Females may be inherently protected against autism, according to a team of Boston and European scientists. The finding may help explain why males have a significantly greater risk for the disorder.
It’s been long known that boys are more often affected by autism spectrum disorders, outnumbering girls four to one. However, it has remained unclear why there is a gender imbalance. Is it that males are more biologically susceptible to the disorder or are females somehow protected from it?
In a new study, scientists studied thousands of pairs of twins and found evidence that supports the idea that girls are protected.
“The first step is to understand what is going on. The question is whether being a girl actually truly prevents one from manifesting symptoms of autism,” said study leader Elise Robinson, Ph.D., an instructor in analytic and translational genetics at Massachusetts General Hospital and Harvard Medical School.
Researchers used two large databases of thousands of fraternal twins. These included information regarding any autistic behaviors, including problems with social interactions, communication and repetitive behaviors.
Since siblings share similar genetic risk factors and environmental exposures, studying the autistic traits of children within one family was one way of trying to isolate the role gender could play in the disorder.
The researchers found that females needed to have a greater burden of familial risk factors in order to manifest classical autistic behaviors—a sign that girls are protected.
This was done by comparing siblings of two groups: girls whose behaviors put them in the top 10th percentile of autistic behaviors and boys who were similarly ranked.
If gender had a protective effect, girls would be more likely to have a sibling with autistic traits than boys in the same group. This is because girls would need more familial risk factors to overcome the protective effect, and those same risk factors would also be found in their siblings.
John Gabrieli, Ph.D., a neuroscientist at the McGovern Institute for Brain Research at the Massachusettts Institute of Technology, said that the study was striking because it showed that something biological—in the genes or environment—is “muting” autistic traits in girls.
“It’s worth studying, practically, because it is so impressive. Because if you understood some of these mechanisms, maybe it would be a suggestion of a treatment for boys or prevention for boys, or a naturally-occurring preventive treatment,” Gabrieli said.
Next, the researchers will be investigating what factors could be protecting females from autism. That will be trickier to discern.
Robinson said she hopes to examine the known genetic risk factors in larger populations, to see if they cause greater risk to boys than girls. Robinson noted that autism in females may include different traits.
“The other option is being a girl changes the way a lot of these behaviors are manifested, so girls who are at risk may be protected from showing these traits that are extremely typical of autism as it is currently defined,” Robinson said.
“But they might show different behaviors or have different types of behavior problems we don’t understand yet, and I think it’s important to tease things apart.”