One of every five ADHD kids in the study exhibited signs of autism such as slow language development, difficulty interacting with others and problems with emotional control, said study co-author Dr. Joseph Biederman, director of the pediatric psychopharmacology unit at Massachusetts General Hospital.
These kids also showed problems with "executive function," or the ability to plan, organize and conceptualize future action, said Biederman, a professor of psychiatry at Harvard Medical School.
Fewer than 1 percent of kids in the non-ADHD comparison group exhibited any traits linked to autism, according to the study appearing in the September issue of Pediatrics.
"These children are not having the full diagnosis of autism, but they have symptoms of autism," Biederman said. "It may be important to screen children with ADHD for autistic traits because they may need more support, particularly in the educational and interpersonal domains."