A single gene may help unlock the mystery of why autism is more common in boys than girls, scientists report in the journal Molecular Psychiatry this week.

Autism occurs in boys at a rate of four to 10 times higher than girls but until now it has been unclear why.

Researchers examined DNA samples from the Autism Genetic Resource Exchange (AGRE), which includes DNA from thousands of individuals who have a family member with autism. They found that a variant of a gene called CACNA1G is more common among boys with autism than girls.

“This alternate form of CACNA1G consistently increased the correlation to autism spectrum disorders, suggesting that inheriting the gene may heighten a child’s risk of developing autism,” said Dr. Stanley Nelson, professor of human genetics at the University of California at Los Angeles who led the study. “We found that a common form of the gene occurs more frequently in the DNA of families that have two or more sons affected by autism but no affected daughters. Our study may explain why boys are more susceptible to the disorder than girls.”

It remains unclear how or why this gene affects the risk of getting autism and having the gene variant alone does not automatically mean a person will have the disorder.

“This variant is a single piece of the puzzle,” Nelson said. “We need a larger sample size to identify all of the genes involved in autism and to solve the whole puzzle of this disease.”

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