Heritability of Aggression and Irritability: A Twin Study of the Buss-Durkee Aggression Scales in Adult Male Subjects Emil F. Coccaro, C.S. Bergeman, Richard J. Kavoussi, and A.D. Seroczynski To determine the degree of genetic and environmental influences on assessments of aggression and irritability in male subjects, the "Motor Aggression" subscales of the Buss-Durkee Hostility Inventory (BDHI) were mailed to 1208 male twins in the Vietnam Era Twin Registry. Data from monozygotic 182 and 118 dizygotic twin pairs were available and were analyzed using model-fitting procedures. Three of the four BDHI subscales demonstrated significant heritability of a nonadditive nature: 40% for Indirect Assault, 37% for Irritability, and 28% for Verbal Assault. Additive genetic variance accounted for 47% of the individual differences in Direct Assault. Nonshared, but not shared, environmental influences contributed to explaining the variance in the model, with estimates ranging from 53% (Direct Assault) to 72% (Verbal Assault). Because some of these BDHI scales have been shown to correlate with indices of central serotonin function, it is possible that impulsive aggression, as reflected by these scales, is heritable in men. © 1997 Society of Biological Psychiatry Key Words: Aggression, irritability, genetics, environment, twin study BIOL PSYCHIATRY1997;41;273--284 ln~oducfion Aggressive impulses and behavior constitute an important dimension of human personality (Buss and Plomin 1984). Individuals in whom these impulses and behavior are unchecked invariably manifest prominent aggressivity as- sociated with socially unacceptable behaviors and impair- ment of interpersonal and/or cognitive function. Although the number of individuals with prominent aggressive behavior is unknown, the negative impact of these indi- From the Clinical Neuroscience Research Unit, Department of Psychiatry, Address reprint requests to Emil F. Coccaro, MD, Clinical Neuroscience Research Unit, Department of Psychiatry, Medical College of Pennsylvania at Eastern Pennsylvania Psychiatric Institute, 3200 Henry Ave, Philadelphia, PA 19129. Received July 24, 1995; revised May 21, 1996. viduals upon society is significant. The purpose of the present study was to assess genetic and environmental influences on individual differences for self-reported ag- gressive behavior. The roots of aggressive behavior in humans are com- plex and multidetermined. In brief, developmental, soci- etal, and biogenetic influences have all been invoked as etiologic of modulatory factors in aggressive behavior (Baron and Richardson 1994). Among these influences, biogenetic factors have received less attention. Biogenetic factors include genetic influences or abnormalities (e.g., those that lead to an abnormality in brain function), neurochemical abnormalities (e.g., reduction in central serotonergic system function), and acquired neurological abnormalities (e.g., injury to frontal lobes). Although the © 1997 Society of Biological Psychiatry 0006-3223/97/$17.00 PII S0006-3223(96)00257-0