A comparison of autism-like behaviors in nearly 10,000 pairs of fraternal twins suggests that girls are somehow protected from the disorder.
The findings, published 19 February in the Proceedings of the National Academy of Sciences, may partly explain why autism is four times more common in boys than girls — one of the oldest and most puzzling statistics in the field.
The study measured autism traits — such as conversational abilities, social preferences and repetitive behaviors — in children in the general population. Among children who have many autism symptoms, girls are more likely than boys to have siblings who also have the traits, the study found.
The findings suggest that girls have a baseline level of protection, and don’t display many autism traits unless they’re “loaded up to the gills with risk factors,” says lead investigator Angelica Ronald, senior lecturer in psychological sciences at Birkbeck, University of London.
Risk factors in these families may include inherited genetic variants, shared environmental influences or some combination of both, she says.
The study does not address the larger question of how this protective effect might work. It might be rooted in biological differences between the sexes. Or it might not really be a matter of protection at all, but rather the result of bias in how clinicians diagnose the disorder, the researchers say.
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