Autism's Earliest Symptoms Not Evident in Children under Six Months
Thursday, February 25, 2010

Condition is characterized by a slow decline rather than an abrupt loss of skills, study says

A study of the development of autism in infants, comparing the behavior of the siblings of children diagnosed with autism to that of babies developing normally, has found that the nascent symptoms of the condition — a lack of shared eye contact, smiling and communicative babbling — are not present at six months, but emerge gradually and only become apparent during the latter part of the first year of life.

Researchers conducted the study over five years by painstakingly counting each instance of smiling, babbling and eye contact during examinations until the children were 3. They found that by 12 months the two groups’ development had diverged significantly. Intentional social and communicative behavior among children developing normally increased, while among infants later diagnosed with autism it decreased dramatically. The study is published online early and will appear in the March issue of the Journal of the American Academy of Child & Adolescent Psychiatry.

“This study provides an answer to when the first behavioral signs of autism become evident,” said Sally Ozonoff, the study’s lead author, a professor of psychiatry and behavioral sciences and a researcher with the UC Davis MIND Institute. “Contrary to what we used to think, the behavioral signs of autism appear later in the first year of life for most children with autism. Most babies are born looking relatively normal in terms of their social abilities but then, through a process of gradual decline in social responsiveness, the symptoms of autism begin to emerge between 6 and 12 months of age.”

Children with a sibling already diagnosed with autism are known to be among those at greatest risk of developing the disorder. The current study included 25 high-risk children who met criteria for autism at 3 years of age, matched with 25 low-risk peers who were developing normally. It was conducted at the MIND Institute and the University of California, Los Angeles. The sole inclusion criterion for the high-risk group was having a sibling with autism; low-risk participants had to have been born after 36 weeks gestation and have no autistic family members.

The children’s development was evaluated at 6, 12, 18, 24 and 36 months of age using a series of widely implemented diagnostic tools, including the Autism Diagnostic Observation Schedule (ADOS) and the Autism Diagnostic Interview-Revised (ADI-R). Examiners were not told which babies were at high or low risk when evaluating the participants’ development.

The researchers found that there were few discernable differences between the two groups at the outset, but that after six months, 86 percent of the infants who developed autism showed declines in social communication that were outside the range for typical development. “After six months,” the study found, “the autism spectrum disorder group showed a rapid decline in eye contact, social smiling and examiner-rated social responsiveness.” Group differences were significant by 12 months in eye contact and social smiling and all other measures by 18 months, the study found.

Ozonoff said that the study does not address the etiology of autism or causality. In this study, the infants who participated were at high risk due to having strong family histories of autism, suggesting that genetics plays a major role in the later autism diagnoses, despite the fact that their symptoms were not apparent at birth.

Adapted from a MIND Institute press release.

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