The Evolving ADHD Phenotype in the Externalizing Context.

Attention deficit hyperactivity disorder (ADHD) is a developmental precursor for future conduct and other externalizing problems. Despite its familiarity, research in the past decade suggests that refining the ADHD phenotype will yield dividends for clinical prediction and treatment specification as well as mechanistic discovery and theory. ADHD is a useful category, yet it comprises multiple constitutive traits requiring further specification. The field is now poised to shift to a useful integration of novel dimensional traits into a refined ADHD phenotype. This shift will need to recognize the importance of both the established ADHD symptom dimensions and other trait dimensions to create new presentations, types, or specifiers in the nosology. Clinical issues include the role of sluggish, disengaged cognitive style of inattention with hypoactivity. Dispositional traits related to emotional dysregulation will be key as well; these include negative affect and irritability (anger dysregulation). In the cognitive sphere, along with ongoing work on executive functions and reward discounting, new insights related to cognitive information gain or neural gain (a mechanism by which relevant neural connections strengthen during rapid information uptake and decision making) may explain other cognitive findings and relate to dispositional traits and clinical features. Due to its early gateway role, clinical prediction algorithms to evaluate course of ADHD and advisability of intervention will be valuable. A neurodevelopmental, early origins perspective, including early developmental programming in the prenatal period, is increasingly informing etiological understanding of ADHD. Nonclinical trait measures are seen as early precursors of ADHD, and ADHD is then a precursor of more serious externalizing and other complications later. This view opens new opportunities for risk detection and prevention. Clinical prediction algorithms should benefit from inclusion of low-cost, readily deployable trait measures discussed here, including selected temperament and cognition measures, which appear to enhance predictive power.