May 4, 2007 -- Toddler siblings of autistic children are more likely to exhibit some of the same atypical social behaviors as their brothers and sisters with autism, even when they don't go on to develop the disorder, new research shows.
The findings bolster the evidence for a strong genetic component to autism and show that siblings of children with the disorder are at high risk for some of the same social functioning deficits as their brothers or sisters.
University of California, San Diego assistant professor of psychology Leslie Carver, PhD, presented the findings at the 2007 International Meeting for Autism Research in Seattle.
Studying at-Risk Siblings
The risk that the younger sibling of an autistic child will also develop autism or a related disorder is estimated to be around 2% to 8%, compared to the latest CDC estimate that 1 in 150 children may have autism or a related disorder.
In an effort to better understand this risk and to identify the earliest behavioral and biomedical markers of autism and related disorders, leading autism researchers and research organizations established the High Risk Baby Siblings Research Consortium in 2003.
"Studying this population should help us identify at-risk children earlier so that we can get them the help they need as early as possible," Alison Singer, of the advocacy group Autism Speaks, tells WebMD. "It may also give us important clues about the early onset of autism."
In the newly reported sibling research, Carver and colleagues compared the social referencing reactions of toddlers with and without autistic siblings.
Social referencing refers to regulating your own behavior in response to the behavior of others. It is expected that toddlers tend to begin social referencing toward the end of their first year of life.
But this reaction tends to be impaired in children with autism.
The study involved 18 18-month-old siblings of children with autism (deemed high-risk) and 28 18-month-olds with no family history of the disorder (deemed low-risk).
In the behavioral portion of the experiment, the children were presented with three new toys; their caregivers were trained to react to the toys with facial expressions and vocal signals that were positive, negative, or neutral. The interactions between the toddlers and the caregivers were videotaped.
The high-risk toddlers were found to differ in almost every aspect of social referencing from their lower-risk counterparts. While they looked to adults as quickly to gauge their reactions, they did so about 30% less often. And they were less likely to respond to the cues they got from the adults.
Andy Shih, PhD, who manages the Baby Sibling Research Consortium, says the findings underscore the importance of closely monitoring the high-risk siblings of children with autism.
Shih is chief science officer for Autism Speaks.
"Clearly it is not just the siblings [with autism] who are being affected," he says. "In order to help support families dealing with autism, greater attention needs to be focused on all the children."
Singer's oldest daughter Jodie, now age 10, is autistic, while Jodie's 7-year-old sister Lauren is not.
Singer says her youngest daughter was a late talker who required two and a half years of speech therapy.
"I was, of course, frantic early on," she says. "I watched her like a hawk for signs. Parents who have a child with autism know the red flags, but all parents need to know the early warning signs of autism."
Autism spectrum disorders include autistic disorder, Asperger's syndrome, and pervasive developmental disorder (including atypical autism). These disorders involve impairments with social, communicative, and behavioral skills.