ORIGINAL PAPER Influence of the inducible nitric oxide synthase gene (NOS2A) on inflammatory bowel disease susceptibility M. Carmen Martín & Alfonso Martinez & J. Luis Mendoza & Carlos Taxonera & Manuel Díaz-Rubio & Miguel Fernández-Arquero & Emilio G. de la Concha & Elena Urcelay Received: 31 May 2007 / Accepted: 10 August 2007 / Published online: 23 October 2007 # Springer-Verlag 2007 Abstract The great amount of nitric oxide (NO) produced by the inducible isoform of NO synthase (iNOS) exerts del- eterious effects, and iNOS expression is raised in the colonic mucosa of inflammatory bowel disease (IBD) patients. This is the first association analysis of polymorphisms within the NOS2A extended gene with IBD susceptibility. We analyzed 336 patients of Crohn’ s disease (CD), 355 of ulcerative co- litis (UC), and 536 healthy controls from a Spanish popu- lation. We tested a (CCTTT)n microsatellite, a (-/TAAA) insertion, and two single nucleotide polymorphisms (SNPs) flanking them (rs2779251 and rs2779248) in the NOS2A promoter, together with two SNPs in the coding region: one within exon 10, D385D (rs1137933), and another mapping to exon 16, S608L (rs2297518). Analysis of these markers evidenced differences among IBD patients and healthy controls. Allele (CCTTT) 13 is related to higher UC risk (p =0.001; odds ratio [OR] [95% confidence interval, CI]= 1.64 [1.20–2.23]). Carriers of minor alleles of the two promoter SNPs analyzed showed an association with UC predisposition, and common allele homozygotes of the two exonic SNPs were more frequent among CD patients than among controls. Concordantly, one out of the three haplotypes carrying both exonic risk alleles was found to increase CD susceptibility (p =0.007; OR [95%CI]=1.74 [1.13–2.67]). Therefore, the NOS2A gene seems to be involved in IBD aetiology. Keywords Nitric oxide synthase (NOS) . Inflammatory bowel diseases (IBD) . Genetic susceptibility Introduction Nitric oxide (NO) has been involved in the pathogenesis of several diseases because it was first described as a phys- iological modulator of endothelial permeability (Moncada et al. 1989). Other permeability-modulating factors also play a role in inflammatory bowel disease (IBD) suscepti- bility (Buhner et al. 2006), and chronic intestinal inflamma- tion has been associated with an increase in NO synthesis (Kolios et al. 1998; Kubes and McCafferty 2000). Colonic levels of NO in IBD patients are two to five times those in controls or in remitting IBD subjects (Rachmilewitz et al. 1998). NO acts as a switch modulating the Th1/Th2 re- sponse in several autoimmune diseases (Kolb and Kolb- Bachofen 1998), and it is also closely linked to oxidative stress and apoptosis signaling (Kruidenier et al. 2003), as well as to the antibacterial mechanisms of phagocytes (Cho and Chae 2004). The three main isoforms of NO synthase (NOS) are found in the colon: eNOS in the colonic endothelium, nNOS in myenteric innervation, and iNOS, in both epithelium and endothelium (Kubes and McCafferty 2000). The first two isozymes are constitutively expressed and the inducible isoform, iNOS, has an increased expression in IBD (Kolios et al. 2004; Kubes and McCafferty 2000). This increase was first described in the colonic mucosa of rhesus mon- keys (Ribbons et al. 1997) and ratified in a murine IBD model (Porras et al. 2006). Higher amounts of enzyme have Immunogenetics (2007) 59:833–837 DOI 10.1007/s00251-007-0255-1 M. C. Martín (*) : A. Martinez : M. Fernández-Arquero : E. G. de la Concha : E. Urcelay Servicio de Inmunología Clínica, Hospital Clínico San Carlos, 1a planta Sur, c/ Profesor Martín Lagos s/n, 28040 Madrid, Spain e-mail: cmartal@terra.es J. L. Mendoza : C. Taxonera : M. Díaz-Rubio Department of Gastroenterology, Hospital Clínico San Carlos, Madrid, Spain