D A van Heel

Recent advances in coeliac disease

The management of coeliac disease is an increasing part of a gastroenterologist’s workload. Recent prevalence studies suggest ∼1% of the general UK population have positive coeliac serology, which combined with increasing population and primary care awareness is leading to more and more referrals. The majority of contemporary referrals are now initially diagnosed by highly sensitive and specific serological tests followed by readily performed endoscopic biopsy (fig 1). Consequently, we now identify many more patients with no or only mild clinical symptoms, making the classical scenario of diarrhoea/steatorrhoea and weight loss a comparative rarity. Much of the early data on clinical aspects of classical coeliac disease (that is, published pre ∼1990) may not be applicable to contemporary coeliac disease. These changes in clinical practice have been paralleled by a dramatic increase in our knowledge of disease pathogenesis, making coeliac disease the best understood human “autoimmune” disorder. In this review article, we present selected major recent advances in both clinical and basic science aspects of coeliac disease, focusing on the many high quality studies published within the last five years. Figure 1  Contemporary and classical diagnosis of coeliac disease. In the past, coeliac disease was mainly diagnosed after clinical presentation. This remains the description of disease in many textbooks. Nowadays, many more patients are referred on the basis of positive serological tests. Endoscopy and “routine” duodenal biopsy (without prior suspicion of coeliac disease) may also lead to diagnosis. *Serology, duodenal histology, HLA-DQ genotyping. Adapted from Green et al 2005.106 ### General population based prevalence studies of undetected coeliac disease Several serological screening studies from Europe, South America, Australasia, and the USA have shown that approximately 0.5–1% of these populations may have undetected coeliac disease. The most consistent estimate reported from the largest population based studies is approximately 1%. The prevalence is even higher in first and second degree relatives of people with coeliac …

Genotype-phenotype analysis of the Crohn’s disease susceptibility haplotype on chromosome 5q31

Background and aims: Recent molecular data suggest that genetic factors may underlie the disease heterogeneity observed in both ulcerative colitis (UC) and Crohn’s disease (CD). A locus on chromosome 5q has been implicated in susceptibility to CD, and recently refined by linkage disequilibrium mapping to a conserved 250 kb haplotype (5q31). No data regarding the contribution of this locus to clinical phenotype exist. In this case control study, we investigated the contribution of this haplotype to both susceptibility and phenotype of CD and UC. Patients and methods: We studied 330 Caucasian CD and 457 UC patients recruited from a single UK centre. Association with disease susceptibility and phenotype was analysed with haplotypes reconstructed from three single nucleotide polymorphisms chosen to span this susceptibility region. Evidence for possible genetic epistasis between IBD5 and NOD2/CARD15 was sought. Results: Linkage disequilibrium across this region was confirmed, with two haplotypes comprising 88% of all chromosomes. Susceptibility to CD, but not to UC, was associated with homozygosity for a common haplotype, H2 (pc=0.002; relative risk (RR) 2.0). Genotype-phenotype analyses demonstrated that this association was particularly strong in patients with perianal disease (pc=0.0005; RR 1.7), especially in individuals homozygous for this haplotype (pc=0.0005; RR 3.0). Importantly, no association with H2 was found in 186 patients without perianal disease. No evidence of epistasis between IBD5 and NOD2/CARD15 was demonstrated. Conclusions: The IBD5 risk haplotype is associated with CD only. Genotype-phenotype analysis reveals that the strongest association is observed in patients with perianal CD. While the precise gene involved is unclear, these data provide further molecular evidence for a genetic basis of the clinical heterogeneity of CD.

Coeliac disease-associated risk variants in TNFAIP3 and REL implicate altered NF-κB signalling

Objective: Our previous coeliac disease genome-wide association study (GWAS) implicated risk variants in the human leucocyte antigen (HLA) region and eight novel risk regions. To identify more coeliac disease loci, we selected 458 single nucleotide polymorphisms (SNPs) that showed more modest association in the GWAS for genotyping and analysis in four independent cohorts. Design: 458 SNPs were assayed in 1682 cases and 3258 controls from three populations (UK, Irish and Dutch). We combined the results with the original GWAS cohort (767 UK cases and 1422 controls); six SNPs showed association with p<1×10−04 and were then genotyped in an independent Italian coeliac cohort (538 cases and 593 controls). Results: We identified two novel coeliac disease risk regions: 6q23.3 (OLIG3-TNFAIP3) and 2p16.1 (REL), both of which reached genome-wide significance in the combined analysis of all 2987 cases and 5273 controls (rs2327832 p = 1.3×10−08, and rs842647 p = 5.2×10−07). We investigated the expression of these genes in the RNA isolated from biopsies and from whole blood RNA. We did not observe any changes in gene expression, nor in the correlation of genotype with gene expression. Conclusions: Both TNFAIP3 (A20, at the protein level) and REL are key mediators in the nuclear factor kappa B (NF-κB) inflammatory signalling pathway. For the first time, a role for primary heritable variation in this important biological pathway predisposing to coeliac disease has been identified. Currently, the HLA risk factors and the 10 established non-HLA risk factors explain ∼40% of the heritability of coeliac disease.

Synergy between TLR9 and NOD2 innate immune responses is lost in genetic Crohn's disease

Background: Nucleotide binding oligomerisation domain 2 (NOD2; also known as CARD15) mutations are associated with Crohn’s disease but how mutations cause disease is poorly understood. Innate immune responses are reportedly enhanced by combined NOD2 ligand (muramyl dipeptide, MDP) and Toll-like receptor 4 ligand (TLR4, lipopolysaccharide) stimulation. Intestinal TLR signalling has a dual role—maintaining intestinal homeostasis and protection from injury as well as initiating inflammatory responses. TLR9 is functional in the intestinal epithelium where it is most strongly expressed in Paneth cells. Aims: To study possible interactions between CpG DNA (TLR9 ligand) and MDP using primary human cells of differing NOD2 genotypes. Subjects: NOD2 wild-type healthy controls (n = 7) and NOD2 homozygous Crohn’s disease patients (n = 19), age and sex matched. Methods: Peripheral blood mononuclear cells were stimulated with CpG DNA and MDP. Cytokines were measured by enzyme linked immunosorbent assay. Results: Tumour necrosis factor α (TNF-α) and interleukin 8 (IL-8) responses to CpG DNA were similar in NOD2 wild-type and homozygous mutant cells. Concomitant NOD2 stimulation had a marked synergistic effect on CpG DNA induced TNF-α responses at 10–100 ng/ml MDP. A mean 2.1-fold increase in CpG DNA induced TNF-α responses and a mean 3.7-fold increase in IL-8 responses were observed in NOD2 wild-type cells with 10 ng/ml MDP. This effect was abolished in NOD2 homozygous cells. Conclusions: NOD2 stimulation normally enhances innate immune responses to CpG DNA. This marked synergistic effect is lost in Crohn’s disease patients homozygous for NOD2 mutations, with implications for TLR mediated intestinal homeostasis and inflammation.

Associations with tight junction genes PARD3 and MAGI2 in Dutch patients point to a common barrier defect for coeliac disease and ulcerative colitis.

Background: Coeliac disease (gluten-sensitive enteropathy; GSE) and inflammatory bowel disease (IBD) are common gastrointestinal disorders. Both display enhanced intestinal permeability, initiated by gluten exposure (GSE) or bacterial interactions (IBD). Previous studies showed the association of both diseases with variants in MYO9B, presumably involved in epithelial permeability. Aim: It was hypothesised that genetic variants in tight junction genes might affect epithelial barrier function, thus contributing to a shared pathogenesis of GSE and IBD. Methods: This hypothesis was tested with a comprehensive genetic association analysis of 41 genes from the tight junction pathway, represented by 197 tag single nucleotide polymorphism (SNP) markers. Results: Two genes, PARD3 (two SNPs) and MAGI2 (two SNPs), showed weak association with GSE in a Dutch cohort. Replication in a British GSE cohort yielded significance for one SNP in PARD3 and suggestive associations for two additional SNPs, one each in PARD3 and MAGI2. Joint analysis of the British and Dutch data further substantiated the association for both PARD3 (rs10763976, p = 6.4×10−5; OR 1.23, 95% CI 1.11 to 1.37) and MAGI2 (rs6962966, p = 7.6×10−4; OR 1.19, 95% CI 1.08 to 1.32). Association was also observed in Dutch ulcerative colitis patients with MAGI2 (rs6962966, p = 0.0036; OR 1.26, 95% CI 1.08 to 1.47), and suggestive association with PARD3 (rs4379776, p = 0.068). Conclusions: These results suggest that coeliac disease and ulcerative colitis may share a common aetiology through tight junction-mediated barrier defects, although the observations need further replication.

Analysis of the IBD5 locus and potential gene-gene interactions in Crohn’s disease

Background and aims: Genetic variation in the chromosome 5q31 cytokine cluster (IBD5 risk haplotype) has been associated with Crohn’s disease (CD) in a Canadian population. We studied the IBD5 risk haplotype in both British and Japanese cohorts. Disease associations have also been reported for CARD15/NOD2 and TNF variants. Complex interactions between susceptibility loci have been shown in animal models, and we tested for potential gene-gene interactions between the three CD associated loci. Methods: Family based association analyses were performed in 457 British families (252 ulcerative colitis, 282 CD trios) genotyped for the IBD5 haplotype, common CARD15, and TNF−857 variants. To test for possible epistatic interactions between variants, transmission disequilibrium test analyses were further stratified by genotype at other loci, and novel log linear analyses were performed using the haplotype relative risk model. Case control association analyses were performed in 178 Japanese CD patients and 156 healthy controls genotyped for the IBD5 haplotype. Results: The IBD5 haplotype was associated with CD (p=0.007), but not with UC, in the British Caucasian population. The CARD15 variants and IBD5 haplotype showed additive main effects, and in particular no evidence for epistatic interactions was found. Variants from the IBD5 haplotype were extremely rare in the Japanese. Conclusions: The IBD5 risk haplotype is associated with British CD. Genetic variants predisposing to CD show heterogeneity and population specific differences.

T cells in peripheral blood after gluten challenge in coeliac disease

Background: Current understanding of T cell epitopes in coeliac disease (CD) largely derives from intestinal T cell clones in vitro. T cell clones allow identification of gluten peptides that stimulate T cells but do not quantify their contribution to the overall gluten specific T cell response in individuals with CD when exposed to gluten in vivo. Aims: To determine the contribution of a putative dominant T cell epitope to the overall gliadin T cell response in HLA-DQ2 CD in vivo. Patients: HLA-DQ2+ individuals with CD and healthy controls. Methods: Subjects consumed 20 g of gluten daily for three days. Interferon γ (IFN-γ) ELISPOT was performed using peripheral blood mononuclear cells (PBMC) to enumerate and characterise peptide and gliadin specific T cells before and after gluten challenge. Results: In 50/59 CD subjects, irrespective of homo- or heterozygosity for HLA-DQ2, IFN-γ ELISPOT responses for an optimal concentration of A-gliadin 57–73 Q-E65 were between 10 and 1500 per million PBMC, equivalent to a median 51% of the response for a “near optimal” concentration of deamidated gliadin. Whole deamidated gliadin and gliadin epitope specific T cells induced in peripheral blood expressed an intestinal homing integrin (α4β7) and were HLA-DQ2 restricted. Peripheral blood T cells specific for A-gliadin 57–73 Q-E65 are rare in untreated CD but can be predictably induced two weeks after gluten exclusion. Conclusion: In vivo gluten challenge is a simple safe method that allows relevant T cells to be analysed and quantified in peripheral blood by ELISPOT, and should permit comprehensive high throughput mapping of gluten T cell epitopes in large numbers of individuals with CD.

Lack of association of MYO9B genetic variants with coeliac disease in a British cohort

Background and aims: Development of coeliac disease involves an interaction between environmental factors (especially dietary wheat, rye, and barley antigens) and genetic factors (there is strong inherited disease susceptibility). The known human leucocyte antigen (HLA)-DQ2 and -DQ8 association explains only a minority of disease heritability. A recent study in the Dutch population suggested that genetic variation in the 3′ region of myosin IXB (MYO9B) predisposes to coeliac disease. MYO9B is a Rho family GTPase activating protein involved in epithelial cell cytoskeletal organisation. MYO9B is hypothesised to influence intestinal permeability and hence intestinal antigen presentation. Methods: Four single nucleotide polymorphisms were chosen to tag all common haplotypes of the MYO9B 3′ haplotype block (exons 15–27). We genotyped 375 coeliac disease cases and 1366 controls (371 healthy and 995 population based). All individuals were of White UK Caucasian ethnicity. Results: UK healthy control and population control allele frequencies were similar for all MYO9B variants. Case control analysis showed no significant association of any variant or haplotype with coeliac disease. Conclusions: Genetic variation in MYO9B does not have a major effect on coeliac disease susceptibility in the UK population. Differences between populations, a weaker effect size than originally described, or possibly a type I error in the Dutch study might explain these findings.

Human keratin 8 mutations that disturb filament assembly observed in inflammatory bowel disease patients

We have identified miss-sense mutations in keratin 8 in a subset of patients with inflammatory bowel disease (Crohn disease and ulcerative colitis). Inflammatory bowel diseases are a group of disorders that are polygenic in origin and involve intestinal epithelial breakdown. We investigated the possibility that these keratin mutations might contribute to the course of the disease by adversely affecting the keratin filament network that provides mechanical support to cells in epithelia. The mutations (Gly62 to Cys, Ile63 to Val and Lys464 to Asn) all lie outside the major mutation hotspots associated with severe disease in epidermal keratins, but using a combination of in vitro and cell culture assays we show that they all have detrimental effects on K8/K18 filament assembly in vitro and in cultured cells. The G62C mutation also gives rise to homodimer formation on oxidative stress to cultured intestinal epithelial cells, and homodimers are known to be polymerization incompetent. Impaired keratin assembly resulting from the K8 mutations found in some inflammatory bowel disease patients would be predicted to affect the maintenance and re-establishment of mechanical resilience in vivo, as required during keratin cytoskeleton remodeling in cell division and differentiation, which may lead to epithelial fragility in the gut. Simple epithelial keratins may thus be considered as candidates for genes contributing to a risk of inflammatory bowel disease.

Probiotics in inflammatory bowel disease: is it all gut flora modulation?

Understanding probiotic action may permit modulation of the immune system, both locally and systemically There is considerable public, media, and scientific interest in “natural” products, including probiotics, in modulating intestinal inflammation and health.1 Intestinal microflora are intimately involved in the generation of immunocompetent cells and tuning the balance between T helper 1 (Th1) and Th2 immunity during the development of the gut associated immune system. It is now generally accepted that the intestinal bacterial flora contributes significantly to the pathogenesis of inflammatory bowel disease (IBD) along with mucosal immune dysregulation and genetic susceptibility. Considerable research is focused on modifying the intestinal flora with probiotic bacteria to attenuate inflammatory activity and prevent relapses in ulcerative colitis, Crohn’s disease, and pouchitis. Although both Lactobacillus species and Bifidobacterium species are frequently used, the optimum use of probiotics in IBD requires greater understanding of their effects on the immune system. A rationale for the use of probiotics in IBD stems from reports of dysbiosis in the intestinal flora in ulcerative colitis, Crohn’s disease, and pouchitis, either by conventional anaerobic culture or by analysis using molecular probes. It is however unclear whether such alterations in intestinal flora drives the inflammation or is a consequence of it. The practical application of probiotic strategy has been especially encouraged by the positive results of a trial in its use for the prevention and treatment of pouchitis.2,3 The multispecies probiotics used pose special challenges in identifying precise mechanism of action, although alterations in faecal flora have been demonstrated.4 Despite some positive trials, generalisation from pouchitis to their use for all forms of IBD appears somewhat premature, however, as for example, a trial of administration of Lactobacillus GG after surgical resection for Crohn’s disease proved ineffective in preventing relapse.5 Further studies are therefore …