This paper used data from a large sample of adolescents and young adults to explore the association of various behavioral and personality measures of externalizing and impulsivity with GABRA2, a gene previously associated with externalizing disorders. Our results illustrate the critical importance of the precision of phenotypic definition for genetic association studies. There are three particularly notable findings that emerge: (1) the association between GABRA2 and externalizing behavior is limited to subclinical self-reports of externalizing behavior and is not found with diagnostic level DSM symptom counts for any externalizing disorder in either the adolescent or young adult samples; (2) the association between GABRA2 and personality measures of impulsivity is observed only with Zuckerman’s SSS and NEO Extraversion, not the BIS or NEO Conscientiousness; (3) the association with SSS and extraversion is limited to the adolescent sample, illustrating the developmental shifts that can occur in gene–behavior associations. We discuss each of these primary findings further below.
