Mutations in CARD15 and smoking confer susceptibility to Crohn's disease in the Danish population

Review article: impact of cigarette smoking on intestinal inflammation-direct and indirect mechanisms

BACKGROUND

The inflammatory bowel diseases, Crohn's disease and ulcerative colitis are related multifactorial diseases. Their pathogenesis is influenced by each individual's immune system, the environmental factors within exposome and genetic predisposition. Smoking habit is the single best-established environmental factor that influences disease phenotype, behaviour and response to therapy.

AIM

To assess current epidemiological, experimental and clinical evidence that may explain how smoking impacts on the pathogenesis of inflammatory bowel disease.

METHODS

A Medline search for 'cigarette smoking', in combination with terms including 'passive', 'second-hand', 'intestinal inflammation', 'Crohn's disease', 'ulcerative colitis', 'colitis'; 'intestinal epithelium', 'immune system', 'intestinal microbiota', 'tight junctions', 'mucus', 'goblet cells', 'Paneth cells', 'autophagy'; 'epigenetics', 'genes', 'DNA methylation', 'histones', 'short noncoding/long noncoding RNAs'; 'carbon monoxide/CO' and 'nitric oxide/NO' was performed.

RESULTS

Studies found evidence of direct and indirect effects of smoking on various parameters, including oxidative damage, impairment of intestinal barrier and immune cell function, epigenetic and microbiota composition changes, that contribute to the pathogenesis of inflammatory bowel disease.

CONCLUSIONS

Cigarette smoking promotes intestinal inflammation by affecting the function and interactions among intestinal epithelium, immune system and microbiota/microbiome.

Genetically determined high activities of the TNF-alpha, IL23/IL17, and NFkB pathways were associated with increased risk of ankylosing spondylitis

Background

Ankylosing spondylitis (AS) results from the combined effects of susceptibility genes and environmental factors. Polymorphisms in genes regulating inflammation may explain part of the heritability of AS.

Methods

Using a candidate gene approach in this case-control study, 51 mainly functional single nucleotide polymorphisms (SNPs) in genes regulating inflammation were assessed in 709 patients with AS and 795 controls. Data on the patients with AS were obtained from the DANBIO registry where patients from all of Denmark are monitored in routine care during treatment with conventional and biologic disease modifying anti-rheumatic drugs (bDMARDs).

The results were analyzed using logistic regression (adjusted for age and sex).

Results

Nine polymorphisms were associated with risk of AS (p < 0.05). The polymorphisms were in genes regulating a: the TNF-α pathway (TNF -308 G > A (rs1800629), and − 238 G > A (rs361525); TNFRSF1A -609 G > T (rs4149570), and PTPN22 1858 G > A (rs2476601)), b: the IL23/IL17 pathway (IL23R G > A (rs11209026), and IL18–137 G > C (rs187238)), or c: the NFkB pathway (TLR1 743 T > C (rs4833095), TLR4 T > C (rs1554973), and LY96–1625 C > G (rs11465996)).

After Bonferroni correction the homozygous variant genotype of TLR1 743 T > C (rs4833095) (odds ratios (OR): 2.59, 95% confidence interval (CI): 1.48–4.51, p = 0.04), and TNFRSF1A -609 G > T (rs4149570) (OR: 1.79, 95% CI: 1.31–2.41, p = 0.01) were associated with increased risk of AS and the combined homozygous and heterozygous variant genotypes of TNF -308 G > A (rs1800629) (OR: 0.56, 95% CI: 0.44–0.72, p = 0.0002) were associated with reduced risk of AS.

Conclusion

We replicated associations between AS and the polymorphisms in TNF (rs1800629), TNFRSF1A (rs4149570), and IL23R (rs11209026). Furthermore, we identified novel risk loci in TNF (rs361525), IL18 (rs187238), TLR1 (rs4833095), TLR4 (rs1554973), and LY96 (rs11465996) that need validation in independent cohorts. The results suggest that genetically determined high activity of the TNF-α, IL23/IL17, and NFkB pathways increase risk of AS.

Genetic polymorphisms associated with psoriasis and development of psoriatic arthritis in patients with psoriasis

Background

Psoriasis (PsO) is a chronic inflammatory disease with predominantly cutaneous manifestations. Approximately one third of patients with PsO develop psoriatic arthritis (PsA), whereas the remaining proportion of patients has isolated cutaneous psoriasis (PsC). These two phenotypes share common immunology, but with different heredity that might in part be explained by genetic variables.

Methods

Using a candidate gene approach, we studied 53 single nucleotide polymorphisms (SNPs) in 37 genes that regulate inflammation. In total, we assessed 480 patients with PsO from DERMBIO, of whom 151 had PsC for 10 years or more (PsC10), 459 patients with PsA from DANBIO, and 795 healthy controls. Using logistic regression analysis, crude and adjusted for age and gender, we assessed associations between genetic variants and PsO, PsC10, and PsA, as well as associations between genetic variants and development of PsA in PsO.

Results

Eleven polymorphisms in 10 genes were nominally associated with PsO and/or PsC and/or PsA (P < 0.05). After correction for multiple testing with a false discovery rate of 5%, two SNPs remained significant: TNF (rs361525) was associated with PsO, PsC10, and PsA; and IL12B (rs6887695) was associated with PsO.

Conclusion

Among a cohort of Danish patients with moderate-to-severe psoriasis, two SNPs in the IL12B and TNF genes were associated with susceptibility of psoriasis. None of the SNPs were specifically associated with isolated cutaneous psoriasis or psoriatic arthritis.

Genetic and environmental factors significant for the presentation and development of inflammatory bowel disease

OBJECTIVES

The aim of the study was to evaluate associations between inflammatory bowel disease (IBD) presentation and variants in NOD2, TLR4, TNF-α, IL-6, IL-1β, and IL-RN genes in order to identify possible environmental factors that may affect IBD occurrence, investigate potential predictors for surgical treatment of IBD, and correlate the presence of granulomas in biopsy specimens with clinical characteristics of Crohn's disease (CD) patients.

PATIENTS AND METHODS

We genotyped 167 IBD patients using PCR-based methodology and tested for disease genotype-phenotype associations.

RESULTS

In CD patients ileal localization of disease was more frequent in NOD2 variant carriers. Ileal CD was associated with IL-6 GC+CC genotypes, identifying C allele as a possible marker of increased risk for ileal CD. In CD patients a positive family history for IBD was related to earlier onset of disease, higher risk for CD-related surgery, and appendectomy. CD patients who are TLR4 299Gly carriers are at higher risk for surgery at onset of the disease compared with TLR4 299Asp variant carriers. The presence of granuloma in biopsy specimens was more frequent in patients in whom a diagnosis of CD was made during emergency surgery. Multivariate analysis showed that CD carriers of the 299Gly allele had a 4.6-fold higher risk for emergency surgery before CD diagnosis is established compared with noncarriers, suggesting an aggressive disease course. Granuloma in endoscopic biopsies is detected 5.4-fold more frequently in patients treated surgically at the time of diagnosis.

CONCLUSION

Genetic variants together with epidemiological and clinical data of IBD patients could potentially be used as predictors of the disease course.

Genetic Influences on the Development of Fibrosis in Crohn's Disease

Fibrostenotic strictures are an important complication in patients with Crohn’s disease (CD), very often necessitating surgery. This fibrotic process develops in a genetically susceptible individual and is influenced by an interplay with environmental, immunological, and disease-related factors. A deeper understanding of the genetic factors driving this fibrostenotic process might help to unravel the pathogenesis, and ultimately lead to development of new, anti-fibrotic therapy. Here, we review the genetic factors that have been associated with the development of fibrosis in patients with CD, as well as their potential pathophysiological mechanism(s). We also hypothesize on clinical implications, if any, and future research directions.

Polymorphisms in the Toll-Like Receptor and the IL-23/IL-17 Pathways Were Associated with Susceptibility to Inflammatory Bowel Disease in a Danish Cohort

BACKGROUND

The inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC), result from the combined effects of susceptibility genes and environmental factors. Previous studies have shown that polymorphisms in the Toll-like receptor (TLR), the apoptosis, the IL-23/IL-17 and the interferon gamma (IFNG) pathways are associated with risk of both CD and UC.

METHODS

Using a candidate gene approach, 21 functional single nucleotide polymorphisms (SNPs) in 15 genes were assessed in a clinical homogeneous group of severely diseased ethnic Danish patients consisting of 624 patients with CD, 411 patients with UC and 795 controls. The results were analysed using logistic regression.

RESULTS

The polymorphisms TLR5 (rs5744174) and IL12B (rs6887695) were associated with risk of CD, and TLR1 (rs4833095) and IL18 (rs187238) were associated with risk of both CD and UC (p<0.05). After Bonferroni correction for multiple testing, the homozygous variant genotype of TLR1 743 T>C (rs4833095) was associated with increased risk CD (OR: 3.15, 95% CI: 1.59-6.26, p = 0.02) and CD and UC combined (OR: 2.96, 95% CI: 1.64-5.32, p = 0.005).

CONCLUSION

Our results suggest that genetically determined high activity of TLR1 and TLR5 was associated with increased risk of both CD and UC and CD, respectively. This supports that the host microbial composition or environmental factors in the gut are involved in risk of IBD. Furthermore, genetically determined high activity of the IL-23/IL-17 pathway was associated with increased risk of CD and UC. Overall, our results support that genetically determined high inflammatory response was associated with increased risk of both CD and UC.

Distinctive colonic mucosal cytokine signature in new-onset, untreated pediatric Crohn disease

OBJECTIVE

The aim of the study was to compare the colonic mucosal immune response in children with new, untreated Crohn disease (CD-New), CD in remission (CD-Remission), and unaffected children (CTRL [controls]).

METHODS

We performed flow cytometry of mitogen-stimulated colonic lamina propria mononuclear cells isolated from colonic biopsies and 72-hour biopsy explant cultures, and analyzed the supernatant by an unbiased multiplex cytokine array of 45 analytes.

RESULTS

Thirty-six children were studied (mean age 14 ± 3 years, 14 girls): 12 CD-New, 11 CD-Remission, and 13 CTRL. We found that stimulation of lamina propria mononuclear cells isolated from colonic biopsies induced comparable intracellular cytokine levels of interferon (IFN-γ), interleukin (IL)-17, and tumor necrosis factor (TNF)-α in T cells from CD-New, CD-Remission, and CTRL, suggesting that mucosal innate inflammation plays a larger role than activated T cells in CD-New. To measure factors released during the ongoing inflammatory response in CD-New, we cultured colonic biopsy explants and uncovered 13/45 factors that were significantly higher in CD-New versus CD-Remission, whereas 10 were increased in CD-New over CTRL. Ingenuity Pathway Analysis software revealed the anticipated interconnectivity of TNF-α, IL-6, and CSF-2 in CD-New of the colon. A novel subnetwork of chemokines was, however, evident, whereas IL-17a appeared as a peripheral factor. Principal component analysis and hierarchal clustering showed that CD-New and CD-Remission separated into distinct subgroups based on the 13 factors.

CONCLUSIONS

At diagnosis of inflammatory bowel disease, the colonic cytokine response contains a predominance of innate immune factors, with chemoattractants and vascular adhesion molecules playing a central role.

Polymorphisms in the inflammatory pathway genes TLR2, TLR4, TLR9, LY96, NFKBIA, NFKB1, TNFA, TNFRSF1A, IL6R, IL10, IL23R, PTPN22, and PPARG are associated with susceptibility of inflammatory bowel disease in a Danish cohort

BACKGROUND

The inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC), result from the combined effects of susceptibility genes and environmental factors. Polymorphisms in genes regulating inflammation may explain part of the genetic heritage.

METHODS

Using a candidate gene approach, 39 mainly functional single nucleotide polymorphisms (SNPs) in 26 genes regulating inflammation were assessed in a clinical homogeneous group of severely diseased patients consisting of 624 patients with CD, 411 patients with UC and 795 controls. The results were analysed using logistic regression.

RESULTS

Sixteen polymorphisms in 13 genes involved in regulation of inflammation were associated with risk of CD and/or UC (p ≤ 0.05). The polymorphisms TLR2 (rs1816702), NFKB1 (rs28362491), TNFRSF1A (rs4149570), IL6R (rs4537545), IL23R (rs11209026) and PTPN22 (rs2476601) were associated with risk of CD and the polymorphisms TLR2 (rs1816702), TLR4 (rs1554973 and rs12377632), TLR9 (rs352139), LY96 (rs11465996), NFKBIA (rs696), TNFA (rs1800629), TNFRSF1A (rs4149570), IL10 (rs3024505), IL23R (rs11209026), PTPN22 (rs2476601) and PPARG (rs1801282) were associated with risk of UC. When including all patients (IBD) the polymorphisms TLR2 (rs4696480 and rs1816702), TLR4 (rs1554973 and rs12377632), TLR9 (rs187084), TNFRSF1A (rs4149570), IL6R (rs4537545), IL10 (rs3024505), IL23R (rs11209026) and PTPN22 (rs2476601) were associated with risk. After Bonferroni correction for multiple testing, both the homozygous and the heterozygous variant genotypes of IL23R G>A(rs11209026) (OR(CD,adj): 0.38, 95% CI: 0.21-0.67, p = 0.03; OR(IBD,adj) 0.43, 95% CI: 0.28-0.67, p = 0.007) and PTPN22 1858 G>A(rs2476601) (OR(CD,unadj) 0.54, 95% CI: 0.41-0.72, p = 7*10-4; OR(IBD,unadj): 0.61, 95% CI: 0.48-0.77, p = 0.001) were associated with reduced risk of CD.

CONCLUSION

The biological effects of the studied polymorphisms suggest that genetically determined high inflammatory response was associated with increased risk of CD. The many SNPs found in TLRs suggest that the host microbial composition or environmental factors in the gut are involved in risk of IBD in genetically susceptible individuals.

Biomarkers in inflammatory bowel diseases: Current status and proteomics identification strategies

Unambiguous diagnosis of the two main forms of inflammatory bowel diseases (IBD): Ulcerative colitis (UC) and Crohn’s disease (CD), represents a challenge in the early stages of the diseases. The diagnosis may be established several years after the debut of symptoms. Hence, protein biomarkers for early and accurate diagnostic could help clinicians improve treatment of the individual patients. Moreover, the biomarkers could aid physicians to predict disease courses and in this way, identify patients in need of intensive treatment. Patients with low risk of disease flares may avoid treatment with medications with the concomitant risk of adverse events. In addition, identification of disease and course specific biomarker profiles can be used to identify biological pathways involved in the disease development and treatment. Knowledge of disease mechanisms in general can lead to improved future development of preventive and treatment strategies. Thus, the clinical use of a panel of biomarkers represents a diagnostic and prognostic tool of potentially great value. The technological development in recent years within proteomic research (determination and quantification of the complete protein content) has made the discovery of novel biomarkers feasible. Several IBD-associated protein biomarkers are known, but none have been successfully implemented in daily use to distinguish CD and UC patients. The intestinal tissue remains an obvious place to search for novel biomarkers, which blood, urine or stool later can be screened for. When considering the protein complexity encountered in intestinal biopsy-samples and the recent development within the field of mass spectrometry driven quantitative proteomics, a more thorough and accurate biomarker discovery endeavor could today be performed than ever before. In this review, we report the current status of the proteomics IBD biomarkers and discuss various emerging proteomic strategies for identifying and characterizing novel biomarkers, as well as suggesting future targets for analysis.

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

Background

Genetic 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.

Methods

Three 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.

Results

We 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).

Conclusions

The 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.

Diet and risk of inflammatory bowel disease

BACKGROUND

A better understanding of the environmental factors leading to inflammatory bowel disease should help to prevent occurrence of the disease and its relapses.

AIM

To review current knowledge on dietary risk factors for inflammatory bowel disease.

METHODS

The PubMed, Medline and Cochrane Library were searched for studies on diet and risk of inflammatory bowel disease.

RESULTS

Established non-diet risk factors include family predisposition, smoking, appendectomy, and antibiotics. Retrospective case-control studies are encumbered with methodological problems. Prospective studies on European cohorts, mainly including middle-aged adults, suggest that a diet high in protein from meat and fish is associated with a higher risk of inflammatory bowel disease. Intake of the n-6 polyunsaturated fatty acid linoleic acid may confer risk of ulcerative colitis, whereas n-3 polyunsaturated fatty acids may be protective. No effect was found of intake of dietary fibres, sugar, macronutrients, total energy, vitamin C, D, E, Carotene, or Retinol (vitamin A) on risk of ulcerative colitis. No prospective data was found on risk related to intake of fruits, vegetables or food microparticles (titanium dioxide and aluminium silicate).

CONCLUSIONS

A diet high in protein, particular animal protein, may be associated with increased risk of inflammatory bowel disease and relapses. N-6 polyunsaturated fatty acids may predispose to ulcerative colitis whilst n-3 polyunsaturated fatty acid may protect. These results should be confirmed in other countries and in younger subjects before dietary counselling is recommended in high risk subjects.

Assessment of heterogeneity between European Populations: a Baltic and Danish replication case-control study of SNPs from a recent European ulcerative colitis genome wide association study

BACKGROUND

Differences in the genetic architecture of inflammatory bowel disease between different European countries and ethnicities have previously been reported. In the present study, we wanted to assess the role of 11 newly identified UC risk variants, derived from a recent European UC genome wide association study (GWAS) (Franke et al., 2010), for 1) association with UC in the Nordic countries, 2) for population heterogeneity between the Nordic countries and the rest of Europe, and, 3) eventually, to drive some of the previous findings towards overall genome-wide significance.

METHODS

Eleven SNPs were replicated in a Danish sample consisting of 560 UC patients and 796 controls and nine missing SNPs of the German GWAS study were successfully genotyped in the Baltic sample comprising 441 UC cases and 1156 controls. The independent replication data was then jointly analysed with the original data and systematic comparisons of the findings between ethnicities were made. Pearson's χ2, Breslow-Day (BD) and Cochran-Mantel-Haenszel (CMH) tests were used for association analyses and heterogeneity testing.

RESULTS

The rs5771069 (IL17REL) SNP was not associated with UC in the Danish panel. The rs5771069 (IL17REL) SNP was significantly associated with UC in the combined Baltic, Danish and Norwegian UC study sample driven by the Norwegian panel (OR = 0.89, 95% CI: 0.79-0.98, P = 0.02). No association was found between rs7809799 (SMURF1/KPNA7) and UC (OR = 1.20, 95% CI: 0.95-1.52, P = 0.10) or between UC and all other remaining SNPs. We had 94% chance of detecting an association for rs7809799 (SMURF1/KPNA7) in the combined replication sample, whereas the power were 55% or lower for the remaining SNPs.Statistically significant PBD was found for OR heterogeneity between the combined Baltic, Danish, and Norwegian panel versus the combined German, British, Belgian, and Greek panel (rs7520292 (P = 0.001), rs12518307 (P = 0.007), and rs2395609 (TCP11) (P = 0.01), respectively).No SNP reached genome-wide significance in the combined analyses of all the panels.

CONCLUSIONS

This replication study supports an important role for the studied rs5771069 (IL17REL) SNP, but not for rs7809799 (SMURF1/KPNA7), in UC etiology in the Danish, Baltic, and Norwegian populations. Significant genetic heterogeneity was suggested for rs7520292, rs12518307, and rs2395609 (TCP11) in UC etiology between the Nordic and the other European populations.

Challenges associated with identifying the environmental determinants of the inflammatory bowel diseases

In the last several years there has been an explosion in the discovery of inflammatory bowel disease (IBD) susceptibility genes; however, similar advances in identifying and defining environmental risk factors associated with IBD have lagged behind. Moreover, many studies that have explored the same or similar environmental risk factors of IBD have demonstrated disparate results and come to conflicting conclusions. In order for the field to move forward, it is important to understand and resolve why these differences exist. This significant heterogeneity has blurred the identification of the fundamental environmental determinants of IBD. The purpose of this review article is to explore the factors that have likely contributed to the heterogeneity among observational studies of environmental risk factors in IBD. In doing so, it is hoped that methodological standardization may lead to consistent environmental associations.

Cyclooxygenase-2 (COX-2) polymorphisms and risk of inflammatory bowel disease in a Scottish and Danish case-control study

BACKGROUND

Inflammatory bowel diseases (IBDs) are a result of interactions between luminal pathogens and the intestinal immune response. Cyclooxygenase-2 (COX-2) plays a key role in the regulation of the inflammatory response upon stimulation by luminal pathogens via Toll-like receptors.

METHODS

Genotypes of the COX-2/PTGS2/PGHS2 A-1195G (rs689466), G-765C (rs20417), and T8473C (rs5275) polymorphisms were assessed in a Scottish and Danish case-control study including 732 Crohn's disease (CD) cases, 973 ulcerative colitis (UC) cases, and 1157 healthy controls using logistic regression.

RESULTS

Carriers of the COX-2 A-1195G variant allele had increased risk of UC (odds ratio [OR], 95% confidence interval [CI] = 1.25 [1.02-1.54], P = 0.03) and of both UC and IBD among never smokers (OR [95% CI] = 1.47 [1.11-1.96], P = 0.01 and OR [95% CI] = 1.37 [1.06-1.77], P = 0.02, respectively). Furthermore, this variant genotype was associated with increased risk of diagnosis of UC before age 40 years and with extensive UC (OR [95% CI] = 1.34 [1.11-1.62], P = 0.002 and OR [95% CI] = 1.32 [1.03-1.69], P = 0.03, respectively).

CONCLUSIONS

COX-2 A-1195G polymorphism was associated with the risk of UC, especially among never-smokers, suggesting that low activity of COX-2 may predispose to UC. Our results suggest that inclusion of smoking status may be essential for the evaluation of the role of genetic predisposition to IBD.

Polymorphisms in NF-κB, PXR, LXR, PPARγ and risk of inflammatory bowel disease

AIM: To investigate the contribution of polymorphisms in nuclear receptors to risk of inflammatory bowel disease (IBD).

METHODS: Genotypes of nuclear factor (NF)-κB (NFKB1) NFκB -94ins/del (rs28362491); peroxisome proliferator-activated receptor (PPAR)-γ (PPARγ) PPARγ Pro12Ala (rs 1801282) and C1431T (rs 3856806); pregnane X receptor (PXR) (NR1I2) PXR A-24381C (rs1523127), C8055T (2276707), and A7635G (rs 6785049); and liver X receptor (LXR) (NR1H2) LXR T-rs1405655-C and T-rs2695121-C were assessed in a Danish case-control study of 327 Crohn’s disease patients, 495 ulcerative colitis (UC) patients, and 779 healthy controls. Odds ratio (OR) and 95% CI were estimated by logistic regression models.

RESULTS: The PXR A7635G variant, the PPARγ Pro12Ala and LXR T-rs2695121-C homozygous variant genotypes were associated with risk of UC (OR: 1.31, 95% CI: 1.03-1.66, P = 0.03, OR: 2.30, 95% CI: 1.04-5.08, P = 0.04, and OR: 1.41, 95% CI: 1.00-1.98, P = 0.05, respectively) compared to the corresponding homozygous wild-type genotypes. Among never smokers, PXR A7635G and the LXR T-rs1405655-C and T-rs2695121-C variant genotypes were associated with risk of IBD (OR: 1.41, 95% CI: 1.05-1.91, P = 0.02, OR: 1.63, 95% CI: 1.21-2.20, P = 0.001, and OR: 2.02, 95% CI: 1.36-2.99, P = 0.0005, respectively) compared to the respective homozygous variant genotypes. PXR A7635G (rs6785049) variant genotype was associated with a higher risk of UC diagnosis before the age of 40 years and with a higher risk of extensive disease (OR: 1.34, 95% CI: 1.03-1.75 and OR: 2.49, 95% CI: 1.24-5.03, respectively).

CONCLUSION: Common PXR and LXR polymorphisms may contribute to risk of IBD, especially among never smokers.

The impact of smoking in Crohn's disease: no smoke without fire

Smoking habit is the most widely accepted environmental factor affecting the incidence and disease progression in the inflammatory bowel diseases. The contrasting effects in Crohn's disease (CD) and ulcerative colitis are unexplained. The purpose of this review is to summarise the existing data on the effects of smoking in CD on disease history, recurrence after surgery, effects on drug responses and to review available evidence that carriage of some of the known susceptibility genes may be disproportionate in smokers with CD. The review also highlights potential mechanisms involved and factors that might affect patients' smoking habits. The clinical and scientific implications of the data are discussed.

Genetic variants of glutathione S-transferases mu, theta, and pi display no susceptibility to inflammatory bowel disease in the Danish population

INTRODUCTION

A combination of genetic predisposition and interactions with environmental factors are believed to be responsible for disease phenotype and disease progression in inflammatory bowel diseases. The harmful effect of smoking and other environmental factors is believed to be highly dependent on the activity of detoxification enzymes. The aims of the study were to examine possible associations between the detoxifying glutathione S-transferases (GSTs) family mu, theta and pi gene variants and inflammatory bowel disease, and secondly to examine a potential genotype-genotype interaction between these variants. Genotype-disease phenotype associations and a possible interaction between genotype and cigarette smoking were also assessed.

METHODS

Three hundred and eighty-eight patients with Crohn's disease (CD), 565 patients with ulcerative colitis (UC) and 796 healthy Danish controls were included in the study. Genomic DNA was used for genotyping of the GST genes using PCR or real-time PCR.

RESULTS

No associations were found between GST genotypes and inflammatory bowel diseases. Neither did a combination of the GST genotypes reveal any associations. No genotype-disease phenotype associations were found. Smoking was positively associated with CD and negatively associated with UC. An interaction between smoking and GSTM1*0 genotype was found for UC, where the GSTM1*0 genotype appear to strengthen the protective effect of smoking on disease susceptibility.

CONCLUSION

The GST genotypes do not seem to be important in susceptibility of inflammatory bowel disease in the Danish population. Nor did we find convincing evidence of associations between GST genotype and phenotypic features of inflammatory bowel diseases.

The polymorphism rs3024505 proximal to IL-10 is associated with risk of ulcerative colitis and Crohns disease in a Danish case-control study

Background

Crohns disease (CD) and ulcerative colitis (UC) are characterized by a dysregulated inflammatory response to normal constituents of the intestinal flora in the genetically predisposed host. Heme oxygenase-1 (HO-1/HMOX1) is a powerful anti-inflammatory and anti-oxidant enzyme, whereas the pro-inflammatory interleukin 1β (IL-1β/IL1B) and anti-inflammatory interleukin 10 (IL-10/IL10) are key modulators for the initiation and maintenance of inflammation. We investigated whether single nucleotide polymorphisms (SNPs) in the IL-1β, IL-10, and HO-1 genes, together with smoking, were associated with risk of CD and UC.

Methods

Allele frequencies of the IL-1β T-31C (rs1143627), and IL-10 rs3024505, G-1082A (rs1800896), C-819T (rs1800871), and C-592A (rs1800872) and HO-1 A-413T (rs2071746) SNPs were assessed using a case-control design in a Danish cohort of 336 CD and 498 UC patients and 779 healthy controls. Odds ratio (OR) and 95% confidence interval (95% CI) were estimated by logistic regression models.

Results

Carriers of rs3024505, a marker polymorphism flanking the IL-10 gene, were at increased risk of CD (OR = 1.40, 95% CI: 1.06-1.85, P = 0.02) and UC (OR = 1.43, 95% CI: 1.12-1.82, P = 0.004) and, furthermore, with risk of a diagnosis of CD and UC at young age (OR = 1.47, 95% CI: 1.10-1.96) and OR = 1.35, 95% CI: 1.04-1.76), respectively). No association was found between the IL-1β, IL-10 G-1082A, C-819T, C-592A, and HO-1 gene polymorphisms and CD or UC. No consistent interactions between smoking status and CD or UC genotypes were demonstrated.

Conclusions

The rs3024505 marker polymorphism flanking the IL-10 gene was significantly associated with risk of UC and CD, whereas no association was found between IL-1β or HO-1 gene polymorphisms and risk of CD and UC in this Danish study, suggesting that IL-10, but not IL-1β or HO-1, has a role in IBD etiology in this population.

Differences in genetic background between active smokers, passive smokers, and non-smokers with Crohn's disease

OBJECTIVES

Smoking behavior and genetic variations are important factors for the development of Crohn's disease (CD), but studies investigating the interaction between smoking and genetic background are scarce. We studied allelic associations of 19 confirmed variants located in 14 CD-associated genes or loci, in CD patients stratified for active smoking at diagnosis and passive smoking in childhood.

METHODS

Genotyping data of 19 CD-associated single-nucleotide polymorphisms (SNPs) were available for 310 CD patients and 976 controls. Data on active smoking at diagnosis and passive smoking in childhood were obtained through a written questionnaire and a review of medical charts.

RESULTS

The loci associated in smoking, but not in non-smoking, CD patients were 5p13.1 (rs17234657), DLG5 (rs2165047), NKX2-3 (rs10883365), and NOD2 (R702W). The loci associated in non-smoking, but not in smoking, CD patients were IL23R (rs7517847), 5p13.1 (rs9292777), IRGM (rs13361189 and rs4958847), IL12B (rs6887695), and CCNY (rs3936503). PTPN2 (rs2542151) was only associated in the smoking CD cohort (P=0.041), and not in the entire cohort (P=0.23) or in the non-smoking CD cohort (P=0.80). In passively smoking CD patients, associations with 13 SNPs in 9 loci were found, including PTPN2. In non-passive smoking CD patients, only associations with NOD2 (1007fsinsC and G908R) were found.

CONCLUSIONS

The difference in associated genes between smoking and non-smoking CD patients implies a complex gene-environment interaction. Therefore, genetic studies of CD should be stratified for smoking behavior, as otherwise moderately associated genes such as PTPN2 can be missed.

Differential effects of NOD2 polymorphisms on colorectal cancer risk: a meta-analysis

INTRODUCTION

Since Kurzawski et al. described an association between the 3020insC NOD2 single nucleotide polymorphism and the risk of colorectal cancer(CRC) in 2004, reports published in the past several years have controversial results regarding the relationship between the development of CRC and NOD2 gene polymorphisms. To clarify the potential role of NOD2 P286S, R702W, G908R, and 3020insC polymorphisms in CRC patients, we have undertaken a systematic review and meta-analysis of published articles.

MATERIALS AND METHODS

Studies reporting on NOD2 polymorphisms and CRC were searched in the PubMed, EMBASE, and the Science Citation Index from the inception of each database to May, 2009. The search strategy included the keywords "CRC", "colon cancer", "rectal cancer", "polymorphism", and "NOD2/CARD15".

RESULT

Eight eligible case-control studies about Caucasians from four countries contributed data on 5,888 subjects (cases: 3,524; controls: 2,364). Compared to the wild genotype, the R702W, G908R, and 3020insC polymorphisms were associated with an increased risk of CRC (odds ratio (OR): 1.59, 1.98, 1.44; 95% confidence interval (CI): 1.09-2.32, 1.14-3.44, 1.13-1.84; P = 0.02, 0.01, 0.003). However, P268S polymorphism did not influence CRC risk (OR: 1.27; CI: 0.32-5.00; P = 0.73).

CONCLUSIONS

These findings indicate that NOD2 R702W, G908R, and 3020insC polymorphisms contribute to CRC susceptibility in Caucasians. Meta-analysis of these polymorphisms in NOD2 gene will help determine their role in CRC carcinogenesis.

Research progress in susceptible genes of inflammatory bowel disease

The mechanism of inflammatory bowel disease (IBD) is partially understood, but it is certain that a genetic predisposition, through the inheritance of a number of contributory genetic polymorphisms, contributes to the pathogenesis of IBD. These variant forms of genes may be associated with an abnormal response to normal luminal bacteria. Those genes that have been consistently associated with IBD thus far primarily fall into one of three classes: those affecting bacterial recognition, those affecting immune response, and a third group affecting mucosal transport polarity or mucosal transporter function. This article reviews the IBD related genes mentioned above.

Cyclooxygenase-2, multidrug resistance 1, and breast cancer resistance protein gene polymorphisms and inflammatory bowel disease in the Danish population

OBJECTIVE

Crohn's disease (CD) and ulcerative colitis (UC) are characterized by an impaired mucosal defence to normal constituents of the intestinal flora and a dysregulated inflammatory response. The purpose of the study was to investigate whether single nucleotide polymorphisms (SNPs) in genes involved in these processes were associated with CD and UC.

MATERIAL AND METHODS

Allele frequencies of the cyclooxygenase 2 (COX-2/PTGS2/PGHS2) G-765C and breast cancer resistance protein (BCRP/ABCG2) C421A as well as allele and haplotype frequencies of multidrug resistance 1 (MDR1, ABCB1) SNPs G2677T/A, C3435T and G-rs3789243-A (intron 3) were assessed in a Danish case-control study comprising 373 CD and 541 UC patients and 796 healthy controls.

RESULTS

Carriers of the homozygous COX-2 and MDR1 intron 3 variant had a relatively high risk of CD, odds ratio (95% CI) (OR (95% CI))=2.86 ((1.34-5.88) p=0.006) and 1.39 ((0.99-1.92) p=0.054), respectively, and for UC of 2.63 ((1.33-5.26) p=0.005) and 1.28 ((0.96-1.51) p=0.093), respectively, assuming complete dominance. No association was found for BCRP or other MDR1 SNPs, or for selected MDR1 haplotypes. No effect-modification of smoking habit at the time of diagnosis was found.

CONCLUSIONS

An effect of the COX-2 polymorphism on both CD and UC was shown which is compatible with the presence of a recessive allele in linkage equilibrium with the SNP marker in the COX-2 gene. The polymorphism located in intron 3 of the MDR1 gene showed a weak association with CD, and a marginally suggestive association with UC.

The multidrug resistance 1 (MDR1) gene polymorphism G-rs3789243-A is not associated with disease susceptibility in Norwegian patients with colorectal adenoma and colorectal cancer; a case control study

Background

Smoking, dietary factors, and alcohol consumption are known life style factors contributing to gastrointestinal carcinogenesis. Genetic variations in carcinogen handling may affect cancer risk. The multidrug resistance 1(MDR1/ABCB1) gene encodes the transport protein P-glycoprotein (a phase III xenobiotic transporter). P-glycoprotein is present in the intestinal mucosal lining and restricts absorption of certain carcinogens, among these polycyclic aromatic hydrocarbons. Moreover, P-glycoprotein transports various endogenous substrates such as cytokines and chemokines involved in inflammation, and may thereby affect the risk of malignity. Hence, genetic variations that modify the function of P-glycoprotein may be associated with the risk of colorectal cancer (CRC). We have previously found an association between the MDR1 intron 3 G-rs3789243-A polymorphism and the risk of CRC in a Danish study population. The aim of this study was to investigate if this MDR1 polymorphism was associated with risk of colorectal adenoma (CA) and CRC in the Norwegian population.

Methods

Using a case-control design, the association between the MDR1 intron 3 G-rs3789243-A polymorphism and the risk of colorectal carcinomas and adenomas in the Norwegian population was assessed in 167 carcinomas, 990 adenomas, and 400 controls. Genotypes were determined by allelic discrimination. Odds ratio (OR) and 95 confidence interval (95% CI) were estimated by binary logistic regression.

Results

No association was found between the MDR1 polymorphism (G-rs3789243-A) and colorectal adenomas or cancer. Carriers of the variant allele of MDR1 intron 3 had odds ratios (95% CI) of 0.97 (0.72–1.29) for developing adenomas, and 0.70 (0.41–1.21) for colorectal cancer, respectively, compared to homozygous wild type carriers.

Conclusion

The MDR1 intron 3 (G-rs3789243-A) polymorphism was not associated with a risk of colorectal adenomas or carcinomas in the present Norwegian study group. Thus, this MDR1 polymorphism does not seem to play an important role in colorectal carcinogenesis in this population.

Research progress in susceptibility genes of inflammatory bowel disease

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is a group of non-specific chronic inflammatory conditions of the gastrointestinal tract with unknown complex etiology. Epidemiologic data indicate genetic contribution to IBD pathogenesis, which include familial aggregation, twin studies, racial and ethnic differences in disease prevalence. The most widely adopted approaches to identifying susceptibility genes in IBD include linkage studies, genome-wide association (GWA) studies and microarray. The first two technologies have confirmed NOD2, IL23R and other genes implicated in IBD pathogenesis and advances in microarray technology makes it possible to diagnose IBD at gene expression level. This article reviewed IBD related genes and introduced application of microarray to IBD research.