Associations of MAOA-VNTR or 5HTT-LPR alleles with attention-deficit hyperactivity disorder symptoms are moderated by platelet monoamine oxidase B activityWargelius, Hanna-Linna; Malmberg, Kerstinb; Larsson, Jan-Olovb; Oreland, LarsaPsychiatric Genetics: February 2012 - Volume 22 - Issue 1 - p 42–45 doi: 10.1097/YPG.0b013e328347c1ab Brief Reports Abstract In Brief Author Information The monoamine systems have been suggested to play a role in the biological basis of attention-deficit hyperactivity disorder (ADHD) symptoms. Thus, polymorphisms, for example, in the monoamine oxidase A (MAOA) and the serotonin transporter (5HTT) genes have been associated with ADHD-like phenotypes. Furthermore, platelet monoamine oxidase B (MAOB) activity has frequently been linked to impulsiveness-related traits. In this study, we have studied ADHD symptoms with regard to the combination of platelet MAOB activity and MAOA-variable number of tandem repeats (VNTR) or 5HTT-LPR genotype. The study group consisted of 156 adolescent twin pairs, that is, 312 individuals, who participated in a previous study. ADHD symptoms were scored with a structured clinical interview of both the twins and a parent using Kiddie Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version. The presence of a short 5HTT-LPR or short MAOA-VNTR allele, in combination with high levels of platelet MAOB enzyme activity was associated with higher scores of ADHD-like problems (P<0.001 and 0.01, respectively). This re-examination of ADHD scores in a nonclinical sample suggests that effects of MAOA-VNTR and 5HTT-LPR are moderated by platelet MAOB activity. Supplemental Digital Content is available in the article. aDepartment of Neuroscience, Uppsala University, Uppsala bKarolinska Institutet, Department of Women's and Children's Health, Stockholm, Sweden Correspondence to Hanna-Linn Wargelius, MSc, Department of Neuroscience, Uppsala University, Husargatan 3 PO box 593, Uppsala 751 24, Sweden Tel: +46 18 471 49 02; fax: +18 51 15 40; e-mail: firstname.lastname@example.org Hanna-Linn Wargelius and Kerstin Malmberg contributed equally to this study Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Website (www.psychgenetics.com). Received June 9, 2010 Accepted March 17, 2011 © 2012 Lippincott Williams & Wilkins, Inc.