Research report Monoamine oxidase (MAO) intron 13 polymorphism and platelet MAO-B activity in combat-related posttraumatic stress disorder Nela Pivac a, ⁎ , Jelena Knezevic a , Dragica Kozaric-Kovacic b , Martina Dezeljin a , Maja Mustapic a , Davor Rak b , Tanja Matijevic a , Jasminka Pavelic a , Dorotea Muck-Seler a a Rudjer Boskovic Institute, Division of Molecular Medicine, POBox 180, HR-10002 Zagreb, Croatia b University Hospital Dubrava, Referral Centre for the Stress-Related Disorders, Avenija Gojka Suska 6, HR-10000 Zagreb, Croatia Received 10 November 2006; received in revised form 5 January 2007; accepted 9 January 2007 Available online 7 February 2007 Abstract Background: The neurobiology of posttraumatic stress disorder (PTSD) involves alterations in multiple neuroendocrine and neurotransmitter systems. Platelet monoamine oxidase (MAO-B) has been associated with susceptibility to various psychiatric disorders, personality traits and behaviors. Methods: Platelet MAO-B activity and MAO-B intron 13 polymorphism (a G/A substitution) were determined in male war veterans (n = 106) with DSM-IV diagnosed current and chronic PTSD, divided into subgroups of PTSD patients with (n =28) or without (n = 78) psychotic features, combat exposed veterans (n = 41) who did not develop PTSD, and healthy control men (n = 242). Results: Two-way ANOVAs revealed a significant effect of diagnosis and smoking, a significant effect of smoking, no significant effect of genotype, and no significant interaction between genotype, smoking or diagnosis, on platelet MAO-B activity. One-way ANOVAs showed significantly lower platelet MAO-B activity in smokers than in nonsmokers. After controlling for smoking, veterans with psychotic PTSD had significantly higher platelet MAO-B activity than veterans with or without PTSD, or healthy subjects. Limitations: The results were obtained on peripheral biochemical marker, i.e. platelet MAO activity. Conclusions: The MAO-B intron 13 polymorphism was not functional, and did not affect platelet MAO-B activity. The allele frequencies of the MAO-B genotype were similarly distributed among healthy controls and veterans with or without PTSD and/or psychotic symptoms. The results suggest that platelet MAO-B activity, controlled for smoking status, might be used as a peripheral marker of the psychotic symptoms in PTSD. © 2007 Elsevier B.V. All rights reserved. Keywords: Combat-related posttraumatic stress disorder; MAO-B intron 13 polymorphism; Platelet MAO-B activity; Psychotic symptoms 1. Introduction Several neurobiological systems are dysfunctional in posttraumatic stress disorder (PTSD), and those that have been most explored include the hypothalamic– pituitary–adrenal axis, noradrenergic, dopaminergic and Journal of Affective Disorders 103 (2007) 131 – 138 www.elsevier.com/locate/jad ⁎ Corresponding author. Tel.: +385 1 4571 207; fax: +385 1 4561 010. E-mail address: npivac@irb.hr (N. Pivac). 0165-0327/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jad.2007.01.017