IBD Susceptibility Research Articles

IRGM gene variants are associated with susceptibility to Crohn's disease in the German population

Background & Aims: Genome-wide association studies identified the autophagy gene IRGM as susceptibility gene for Crohn's disease (CD), but its impact in ulcerative colitis (UC), its phenotypic effects and potential epistatic interactions with other IBD susceptibility genes are less clear which we therefore analyzed in this detailed study.

Tu1916 Evidence of Parent-of-Origin Effects in IBD Susceptibility

Tu1916 Evidence of Parent-of-Origin Effects in IBD Susceptibility

P450 The impact of PPARγ genetic variants on IBD susceptibility and IBD disease course

P450 The impact of PPARγ genetic variants on IBD susceptibility and IBD disease course

Functional Studies on the IBD Susceptibility Gene IL23R Implicate Reduced Receptor Function in the Protective Genetic Variant R381Q

Genome-wide association studies (GWAS) in several populations have demonstrated significant association of the IL23R gene with IBD (Crohn's disease (CD) and ulcerative colitis (UC)) and psoriasis, suggesting that perturbation of the IL-23 signaling pathway is relevant to the pathophysiology of these diseases. One particular variant, R381Q (rs11209026), confers strong protection against development of CD. We investigated the effects of this variant in primary T cells from healthy donors carrying IL23RR381 and IL23RQ381 haplotypes. Using a proprietary anti-IL23R antibody, ELISA, flow cytometry, phosphoflow and real-time RT-PCR methods, we examined IL23R expression and STAT3 phosphorylation and activation in response to IL-23. IL23RQ381 was associated with reduced STAT3 phosphorylation upon stimulation with IL-23 and decreased number of IL-23 responsive T-cells. We also observed slightly reduced levels of proinflammatory cytokine secretion in IL23RQ381 positive donors. Our study shows conclusively that IL23RQ381 is a loss-of-function allele, further strengthening the implication from GWAS results that the IL-23 pathway is pathogenic in human disease. This data provides an explanation for the protective role of R381Q in CD and may lead to the development of improved therapeutics for autoimmune disorders like CD.

79 Ipilimumab-Related Colitis in Patients with Advanced Melanoma Receiving Ipilimumab Therapy: Histopathologic and Serologic Characterization

Background: Natural history observations in early onset IBD have prompted the increasing use of anti-TNFα therapy. Inter-individual variation, however, is seen in efficacy outcomes. These differences may be explained in part by genetic variability as it relates to disease pathogenesis or directed to the mechanism of action of these therapies. Recent GWA studies in IBD have increased our understanding of the genetic susceptibility to IBD and provide insight regarding the various mechanisms of inflammation. We hypothesize that interindividual differences in therapeutic outcomes to anti-TNFαmay be associated with IBD susceptibility genes. Aim: Test associations of GWA identified IBD susceptibility loci (34 SNPs) with infliximab (IFX) responsiveness in pediatric IBD patients. Methods: Complete follow up and GWAS data was available on 63 children receiving IFX. Harvey Bradshaw index (HBI) was used to calculate disease activity. Outcomes were primary nonresponse: no change or increase in HBI at week 10; and secondary loss of response: drop in HBI by >3 points at week 10 (response) and then increase to or above baseline HBI week 14 or later. Chi square testing examined the association between 34 SNPs and IFX responsiveness. Time to loss of response was calculated using Kaplan Meier analysis. Results: Six SNPs (Table 1) were associated with primary non-response (p < 0.05). There were 5 different SNPs (Chromosome) associated with loss of response; rs11174631 (12q12); OR =10.6, p= 0.03; rs8049439 (16p11); OR = 3.8, p= 0.03, rs2456449 (8q24); OR= 4.8, p = 0.02, rs10044354 (5q15); OR = 3.8, p = 0.03, rs6908425 (6p22); OR = 4.1, p = 0.03. Of these 5 SNPs, 4 were also associated with the time to loss of response (median 9 months): rs11174631 (p= 0.03), rs2456449 (p = 0.03), rs10044354 (p = 0.04), rs6908425 (p = 0.02). Conclusion: These findings suggest that there may be different genetic predictors and perhaps biological explanations for primary non response vs. secondary loss of response. Replication studies are currently underway. Defining predictors of response to anti-TNFα will allow the identification of patients with a high probability of response before initiating therapy so to negate exposure to ineffective therapies and protect patients from treatment related serious adverse events. Primary Non Response

80 Increased Risk of Inflammatory Bowel Disease After Salmonella or Campylobacter Gastroenteritis: A Population-Based Cohort Study

Background: Natural history observations in early onset IBD have prompted the increasing use of anti-TNFα therapy. Inter-individual variation, however, is seen in efficacy outcomes. These differences may be explained in part by genetic variability as it relates to disease pathogenesis or directed to the mechanism of action of these therapies. Recent GWA studies in IBD have increased our understanding of the genetic susceptibility to IBD and provide insight regarding the various mechanisms of inflammation. We hypothesize that interindividual differences in therapeutic outcomes to anti-TNFαmay be associated with IBD susceptibility genes. Aim: Test associations of GWA identified IBD susceptibility loci (34 SNPs) with infliximab (IFX) responsiveness in pediatric IBD patients. Methods: Complete follow up and GWAS data was available on 63 children receiving IFX. Harvey Bradshaw index (HBI) was used to calculate disease activity. Outcomes were primary nonresponse: no change or increase in HBI at week 10; and secondary loss of response: drop in HBI by >3 points at week 10 (response) and then increase to or above baseline HBI week 14 or later. Chi square testing examined the association between 34 SNPs and IFX responsiveness. Time to loss of response was calculated using Kaplan Meier analysis. Results: Six SNPs (Table 1) were associated with primary non-response (p < 0.05). There were 5 different SNPs (Chromosome) associated with loss of response; rs11174631 (12q12); OR =10.6, p= 0.03; rs8049439 (16p11); OR = 3.8, p= 0.03, rs2456449 (8q24); OR= 4.8, p = 0.02, rs10044354 (5q15); OR = 3.8, p = 0.03, rs6908425 (6p22); OR = 4.1, p = 0.03. Of these 5 SNPs, 4 were also associated with the time to loss of response (median 9 months): rs11174631 (p= 0.03), rs2456449 (p = 0.03), rs10044354 (p = 0.04), rs6908425 (p = 0.02). Conclusion: These findings suggest that there may be different genetic predictors and perhaps biological explanations for primary non response vs. secondary loss of response. Replication studies are currently underway. Defining predictors of response to anti-TNFα will allow the identification of patients with a high probability of response before initiating therapy so to negate exposure to ineffective therapies and protect patients from treatment related serious adverse events. Primary Non Response

Association between CTLA-4 gene promoter (49 A/G) in exon 1 polymorphisms and inflammatory bowel disease in the Tunisian population.

Background/Aim:To investigate the possible association between the polymorphism of the CTLA-4 exon 1 +49 A/G and susceptibility to Crohn's disease (CD) and ulcerative colitis (UC) in the Tunisian population.Methods:The +49 A/G dimorphism was analyzed in 119 patients with CD, 65 patients with UC, and 100 controls by the polymerase chain reaction–restriction fragment length polymorphism method.Results:Significantly higher frequencies of the CTLA-4 +49A allele and A/A homozygous individuals were observed in patients with CD when compared with controls (pc = 0.0023 and pc = 0.0003, respectively). Analysis of CTLA-4 A/G polymorphism with respect to sex in CD showed a significant difference in A/A genotypes between female patients and controls (pc = 0.0001 and pc = 0.038, respectively). There were no differences in the subgroups of patients with CD.Conclusions:Forty-nine A alleles and AA genotype are associated with CD susceptibility in Tunisians. Other genes involved in the T-cell regulation remain strong candidates for IBD susceptibility and require further investigation.

CARD15 Genotype-Phenotype Relationships in a Small Inflammatory Bowel Disease Population with Severe Disease Affection Status

Inflammatory bowel disease (IBD; MIM# 266600) is subdivided on the basis of clinical findings as either Crohn's disease (CD), ulcerative colitis (UC), or indeterminate colitis (IC). Three previously described mutations within the IBD susceptibility gene CARD15 (R702W, G908R, 1007fs) increase susceptibility to CD with a terminal ileal and/or ileocolonic location and fibrostenosing behavior. We undertook an association study using 477 unrelated IBD patients (248 CD, 172 UC, 57 IC) and 104 population controls to determine whether these previously described associations could be replicated in a small, accurately phenotyped cohort. Case-control and family-based approaches were employed to analyze CARD15 mutant allele and haplotype data. Analyses were initially performed in unstratified IBD cohorts. The R702W mutant allele was associated with CD on case-control analysis (q=0.036, P=.004), and 1007fs with CD on pedigree disequilibrium testing (P=.020). All 3 CARD15 mutations increased susceptibility to a variety of CD subphenotypic manifestations, including early-onset CD in individuals with a family history of IBD, and CD complicated by extraintestinal disease. We also present evidence to suggest that R702W may predispose to a more generalized form of CD. Additionally, we confirm that CARD15 mutations are associated with terminal ileal/ileocolonic, and to a lesser extent, fibrostenosing CD.

CTLA4/CT60 POLYMORPHISM IS NOT RELEVANT IN SUSCEPTIBILITY TO AUTOIMMUNE INFLAMMATORY INTESTINAL DISORDERS

Aim: The aim of this work was to investigate the possible influence of the recently described CT60 A/G (SNP 3087243) dimorphism of the CTLA4 gene, which interestingly has been recently associated with functional relevance and with susceptibility to a variety of autoimmune diseases, in the susceptibility to IBD and celiac disease. Methods: We analysed a case-control cohort composed of a total of 528 Spanish IBD patients (284 with Crohn's disease and 244 with ulcerative colitis) and 454 unrelated healthy individuals, and additionally a group of 90 celiac disease families. CT60 genotyping was performed using a Taqman 5' allelic discrimination assay. Results: After comparing IBD patients with the control population we found no significant deviation in the distribution of the alleles or genotypes of CTLA4/CT60 dimorphism. In addition, using familial and case-control analysis, no evidence for a statistically significant association was observed between CTLA4/CT60 and celiac disease susceptibility. Summary: In this work we investigated for the first time the role of CTLA4/CT60 polymorphism in IBD susceptibility and no association was observed. In addition we have observed that CTLA4/CT60 polymorphisms is not relevant for celiac disease predisposition in our population, accordingly with recent studies that observed no association or borderline significance between this genetic marker and celiac disease susceptibility. Conclusion: Our results suggest that the CTLA4/CT60 polymorphism does not play a major role in autoimmune inflammatory intestinal disorders.

THE DLG 5-113A MUTATION IS ASSOCIATED WITH SUSCEPTIBILITY TO EARLY ONSET INFLAMMATORY BOWEL DISEASE AND DEMONSTRATES A COMPLEX GENOTYPE PHENOTYPE RELATIONSHIP

Aims: Genome wide scanning in a cohort of European IBD patients identified a potential IBD locus on chromosome 10. Recently the 113 mutation on the DLG5 gene (Drosophila Discs Large Homolog 5) at 10q23 has been linked to IBD susceptibility in adults. We aimed to study the role of this mutation in a national early-onset population. Methods: Patients diagnosed with IBD <16 years were recruited. Full clinical phenotype including growth data were obtained. Parental DNA was also collected to allow Transmission Disequilibrium Testing (TDT) to be performed (Both parents collected in 69% of cases). The DLG5-113A G·A missense mutation was genotyped using the Taqman system. A validated scoring system for deprivation category (DEPCAT score) was used to judge social class (scored 1-7, 1 = no deprivation 7 = maximum deprivation). Results: A total of 296 patients (197 CD, 73 UC, 26 IC) were analysed. TDT demonstrated an association with IBD (p = 0.045) but not CD(p = 0.18) or UC(p = 0.10). The allele frequency for IBD patients was 12.9%, with no significant differences between CD, UC and IC. 24.9% of patients were carriers of the mutant allele. Carrier status was associated with higher weight and height centile (75-91st) for IBD (p = 0.004, 0.006 respectively) and CD (p = 0.008, p = 0.002 respectively). Carrier status was also associated with higher social class (DEPCAT score 1) for IBD (0.0005) but not CD or UC (p = 0.06 for both). Carrier status was protective for a lower social class (DEPCAT score 3) for IBD and UC (p = 0.02, 0.04 respectively). Mutation carriage was uncommon in CD patients with joint extraintestinal manifestations (EIM's) (5.9% vs. 24.9%), and skin EIM's (erythema nodosum) (9.5% vs. 24.8%) but did not reach statistical significance (p = 0.07, p = 0.11 respectively). Summary: The DLG-5 113A mutation is associated with susceptibilty to IBD in this population. It is associated with higher height and weight centile at diagnosis of IBD and CD, is commoner in the highest social class and is uncommon in the presence of EIM's. Conclusion: The DLG-5 113A mutation confers susceptibility to early onset IBD. In addition, the data reveal complex gene-environmental interactions, and genotype phenotype relationships.

The contribution of HLA genes to IBD susceptibility and phenotype

The human leukocyte antigen (HLA) region located on chromosome 6p encodes the highly polymorphic, classical class I and II genes essential for normal lymphocyte function; it also encodes a further 224 genes. Many early studies investigating this region were limited by small sample size, poor statistical methodology, population stratification and variable disease definition. Although more recent studies have improved study design, investigators are still challenged by the complex patterns of linkage disequilibrium across this gene-dense region, and by the disease heterogeneity characteristic of all genetically complex disorders. However, a number of important observations have emerged from recent studies: (1) the HLA harbours gene(s) that determine susceptibility to colonic inflammation in both ulcerative colitis (UC) and Crohn's disease (CD); (2) most of the specific associations with UC and CD appear to differ; (3) associations between different ethnic groups differ; (4) markers in the HLA might predict the course of disease and the development of complications, notably the extraintestinal manifestations of disease.

Analysis of the CARD15 variants R702W, G908R and L1007fs in Italian IBD patients.

CARD15 on chromosome 16 is the only IBD susceptibility gene identified among several mapped loci. Its recurrent variants R702W, G908R and L1007fs have shown significant association with Crohn's disease (CD), but not with ulcerative colitis (UC), in different Caucasian populations. We analysed these three variants in 184 CD and 92 UC Italian patients and in 177 healthy controls. L1007fs and G908R were independently associated with CD, while R702W showed a nonsignificant increase. After combining the three variants together, 32.6% of CD patients were positive vs 18.6% of the controls. The association was stronger for homozygotes and compound heterozygotes, OR 13.9 (1.8-108), and weaker but still significant for simple heterozygotes, OR 1.7 (1.0-2.9). An excess of homozygotes/compound heterozygotes also resulted from the comparison with Hardy-Weinberg expectations. Phenotype-genotype correlations were analysed first by univariate logistic regression and then by multivariate analysis, the effect of CARD15 positivity being adjusted according to the status of smoking, familiarity and sex, so as to focus on the predictivity of genetic and environmental risk factors on the clinical phenotype. Significant risk estimates of the CARD15 genotype were obtained for stricturing vs inflammatory behaviour, OR 2.76 (1.2-6.3), and for penetrating behaviour, 2.59 (1.0-6.6), and marginally significant for ileal vs colic location, OR 3.0 (0.9-9.8). Our findings indicate that the association of the CARD15 genotype with behaviour and location of disease holds also for the Italian population.

The Study of the Ibd Susceptibility Genes on Chromosome 5 and Chromosome 19

The Study of the Ibd Susceptibility Genes on Chromosome 5 and Chromosome 19