In what may help explain why autism is far less common in girls than boys, new research suggests that females have a “protective effect” against the developmental disorder.

Statistics show that autism is nearly five times more common in boys than girls, but it’s long been unclear why the gender disparity exists.

In a study published this week, researchers found evidence to suggest that there is something about girls that’s warding off the development of autism, though it remains uncertain exactly what factors are providing that protection.

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Researchers led by Elise Robinson of Harvard Medical School looked at nearly 10,000 sets of 12-year-old fraternal twins from the United Kingdom and Sweden, identifying the level of autistic traits present in each child. When they focused on the girls and boys in the study with the highest number of autistic traits, the researchers found that as a group, the most affected girls had more family risk factors for the developmental disorder, on average, than the most affected boys.

In other words, the researchers found that more risk factors needed to be present for a girl to show signs of autism than for a boy.

“This finding suggests that there is a component of (the) female sex that protects girls from ASDs,” the study authors wrote in their findings published in the Proceedings of the National Academy of Sciences.

“An understanding of the biology underlying female advantage could greatly aid progress in understanding the phenomenology of autistic behavior and in identifying prevention factors for ASDs,” they wrote.