Autism is diagnosed around four times more often in boys than girls, a striking disparity that has puzzled scientists for years.
Now, new research may offer a clue as to what is driving the gap.
A study published in the American Journal of Human Genetics explored genetic differences that could help explain why autism is diagnosed more frequently in males.
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Corresponding author Dr. Huda Zoghbi, Distinguished Service Professor at Baylor College of Medicine and director of the Duncan Neurological Research Institute, told Newsweek that the researchers focused on genetic differences passed from healthy mothers to sons with autism.
"We were excited to see that some differences that we think are contributing to autism are actually inherited from a healthy parent," Zoghbi said.
The team studied differences on the X chromosome. Because females typically have two X chromosomes while males have one, Zoghbi said a mother may be protected from the effects of a particular variant by her second X chromosome, while her son could be more vulnerable.
"We think cases like this could help explain why more males are diagnosed with autism than females," she said.
Autism spectrum disorder (ASD) affects communication, social interaction, and behavior.
Scientists have increasingly questioned whether the diagnostic disparity between males and females is driven by biological differences alone, or whether girls are also more likely to be missed by existing diagnostic approaches.
The researchers examined genetic data from 8,245 families, including 9,437 autistic individuals. They identified 22 rare candidate variants in regulatory regions of the MECP2 gene.
Clinical psychologist Karen Sheridan, who was not involved in the research, said the findings were promising but said they should not be applied too broadly.
"Autism is a highly heterogeneous neurodevelopmental condition, and one genetic mechanism cannot explain autism in all boys," Sheridan told Newsweek.
She also stressed that showing a variant alters gene expression in laboratory-grown neurons does not prove that it caused an individual's autism.
The findings could ultimately have implications for diagnosis.
"We hope that as we develop a better understanding of the genetics of autism, genetic testing will have a role to play in diagnosis of both boys and girls," Zoghbi said. "This work helps illustrate that the genetic causes of autism in boys and girls might be different, which could ultimately help improve diagnosis for girls."
But genetic susceptibility and differences in diagnosis rates are not necessarily the same thing. Sheridan cautioned against attributing the four-to-one disparity primarily to genetics, noting that autism research and diagnostic expectations have historically focused heavily on male presentations.
Girls and women may display less conspicuous repetitive behaviors or use camouflaging strategies that make autistic characteristics less apparent, potentially contributing to later or missed diagnoses.
A large Swedish study published earlier this year found that while boys are diagnosed more frequently during childhood, girls begin to close the gap during adolescence, with diagnosis rates becoming increasingly similar by early adulthood.
Sheridan said biological differences may contribute to autism susceptibility, but differences in recognition, referral and assessment may also influence who ultimately receives a diagnosis.
"We must be careful not to confuse discovering why some boys may be genetically susceptible to autism with explaining why so many girls and women have historically gone undiagnosed," she said.
Reference
Meyer-Schuman, R., Cherry, F., Sui, Y., Papastathopoulos-Katsaros, A., Zhong, Y., Li, Y., Wang, T., Hennick, K., Karunakaran, D., Berk-Rauch, H., Liu, Z., Chakravarti, A., Nowakowski, T., Eichler, E.E. and Zoghbi, H. (2026). A massively parallel reporter assay of MECP2 cis-regulatory elements reveals genetic candidates for male-biased autism. The American Journal of Human Genetics. [online] doi:10.1016/j.ajhg.2026.09.011.
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