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By Serena Gordon

HealthDay Reporter

MONDAY, April 29, 2019 (HealthDay News) -- Although autism is typically diagnosed around age 3 or 4, new research suggests it can be spotted soon after a child's first birthday.

Diagnosing autism spectrum disorders early is "extremely important because the brain is really plastic during early development," said the study's lead author, Karen Pierce.

The study found that 84% of those diagnosed early still met the criteria for having an autism spectrum disorder when they were re-evaluated at 3 years of age.

Of the remaining 16% thought to have an autism spectrum disorder early in life, most were later found to have a language or other developmental delay. Only about 2% of kids thought to have an autism spectrum disorder around 1 year of age ended up not having autism or another developmental delay, said Pierce. She's co-director of the University of California, San Diego autism center.

Pierce said that during early life, the brain is busy making connections. By age 3 or 4, many connections have already been made.

"If you can identify and start treating autism spectrum disorders before those connections are made, maybe more effective connections will be made. We still need to see what the impact will be if children come in for treatment as early as 24 months, but we believe from a neuroscience perspective, kids will have better outcomes," Pierce said.

Approximately one in 59 children in the United States has an autism spectrum disorder, according to the study authors. Signs may be evident within the first year of life. These may include not responding to their name and not practicing "joint attention behaviors." For example, if you point at an object and say, "Look, Johnny," while most kids will look where you're pointing, a child with autism may not.

Other clues might be the presence or absence of restrictive or repetitive behaviors, Pierce said. "A child with an autism spectrum disorder might take their toys and line them up, without really playing," she noted.

The study included almost 1,300 toddlers (aged 1 to 3) who were referred by their doctors or whose parents had expressed concern.

The youngsters had four hours of testing by a licensed psychologist, said Pierce, who is also a professor of neurosciences. The children were re-evaluated again before they were 3.5 years old.

In youngsters diagnosed at 12 or 13 months, only 50% were still considered to have an autism spectrum disorder at 3. The researchers said their findings show that the autism diagnosis becomes stable at about 14 months.

Of the children who weren't identified as having autism at the early testing, 24% were found to have autism at the later evaluation, the findings showed.

Pierce said it usually seemed as if these kids had a language delay or other developmental disorder, and at the early test, they only showed subtle signs of social impairment.

"This finding shows that doctors should do repeat screening because we don't want to miss any kids," she said.

Dr. Andrew Adesman is chief of developmental and behavioral pediatrics at Cohen Children's Medical Center in New Hyde Park, N.Y.

Adesman, who wasn't involved in the current study, said, "Although this study suggests that a diagnosis of an autism spectrum disorder may not be stable if a child is younger than 14 months of age, parents should definitely share any concerns they have with their pediatrician about their child's development at any age."

He, too, said the study results suggest that an autism diagnosis may be stable as early as 14 months.

"Although there is a tendency for parents and professionals to take a 'wait and see' approach when it comes to developmental concerns in very young children, the findings from the study suggest that it is important to intervene early when a child as young as 14 months is showing signs of an autism spectrum disorder," Adesman said.

The study was published online April 29 in JAMA Pediatrics.

More information

Learn more about getting an autism diagnosis from the U.S. Centers for Disease Control and Prevention.