Autism in women is rare: men are four times as likely to be diagnosed with autism spectrum disorder, and so scientists haven’t spent as much time studying the disorder's genetic imprint in women. A newly identified gene could change that, according to a study published in Nature today. The gene has been found to play a role in severe autism in women — as well as some men. The finding could motivate more researchers to study the disorder in families in which multiple women are affected by autism.
studying autism in women is beneficial for autism research as a whole
Women experience something called the "female protective effect," which means they need either more severe mutations or many more than men to develop the disorder, says Tychele Turner, an autism researcher at The University of Washington and a co-author of the study. That also means that studying autism in women could be very beneficial for autism research as a whole: women might be more useful to reveal which mutations cause severe autism, Turner says. This is exactly what her research group achieved, after all.
In the study, Turner and her team analyzed the genes of 13 unrelated women with severe autism, who also have relatives affected by the disorder. They found that a gene called CTNND2 has more mutations than one would expect to see in someone without autism, which led them to conclude that the gene probably played a role.
"We assessed thousands of additional patients to determine if the genetic signal we found was real."
A genetics study with only 13 participants isn’t all that convincing, though. So, the researchers sifted through genetic data from thousands of other people, gathered from past studies. "We assessed thousands of additional patients to determine if the genetic signal we found was real," Turner says. The additional patients showed that, in general, people with autism tend to have mutations in this gene more often than people without. "There are a number of cases — more than we would have expected — that have a severe mutation in this gene."
Still, finding that these mutations occur more often in people with severe autism doesn’t mean the mutations cause the disorder or its symptoms. So, the researchers tinkered with the genes of zebrafish, to make the animals express the mutations. The researchers found that the mutations caused problems in a biological pathway — a set of molecular changes that are linked in the body — that has previously been associated with autism. Researchers then moved to mice, where they muted the CTNND2 gene. As a result, neurons in the hippocampus, a sea horse-shaped area which is important for long-term memory, didn't "talk" to each other as much.
"The findings are very exciting," says Kevin Pelphrey, an autism researcher at Yale University who didn’t participate in the study. The fact that they looked at zebrafish and mice to see the effects of the gene, and modeled its role in neuron development is very novel, he says. "They go well beyond finding this gene." The overall approach employed by Turner’s team is "groundbreaking in terms of the methods and the extent to which these researchers demonstrate how the gene can lead to autism."
"underrepresented patients are very important, and we should study them."
Now that the study has been published, Turner has moved on to researching autism in a more commonly researched population: men. But she thinks her work might jump-start more research on women with autism. Families with multiple affected women are "extremely rare and they have been underrepresented in previous large-scale genetic screens," Turner says. But "underrepresented patients are very important, and we should study them — just because they are more rare doesn’t mean that they should be excluded from our study."
"The finding will lead other researchers to adopt this ground-breaking approach," Pelphrey says. The implications for treatment aren’t immediate, however. Instead, the findings will serve as a basis for the study of mechanisms that lead to autism, especially autism in women. And further research on this gene and its function could eventually mean gene therapies or drug therapies down the line. "It will take time to develop these therapies," Pelphrey says. "But the findings in this paper pave a pathway forward."