High level of male hormone in girls reveals autism clue
Studies of girls who make an unusually large amount of male sex hormone in their bodies have backed the idea that autism is caused by an "extreme male brain".
Prof Simon Baron-Cohen and Sally Wheelwright have uncovered new evidence that testosterone and other sex hormones thought to shape sex differences may cause autism by pushing brain development beyond that of a typical male.
In a study published in the journal Hormones and Behaviour, the team, with colleagues at City University, studied 34 girls with congenital adrenal hyperplasia (CAH) who, for genetic reasons, have high levels of a form of testosterone, and compared them with 24 unaffected sisters.
They found that the CAH girls, who develop some male physical characteristics, have more autistic traits than typical females.
Although they are not classed as having autism, which is marked by an inablilty to recognise and show emotions, they are closer to this end of the spectrum.
"These results suggest that prenatal exposure to high levels of testosterone influences some autistic traits and that hormonal factors may be involved in vulnerability to autism", said Prof Baron-Cohen of Cambridge University, the leading proponent of the "extreme male brain" theory.
To back this work, the team is to launch a new study of the mirror image condition, called androgen insensitivity syndome (AIS).
These individuals, such as Danielle Fray, 33, from Suffolk, are chromosomally male (XY) but are feminised because they have no docking sites in their bodies for testosterone.
A range of ambiguous genitalia result. In extreme cases they are raised as girls, and discover they are chromosomally male at puberty, only when they fail to menstruate because they lack ovaries.
"This is a very rare group, but we predict that they should have even fewer autistic traits than typical males or females," said Prof Baron-Cohen, adding that the study will also benefit those with AIS by highlighting their special needs.
"We are keen to encourage people with AIS to visit our website at www.cambridgepsychology.com/gender to help our research" he said.
The Cambridge team has assembled a wide range of support for the theory, which says that people with autism match an extreme of the male profile, with a particularly intense drive to systemise – find the laws that govern how a system works – and an unusually low drive to empathise.
Puberty tends to come earlier in boys with autism, supporting the idea that they have higher testosterone levels.
In physical terms, children with autism tend to have masculinised brains, being larger with a thinner corpus callosum and less long-range connectivity when compared with female brains.
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