ADHD and autism spectrum disorders (ASD) are neurodevelopmental disorders with a complex presentation and etiology. They are both considered to be heritable conditions with a widely accepted genetic component to the etiology and efforts to find susceptibility genes underlying these disorders are gradually yielding interesting findings (Faraone, 2006, Grice, 2006). The challenge for genetics studies for the individual disorders will be elucidation of the relationships between susceptibility genes and the complex phenotype.

Given the genetic underpinnings of both disorders it is not unreasonable to ask the question as to whether there is shared genetic vulnerability. Genetic overlap is not widely reported in the literature and there is a relative dearth of direct investigation of this question. Evidence suggests a role for genes involved in the dopaminergic and serotonergic systems in both ADHD and autism but it is not clear if genetic variation in genes involved in these systems is similar. Further investigation is warranted to directly investigate potential overlap and subsequently to address the complex task of understanding the relationship between genetic susceptibility, possible common endophenotypes and the clinical phenotype. It is likely that multiple mechanisms, both genetic and environmental may be at play.

A discussion of the existing literature with respect a putative overlap in genetic vulnerability and the clinical phenotype is presented. Furthermore the specific challenges for research in assessing these factors in future studies is discussed.