Autism among siblings more common than once thought
■ Nearly 19% of infants who have an older brother or sister with an ASD also developed autism by age 3, a study shows.
By Christine S. Moyer — Posted Aug. 22, 2011
Pediatricians should closely monitor infants who have older siblings with an autism spectrum disorder, because those infants have an increased risk of having autism, a study shows.
The study, published online Aug. 15 in Pediatrics, found that 19% of such infants had an ASD when they were 3. Autism spectrum disorder includes autistic disorder, Asperger's syndrome and pervasive developmental disorder not otherwise specified.
The autism risk is even greater among children who have several older siblings with one of the neurodevelopmental disorders.
The 19% increase is up from previous estimates that autism occurred in 3% to 10% of children who have a sibling with the condition.
Lead study author Sally Ozonoff, PhD, said pediatricians should ask parents of high-risk infants questions about the baby's development during well-child visits. Such questions could include whether the child is interested in people and whether the infant is babbling.
If a red flag is identified, doctors are encouraged to refer the patient to a specialist for further testing and treatment. Warning signs include children who do not respond to their name by age 1 and those who avoid eye contact, have delayed speech and language skills, and repeat words or phrases, according to the Centers for Disease Control and Prevention.
Early specialized intervention could help reduce symptoms of the condition and overall disability, the study said.
Ozonoff encouraged pediatricians to think of the 19% increase as an average risk for children with older autistic siblings. She said the risk is higher for some children and lower for others.
"We can't say what a family's actual specific risk is," said Ozonoff, a professor of psychiatry and behavioral sciences at the UC Davis MIND Institute in California.
An average of 1 in 110 children in the United States has an ASD, the CDC said. Often, there are developmental concerns about the child before age 3.
Researchers examined data on 664 infants who were part of the Baby Siblings Research Consortium, an international network that pools data from individually funded research sites to study the earliest behavioral and biomedical markers of ASDs.
Participants in the Pediatrics study were from the U.S. and Canada. Each had at least one older sibling diagnosed with an ASD.
The infants were followed from early life to 36 months, when they were screened using the Autism Diagnostic Observation Schedule and the Mullen Scales of Early Learning. The diagnostic observation schedule assesses autism symptoms, and the scales of early learning measure nonverbal cognitive skills, language abilities and motor skills.
Researchers found that ASDs were more common among male infants, with 26% diagnosed with one of the conditions compared with 9% of females. Among participants who had multiple siblings with an ASD, 32% developed one of the conditions.
"Although the results were really alarming, it's important to keep in mind that overall, about 80% of the infants [in the study] did not develop autism," Ozonoff said.