early stages of development, the sexual differentiation of the brain occurs atypically in transsexuals, and not that they are “simply” psychotic, as a psychiatrist from Limburg recently dared to assert.

This article is posted on Friday 3 April 2009 om 11:11 uur.