Given estimates that one in 110 children in the U.S. is now affected by autism, speculation has reached a fevered pitch about what the autism risk factors actually are. New research highlights the possible role that family genetics might play, finding the likelihood that families with one or more autistic child will have another is far greater than previously thought.
The new study, published Monday in the journal Pediatrics, found that nearly 19 percent of infants with an older autistic sibling also developed an autism spectrum disorder (ASD). That figure represents a dramatic increase over previous sibling recurrence estimates, which ranged from 3 to 14 percent.
"For families with an autistic child, this is of high central interest to them -- this question of 'How likely am I to have another one?'" said Sally Ozonoff, Ph.D., a professor at the University of California at Davis' M.I.N.D. Institute and the study's lead author. "Previously the only answers we had were a bit outdated. This gives us a more updated picture."
The authors of the new study found that sex was a major predictor of recurrence, with males at an almost threefold risk of ASD. In addition, having multiple children with ASD seemed to play a key role in whether or not subsequent children developed autism.
"For families with two or more children with autism, the rate of recurrence was 32 percent," said Ozonoff, who admitted she was personally surprised by the finding. "That means there's almost a one-in-three chance that the next infant is going to have autism, which is very high. That does suggest that some families have higher genetic risk than others."
The new study is the largest to look at autism sibling recurrence rates to date, bringing together data collected from 12 sites participating in the Baby Siblings Research Consortium -- an international research effort funded by the advocacy group Autism Speaks.
"It's a very well done study," said James McPartland, Ph.D., an assistant professor of child psychiatry and psychology at Yale's Child Study Center, who was not associated with the research. He said he was not particularly surprised by the overall results, explaining they were consistent with increases in baseline autism prevalence. He cautioned, however, that they should not necessarily be perceived as bad news.
"These kinds of studies raise fears about increasing prevalence," McPartland said. "It's very unclear whether the increase that we see is due to changes in the biology of the world or improvements in diagnostic quality. If these kids were always there and now we're just recognizing them and treating them earlier, that's a positive thing."
Indeed, the authors of the new study suggest that the findings could be helpful in reminding parents of children with autism to closely monitor the development of their infants in order to get them into early intervention as needed. Previous studies have shown that early intervention can be helpful in improving language ability and behavior in children with ASD.
"For parents of children with autism, it's probably emphasizing things they already know -- that they should closely monitor their children and talk to health care providers to better recognize those early symptoms," said Alycia Halladay, Ph.D., director of research for environmental sciences at Autism Speaks. She added that the current study did not address causality, but simply "noticed that a strong family history was associated with a higher risk."
The study's authors also point out that the new figures can help families better assess their situation in genetic counseling and family planning, as it provides them with more accurate risk recurrence estimates.
But Ozonoff said that parents should not necessarily be disheartened by the updated figures.
"Even though these rates surprised and absolutely alarmed us, more than 80 percent of the infants we studied did not meet the criteria [for autism]," she told HuffPost. "For a family that has a newborn and a child with autism, they should absolutely keep that in mind."