Wendy S. Slutske1, A. C. Heath2, P. A. F. Madden2, K. K. Bucholz2, S. H. Dinwiddie2, M. P. Dunne3, D. J. Statham3, & N. G. Martin3
Previous analyses of data from the Australian Twin Register have demonstrated substantial genetic influences on both conduct disorder risk (Slutske et al., 1997, J. Abn. Psych., 106, 266-279) and alcohol dependence risk (Heath et al., 1997, Psych. Med., 27, 1381-1396), and that the correlation between conduct disorder (CD) and alcohol dependence risk (AD) was largely due to genetic factors (Slutske et al., in press, J. Abn. Psych.). In this paper, we examined the extent to which the common genetic risk for CD and AD can be explained by genetic influences on personality factors. The sample consisted of 2,231 female, male, and unlike-sex adult twin pairs from the Australian Twin Register who were administered a semi-structured psychiatric interview by telephone and completed short forms of the Eysenck Personality Questionnaire (EPQ) and Tridimensional Personality Questionnaire (TPQ). Scores on the seven EPQ and TPQ scales were combined into 3 higher-order factors: positive emotionality (EPQ Extraversion, TPQ Reward Dependence), negative emotionality (EPQ Neuroticism, TPQ Harm Avoidance), and behavioral undercontrol (EPQ Psychoticism and Lie, TPQ Novelty Seeking). The associations between positive emotionality, negative emotionality and CD and AD risk were modest (rs = .05-.21); the associations between behavioral undercontrol and CD and AD risk were substantially higher (rs = .37-.49). Genetic influences on behavioral undercontrol accounted for about 50% of the genetic variation in CD and AD risk, and nearly 100% of the common genetic risk for CD and AD. The hypothesis that behavioral undercontrol accounted for all of the common genetic risk for CD and AD could not be rejected. These results suggest that genetically-influenced personality factors, especially behavioral undercontrol, account for much of the comorbidity between CD and AD.
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1Department of Psychology, University of Missouri, Columbia, MO 65211 2Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110 3Epidemiology Unit, Queensland Institute of Medical Research, Brisbane, Australia 4029 4Supported by NIH grants AA07535, AA07728, AA10249, AA00264, post-doctoral training grants MH17104 and DA07261, and by a grant from the Australian NH&MRC.