NOD2 Variants Research Articles

Commentary: predicting complicated Crohn's disease and surgery - phenotypes, genetics, serology and psychological characteristics of a population-based cohort - authors’ reply

Summary Background Predictors of complicated Crohn's disease (CD), defined as stricturing or penetrating behaviour, and surgery have largely been derived from referral centre populations. Aim To investigate whether serological markers, susceptibility genes or psychological characteristics are associated with complicated CD or surgery in a population-based cohort. Methods One hundred and eighty-two members of the Manitoba IBD Cohort with CD phenotyped using the Montreal classification underwent genetic and serological analysis at enrolment and after 5 years. One hundred and twenty-seven had paired sera at baseline and 5 years later and their data were used to predict outcomes at a median of 9.3 years. Serological analysis consisted of a seven antibody panel, and DNA was tested for CD-associated NOD2 variants (rs2066845,rs2076756,rs2066847), ATG16L1 (rs3828309, rs2241880) and IL23R (rs11465804). Psychological characteristics were assessed using semi-structured interviews and validated survey measures. Results Sixty-five per cent had complicated CD and 42% underwent surgery. Multivariate analysis indicated that only ASCA IgG-positive serology was predictive of stricturing/penetrating behaviour (OR = 3.01; 95% CI: 1.28–7.09; P = 0.01) and ileal CD (OR = 2.2; 95% CI: 1.07–4.54, P = 0.03). Complicated CD behaviour was strongly associated with surgery (OR = 5.6; 95% CI: 2.43–12.91; P < 0.0001), whereas in multivariate analysis, only ASCA IgG was associated (OR = 2.66; 95% CI, 1.40–5.06, P = 0.003). ASCA titre results were similar at baseline and follow-up. Psychological characteristics were not significantly associated with disease behaviour, serological profile or genotype. Conclusions ASCA IgG at baseline was significantly associated with stricturing/penetrating disease at 9–10 years from diagnosis. Stricturing/penetrating disease was significantly associated with surgery. In a model including serology, the genotypes assessed did not significantly associate with complicated disease or surgery.

Predicting complicated Crohn's disease and surgery: phenotypes, genetics, serology and psychological characteristics of a population-based cohort

Predictors of complicated Crohn's disease (CD), defined as stricturing or penetrating behaviour, and surgery have largely been derived from referral centre populations. To investigate whether serological markers, susceptibility genes or psychological characteristics are associated with complicated CD or surgery in a population-based cohort. One hundred and eighty-two members of the Manitoba IBD Cohort with CD phenotyped using the Montreal classification underwent genetic and serological analysis at enrolment and after 5years. One hundred and twenty-seven had paired sera at baseline and 5years later and their data were used to predict outcomes at a median of 9.3years. Serological analysis consisted of a seven antibody panel, and DNA was tested for CD-associated NOD2 variants (rs2066845,rs2076756,rs2066847), ATG16L1 (rs3828309, rs2241880) and IL23R (rs11465804). Psychological characteristics were assessed using semi-structured interviews and validated survey measures. Sixty-five per cent had complicated CD and 42% underwent surgery. Multivariate analysis indicated that only ASCA IgG-positive serology was predictive of stricturing/penetrating behaviour (OR=3.01; 95% CI: 1.28-7.09; P=0.01) and ileal CD (OR=2.2; 95% CI: 1.07-4.54, P=0.03). Complicated CD behaviour was strongly associated with surgery (OR=5.6; 95% CI: 2.43-12.91; P<0.0001), whereas in multivariate analysis, only ASCA IgG was associated (OR=2.66; 95% CI, 1.40-5.06, P=0.003). ASCA titre results were similar at baseline and follow-up. Psychological characteristics were not significantly associated with disease behaviour, serological profile or genotype. ASCA IgG at baseline was significantly associated with stricturing/penetrating disease at 9-10years from diagnosis. Stricturing/penetrating disease was significantly associated with surgery. In a model including serology, the genotypes assessed did not significantly associate with complicated disease or surgery.

Isolated Active Ileitis

Ileal intubation is being increasingly performed at colonoscopy and has in turn lead to an increasingly recognized subgroup of patients-those with mild terminal ileal inflammation, an entity that we have coined isolated active ileitis (IAI). The aims of this study were to define the natural history of IAI and determine if IAI shares a similar genetic and serologic profile with Crohn's disease (CD). Patients with IAI were identified from our institution's histopathology and endoscopy databases. Cases attended for repeat colonoscopy and blood were analyzed for the expression of antineutrophil cytoplasmic antibody, anti-OmpC, anti-Saccharomyces cerevisiae antigen (ASCA) IgA, ASCA IgG, and anti-CBir antibodies and NOD2 genotyping. Age and sex-matched healthy controls, CD, and UC cases were also recruited. Sixty-three patients with IAI were recruited. There was no significant difference in the prevalence of antibodies between IAI cases and healthy controls for antineutrophil cytoplasmic antibody, OmpC, ASCA IgA, or ASCA IgG. The presence of all 5 antibodies was significantly higher in the CD group than the IAI group, P < 0.05. There were 28.6% of CD cases that carried one or more NOD2 variants, compared to 26.2% of the IAI cohort and 6.1% of healthy controls. Forty-three cases underwent follow-up ileocolonoscopy. Six of 43 cases (14%) had definite CD. A majority of IAI cases developed persistent symptoms and terminal ileal abnormalities; however, only 14% developed classical, histological, or radiological features of CD. Although patients with IAI have a low level of seropositivity, similar to healthy controls, they do share an excess of NOD2 mutations with CD cases.

OP0241 Anti-Flagellin Antibodies in Ankylosing Spondylitis (AS) Implicate Subclinical Bowel Inflammation and Differentiate as from Mechanical Back Pain Patients

BackgroundSerum antibody reactivity to microbial antigens may provide important clues to the role of gut-derived microbial antigens in ankylosing spondylitis (AS). Anti-flagellin (anti-CBir1) serum reactivity in Crohn’s disease (CD) is...

SP0009 The Expanding Spectrum of Autoinflammation

The term autoinflammation was coined by McDermott and colleagues in 1999 to describe inflammatory conditions with apparently unprovoked inflammation without high titer autoantibodies or antigen-specific T lymphocytes. Unlike autoimmune diseases,...

Age-of-onset-dependent influence of NOD2 gene variants on disease behaviour and treatment in Crohn’s disease

BackgroundInfluence of genetic variants in the NOD2 gene may play a more important role in disease activity, behaviour and treatment of pediatric- than adult-onset Crohn’s disease (CD).Methods85 pediatric- and 117 adult-onset CD patients were tested for the three main NOD2 CD-associated variants (p.R702W, p.G908R and p.10007fs) and clinical data of at least two years of follow-up were compared regarding disease behaviour and activity, response to therapy and bone mineral density (BMD).ResultsChronic active and moderate to severe course of CD is associated in patients with pediatric-onset (p=0.0001) and NOD2 variant alleles (p=0.0001). In pediatric-onset CD the average PCDAI-Score was significantly higher in patients carrying NOD2 variants (p=0.0008). In addition, underweight during course of the disease (p=0.012) was associated with NOD2 variants. Interestingly, osteoporosis was found more frequently in patients carrying NOD2 variant alleles (p=0.033), especially in pediatric-onset CD patients with homozygous NOD2 variants (p=0.037). Accordingly, low BMD in pediatric-onset CD is associated with a higher PCDAI (p=0.0092), chronic active disease (p=0.0148), underweight at diagnosis (p=0.0271) and during follow-up (p=0.0109). Furthermore, pediatric-onset CD patients with NOD2 variants are more frequently steroid-dependent or refractory (p=0.048) and need long-term immunosuppressive therapy (p=0.0213).ConclusionsThese data suggests that the presence of any of the main NOD2 variants in CD is associated with osteoporosis and an age of onset dependent influence towards underweight, higher disease activity and a more intensive immunosuppressive therapy. This observation supports the idea for an early intensive treatment strategy in children and adolescent CD patients with NOD2 gene variants.

Extended haplotype association study in Crohn’s disease identifies a novel, Ashkenazi Jewish-specific missense mutation in the NF-κB pathway gene, HEATR3

The Ashkenazi Jewish population has a several-fold higher prevalence of Crohn’s disease compared to non-Jewish European ancestry populations and has a unique genetic history. Haplotype association is critical to Crohn’s disease etiology in this population, most notably at NOD2, in which three causal, uncommon, and conditionally independent NOD2 variants reside on a shared background haplotype. We present an analysis of extended haplotypes which showed significantly greater association to Crohn’s disease in the Ashkenazi Jewish population compared to a non-Jewish population (145 haplotypes and no haplotypes with P-value < 10−3, respectively). Two haplotype regions, one each on chromosomes 16 and 21, conferred increased disease risk within established Crohn’s disease loci. We performed exome sequencing of 55 Ashkenazi Jewish individuals and follow-up genotyping focused on variants in these two regions. We observed Ashkenazi Jewish-specific nominal association at R755C in TRPM2 on chromosome 21. Within the chromosome 16 region, R642S of HEATR3 and rs9922362 of BRD7 showed genome-wide significance. Expression studies of HEATR3 demonstrated a positive role in NOD2-mediated NF-κB signaling. The BRD7 signal showed conditional dependence with only the downstream rare Crohn’s disease-causal variants in NOD2, but not with the background haplotype; this elaborates NOD2 as a key illustration of synthetic association.

Association of the MEFV Gene Variations With Inflammatory Bowel Disease in Turkey

Association of NOD2 (CARD15) gene mutations with inflammatory bowel diseases (IBD) is well known. We herein aimed to investigate the role of familial Mediterranean fever-associated MEFV variations in IBD patients as additional regional-specific risk factor. One hundred thirty-seven (78 female, 56.9%) IBD patients [62 Crohn's disease (CD), 75 ulcerative colitis (UC)] were enrolled into the study. The diagnosis of all patients was confirmed by colonoscopy, histopathology, and the clinical findings. One hundred one healthy donors' samples were used as healthy controls. All patients were genotyped for the most common E148Q, M608I, M694V, and V726A variations of the MEFV and R702W, G908R, and 1007fs of the NOD2. The overall MEFV variation frequency was found to be higher in the IBD (25.5%) patients (28% in UC, 22.6% in CD) compared with controls (9.9%, P=0.006). This association was stronger with the penetrant exon 10 variations (M694V, M680I, V726A; odds ratio =4.5, P=0.001). Contribution of M694V was higher compared with the other variations (14.5% in CD, 17.3% in UC and 3% in controls, odds ratio =6.039, 95% confidence intervals, 1.7-20.7, P=0.002). The overall frequency of 3 NOD2 variants in the IBD group was not different from that of controls. The results of this study suggest that the MEFV variations may be an additional susceptibility factor for IBD in certain parts of the world where the carrier rate is high, and the genetic background of the IBD patients may show regional changes.

P678 Relation between a single nucleotide polymorphism in MORC4, NOD2 variants and outcome after allogeneic stem cell transplantation for haematological malignancies

P678 Relation between a single nucleotide polymorphism in MORC4, NOD2 variants and outcome after allogeneic stem cell transplantation for haematological malignancies

Non-selective betablocker therapy decreases intestinal permeability and serum levels of LBP and IL-6 in patients with cirrhosis

We evaluated the gastrointestinal permeability and bacterial translocation in cirrhotic patients with portal hypertension (PHT) prior to and after non-selective betablocker (NSBB) treatment. Hepatic venous pressure gradient (HVPG) was measured prior to and under NSBB treatment. Gastroduodenal and intestinal permeability was assessed by the sucrose-lactulose-mannitol (SLM) test. Anti-gliadin and anti-endomysial antibodies were measured. Levels of LPS-binding protein (LBP) and interleukin-6 (IL-6) were quantified by ELISA, and NOD2 and toll-like receptor 2 (TLR2) polymorphisms were genotyped. Fifty cirrhotics were included (72% male, 18% ascites, 60% alcoholic etiology). Abnormal gastroduodenal and intestinal permeability was found in 72% and 59% of patients, respectively. Patients with severe portal hypertension (HVPG ≥20 mm Hg; n=35) had increased markers of gastroduodenal/intestinal permeability (urine sucrose levels p=0.049; sucrose/mannitol ratios p=0.007; intestinal permeability indices p=0.002), and bacterial translocation (LBP p=0.002; IL-6 p=0.025) than patients with HVPG <20 mm Hg. A substantial portion of patients showed elevated levels of anti-gliadin antibodies (IgA: 60%, IgG: 34%) whereas no anti-endomysial antibodies were detected. A significant correlation of portal pressure (i.e., HVPG) with all markers of gastroduodenal/intestinal permeability and with LBP and IL-6 levels was observed. NOD2 and TLR2 risk variants were associated with abnormal intestinal permeability and elevated markers of bacterial translocation. At follow-up HVPG measurements under NSBB, we found an amelioration of gastroduodenal/intestinal permeability and a decrease of bacterial translocation (LBP - 16% p=0.018; IL-6 - 41% p<0.0001) levels, which was not limited to hemodynamic responders. Abnormal SLM test results and higher LBP/IL-6 levels were associated with a higher risk of variceal bleeding during follow-up but not with mortality. Abnormal gastroduodenal/intestinal permeability, anti-gliadin antibodies, and bacterial translocation are common findings in cirrhotic patients and are correlated with the degree of portal hypertension. NSBB treatment ameliorates gastroduodenal/intestinal permeability and reduces bacterial translocation partially independent of their hemodynamic effects on portal pressure, which may contribute to a reduced risk of variceal bleeding.

Limited Evidence for Parent-of-Origin Effects in Inflammatory Bowel Disease Associated Loci

BackgroundGenome-wide association studies of two main forms of inflammatory bowel diseases (IBD), Crohn’s disease (CD) and ulcerative colitis (UC), have identified 99 susceptibility loci, but these explain only ∼23% of the genetic risk. Part of the ‘hidden heritability’ could be in transmissible genetic effects in which mRNA expression in the offspring depends on the parental origin of the allele (genomic imprinting), since children whose mothers have CD are more often affected than children with affected fathers. We analyzed parent-of-origin (POO) effects in Dutch and Indian cohorts of IBD patients.MethodsWe selected 28 genetic loci associated with both CD and UC, and tested them for POO effects in 181 Dutch IBD case-parent trios. Three susceptibility variants in NOD2 were tested in 111 CD trios and a significant finding was re-evaluated in 598 German trios. The UC-associated gene, BTNL2, reportedly imprinted, was tested in 70 Dutch UC trios. Finally, we used 62 independent Indian UC trios to test POO effects of five established Indian UC risk loci.ResultsWe identified POO effects for NOD2 (L1007fs; OR = 21.0, P-value = 0.013) for CD; these results could not be replicated in an independent cohort (OR = 0.97, P-value = 0.95). A POO effect in IBD was observed for IL12B (OR = 3.2, P-value = 0.019) and PRDM1 (OR = 5.6, P-value = 0.04). In the Indian trios the IL10 locus showed a POO effect (OR = 0.2, P-value = 0.03).ConclusionsLittle is known about the effect of genomic imprinting in complex diseases such as IBD. We present limited evidence for POO effects for the tested IBD loci. POO effects explain part of the hidden heritability for complex genetic diseases but need to be investigated further.

A rapid method for combined analysis of common and rare variants at the level of a region, gene, or pathway

Previously described methods for the combined analysis of common and rare variants have disadvantages such as requiring an arbitrary classification of variants or permutation testing to assess statistical significance. Here we propose a novel method which implements a weighting scheme based on allele frequencies observed in both cases and controls. Because the test is unbiased, scores can be analyzed with a standard t-test. To test its validity we applied it to data for common, rare, and very rare variants simulated under the null hypothesis. To test its power we applied it to simulated data in which association was present, including data using the observed allele frequencies of common and rare variants in NOD2 previously reported in cases of Crohn’s disease and controls. The method produced results that conformed well to those expected under the null hypothesis. It demonstrated more power to detect association when rare and common variants were analyzed jointly, the power further increasing when rare variants were assigned higher weights. 20,000 analyses of a gene containing 62 variants could be performed in 80 minutes on a laptop. This approach shows promise for the analysis of data currently emerging from genome wide sequencing studies.

Lactase persistence, NOD2 status and Mycobacterium avium subsp. paratuberculosis infection associations to Inflammatory Bowel Disease

BackgroundInflammatory Bowel Disease (IBD), which includes both Crohn’s disease (CD) and ulcerative colitis (UC), is caused by a complex interplay involving genetic predisposition, environmental factors and an infectious agent. Mycobacterium avium subsp. paratuberculosis (MAP) is a promising pathogen candidate since it produces a chronic intestinal inflammatory disease in ruminants that resembles CD in humans. MAP is a ubiquitous microorganism, although its presence in the food chain, especially in milk from infected animals, is what made us think that there could be an association between lactase persistence (LP) and IBD. The LCT mutation has brought adaptation to dairy farming which in turn would have increased exposure of the population to infection by MAP. NOD2 gene mutations are highly associated to CD.MethodsIn our study, CD and UC patients and controls from the North of Spain were genotyped for the lactase gene (LCT) and for three NOD-2 variants, R702W, G908R and Cins1007fs. MAP PCR was carried out in order to assess MAP infection status and these results were correlated with LCT and NOD2 genotypes.ResultsAs for LP, no association was found with IBD, although UC patients were less likely to present the T/T−13910 variant compared to controls, showing a higher C-allele frequency and a tendency to lactase non-persistence (LNP). NOD2 mutations were associated to CD being the per-allele risk higher for the Cins1007fs variant. MAP infection was more extended among the healthy controls (45.2%) compared to CD patients (21.38%) and UC patients (19.04%) and this was attributed to therapy. The Asturian CD cohort presented higher levels of MAP prevalence (38.6%) compared to the Basque CD cohort (15.5%), differences also attributed to therapy. No interaction was found between MAP infection and LCT or NOD2 status.ConclusionsWe conclude that LP is not significantly associated with IBD, but that MAP infection and NOD2 do show not mutually interacting associations with IBD.

Host Genes Related to Paneth Cells and Xenobiotic Metabolism Are Associated with Shifts in Human Ileum-Associated Microbial Composition

The aim of this study was to integrate human clinical, genotype, mRNA microarray and 16 S rRNA sequence data collected on 84 subjects with ileal Crohn’s disease, ulcerative colitis or control patients without inflammatory bowel diseases in order to interrogate how host-microbial interactions are perturbed in inflammatory bowel diseases (IBD). Ex-vivo ileal mucosal biopsies were collected from the disease unaffected proximal margin of the ileum resected from patients who were undergoing initial intestinal surgery. Both RNA and DNA were extracted from the mucosal biopsy samples. Patients were genotyped for the three major NOD2 variants (Leufs1007, R702W, and G908R) and the ATG16L1T300A variant. Whole human genome mRNA expression profiles were generated using Agilent microarrays. Microbial composition profiles were determined by 454 pyrosequencing of the V3–V5 hypervariable region of the bacterial 16 S rRNA gene. The results of permutation based multivariate analysis of variance and covariance (MANCOVA) support the hypothesis that host mucosal Paneth cell and xenobiotic metabolism genes play an important role in host microbial interactions.

PTU-092 Crohn's disease associated NOD2 variants show differential activation of NF-κb in response to auto-signalling and muramyl dipeptide

IntroductionSingle nucleotide polymorphisms (SNPs) located of the NOD2/CARD15 gene (nucleotide-binding oligomerization domain containing 2/caspase recruitment domain family, member 15) are associated with increased susceptibility to Crohn's disease (CD). These SNPs...

Next generation exome sequencing of paediatric inflammatory bowel disease patients identifies rare and novel variants in candidate genes

BackgroundMultiple genes have been implicated by association studies in altering inflammatory bowel disease (IBD) predisposition. Paediatric patients often manifest more extensive disease and a particularly severe disease course. It is...

Sa1996 Crohn's Disease Associated NOD2 Variants Show Differential Activation of NFkB in Response to Autosignaling and Muramyl Dipeptide

Introduction Single nucleotide polymorphisms (SNPs) located of the NOD2/CARD15 gene (nucleotide-binding oligomerization domain containing 2/caspase recruitment domain family, member 15) are associated with increased susceptibility to Crohn9s disease (CD). These SNPs are thought to disrupt the sensing of bacterial muramyl dipeptide (MDP) at the C-terminus of the NOD2 protein. The precise contribution of each of these SNPs (SNP5, 8, 12 and 13) to NF-κB activation by means of NOD2-auto-signalling and stimulation with MDP has not been investigated at low levels of NOD2 expression. Data regarding the linkage disequilibrium (LD) between these CD-associated SNPs are scarce. Methods NOD2 variant constructs (rs2066842 (SNP5), rs2066844 (SNP8), rs2066845 (SNP12) and rs2066847 (SNP13), SNP5+8, SNP5+12 and SNP5+13) were created by site-directed mutagenesis of a pCMV plasmid containing wild-type N-terminal FLAG-NOD2. NF-κB luciferase assays were performed on HEK293 cells following transient transfection (20 h) with wildtype (WT) and NOD2 variant constructs, titrating NOD2 from 1 to 100 ng/well. The NF-κB luciferase response of NOD2 (1 ng)-transfected HEK293 cells to MDP (10 μg/well) was measured. Two-way ANOVA and unpaired t-tests were used. By means of Haploview-analysis of sequencing data of the exons and exon-intron boundaries in 24 paediatric Caucasian Crohn9s disease patients, we assessed the LD between SNP5 and SNP8, 12 and 13. Results Two-way ANOVA demonstrated an effect of NOD2 genotype and concentration on auto-signalling at low levels of expression (p 2 Conclusion Our combined genetic and functional analyses demonstrate that the association of SNP5 with Crohn9s disease is unlikely due to LD with other SNPs. At low levels of NOD2 expression, NOD2 variant constructs differ from WT in their auto-signalling and MDP-stimulated activation of NF-κB. Competing interests None declared.

Prevalence of genetic variants associated with inflammatory bowel disease in a healthy First Nations cohort

Inflammatory bowel disease is the result of both genes and environment. Canadian First Nations people, despite living in a region with a high prevalence of inflammatory bowel disease, are relatively protected from this disease. We aimed to compare the carriage of genetic variants associated with inflammatory bowel disease in healthy First Nations and white people. DNA was extracted from the venous blood of healthy First Nations (n = 340) and white (n = 285) participants from Manitoba. Genotyping was performed for 69 single nucleotide polymorphisms (SNPs) with known or suspected associations with inflammatory bowel disease. We compared the genotypes between groups by logistic regression, adjusting for multiple testing. We calculated a risk score for the NOD2 gene by adding the number of risk alleles at three important NOD2 SNPs (G908R, R702W and 3020insC). We found genetic variation between white and First Nations participants at 45 of 69 SNPs. Notably, carriage of the ATG16L1 T300A mutation was lower in First Nations participants (p = 4.1 × 10(-30)). Cumulative carriage of important NOD2 variants was significantly lower among First Nations participants (3.9% v. 15.2%; p < 0.0001 for risk score) than among white participants. Risk variants in IL23R (p = 0.014) and IL12B (p = 1.2 × 10(-16)), among others, were more prevalent among First Nations participants than among white participants. The low prevalence of variants associated with bacterial processing and handling in First Nations people may explain their relative protection from inflammatory bowel disease. Increased carriage of a number of risk variants, for example in the interleukin-23/Th17 pathway, is especially intriguing given their importance in other inflammatory diseases of high incidence in First Nations populations.

Common NOD2 risk variants in African Americans with Crohnʼs disease are due exclusively to recent Caucasian admixture

Crohn's disease (CD) is highly heritable. NOD2 has emerged as the main susceptibility gene among individuals of European ancestry; however, NOD2 does not appear to contribute to CD susceptibility among many non-European populations. Today's African American (AA) population represents an admixture of West African (80%) and European (20%) ancestry. Since genotype-based tools are becoming increasingly available for CD, it is important that we validate the risk variants in different populations, such as admixed AAs. We analyzed the NOD2 variants among admixed AAs (n = 321, 240 with CD and 111 healthy controls [HCs]) and nonadmixed West Africans (n = 40) by genotyping four known disease-causing NOD variants. We extracted the publicly available 1000 Genomes data on NOD2 variants from 500 subjects of West African origin. Association with disease was evaluated by logistic regression. An association with CD was found for the classical single nucleotide polymorphism (SNP) 1007fs (2.6% CD, 0% HC, P = 0.012); there was no association when the genotypic and allelic frequencies of the risk alleles were compared for SNPs R702W and G908R. No known NOD2 risk alleles were seen in either the West African cohort or in subjects of African ancestry from the 1000 Genomes project. The NOD2 gene is a risk for CD in AAs, although the allele frequencies and the attributable risk are much lower compared with Caucasians. The risk alleles are not seen in the West African population, suggesting that the risk for CD contributed by NOD2 among AAs is due exclusively to recent European admixture.

A case-only study of gene-environment interaction between genetic susceptibility variants in NOD2 and cigarette smoking in Crohn's disease aetiology

BackgroundGenetic variation in NOD2 and cigarette smoking are well-established risk factors for the development of Crohn's disease (CD). However, little is known about a potential interaction between these risk factors. We investigated gene-environment interactions between CD-associated NOD2 alleles and cigarette smoking in a large sample of patients with CD.MethodsThree previously reported CD-associated variants in NOD2 (R702W, G908R, 1007fs) were genotyped in 1636 patients with CD continuously recruited between 1995 and 2010 based on physician referral. Data on history of smoking behaviour was obtained for all participants through a written questionnaire. Using a case-only design, we performed logistic regression analyses to investigate statistical interactions between NOD2 risk alleles and smoking status.ResultsWe detected a significant negative interaction between carriership of at least one of the NOD2 risk alleles and history of ever having smoked (OR = 0.71; p = 0.005) as well as smoking at the time of CD diagnosis (OR = 0.68; p = 0.005). Subsequent separate analyses of the three variants revealed a significant negative interaction between the 1007fs variant and history of ever having smoked (OR = 0.64; p = 9 × 10-4) and smoking at the time of CD diagnosis (OR = 0.53; p = 7 × 10-5).ConclusionsThe observed significant negative gene-environment interaction suggests that the risk increase for CD conferred simultaneously by cigarette smoking and the 1007fs NOD2 polymorphism is smaller than expected and may point to a biological interaction. Our findings warrant further investigation in epidemiological and functional studies to elucidate pathophysiology as well as to aid in the development of recommendations for disease prevention.