In addition, it's been well-documented that boys are at least four times more likely to have autism than girls, and the new research hints at why this may be.
The study led by the Cold Spring Harbor Laboratory researchers found that girls with autism are more likely to have detectable de novo "events," that is, larger copy number variants and more genes involved in the deletions or duplications.
This suggests that it takes more, genetically speaking, to cause girls to have autism.
"It seems to take more hits or more damage to the genome to lead to autism in girls than in boys," Shih said. "That may start to explain some of the sex biases, that boys are more vulnerable genetically."
Interestingly, Schaaf added, most of the autistic kids in the Simons Simplex Collection were relatively high-functioning, Schaaf said. Among high-functioning autistic people, there's an even greater gender difference, he noted.
Still, much is unknown, including what might make boys more susceptible, Schaaf added.
In addition, the research does little to explain the vast majority of autism cases. Prior research has shown that about 5 percent to 7 percent of autism cases can be explained by a single gene disorder. Another 5 percent seems to be caused by metabolic conditions that affect brain function.
De novo copy number variants explain anywhere from 7 percent to 20 percent of autism cases with no known cause. But for the other 70-plus percent, there is no genetic explanation.
"It doesn't mean we'll [never] know the risk factors for the other 70 percent. Some could be environmental, some could be other genetic mechanism not yet discovered or that our current technology doesn't allow us to identify," Shih said.
It seems, he added, that "we are fast approaching the limitation of this particular technology."'/>"/>
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