Joslyn Gray, 38, of Drexel Hill, Pa., resisted her pediatrician's recommendation that she have her 4-year-old son tested for autism. She didn't think he fit the classic description of autism.
He showed emotion. He showed affection toward her. That wouldn't be possible for someone with autism, Gray believed.
"I didn't understand what autism was and the vast spectrum of the disorder," said Gray, who blogs for Babble.com, a Disney-owned online parenting magazine (Disney is also the parent company of ABC News). "I got him evaluated because I didn't want to be seen as a mom in denial."
Gray's son was diagnosed with Asperger's syndrome -- a higher functioning form of autism -- at age 4. In hindsight, Gray said she could see how his symptoms progressed until his diagnosis, and his diagnosis prompted her to have her daughter tested too. Two years later, in January 2012, her daughter, now 10 years old, received the same diagnosis as her brother.
The latest statistics released by the U.S. Centers for Disease Control and Prevention estimate that autism spectrum disorder increased by 23 percent from 2006 to 2008 to include nearly one in 88 children.
Experts said the growing numbers reflect an all-encompassing disorder that just as often includes children who speak or don't speak, make eye or don't make eye contact, recognize their names or not.
While experts remain perplexed about what causes autism, Gray said for her kids, she knew the answer.
"In our case, it's so clearly genetic," she said, even though medical experts cannot yet confirm the exact cause of any autism diagnosis. "There's no doubt in my mind."
And many scientists agree that the growing autism numbers may in part be attributed to certain genetic mutations that are most likely inherited from the father, according to the combined findings of three studies published Wednesday in the journal Nature.
The studies are the largest to date to use whole-exome sequencing, which decodes the protein in both children and their parents, an arguably more precise method of detecting genetic mutations in multiple genes that may be associated with autism.
The findings from one of the studies supports mounting evidence suggesting that the older the father, the higher the chance the child may develop some form of autism.
In another study, researchers who compared siblings with and without autism found that the sibling with autism had two different mutations of the gene SCN2A.
Genetic mutations found in the child with autism that were not found in either parent are likely not associated with autism, one of the studies concluded.
But these findings further suggest that autism is a genetically complex disease, Dr. Daniel Geshwind, a professor of neurology and psychiatry at UCLA, told ABCNews.com. Several genes contribute, as the average risk imparted by one mutation is typically not enough.
There are currently upward of 1,000 genes that seem to play some role in autism, but it's still not clear exactly what that role is.
"The genes highlighted are clearly the most convincing susceptibility genes that have been identified so far, but they only explain a small picture of autism," said Dr. Mark Daly, chief of the analytic and translational genetics at Massachusetts General Hospital, and co-author of one of the studies.