Brains with a typically male design have been linked to an increased risk of autism.
The discovery provides the first anatomical evidence for the “extreme male brain” theory which argues that the developmental disorder arises from exaggerated male traits.
Autism spectrum disorder (ASD) is known to be two to five times more common in men than in women.
The condition varies greatly in severity and is marked by poor social communication skills, a narrowing of focus and obsessional tendencies – traits which in their milder form are often associated with men.
Scientists, mathematicians and engineers have been shown to be further along the autistic spectrum than people in less technical occupations.
The new study found that having a characteristically male brain structure was associated with a higher likelihood of being diagnosed with autism.
Scientists compared 98 men and women aged 18 to 42 with “high functioning” autism and the same number of neurologically normal individuals.
Magnetic resonance imaging (MRI) brain scans were used to measure differences in brain structure between the participants.
In particular, the researchers focused on the thickness of the cerebral cortex – the wrinkled and densely packed outer layer of neurons which is responsible for most of what makes us human, including awareness, thought, language and consciousness.
Men and women typically have differing thickness levels in different regions of the cortex.
The results of the research showed that a typically male pattern of cortical thickness was significantly associated with a higher probability of autism.
This was especially noticeable in women with ASD.
Women who had a more male-like brain anatomy were three times more likely to have been diagnosed with autism than those whose brain structure was typically female.
The authors, led by Dr Christine Ecker, from Goethe University in Germany, report their findings in the journal Jama Psychiatry.
They concluded: “Biological female individuals with a more male-typic pattern of brain anatomy were significantly more likely to have ASD than biological female individuals with a characteristically female phenotype (set of traits).
“This finding translates to an estimated variability in population prevalence from 0.2 per cent to 1.3 per cent respectively...
"These findings highlight the need for considering normative sex-related phenotypic diversity when determining an individual's risk for ASD and provide important novel insights into the neurobiological mechanisms mediating sex differences in ASD prevalence.”
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