Autism Spectrum: Why Boys Are At Higher Risk

It is no secret gender plays a key role in the risk for a variety of childhood developmental disorders. Discussion of this issue is often difficult as biases in how boys and girls are raised and evaluated can contribute to confusion. Nevertheless, research progresses in explaining why boys are more likely to develop autism spectrum condition (ASC) and other neurodevelopmental abnormalities.

Baron-Cohen and colleagues from the UK and US recently summarized some of the potential mechanisms for male predominance in autism spectrum. They note a significant male predominance in a group of childhood neurodevelopmental disorders in addition to ASC:

• ADHD
• Conduct disorder
• Developmental reading disorders (dyslexia)
• Specific language impairment
• Tourette Syndrome

They note rates for ASC in boys is 4:1 compared to girls and for full autism is estimated as high as 11:1.

The authors note that predominance of ASC and other neurodevelopmental disorders in boys may be an “extreme expression of the male brain”. This concept states that boys and girls brains begin to differ early in the uterus. These differences result in different strengths and weaknesses. ASC may be an example of the male brain development gone too far.

Females appear to have a stronger drive to empathize (identify and respond to the feelings of others) while the male brain appears to have a stronger drive to systemize (analyze and construct rule based systems). The ASC as extreme male brain theory would propose the ASC brain is just the prototypical male brain gone to far in masculinization.

Males typically have three surges of the male hormone or androgen testosterone. The first surge occurs between 2 and 6 months in the uterus. This surge if felt to be responsible for brain masculization. The second surge occurs in the first six months of life and the third and final surge occurs in adolescence around puberty. If ASC is an example of the extreme male brain, then the fetal testosterone surge might be expected to be higher in those with ASC.

Progress in this front has evolved by comparing fetal testosterone levels with a variety of cognitive, behavioral and and emotional traits. Among normal children the following relationships have be discovered:

Positive associations with fetal testosterone levels (high levels with higher evidence of trait)

• Autistic traits
• Restricted or reduced interests
• Tendency to systemize
• Rightward asymmetry of brain corpus callosum (isthmus)

Negative associations with fetal testosterone (high levels with lower evidence of trait)

• Amount of eye contact
• Quality of social relationships
• Vocabulary size
• Empathy

Studies in those with ASC also appear to support the extreme brain hypothesis. Ten genes related to sex steroid synthesis, transport or metabolism have been linked to ASC or empathy traits. Testosterone levels tend to be higher in males with ASC than those without. Research in progress is likely to provide additional information on the merit of the extreme male brain hypothesis

The authors note there are other theories that might be supported in future research on the gender ratio in ASC. Two of these theories stem from differences in the X and Y chromosome.

A better understanding of why boys are at higher risk of ASC and autism is important. Such understanding might provide insight into avenues for early diagnosis and treatment.

Molecular model of the chemical structure of testosterone from Wikipedia Creative Commons file by Ben Mills. 


Baron-Cohen S, Lombardo MV, Auyeung B, Ashwin E, Chakrabarti B, & Knickmeyer R (2011). Why are autism spectrum conditions more prevalent in males? PLoS biology, 9 (6) PMID: 21695109