BALTIMORE -- About half of children who develop autism may be diagnosable by 14 months of age, researchers found in a small study that dropped the bar for early diagnosis by six months.
BALTIMORE, July 5 -- About half of children who develop autism may be diagnosable by 14 months of age, researchers found in a small study that dropped the bar for early diagnosis by six months.
Toddlers diagnosed early also appeared to have a different developmental trajectory than those with a later diagnosis, reported Rebecca J. Landa, Ph.D., of Johns Hopkins, and colleagues in the July issue of the Archives of General Psychiatry.
These differences "highlight the need for early intervention and for these programs to robustly target social affective, social cognitive, and communication development in toddlers with autism spectrum disorder," they wrote.
A few retrospective studies have set a precedent for provisional diagnosis of autism for children as young as 20 months, but "autism spectrum disorder is rarely diagnosed before age three years," they noted.
To provide further prospective evidence for early detection, the researchers longitudinally studied social and communication development of children from 14 to 36 months of age.
The study included 107 infants at high risk for autism because a sibling had been diagnosed with it and 18 infants at low risk for autism who had no family history of the disorder.
Two children in the control group had impaired development. One had language delay and the other had social delay, but none were classified as having autism in the study.
Both groups were tested for autism at age 14, 24, and 30 or 36 months using the Communication and Symbolic Behavior Scales Developmental Profile. This involved presenting babies with "communication temptations," such as demonstrating how to blow bubbles then putting the closed bubble bottle in front of the child, and probing them for responses to joint attention, receptive language, and an opportunity to play with toys.
The investigators also used the Autism Diagnostic Observation Schedule (ADOS), although it was not designed for children younger than 18 months. It includes semistructured, play-based assessment of social interaction, communication, play, and repetitive behaviors or interests.
ADOS scores were used with clinical judgment to classify children with autism spectrum disorder. Diagnosis as a study outcome was determined at 30 or 36 months "because diagnosis at that age is reliable," Dr. Landa and colleagues said.
In the high-risk group, 30 children were classified as having autism spectrum disorder.
Among them, 16 had a diagnostic impression of autism recorded at 14 months, and all but one of those who had a later diagnosis had been noted to have at least mild developmental impairment by 14 months.
Those with an early diagnosis were significantly less likely than those diagnosed later to be responsive to or initiate nonverbal communication. They also had a significantly smaller repertoire of communication and play behaviors.
The findings between the early-diagnosis group and late-diagnosis group, respectively, at 14 months were:
By 24 months, the two autism groups were similar in behavior and communication, representing a decline in scores for the late-diagnosis group and some small gains for the early diagnosis group at a time when the control group was making great gains.
From 14 to 24 months, the following movements on scores were noted:
"Our data validate parents' reports that autism spectrum disorder may appear after a period of nonautistic development," the researchers wrote, suggesting that children "reach the threshold for diagnosis at different times in the first three years of life."
Therefore, they said early screening would need to be repeated to catch the half of autistic children who do not present symptoms by 14 months.
Because social and communication development slowed before age two but some children diagnosed early made some gains thereafter, the findings "emphasize the urgency to determine whether very early interventions could alter the course of autism spectrum disorder," they added.
However, they cautioned, the study needs to be replicated in more generalizable populations because the only toddlers with autism in the study were at high genetic risk and the majority were white.
Also, sampling bias was likely. Parents reported concerns about 44% of six-month-old infants and 76% of 14-month-olds at study entry.
The researchers said work is under way to develop autism diagnostic tools for children age two and younger who cannot yet speak.