Nearly one-third of children with autism also have clinically significant attention deficit hyperactivity disorder symptoms, according to new research by the Kennedy Krieger Institute.
The study, published in Autism: The International Journal and Practice, also found that children with both autism and ADHD are significantly more impaired on measures of cognitive, social, and learning abilities, compared to those with only autistic symptoms.
The findings are based on research involving more than 160 early school-age children who entered the study as infants or toddlers, well before ADHD is typically diagnosed.
"We are increasingly seeing that these two disorders co-occur and a greater understanding of how they relate to each other could ultimately improve outcomes and quality of life for this subset of children," said Rebecca Landa, M.D., senior study author and director of the Center for Autism and Related Disorders at Kennedy Krieger. "The recent change to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) to remove the prohibition of a dual diagnosis of autism and ADHD is an important step forward."
The results showed that out of 63 children with autism, 18 were rated by their parents as having clinically significant symptoms of ADHD. Researchers also found that early school-age children with both conditions were more likely to have significant cognitive delays and display more severe stereotypic and repetitive autistic behaviors.
"We focused on young school-aged children because the earlier we can identify this subset of children, the earlier we can design specialized interventions," said Dr. Landa. "Tailored interventions may improve their outcomes, which tend to be significantly worse than those of peers with autism only."
The study was funded, in part, by the National Institutes of Mental Health.
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