Autism and ADHD: how far have we come in the comorbidity debate?

The potential for the coexistence of the developmental disorders autism and attention-deficit/hyperactivity disorder (ADHD) in any one individual has for a long time been a contentious issue. While from a neurobiological perspective it is possible, and even highly likely, that ADHD and autism might clinically co-exist, our major diagnostic classification systems (DSM-IV-TR and ICD-10) currently preclude such a dual-diagnosis. The aim of the current review is to summarise current diagnostic criteria and treatment strategies for the two disorders, relevant theories of developmental dysfunction, and update the state of the debate regarding comorbidity. Evidence from clinical, neuroimaging and neuropsychological domains is considered, and similarities and differences between the two disorders are identified. Suggestions for future research into the comorbid profiles of these disorders are proposed, with a strong emphasis placed on the neuropsychological assessment of executive functioning as a potentially useful tool for both identifying similarities, and differentiating the disorders.