MONDAY, Jan. 23 (HealthDay News) -- Many children with autism also have other developmental or psychiatric conditions, including learning disabilities, speech delays, attention or seizure disorders and anxiety.

According to new research, some of those co-occurring conditions may explain why autism diagnoses often change as children get older.

In a survey by researchers at Johns Hopkins Bloomberg School of Public Health in Baltimore, more than one-third of parents with children between 6 and 17 years old reported that their child's diagnosis of autism had changed over time.

"We don't know what changed the diagnosis. However, we want to deliver the message that it's important to look at the other coexisting conditions, evaluate them before you make a diagnosis, and also recognize these conditions vary by development age," said study author Li-Ching Lee, an associate scientist in the epidemiology and mental health departments at the School of Public Health.

Autism is a neurodevelopment disorder characterized by problems with social interaction, communication and restricted interests and behaviors.

In the study, researchers used 2007-2008 survey data from the parents of nearly 1,400 children aged 3 to 17 who had received a diagnosis of an autism spectrum disorder (ASD), including autism, Asperger disorder -- a mild form of autism, and pervasive developmental disorder-not otherwise specified.

Parents were asked if their child currently had a diagnosis of autism or an ASD, or had had one in the past.

Nearly 26 percent of parents of children aged 3 to 5 reported a change in diagnosis, the researchers said. Nearly 34 percent of parents of children aged 6 to 11 and 35 percent of the parents of 12- to 17-year-olds reported their child was diagnosed with autism at some point but no longer was considered to have autism, the researchers found.

Overall, children with two or more co-occurring developmental or psychiatric conditions were five times more likely than kids with fewer coexisting conditions to continue to have an autism diagnosis, the researchers said.

Kids who had a moderate-to-severe learning disability were 11 times more likely to continue to have an autism diagnosis over time, while kids with a developmental delay were nine times more likely to retain an autism diagnosis, the study authors said.

Researchers didn't look at why certain conditions are associated with a change in autism diagnosis. But some of the symptoms of various development and psychiatric conditions can overlap, so it's possible that having certain ones can lead to a misdiagnosis until the child gets older and their issues become more clear, according to the study.

For example, kids diagnosed with a hearing problem showed a tendency to "lose" their autism diagnosis over time. Researchers speculated that behaviors that initially resembled autism symptoms -- not responding or not engaging -- were later discovered to stem from impaired hearing.

The study is published in the February issue of Pediatrics.

Dr. Joseph Horrigan, assistant vice president and head of medical research for the advocacy group Autism Speaks, cautioned not to make too much of the findings. The children weren't actually followed over time, nor were they actually examined, a methodology that would be the "gold standard" of research.

Because the results were based on a telephone survey, Horrigan said, "I'd be a little cautious about over-interpreting whether this means there's likely to be change in an autism diagnosis or a loss of an autism diagnosis for a given individual."

Nor did researchers look at kids whose diagnosis went the other way -- that is, they were initially not diagnosed with autism but were later diagnosed with it.

However, the findings highlight how often kids with ASD experience other conditions, some of which may be treatable with medications or with educational interventions. These include anxiety, attention-deficit hyperactivity disorder (ADHD), depression, epilepsy and learning disabilities.

"Up until the recent past, there's been a tendency to spend most of the time and energy on the autism and the autism diagnosis, and thinking about a treatment package that's keyed directly to the autism," Horrigan said. "What's important here is they are highlighting some of the most common co-occurring disorders, a number of which are readily amenable to treatments."

An estimated one in 110 U.S. children -- many more boys than girls -- has autism, according to the U.S. Centers for Disease Control and Prevention.

More information

The U.S. National Institute of Mental Health has more on autism.