Children with autism tend to also have other disorders, such as a learning disability or depression, which affect them in different ways as they age, a new study finds.
The findings may explain, in part, why children with autism often see a change in their diagnoses as they grow older, the study suggests.
The study was based on 1,366 children who had taken part in a national health survey who either were currently diagnosed with autism, or had been in the past but no longer had the diagnosis.
"Parents should have their child checked for other conditions to make sure an autism diagnosis is properly determined," said study researcher Li-Ching Lee, a psychiatric epidemiologist at the Johns Hopkins Bloomberg School of Public Health.
"That way, a more appropriate intervention for the child can be planned as early as possible," Lee said.
The study is published today (Jan. 23) in the journal Pediatrics.
Making a proper diagnosis can often be difficult
Autistic spectrum disorders — including autism, Asperger's syndrome and other developmental disorders — affect a child's ability to communicate and interact with people.
About 1 in 110 children in the U.S. is currently diagnosed with an autism spectrum disorder, according to the Centers for Disease Control and Prevention. Boys are four times more likely to have autism than girls.
Symptoms of co-existing medical conditions, such as learning disabilities, hearing and speech problems, depression and anxiety, have been shown to overlap with symptoms of autism, often making it difficult for doctors to make a proper diagnosis.
Previous studies have shown that children with autism have higher rates of co-existing conditions than normally developing children, and those with developmental delays who don't have autism.
How long an autism diagnosis lasts seem to vary over time. One study found that more than 10 percent of children diagnosed with autism at age 2 no longer had the disorder at age 9.
"We're not saying that a child who was diagnosed with autism at age 2 won’t have autism later in life," said lead author Heather Close, a researcher at the Department of Epidemiology at the Johns Hopkins Bloomberg School of Public Health.
"But there are other mechanisms at work that we don't know about that could take place," she said.
More than one diagnosis is likely
The new study included 2007 data from the National Survey of Children's Health. Parents were surveyed about their child's physical and mental health, current and past medical, behavioral and developmental diagnoses and health care needs.
Researchers looked at data for children in three age groups, including young children who were 3 to 5 years old, children who were 6 to 11 years old and teenagers who were 12 to 17 years old.
They found that young children with a current diagnosis of autism were 11 times more likely to have a learning disability, and nine times more likely to have another developmental delay, than young children diagnosed with autism in the past who no longer had a diagnosis.
Of those in the 6- to 11-year old group, children with a current diagnosis of autism were almost four times more likely to have a past speech problem and suffer from anxiety than those who no longer had a diagnosis.
And among teenagers, those with a current diagnosis of autism were almost four times more likely to have speech problems, and 10 times more likely to have epilepsy than those who no longer had a diagnosis.
"This study looks at a broader population of kids," than previous work, said Tristram Smith, a behavior specialist at the University of Rochester, who was not part of the study.
"It shows that developmental delay and seizures are what can increase the likelihood that autism will stay in someone who has a current diagnosis," Smith said.
Smith said he recommends that parents learn to understand that diagnoses can change, or there can be more than one.
"Parents are often looking for that one answer," he said. "Reality is, it's a moving target, and it's complicated. It can be more than one diagnosis at one time, or it can be different diagnoses at different times too."
Pass it on: Certain co-existing conditions could likely lead to a change in autism diagnosis.
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