Why Is Autism in Girls Less Prevalent than in Boys?

Why does autism affect four times as many boys than girls? Is autism in girls less common, are girls better at hiding it, or are they often excluded from studies?

Nancy, age 13, is the only girl in her class of 12. She attends a private school for children with autism. At her pre-K through 12+ school there are about 2, maybe 3, girls in each class. Autism affects one out of every 68 children in America; four times as many boys than girls have some form of autism, and on the high-functioning end of the spectrum, there are 10 boys for every girl with autism.

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What is autism?

The Centers for Disease Control and Prevention describes autism spectrum disorder (ASD) as a developmental disability that can cause significant social, communication, and behavioral challenges. It’s called a “spectrum” because it refers to several conditions ranging from mild to severe. A person at the high end of the spectrum may be socially awkward. At the opposite end of the spectrum, a person with autism might not be able to speak, have repetitive behaviors, and have difficulty with everyday life.

Nancy’s parents suspected she had autism. She was told, however, “she’s a girl, so it’s unlikely,” her mother said. “Most of the data derived from autism studies come from research done on boys, not girls.”

Girls are often better at socializing than boys; they also may be better at masking their problems in order to fit in. “Girls tend to want to socialize and be part of a group,” said Louis Kraus, MD, a psychiatrist at Rush University Medical Center in Chicago, where he specializes in autism.

Research shows scientific reasons why autism in girls is less common, too.

Why does autism affect more boys than girls?

Tychele Turner, PhD, a senior research follow at the University of Washington, is focusing her work on autism in females. “There are many possible reasons for so few girls receiving a diagnosis of autism,” she said. “They may include under-diagnosis, as girls may have different symptoms or hid their autism more successfully.”

Turner is also a Weatherstone fellow, thanks to a research program funded by Autism Speaks. Through this fellowship, Turner and her colleagues studied girls and their families; the participants in this study had two or more females in their families with autism.

They found 18 unknown genes that were linked to autism. One of those genes, CTNND2, is connected with brain development. Her studies analyzed this gene’s activity in the developing brains of zebra fish, mice, and post-mortem human brain tissue.

The CTNND2 gene produces proteins that likely play a key role in early brain development. The research found mutations in CTNND2, which disrupted the connections that form between brain cells. “In terms of genetics,” Turner wrote, “this means that autism in females tends to involve more genetic “hits,” or severe mutations, than it does in boys.”

Autism in girls

That’s where her Weatherstone research comes into play. Turner and her colleagues used a new gene-sequencing technique to sequence all the genes in a group of girls and women on the autism spectrum.

The results of the study appeared in the journal Nature. “In addition to showing the important role that CTNND2 can play in autism,” Turner said, “our research broke ground in other directions as well.”

Turner wrote, “It clearly demonstrated the power of studying autism genetics in girls and women. Because females need those more powerful genetic hits to develop autism, their genomes are particularly valuable for finding autism-linked genes. We proved the usefulness of this approach by discovering 18 genes that link to autism.”

Turner and her colleagues hope that their findings will guide future research in female autism. She is analyzing the whole-genome sequencing data from thousands of people with autism and their family members; many of the people in this research are participants in the Autism Speaks MSSNG project.

Turner’s goal is to find additional genetic risk factors for autism.

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