MONDAY, August 26, 2013 (MedPage Today) Children with attention deficit hyperactivity disorder (ADHD) were more likely than controls to have autistic traits, and those traits were generally more severe, researchers found.

Compared with children who did not have ADHD, those with the disorder were significantly more likely to show a positive autism trait profile, according to Joseph Biederman, MD, of Massachusetts General Hospital in Boston, and colleagues.

Children with ADHD and autistic traits were significantly more impaired in psychopathology, interpersonal, school, family, and cognitive domains than those with autistic traits and without ADHD, they wrote online in the journal Pediatrics.

Other research has shown a shared heritability of ADHD and autism spectrum disorders and that autism spectrum disorders or autistic traits co-occur in 20% to 30% of children with ADHD. Those studies have also shown that children with both conditions are more impaired, particularly in interpersonal communication and empathy, though these results have not been replicated.

A 2011 study from the CDC and Maternal and Child Health Bureau found that rates of autism and ADHD were on the rise from 1997 to 2008.

Researchers have long sought to better understand the workings of social behavior "and it's interesting that we have clear ideas of what kids shouldn't do socially, but often we don't know what they should do," noted Catherine Lord, PhD, of Weill Cornell Medical College in White Plains, N.Y.

"We need to find out more what it is that these kids were having trouble with, how does it overlap with autism, and what we can do to help them," Lord said in an interview with MedPage Today.

The study "reinforces the long-standing idea that children referred for evaluation of ADHD may have a more complex picture," added David Urion, MD, of Boston Children's Hospital.

"The main aim of the current study was to examine the prevalence and correlates of [autism traits] in youth with ADHD," according to the report, through an analysis of 469 children.

Participants were gathered through other longitudinal, case-control family studies at Massachusetts General Hospital and patients attending the pediatric medical clinic and included those ages 6 to 18, with a mean age of 11.3. Control patients were not excluded for having other psychiatric disorders.

Nearly all of the participants were white (99%). Roughly half (52%) required tutoring, repeated a grade, or took a special class.

Among controls, a third of the 27% who had academic difficulties met criteria for one or more psychiatric disorders, versus 28% of those without academic difficulty. For those with ADHD, three quarters had academic difficulty, 81% of which met criteria for one or more psychiatric disorders; among those not having academic problems, 73% met the criteria for psychiatric disorders.

"These numbers suggest that the presence of a psychiatric illness may account for the increased prevalence of academic functioning difficulties," they wrote.

More children with ADHD had autistic traits than did children without ADHD. Those with autistic traits and ADHD had higher rates of additional ADHD-related symptoms, including clumsiness, equal parts inattention and hyperactivity, hyperactivity, peer fighting, and rejection by peers, compared with those who only had ADHD.

Those with ADHD overall had a significantly higher prevalence of all comorbid psychiatric conditions, including disruptive behavior disorders, mood disorders, multiple anxiety disorders, language disorders, elimination disorders, and substance use disorders.

Those who also had autistic traits had a higher prevalence of disruptive behaviors, mood disorders, multiple anxiety disorders, and language disorders. They also had more impaired scores in all child behavior checklist clinical and composite scales than those with ADHD alone.

Rates of social disability were higher in both groups with ADHD than control, but higher in those with autistic traits than in those with ADHD alone. Those with autistic traits also had significantly impaired scores in school behavior, spare time problems, activities and problems with peers, and problems with siblings and parents.

Despite a number of methodological problems, the study "raises the interesting point that there is a significant overlap in people being referred for evaluation and treatment of ADHD and those who have some features of autism," Urion told MedPage Today.

He added that future research should evaluate children under the new DSM-5 criteria for autism.

The study was limited by a lack of comparison with those diagnosed with autism spectrum disorders, potential missed diagnosis of autism spectrum disorder in the sample, and generalizability.