S J Moodie

HLA types in celiac disease patients not carrying the DQA1*05-DQB1*02 (DQ2) heterodimer: Results from the European genetics cluster on celiac disease

Genetic susceptibility to celiac disease is strongly associated with HLA-DQA1*05-DQB1*02 (DQ2) and HLA-DQA1*03-DQB1*0302 (DQ8). Study of the HLA associations in patients not carrying these heterodimers has been limited by the rarity of such patients. This European collaboration has provided a unique opportunity to study a large series of such patients. From 1008 European coeliacs, 61 were identified who neither carry the DQ2 nor DQ8 heterodimers. Fifty seven of these encoded half of the DQ2 heterodimer. The remaining 4 patients had a variety of clinical presentations. Three of them carried the DQA1*01-DQB*05 haplotype as did 20/61 of those carrying neither DQ2 nor DQ8. This may implicate a role of the DQA1*01-DQB*05 haplotype. None of these four patients carried the DQB1*06 allele that has previously been reported in this sub-group of patients. Of the 16 DQ2 heterodimer negative patients without DRB1*04 or DRB1*07 haplotypes, it was inferred that none encoded the previously implicated DRB4 gene as none had a DRB1*09 haplotype. These results underline the primary importance of HLA-DQ alleles in susceptibility to celiac disease, and the extreme rarity of celiac patients carrying neither the DQ2 or DQ8 heterodimers nor one half of the DQ2 heterodimer alone.

Coeliac disease: in vivo toxicity of the putative immunodominant epitope

Background: Peptides from α-gliadins have been used to characterise the immunodominant coeliac toxic epitope. A peptide corresponding to amino acid residues 57–73 of A-gliadin causes peripheral blood mononuclear cells from coeliac patients to secrete interferon γ (IFN-γ); gluten specific small intestinal T cell clones proliferate in response to peptides corresponding to residues 57–68 and 62–75 of α-gliadins. We wished to investigate whether a peptide corresponding to residues 56–75 of α-gliadins exacerbates coeliac disease in vivo. Methods: Four adults with coeliac disease, all of whom were on a gluten free diet, underwent three challenges. Peptic-tryptic gliadin (PTG 1 g) served as a positive control. The test peptide and a negative control peptide were studied on separate occasions. The peptides were instilled into the duodenum and biopsies were taken before the infusion, and two, four, and six hours after commencing the infusions, using a Quinton hydraulic multiple biopsy capsule. Biopsy specimens were assessed blindly for villus height to crypt depth ratio (VH:CD), enterocyte cell height (ECH), and intraepithelial lymphocyte (IEL) count. We used the Mann-Whitney U test, with 95% confidence intervals, for statistical analysis. Results: VH:CD and ECH fell, and IEL increased significantly 4–6 hours after commencing infusions with both PTG and the test peptide in all subjects. The negative control peptide caused no significant changes to villus morphology, enterocyte height, or IEL count in any patient. Conclusion: We have confirmed that the putative immunodominant epitope, a peptide corresponding to residues 56–75 of α-gliadins, exacerbates coeliac disease in vivo.

CTLA-4/CD28 gene region is associated with genetic susceptibility to coeliac disease in UK families

Coeliac disease (CD) is a malabsorption disorder characterised by a small intestinal enteropathy that reverts to normal on removal of dietary gluten. Susceptibility to disease has a strong genetic component. Ninety percent of patients in northern Europe have the HLA class II alleles DQA1*0501 and DQB1*0201, which encode the cell surface molecule HLA-DQ2.1 However, haplotype sharing probabilities across the HLA region in affected sib pairs suggest that genes within the MHC complex contribute no more than 40% of the sib familial risk of CD, making the non-HLA linked gene (or genes) the stronger determinant.2 Attempts have been made to identify these loci using genome wide linkage studies. Zhong et al 3 performed an autosomal screen in 45 affected sib pairs from the west coast of Ireland, using 328 microsatellite markers. They found evidence of linkage with lod scores of greater than 2.0 in five areas: 6p23 (separate from HLA), 7q31.3, 11p11, 15q26, and 22cen. A larger genome wide search involving 110 affected Italian sib pairs using 281 markers found no evidence of linkage in these five areas.4 It did, however, propose a novel susceptibility locus at 5qter, important in both symptomatic and silent CD, and another at 11qter, which appeared to differentiate the two forms. In UK families an initial genome wide search,5 followed by a study of 17 candidate regions6 identified five areas with lod scores of greater than 2.0: 6p12, 11p11, 17q12, 18q23, and 22q13. Of these, 11p11 replicates one of the loci identified by Zhong et al 3 and it is likely that this area contains an important non-HLA susceptibility locus. However, in general the results of these studies are disappointingly inconsistent. A number of candidate genes have been investigated in linkage and association studies. Of these, the only region with repeatedly …

A collaborative European search for non-DQA1*05-DQB1*02 celiac disease loci on HLA-DR3 haplotypes: analysis of transmission from homozygous parents

The HLA-DQA1*05 with DQB1*02 alleles are a major risk factor for celiac disease (CD). To search for additional human leukocyte antigen (HLA) risk factors, we looked on the DR3-DQ2 risk haplotype, selected because it carries both DQ risk alleles in cis and is the more represented among CD patients. In a European consortium, we identified 109 families with a parent homozygous for DQA1*05-DQB1*02. We typed ten microsatellites in the extended HLA complex, and applied the homozygous-parent transmission disequilibrium test (HPTDT) and extended-TDT to transmissions from homozygous parents. These methods eliminate confounding due to linkage disequilibrium between candidate disease loci and the known risk factor DQA1*05-DQB1*02, and are favorable when sufficient families are available. We did not find evidence of association with any single marker or allele, although weak evidence for additional risk was observed, represented by preferential transmission of six adjacent markers. We tested the largest ever reported HPTDT population in CD, providing unprecedented power. We did not find significant evidence of additional risk-modifying factors on the DR3 haplotype, independent of DQA1*05-DQB1*02, although a weak tendency was observed for the B8-DR3 haplotype. This effect should be tested in large populations with significant representations of both B8-DR3 and non-B8 DR3 haplotypes.

Recent developments in celiac disease.

Celiac disease is a common disorder associated with a substantially increased standardized mortality ratio if it is left untreated or if the diagnosis is delayed. Diagnostic sensitivity of serologic testing is improved by the addition of IgG-based testing to standard IgA-based serologic testing for endomysial or transglutaminase autoantibodies. The role of intestinal permeability testing as an additional tool for screening and for monitoring the response to a gluten-free diet is discussed. The importance of diagnosing celiac disease in two clinical situations is considered: first, before immune-stimulating therapy with interferon for viral hepatitis is begun and second, in pregnancy when not only maternal but also paternal celiac disease may affect fetal outcome. The strong genetic component of the etiology of celiac disease is illustrated by a monozygotic twin concordance of nearly 90%, with susceptibility conveyed by human leukocyte antigen (HLA) genotypes DQ2 or DQ8 and one or more non-HLA genes. Progress toward identifying these genes from large linkage and association studies is reviewed.

Coeliac disease: Genetic factors and antigen presentation. [French, English]

RésuméLa prévalence de la maladie cœliaque est plus élevée qu’on ne le pensait précédemment et l’affection reste sous diagnostiquée en particulier chez les patients présentant des symptômes peu évidents ou non spécifiques. L’importance du diagnostic, basé sur la biopsie duodénale perendoscopique et la réponse au régime sans gluten, est soulignée par la mise en évidence de l’accroissement des risques de malignité associée à la maladie auto-immune ainsi que de l’ostéoporose chez les patients soumis à un régime sans gluten. Dans cet article, nous discutons les progrès réalisés dans l’identification des gènes porteurs du risque de la maladie et la façon dont ceux-ci nous permettent d’identifier les mécanismes impliqués dans la présentation des gènes et dans l’immunologie de la maladie cœliaque. Une concordance de 70%vs 10% de l’incidence de la maladie chez les jumeaux monozygotes par comparaison aux apparentés démontre la nature héréditaire de la maladie. Le risque génétique est partagé entre le risque attribuable à la région HLA du chromosome 6 et celui attribué à un ou plusieurs gènes situés en dehors de ce site. Plus de 95% des patients atteints de maladie cœliaque sont porteurs de HLA de classe II avec un génotype DQ2 ou DQ8 encodant des molécules de classe II porteuses d’antigène spécifique capable de se lier aux peptides dérivés du gluten. Dans la maladie cœliaque, de petites cellules possèdent un antigène intestinal capable de se lier aux peptides dérivés du gluten par DQ2 ou DQ8 afin de les présenter aux cellules T sensibles au gluten, ce qui entraîne une inflammation intestinale. La liaison des peptides dérivés du gluten à DQ2 ou à DQ8 est nettement améliorée par la transglutaminase, une enzyme tissulaire qui augmente la charge négative des peptides de gluten par une déamination sélective des résidus de la glutamine. Ceci permet d’identifier les fragments peptidiques particuliers dérivés du gluten alimentaire qui contiennent le(s), épitope(s) capable(s) d’initier ou de maintenir la réponse immunitaire. La transglutaminase tissulaire peut aussi être identifiée comme cible des anticorps anti-endomysium présents chez plus de 90% des malades cœliaques ce qui conduit à spéculer sur le rôle central joué par cette enzyme ou peut-être les anticorps eux-mêmes dans la pathogenèse de la maladie cœliaque.SummaryThe prevalence of coeliac disease is higher than previously thought and it remains underdiagnosed especially in patients with non-specific or mild symptoms. The importance of diagnosis, based on duodenal biopsy at endoscopy and response to a gluten free diet, is underlined by evidence of increased risk of malignancy, associated autoimmune disease and osteoporosis in patients remaining on a gluten containing diet. In this review, we discuss progress towards identifying the genes that carry the disease risk and how this has helped in identifying the mechanisms involved in antigen presentation and the immunology of coeliac disease. A disease concordance of 70% versus 10% for monozygotic twins compared to siblings demonstrates the strongly heritable nature of the disease. The genetic risk is divided between the risk attributable to the HLA region on chromosome 6 and the risk attributable to one or more genes outside this region. Over 95% of coeliac patients carry the HLA class II genotype DQ2 or DQ8 encoding class II molecules with specific antigen binding properties capable of binding gluten derived peptides. In coeliac disease, small intestinal antigen presenting cells present gluten derived peptides in association with either DQ2 or DQ8 to gluten sensitive T cells leading to small intestinal inflammation. The binding of gluten derived peptides to DQ2 and DQ8 is greatly enhanced by the action of the enzyme tissue transglutaminase in increasing the negative charge on gluten peptides by selective deamidation of glutamine residues. This has aided progress towards, identifying the particular peptide fragments derived from dietary gluten that contain the epitope(s) capable of initiating or maintaining the immune response. Tissue transglutaminase has also been identified as the target for the anti-endomyseal antibodies present in over 90% of coeliac patients leading to speculation of a central role for this enzyme and perhaps the antibodies themselves in the pathogenesis of coeliac disease.

Maladie cœllaque: facteurs génétiques et présentation des antigènes

RésuméLa prévalence de la maladie cœliaque est plus élevée qu’on ne le pensait précédemment et l’affection reste sous diagnostiquée en particulier chez les patients présentant des symptômes peu évidents ou non spécifiques. L’importance du diagnostic, basé sur la biopsie duodénale perendoscopique et la réponse au régime sans gluten, est soulignée par la mise en évidence de l’accroissement des risques de malignité associée à la maladie auto-immune ainsi que de l’ostéoporose chez les patients soumis à un régime sans gluten. Dans cet article, nous discutons les progrès réalisés dans l’identification des gènes porteurs du risque de la maladie et la façon dont ceux-ci nous permettent d’identifier les mécanismes impliqués dans la présentation des gènes et dans l’immunologie de la maladie cœliaque. Une concordance de 70%vs 10% de l’incidence de la maladie chez les jumeaux monozygotes par comparaison aux apparentés démontre la nature héréditaire de la maladie. Le risque génétique est partagé entre le risque attribuable à la région HLA du chromosome 6 et celui attribué à un ou plusieurs gènes situés en dehors de ce site. Plus de 95% des patients atteints de maladie cœliaque sont porteurs de HLA de classe II avec un génotype DQ2 ou DQ8 encodant des molécules de classe II porteuses d’antigène spécifique capable de se lier aux peptides dérivés du gluten. Dans la maladie cœliaque, de petites cellules possèdent un antigène intestinal capable de se lier aux peptides dérivés du gluten par DQ2 ou DQ8 afin de les présenter aux cellules T sensibles au gluten, ce qui entraîne une inflammation intestinale. La liaison des peptides dérivés du gluten à DQ2 ou à DQ8 est nettement améliorée par la transglutaminase, une enzyme tissulaire qui augmente la charge négative des peptides de gluten par une déamination sélective des résidus de la glutamine. Ceci permet d’identifier les fragments peptidiques particuliers dérivés du gluten alimentaire qui contiennent le(s), épitope(s) capable(s) d’initier ou de maintenir la réponse immunitaire. La transglutaminase tissulaire peut aussi être identifiée comme cible des anticorps anti-endomysium présents chez plus de 90% des malades cœliaques ce qui conduit à spéculer sur le rôle central joué par cette enzyme ou peut-être les anticorps eux-mêmes dans la pathogenèse de la maladie cœliaque.SummaryThe prevalence of coeliac disease is higher than previously thought and it remains underdiagnosed especially in patients with non-specific or mild symptoms. The importance of diagnosis, based on duodenal biopsy at endoscopy and response to a gluten free diet, is underlined by evidence of increased risk of malignancy, associated autoimmune disease and osteoporosis in patients remaining on a gluten containing diet. In this review, we discuss progress towards identifying the genes that carry the disease risk and how this has helped in identifying the mechanisms involved in antigen presentation and the immunology of coeliac disease. A disease concordance of 70% versus 10% for monozygotic twins compared to siblings demonstrates the strongly heritable nature of the disease. The genetic risk is divided between the risk attributable to the HLA region on chromosome 6 and the risk attributable to one or more genes outside this region. Over 95% of coeliac patients carry the HLA class II genotype DQ2 or DQ8 encoding class II molecules with specific antigen binding properties capable of binding gluten derived peptides. In coeliac disease, small intestinal antigen presenting cells present gluten derived peptides in association with either DQ2 or DQ8 to gluten sensitive T cells leading to small intestinal inflammation. The binding of gluten derived peptides to DQ2 and DQ8 is greatly enhanced by the action of the enzyme tissue transglutaminase in increasing the negative charge on gluten peptides by selective deamidation of glutamine residues. This has aided progress towards, identifying the particular peptide fragments derived from dietary gluten that contain the epitope(s) capable of initiating or maintaining the immune response. Tissue transglutaminase has also been identified as the target for the anti-endomyseal antibodies present in over 90% of coeliac patients leading to speculation of a central role for this enzyme and perhaps the antibodies themselves in the pathogenesis of coeliac disease.