Study Explores Why Autism is Different in Girls and Boys

Only one girl for every four boys is diagnosed with autism spectrum disorder (ASD). Girls are less likely to be diagnosed with autism than boys for a number of reasons, and researchers are still trying to understand how the developmental disorder differs between boys and girls.

A new study, published in the journal Brain, found that autism may develop in different regions of the brain in girls than in boys.

“What we are finding in boys isn’t necessarily relevant to what is going on in girls with autism,” Abha Gupta, MD, PhD, assistant professor in developmental-behavioral pediatrics at the Yale School of Medicine and a co-author of the study, tells Verywell.

For the latest study, the researchers compared brain scans and genetic data from about 45 children with ASD to a control group of children who did not have autism.

The results of their analysis also showed that girls with autism have more genetic mutations than boys with autism do—a finding that supports evidence from prior studies.

Evaluating Brain Structure

Gupta says that girls with ASD are understudied because they are diagnosed with autism less often than boys. One reason for this could be down to brain structure differences.

In the latest study, the researchers noted that different areas of the brain are affected in girls and boys with autism. In girls, the changes are seen in an area called the striatum, whereas boys with autism have changes in the temporal lobe.

“We know so little about how autism unfolds in the brain that it is important to know what brain structures might be involved,” Gupta says. “It might help us with more accurate diagnosis, and eventually, having more accurate biomarkers can help us with treatments.”

Researchers evaluated the children who took part in the study using functional magnetic resonance imaging (fMRI) which showed activity in the brain during the scan. The children also underwent genetic analysis.

The two groups of children—those with ASD and those without—had fMRIs of their brains while they watched displays of points of light that moved either like a human body or in a scrambled pattern. The human-like movements are the kind of socially meaningful motion that a person with ASD might not pick up on.

When researchers compared the fMRI results of the girls and boys in both the ASD and non-ASD groups, they found that the girls with ASD showed markedly reduced responses in the sensorimotor, striatal, and frontal regions of the brain compared to the girls without ASD.

Evaluating Genetics

For the second part of the study, the researchers looked at the results of genetic analysis on the boys and girls. They found that girls with ASD had more rare gene variants—which are typically expressed from a few weeks of conception to age 2— that are linked to the striatum of the brain.

The researchers noted that the striatum was also one of the areas of the brain that showed differences in the fMRI scans of the girls with ASD.

The study was a collaboration between experts in the fields of neuroimaging and neurogenetics. Gupta says that researchers “like to collaborate because we find that if our data point to the same regions of the brain that might be involved in autism it gives us a lot of confidence.”

Gupta says that her co-author, Alison Jack, PhD, assistant professor of psychology at George Mason University, has long been studying neural signatures in patterns of brain activity. One goal of the research is to figure out if there are patterns of brain activity that could serve as a biomarker for autism—which could improve how the condition is diagnosed and treated.

Why Girls Are Less Likely to Be Diagnosed

Many factors contribute to the difference in diagnosing ASD between boys and girls, from how clinicians assess the condition to the type of symptoms associated with it.

Gupta says that some of the differences are “probably due to biological differences that make boys more susceptible—like these female protective effects that protect girls versus boys.”

Diagnostic screening and tests for ASD are largely based on research on boys, and therefore they are not always as good at detecting the condition in other children.

Boys and girls with autism may behave differently. The behaviors that girls often show are not necessarily considered to be “typical” of ASD, which means that the diagnosis can be missed.

“Boys tend to have what we call more externalizing symptoms,” Gupta says. “Meaning they’re more outward in their disruptive behaviors.” On the other hand, Gupta says that “girls with autism tend to have more of what we call internalizing symptoms. So, they might be more quiet, more withdrawn.”

Addressing the Diagnostic Gap

The diagnostic disparity in ASD means that many girls with autism do not get a diagnosis, or that a diagnosis does not come until they are much older.

Not only does a lack of diagnosis have immediate effects in childhood, as it means that these children do not have access to support and services, but it can also affect their sense of identity, self, and well-being as they grow up. It can even do harm if they are misdiagnosed with—and even treated for—a different condition.

“We’re just not recognizing them,” Gupta says. “Or maybe we’re recognizing them later in life which is a disservice again to girls because we want to catch this as early as possible to provide support as early as possible.”

Gupta says that while having more accurate biomarkers for girls with ASD could help correct the imbalance in diagnosis, but she is “not quite sure it will be equal” because “there are probably some biological differences that make boys more susceptible than girls.”