Objectives: To give an overview of studies showing evidence of elevated autistic symptoms in ADHD and discuss implications of these findings.
Methods: Relevant published studies are discussed and new epidemiological data from Missouri population-based twin and large sibship samples are presented.
Results: Clinic and population-based studies indicate that autistic symptoms are common in ADHD, particularly for individuals with high levels of both inattentive and hyperactive-impulsive symptoms (combined type ADHD). Progress is being made in distinguishing autistic-like social impairment from social difficulties that may be a direct result of ADHD symptoms. Consistent with the concept of Deficits in Attention, Motor control and Perception (DAMP), individuals with the combination of ADHD and motor coordination difficulties may be particularly likely to exhibit autistic symptoms. The relationship between ADHD and autism symptoms may be stronger for adolescents and young adults than for young children. Emerging evidence suggests some genes can influence both ADHD and autistic symptoms.
Conclusions: Although co-diagnosis of ADHD and autism spectrum disorders has been discouraged, it appears important to assess and treat autistic symptoms in children, adolescents, and young adults with ADHD. Evaluation for autistic symptoms may also be important in defining phenotypes for genetic studies of ADHD.