365 Journal of Personality Disorders, 28(3), pp. 365–378, 2014 © 2014 The Guilford Press ASSOCIATION BETWEEN GENETIC POLYMORPHISMS IN THE SEROTONERGIC SYSTEM AND COMORBID PERSONALITY DISORDERS AMONG PATIENTS WITH FIRST-EPISODE DEPRESSION Jens D. Bukh, MD, PhD, Camilla Bock, MD, PhD, and Lars V. Kessing, MD, DMSc, professor Studies on the association between genetic polymorphisms and person- ality disorders have provided inconsistent results. Using the “enriched sample method,” the authors of the present study aimed to assess the association between polymorphisms in the serotonergic transmitter system and comorbid personality disorders in patients recently diag- nosed with first-episode depression. A total of 290 participants were systematically recruited via the Danish Psychiatric Central Research Register. Diagnoses of personality disorders were assessed by a SCID-II interview, and polymorphisms in the genes encoding the serotonin transporter, serotonin receptors 1A, 2A, 2C, and tryptophan hydroxy- lase 1 were genotyped. The authors found a significant effect of the length polymorphism in the serotonin transporter gene (5-HTTLPR) on cluster B personality disorder (mainly borderline disorder), but no in- fluence on cluster C personality disorder, and no associations between other polymorphisms and personality disorders. The study adds evi- dence to the effect of the serotonin transporter gene specifically on cluster B personality disorders. Since the first promising candidate gene studies of human personality in the mid 1990s (Benjamin et al., 1996; Lesch et al., 1996), several investi- gations of the association between personality traits and various genetic polymorphisms, mainly in the serotonergic and dopaminergic neurotrans- mitter system, have been published. Yet the research has not provided any clear evidence for the influence of specific genes on personality (Mu- This article was accepted under the editorship of Robert F. Krueger and John Livesley. From Psychiatric Center Copenhagen, Rigshospitalet, University Hospital of Copenhagen, Copenhagen, Denmark (J. D. B., L. V. K.); and Herstedvester Detention Center, Denmark (C. B.). This study was supported by the Center for Pharmacogenomics, University of Copenhagen (Danish Research Councils 2052-03-0025). Address correspondence to Jens Drachmann Bukh, Psychiatric Center Copenhagen, Rig- shospitalet, Affective Disorders Research Unit, Department 6233, Blegdamsvej 9, DK-2100 København Ø, Denmark; E-mail: jens.bukh@regionh.dk