Recently, Krueger, Markon, Patrick, and Iacono (2005) proposed that classifications in the upcoming fifth edition of the DSM should reflect the etiologic and clinical commonalities among the components of behavioral disinhibition, under the rubric of externalizing disorders. They pointed out that although the clustering of disorders for diagnostic purposes (based, for example, on comorbidity) is not a new concept, incorporating empirical evidence of biological connections among externalizing disorders and personality traits associated with aggression and impulsivity is an important development with useful implications for both diagnostic taxonomies and treatment planning. The current findings, which build on a growing literature demonstrating a common biological etiology among externalizing disorders, give further credence to such proposed changes.
