Male-to-female transsexuals are more likely to have a genetic variant that may cause weaker testosterone signals in the brain during early development, according to a new study. Researchers say the finding is another piece of evidence that there is a genetic component to these men's strong feelings that they're really women who were born into the wrong body, a theory many experts have long endorsed based on anecdotal evidence.
"People who come to our clinic describe how they knew they were different at a very early age, just three or four years old. This is something that people are born with," Dr [Trudy] Kennedy said [Sydney Morning Herald].
The findings are important, but lead researcher Vincent Harley admits he hasn't discovered a clear, single cause of transsexualism.
While the genetic link was statistically significant, it was weak – 55% of the transsexuals had the [genetic variant], compared with 50% of normal men. Harley agrees that many more genes related to male-to-female transsexualism probably remain to be discovered [New Scientist].
In the study, which will be published in an upcoming issue of Biological Psychiatry, researchers conducted a genetic analysis of 112 male-to-female transsexuals as well as a control group of men. They found that the transsexuals were more likely to have the long version of the androgen receptor gene, which controls how testosterone binds to cells.
It is known that longer versions of the androgen receptor gene are associated with less efficient testosterone signalling. This reduced action of the male sex hormone may have an effect on gender development in the womb, the researchers speculated. "We think that these genetic differences might reduce testosterone action and under masculinise the brain during foetal development," said researcher Lauren Hare [BBC News].
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