New research reveals that siblings of children with autism more frequently have language delays, suggesting that they may also be affected by the genetics of the disease.
Led by researchers at the Washington University School of Medicine in St. Louis, the study not only identified the language delays in siblings but also other subtle characteristics of the disorder. While the mild nature of the traits were not strong enough to yield a diagnosis of autism, the study revealed that they were significantly higher in siblings of autistic children when compared to the general population — equating to one in five siblings.
“Mild symptoms, called quantitative traits, may be confounding studies that compare children with autism to their siblings,” says the study’s lead author, John N. Constantino, MD.
“Researchers presume one child is affected, and the other is not, but our findings suggest that although one child may have autism while the other does not, it’s very possible both children are affected to some degree by genes that contribute to autism.”
The study also revealed that girls may be mildly more affected than previously thought. While few of the female siblings had full-blown autism spectrum disorders, many were identified with the more subtle traits, researchers said.
Notably, this study found that the rate of autism in boys was approximately every three for every two girls affected. It was previously thought that four times as many boys have the disorder when compared to girls.
“The gender difference may not be as pronounced as we once thought it was,” Constantino says. “If we rely only on a professional diagnosis of autism to determine who is affected, then boys vastly outnumber girls. But it may be that many girls are being missed.”
Data for the study was drawn from the Interactive Autism Network, an online registry of more than 35,000 participants who share information to help advance autism research. The team identified 3,000 U.S. children for the study, and parents were asked to provide information about their children using the Social Responsiveness Scale, a survey developed at Washington University that identifies traits associated with autism and autism spectrum disorders such as Asperger Syndrome and Pervasive Developmental Disorder.
Statistics suggest that about 10 percent of children with autism have genetic mutations believed to lead to the disorder. For others, common gene variations create small increases in the potential for the disease.
“It’s not an all-or-nothing condition,” Constantino says. “When we look only at the full syndrome for inherited traits, we miss a lot of individuals who may have genetic susceptibility and subtle aspects of autism. In other words, many siblings of children on the spectrum have significant, subclinical traits of autism, but, for whatever reason, they never actually develop the disorder.”
Among the siblings, the findings revealed that 20 percent had been diagnosed with a language delay or speech problems early in life, and half of them had qualities of speech that are autistic in nature.
Other findings revealed that in families where only one child with autism exists, it is more common for siblings to have no evidence of quantitative traits.
Constantino added that although those severely affected with autism spectrum disorders seldom have their own children, those who are affected with quantitative traits of autism usually grow up to be parents themselves. An understanding how best to predict patterns of transmission in families and identifying the specific genetic and environmental factors underlying those patterns could offer hope for new, more effective interventions that could be used early in the lives of affected children.
The findings appear online and will be published in the November issue of The American Journal of Psychiatry.