Background There is decreased serotonergic function in impulsive aggression and borderline personality disorder (BPD) and genetic association studies suggest a role of serotonergic genes in impulsive aggression and BPD. was significantly higher in individuals with BPD compared to HCs. Those with the “risk” haplotype have higher aggression and impact lability scores and more suicidal/parasuicidal behaviors than those without it. In the logistic regression model impact lability was the only significant predictor and it correctly classified 83.1% of the subjects as “risk” or “non-risk” haplotype carriers. Conclusions We found an R1626 association between the previously explained TPH2 “risk” haplotype and BPD analysis affective lability suicidal/parasuicidal behavior and aggression scores. Keywords: Borderline personality disorder TPH2 suicidal behavior affective instability impulsive aggression Introduction Borderline personality disorder (BPD) is definitely a complex and severe mental disorder characterized by emotional dysregulation R1626 and aggressive behavior (New et al. 2007 Impulsive aggression and Kcnh6 R1626 affective dysregulation/instability are core characteristics of BPD (McGlashan et al. 2005 Siever et al. 2002 Skodol et al. 2002 and contribute considerably to the morbidity and mortality associated with BPD. Impulsive aggression can manifest in a variety of behaviors including damage of house assault domestic violence self-injurious and suicidal behavior or substance abuse (New et al. 1998 Impulsive aggression has consistently been associated with steps of reduced central serotonergic activity such as decreased cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) (Coccaro et al. 1990 Lidberg et al. 2000 Linnoila et al. 1989 Linnoila et al. 1994 Roy et al. 1988 Stanley et al. 2000 Virkkunen et al. 1994 decreased platelet serotonin content material (Goveas et al. 2004 and decreased hormone reactions to serotonergic agonists (Coccaro et al. 1990 Coccaro et al. 1996 Coccaro et al. 1990 Coccaro et al. 1997 Coccaro et al. 1995 Coccaro et al. 1997 Coccaro et al. 1989 New et al. 2004 O’Keane et al. 1992 Reist et al. 1996 Sher et al. 2003 tryptophan depletion enhanced and tryptophan augmentation decreased laboratory-provoked aggression in healthy ladies (Marsh et al. 2002 Moreover aggressive children having a blunted prolactin response to fenfluramine were more likely to have relatives with aggression than those with a normal reactions (Halperin et al. 2003 Furthermore among personality disordered (PD) individuals a reduction in serotonergic function measured by reduced prolactin response to fenfluramine appears to be specifically associated with impulsive aggression but not with additional personality characteristics or major depression (Coccaro et al. 1989 Paris et al. 2004 In summary the link between decreased serotonergic function and impulsive aggression across psychiatric diagnoses is one of the most robust findings in biological psychiatry consistently replicated and supported by a broad range of studies including metabolite endocrine challenge peripheral marker genetic and mind imaging studies (New et al. 1998 Siever 2008 In addition selective serotonin reuptake inhibitors appear to improve anger and feeling instability in non-depressed BPD individuals (Coccaro et al. 1990 Cornelius et al. 1991 New et al. 2004 New et al. 2008 Rinne et al. 2002 While early theories mainly ascribed an environmental etiology growing evidence demonstrates a genetic vulnerability for BPD (Kendler et al. 2008 Siever et al. 2002 Evidence for this includes the inclination for BPD to run in family members (Loranger et al. 1982 White colored et al. 2003 and its higher prevalence among biological than among R1626 adoptive relatives of BPD individuals (New et al. 2008 Pally 2002 More importantly twin studies of BPD display considerable heritability scores of 0.65-0.76 (Coolidge et al. 2001 Ji et al. 2006 Torgersen et al. 2000 and the heritability of core sizes of BPD such as affective instability or impulsive aggression may be more robustly heritable than the analysis itself (Siever et al. 2002 Evidence of decreased serotonergic function in impulsive aggression and BPD along with the evidence for heritability (New et al. 2008 Siever 2008 R1626 led to candidate gene.