The Covariation of Trait Anger and Borderline Personality: A Bivariate Twin-Siblings Study Marijn A. Distel, Mark Patrick Roeling, Jorim J. Tielbeek, and De ´sie van Toor VU University Amsterdam, Amsterdam, the Netherlands Catherine A. Derom University Hospital Gasthuisberg, Katholieke Universiteit Leuven, Belgium Timothy J. Trull University of Missouri–Columbia Dorret I. Boomsma VU University Amsterdam, Amsterdam, the Netherlands Anger can be defined as an emotion consisting of feelings of variable intensity, from mild irritation or annoyance to intense fury and rage. Borderline personality disorder (BPD) is characterized by impulsivity and instability of interpersonal relationships, of self-image, and of negative affects. Borderline personality and trait anger are often observed together. The present study examined the extent to which a genetic association explains the covariation between a trait measure of borderline personality and trait anger. To this end, self-report data of 5,457 twins and 1,487 of their siblings registered with the Netherlands Twin Register and the East Flanders Prospective Twin Survey were analyzed using genetic structural equation modeling. A significant phenotypic correlation was observed between the two traits (rP = .52). This correlation was explained by genetic (54%) and by environmental influences (46%). A shared genetic risk factor is thus one of the explanations for the covariation of borderline personality and trait anger. Keywords: borderline personality, trait anger, twin study, genetic factors Anger can be defined as an emotion that consists of feelings of variable intensity, from mild irritation or annoyance to intense fury and rage (Spielberger, Jacobs, Russell, & Crane, 1983). It can be conceptualized as state anger, referring to an episode of anger occurring at a specified time, or as trait anger, referring to an aspect of personality (Eckhardt, Norlander, & Deffenbacher, 2004). Feelings of anger may be suppressed or directed inward (“anger-in”) or expressed outwardly in some form of aggressive behavior (“anger-out”). Anger has been related to several impor- tant constructs in behavioral medicine and psychological research. For example, high levels of internal expression of anger and trait anger have been associated with increased blood pressure and induced hypertension (Markovitz, Matthews, Wing, Kuller, & Meilahn, 1991; Schneider, Egan, Johnson, Drobny, & Julius, 1986), increased risk for coronary heart diseases (Atchison & Condon, 1993; Williams et al., 2000; Leon, 1992; Kawachi, Spar- row, Spiro, Vokonas, & Weiss, 1996; Eaker, Sullivan, Kelly– Hayes, D’Agonstino, & Benjamin, 2004; Chang, Ford, Meoni, Wang, & Klag, 2002), and mental disorders such as anorexia and bulimia nervosa (Fassino, Daga, Piero, Leombruni, & Rovera, 2001) bipolar disorder (Posternak & Zimmerman, 2002), and borderline personality disorder (Morse et al., 2009). Borderline personality disorder (BPD) is characterized by a pervasive pattern of instability of interpersonal relationships, of self-image, and of negative affects, and marked impulsivity that begins by early adulthood and is present in a variety of contexts (American Psychiatric Association [APA], 2000). BPD is diag- nosed in approximately 1% to 2% of the general population (Lenzenweger, Lane, Loranger, & Kessler, 2007; Torgersen, Krin- glen, & Cramer, 2001) and is associated with a variety of negative outcomes such as self-harm behavior, suicidal behavior, impaired occupational and interpersonal functioning, delinquent behavior, and substance abuse (Skodol et al., 2002). Inappropriate, intense anger or difficulty controlling anger is the most prevalent BPD criterion in clinical samples (Zanarini, Frankenburg, Hennen, Reich, & Silk, 2005), nonclinical samples (Trull, 1995), and in first degree relatives of BPD patients (Zanarini et al., 2004). Further, This article was published Online First December 12, 2011. Marijn A. Distel, Department of Biological Psychology, VU University Amsterdam, Amsterdam, The Netherlands, and EMGO + Institute for Health and Care Research, VU University Medical Center, Amsterdam, the Netherlands; Mark Patrick Roeling, Jorim Tielbeek, and De ´sie van Toor, Department of Biological Psychology, VU University Amsterdam, Am- sterdam, The Netherlands; Catherine A. Derom, Department of Human Genetics, University Hospital Gasthuisberg, Katholieke Universiteit Leu- ven, Belgium; Timothy J. Trull, Department of Psychological Sciences, University of Missouri–Columbia, Columbia, Missouri; and Dorret I. Boomsma, Department of Biological Psychology, VU University Amster- dam, Amsterdam, The Netherlands, EMGO + Institute for Health and Care Research, and Neuroscience Campus Amsterdam, VU University Medical Center, Amsterdam, the Netherlands. The present study was supported by the Borderline Personality Disorder Research Foundation, Spinozapremie (NWO/SPI 56 – 464-14192), and Twin-Family Database for behavior genetics and genomics studies (NWO 480 – 04-004). The authors declare no financial or other conflicts of inter- est. Correspondence concerning this article should be addressed to Marijn A. Distel, Department of Biological Psychology, VU University Amsterdam, Van der Boechorststraat 1, 1081 BT Amsterdam, the Netherlands. E-mail: ma.distel@psy.vu.nl/m.distel@ggzIngeest.nl Journal of Abnormal Psychology © 2011 American Psychological Association 2012, Vol. 121, No. 2, 458 – 466 0021-843X/11/$12.00 DOI: 10.1037/a0026393 458