Cannabinoid Receptor 2 Functional Variant Contributes to the Risk for Pediatric Inflammatory Bowel Disease Caterina Strisciuglio, MD, PhD,* Giulia Bellini, PhD,w Erasmo Miele, MD,z Massimo Martinelli, MD,z Sabrina Cenni, MD,z Chiara Tortora, PhD,w Carlo Tolone, MD,* Emanuele Miraglia del Giudice, MD,* and Francesca Rossi, MD* Goals: We conducted a case-control association analysis to estab- lish the role of a common CB2 functional variant, Q63R, in the susceptibility to inflammatory bowel disease (IBD). Background: Endocannabinoids may limit intestinal inflammation through cannabinoid receptor 1 and/or 2 (CB 1, CB 2) . Study: We genotyped 217 pediatric IBD patients [112 Crohn’s disease (CD), 105 ulcerative colitis (UC)] and 600 controls for the CB2-Q63R variant by Taqman assay. Data were collected from clinical records on age at diagnosis, disease activity, duration and location, extraintestinal manifestations, therapy, clinical relapses, and need for surgery. Results: We found a significant association of the CB2-R63 variant with IBD (allele frequencies, P = 0.04; genotype distributions, P = 0.0006), in particular with CD (allele frequencies, P = 0.002; genotype distributions, P = 0.00005) and with UC only for genotype distributions (P = 0.03). RR carriers showed an increased risk for developing IBD [odds ratio (OR) = 1.82; P = 0.0002 for IBD; OR = 2.02; P = 10 1 for CD; OR = 1.63; P = 0.02 for UC at 95% confidence interval]. Upon genotype-phenotype evaluation, RR patients showed an increased frequency of moderate-to-severe disease activity at diagnosis in the case of both CD and UC (P = 0.01 and P = 0.02, respectively) and also an earlier clinical relapse in UC (P = 0.04). In UC, all the clinical features related to the CB2 risk allele were still significantly associated with the variant when ana- lyzed using a multivariate logistic regression model (P = 0.001). Conclusions: The CB2-Q63R variant contributes to the risk for pediatric IBD, in particular CD. The R63 variant is associated with a more severe phenotype in both UC and CD. Taken together, our data point toward the involvement of the CB2 receptor in the pathogenesis and clinical features of pediatric IBD. Key Words: inflammation, Crohn’s disease, ulcerative colitis, rs35761398 (J Clin Gastroenterol 2016;00:000–000) I nflammatory bowel disease (IBD) is an inflammatory condition of the gastrointestinal tract that comprises 2 main forms: Crohn’s disease (CD) and ulcerative colitis (UC). IBD is characterized by chronic inflammation, remitting and relapsing episodes, and a progressive course at diagnosis. 1 The dysfunction of the mucosal immune system plays a pivotal role in the pathogenesis of IBD. 2–5 Innate and adaptive immunity contribute to triggering and maintaining inflammatory events, resulting in IBD. 3 Furthermore, the production and release of cytokines and chemokines represents an important underlying mecha- nism, able to drive inflammatory events at local and sys- temic levels. 4,5 Despite the therapeutic advances related to an improved knowledge of the disease pathogenesis, alter- native therapeutic approaches are necessary as IBD patients are often resistant to treatment. The endocannabinoid (EC) system has been recently indicated as a possible therapeutic target in IBD. 6–8 The EC system includes the ECs, their G-protein-coupled cannabi- noid receptors type 1 and 2 (CB1 and CB2), and the enzymes for EC metabolism. 9 It has been shown that a CB1 functional variant modulates UC susceptibility and CD phenotype. 10 Moreover, in both forms of IBD, genome-wide asso- ciation studies have revealed a linkage in the region 1p36. 11,12 Interestingly, the CNR2 gene, encoding for CB2, maps in this region. A common CNR2 variant, rs35761398 (CAA/CGG), is associated with autoimmunity imbalance. The relative glutamine-arginine substitution at codon 63, Q63R, affects the response of CB2 to ECs. ECs produce a bias in the balance between the 2 types of Th-cells, suppressing Th1 and enhancing Th2. The CB2-Q63R variant is involved in this process, exerting a different inhibition of these cells according to the presence of Q (AA-allele) or R (GG- allele). 13,14 The presence of R at codon 63 significantly reduces the EC-induced inhibition of its effector cells, sug- gesting the R63 variant as the less functional. 14–18 The marked increase in the incidence of IBD in childhood 19 gives particular importance to our study. In a pediatric population with IBD, genetic susceptibility could be greater than environmental exposure and could influence a more severe disease course, making genetic investigations in pediatric IBD populations rewarding. Pediatric populations can be particularly important in unraveling the genetic basis of IBD. Indeed, genetic advances in children with IBD demonstrated that genes can play different roles in the development and expression of Received for publication June 1, 2016; accepted October 1, 2016. From the Departments of *Women, Child and General and Specialist Surgery; wExperimental Medicine, Division of Pharmacology “Leonardo Donatelli,” The Second University of Naples; and zDepartment of Translational Medical Science, Section of Pedia- trics, University of Naples “Federico II,” Naples, Italy. The authors declare that they have nothing to disclose. Address correspondence to: Caterina Strisciuglio, MD, PhD, Depart- ment of Women, Child and General and Specialist Surgery, SUN, via Luigi De Crecchio, 4, 80138 Napoli, Italy (e-mail: caterina.strisciuglio@unina2.it). 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.jcge.com. Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/MCG.0000000000000755 ORIGINAL ARTICLE J Clin Gastroenterol  Volume 00, Number 00, ’’ 2016 www.jcge.com | 1 Copyright r 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. This paper can be cited using the date of access and the unique DOI number which can be found in the footnotes.