A study of Italian pediatric celiac disease patients confirms that the primary HLA association is to the DQ(alpha 1*0501, beta 1*0201) heterodimer

The Role of Intestinal Microbiota in Celiac Disease and Further Therapeutic Perspectives

Celiac disease (CD) is an immune-mediated enteropathy caused by exposure to gluten and related prolamins in genetically susceptible individuals. It is a complex genetic disorder with multiple contributing genes. Linkage studies have identified several genomic regions that probably contain CD susceptibility genes. The most important genetic factors are HLA-DQ2 and DQ8. Several known environmental triggers promote the onset of CD at any age after gluten introduction in individuals with a genetic background, such as viral infections and intestinal dysbiosis. Recent publications have described the interference of the intestinal microbiome in gluten metabolism, modulation of local immune reactions, and in maintaining normal gut permeability. These results have promoted further lines of research on the benefit of probiotic administration to prevent disease onset or alleviate clinical symptoms along with a gluten-free diet (GFD). The relationship between gut microbiome changes and the onset of CD is incompletely understood, still being the subject of current research. This narrative review analyzes the interplay between environmental factors, intestinal microbiome alterations, and the course of CD. Furthermore, this review sets out to discuss if modulation of intestinal microflora with pre- and probiotics along with a GFD could represent a reliable therapeutic target for celiac patients.

An immunogenetic investigation of 30 autoimmune and autoinflammatory diseases and their links to psychiatric disorders in a nationwide sample

Autoimmune and autoinflammatory diseases (AIIDs) involve a deficit in an individual's immune system function, whereby the immune reaction is directed against self-antigens. Many AIIDs have a strong genetic component, but they can also be triggered by environmental factors. AIIDs often have a highly negative impact on the individual's physical and mental wellbeing. Understanding the genetic underpinning of AIIDs is thus crucial both for diagnosis and for identifying individuals at high risk of an AIID and mental illness as a result thereof. The aim of the present study was to perform systematic statistical and genetic analyses to assess the role of human leukocyte antigen (HLA) alleles in 30 AIIDs and to study the links between AIIDs and psychiatric disorders. We leveraged the Danish iPSYCH Consortium sample comprising 65 534 individuals diagnosed with psychiatric disorders or selected as part of a random population sample, for whom we also had genetic data and diagnoses of AIIDs. We employed regression analysis to examine comorbidities between AIIDs and psychiatric disorders and associations between AIIDs and HLA alleles across seven HLA genes. Our comorbidity analyses showed that overall AIID and five specific AIIDs were associated with having a psychiatric diagnosis. Our genetic analyses found 81 significant associations between HLA alleles and AIIDs. Lastly, we show connections across AIIDs, psychiatric disorders and infection susceptibility through network analysis of significant HLA associations in these disease classes. Combined, our results include both novel associations as well as replications of previously reported associations in a large sample, and highlight the genetic and epidemiological links between AIIDs and psychiatric disorders.

To Be or Not to Be a Pathogen: Candida albicans and Celiac Disease

Celiac disease (CD) is an immune-mediated disorder triggered by the ingestion of gluten and characterized by reversible small-bowel mucosal atrophy in genetically predisposed subjects. Although the prevalence of CD has increased, many aspects of this pathology are still unrecognized. Candida albicans, a commensal of the human gastrointestinal tract, has been linked to CD for a long time based, among others, upon the observation of similarity between the fungal wall component, hyphal wall protein 1, and CD-related gliadin T-cell epitopes. We have recently demonstrated that Candida may switch from commensal to pathogen contingent upon several players, including mast cells, key sentinels of the immune system at the interface between the environment and the host, and the pleiotropic cytokine IL-9. However, other factors are likely to play a role by altering the balance between inflammation and tolerance. In this regard, tryptophan and its metabolites are increasingly being recognized in promoting mucosal homeostasis by balancing the immune response to external cues. Based on these premises, we will discuss how the output of Candida colonization in the gut is highly contextual, being determined at the intersection of many immunological (IL-9/mast cells) and metabolic (tryptophan) pathways that ultimately dictate the Candida commensalism vs. pathogenicity in CD, thus paving the way for novel therapeutic opportunities in CD.

Celiac disease: a comprehensive current review

BACKGROUND

Celiac disease remains a challenging condition because of a steady increase in knowledge tackling its pathophysiology, diagnosis, management, and possible therapeutic options.

MAIN BODY

A major milestone in the history of celiac disease was the identification of tissue transglutaminase as the autoantigen, thereby confirming the autoimmune nature of this disorder. A genetic background (HLA-DQ2/DQ8 positivity and non-HLA genes) is a mandatory determinant of the development of the disease, which occurs with the contribution of environmental factors (e.g., viral infections and dysbiosis of gut microbiota). Its prevalence in the general population is of approximately 1%, with female predominance. The disease can occur at any age, with a variety of symptoms/manifestations. This multifaceted clinical presentation leads to several phenotypes, i.e., gastrointestinal, extraintestinal, subclinical, potential, seronegative, non-responsive, and refractory. Although small intestinal biopsy remains the diagnostic 'gold standard', highly sensitive and specific serological tests, such as tissue transglutaminase, endomysial and deamidated gliadin peptide antibodies, have become gradually more important in the diagnostic work-up of celiac disease. Currently, the only treatment for celiac disease is a life-long, strict gluten-free diet leading to improvement in quality of life, ameliorating symptoms, and preventing the occurrence of refractory celiac disease, ulcerative jejunoileitis, and small intestinal adenocarcinoma and lymphoma.

CONCLUSIONS

The present review is timely and provides a thorough appraisal of various aspects characterizing celiac disease. Remaining challenges include obtaining a better understanding of still-unclear phenotypes such as slow-responsive, potential (minimal lesions) and seronegative celiac disease. The identification of alternative or complementary treatments to the gluten-free diet brings hope for patients unavoidably burdened by diet restrictions.

Breaking Down Barriers: How Understanding Celiac Disease Pathogenesis Informed the Development of Novel Treatments

For decades, the pathogenesis of a variety of human diseases has been attributed to increased intestinal paracellular permeability even though scientific evidence supporting this hypothesis has been tenuous. Nevertheless, during the past decade, there have been a growing number of publications focused on human genetics, the gut microbiome, and proteomics, suggesting that loss of mucosal barrier function, particularly in the gastrointestinal tract, may substantially affect antigen trafficking, ultimately causing chronic inflammation, including autoimmunity, in genetically predisposed individuals. The gut mucosa works as a semipermeable barrier in that it permits nutrient absorption and also regulates immune surveillance while retaining potentially harmful microbes and environmental antigens within the intestinal lumen. Celiac disease (CD), a systemic, immune-mediated disorder triggered by gluten in genetically susceptible individuals, is associated with altered gut permeability. Pre-clinical and clinical studies have shown that gliadin, a prolamine component of gluten that is implicated in CD pathogenesis, is capable to disassembling intercellular junctional proteins by upregulating the zonulin pathway, which can be inhibited by the zonulin antagonist larazotide acetate. In this review, we will focus on CD as a paradigm of chronic inflammatory diseases in order to outline the contribution of gut paracellular permeability toward disease pathogenesis; moreover, we will summarize current evidence derived from available clinical trials of larazotide acetate in CD.

Prevalence of celiac disease in Saudi children with Down syndrome: A retrospective study

Celiac disease (CD) is an immune-mediated disease affecting the small intestine secondary to gluten exposure. The currently available treatment is lifelong adherence to a gluten-free diet (GFD). Several disorders are known to be associated with celiac disease, including Down syndrome (DS). In several studies, the prevalence of CD in DS ranged between 4 and 17%.

CD is prevalent in Arabs; however, few studies have been performed to determine the prevalence of CD in DS patients. Our study aimed to determine the prevalence of CD in Saudi Down syndrome patients using serological markers and small bowel biopsy.

This is a retrospective study in which files relating to Down syndrome patients who were followed up in a general pediatric clinic at King Faisal Specialist Hospital and Research Center were reviewed regarding demographic data, serological markers and biopsy results.

Of the total number of patients reviewed (91), 7 were excluded because data were missing; the remaining 84 patients included 35 females and 49 males. The age range of the patients at the time of screening was from 1 to 18 years. Patient demographic data are shown in Table 1. Among the studied patients, antigliadin antibody (AGA) IgA was high in 27 patients (32.14%), and AGA IgG was high in 44 patients (52.38%). Twelve patients (14.28%) tested positive and 58 (69.04%) tested negative for anti-endomysial antibodies. Anti-tissue glutaminase antibody IgA was found to be high in 13 patients (15.5%) and normal in 54 patients (64.28%). Serum IgA levels were normal in 36 patients (43%) and low in 1 patient (1.2%). Biopsy was performed in 22 patients who tested positive for anti-endomysial or anti-tissue transglutaminase antibodies. The biopsies provided positive results in 9 patients (10.7%).

Our study showed a confirmed prevalence of 10.7% for celiac disease in Saudi patients with Down syndrome based on serology and biopsy; together with previous cases reported in the literature, this result indicates a need to screen these patients for celiac disease.

Contemporary celiac disease diagnosis: is a biopsy avoidable?

PURPOSE OF REVIEW

The duodenal biopsy is the gold standard for the diagnosis of celiac disease. However, given improvements in the performance of serological testing, the possibility of accurately diagnosing celiac disease without the need of a biopsy has attracted interest. The European Society for Paediatric Gastroenterology, Hepatology and Nutrition has revised its recommendations to include a diagnostic algorithm that includes sequential serological testing and human leukocyte antigen genotyping for symptomatic children which would enable a diagnosis of celiac disease to be made in the absence of a confirmatory intestinal biopsy.

RECENT FINDINGS

Recent studies have evaluated the ESPGHAN guidelines and have mostly corroborated that celiac disease can be accurately diagnosed in specific pediatric patient populations without the need of a biopsy. However, two cautionary points have been raised that warrant further consideration - the success of this approach is highly dependent targeting a population with a high pretest probability of celiac disease, as well, the performance of serology assays must be established and the appropriate use of cutoffs is essential.

SUMMARY

The duodenal biopsy will remain the gold standard for diagnosing celiac disease in a majority of patients. However, as serology assays evolve and as a greater understanding of the genetic risk factors of celiac disease is achieved, more patients may be accurately diagnosed without the need for a biopsy.

Genetics and celiac disease: the importance of screening

The prevalence of celiac disease (CD) is increasing. Despite an increased awareness and an improvement in diagnostic testing, the majority of individuals with CD remain undiagnosed. Currently, genetic testing in screening for CD is used only to exclude a diagnosis or reinforce a strong clinical suspicion. In this paper, we review the most current literature regarding genetic testing in CD. In response to important data revealing that an individual's HLA haplotype is one of the strongest known predictors of CD, we propose genetic screening for at-risk infants to stratify individuals based on genetic risk to ultimately create genetic specific screening algorithms.

Common immunogenetic profile in children with multiple autoimmune diseases: the signature of HLA-DQ pleiotropic genes

Type 1 diabetes mellitus (T1DM), celiac disease (CD) and autoimmune thyroid disease (ATD) are autoimmune conditions relatively common in paediatric age and frequently occur in association in the same subject. This event is not by chance and requires an explanation. Here, we studied the distribution of HLA-DQ αβ heterodimers in 334 Italian children with T1DM, ATD and CD alone or in association and in 224 Italian healthy controls. In particular, 164 patients had T1DM (133 alone, 20+ATD, 7+CD and 4+CD+ATD), 118 had ATD (110 alone, 8+CD) and 52 had CD (40 alone, 11+ATD and 1+T1DM). 51 patients suffered from multiple autoimmune diseases. The risk for multiple autoimmune diseases was significantly associated with the increased number of HLA-DQ markers of susceptibility for both T1DM (p = 0.003) and CD (p = 0.006). The presence of one or more diabetogenic DQ molecules significantly increased the probability of developing not only T1DM (p < 0.001) but also CD (p < 0.001) and ATD (p = 0.001). Similarly, the presence of one or more celiac HLA-DQ heterodimers significantly increased the likelihood of developing not only CD (p < 0.001), but also T1DM (p < 0.001) and ATD (p < 0.001). We confirm that the sharing of the immunogenetic background is responsible for the development of multiple autoimmune diseases although with a different risk according to the number and type of susceptible HLA-DQ heterodimers as reported in the algorithm proposed here. It is likely that combinations of DQA1 and DQB1 alleles are the real culprits of the progression towards multiple autoimmune diseases and HLA-DQ genomic typing will improve the capability to predict associated autoimmune diseases in infancy.

Association analysis of the extended MHC region in celiac disease implicates multiple independent susceptibility loci

Celiac disease is a common autoimmune disease caused by sensitivity to the dietary protein gluten. Forty loci have been implicated in the disease. All disease loci have been characterized as low-penetrance, with the exception of the high-risk genotypes in the HLA-DQA1 and HLA-DQB1 genes, which are necessary but not sufficient to cause the disease. The very strong effects from the known HLA loci and the genetically complex nature of the major histocompatibility complex (MHC) have precluded a thorough investigation of the region. The purpose of this study was to test the hypothesis that additional celiac disease loci exist within the extended MHC (xMHC). A set of 1898 SNPs was analyzed for association across the 7.6 Mb xMHC region in 1668 confirmed celiac disease cases and 517 unaffected controls. Conditional recursive partitioning was used to create an informative indicator of the known HLA-DQA1 and HLA-DQB1 high-risk genotypes that was included in the association analysis to account for their effects. A linkage disequilibrium-based grouping procedure was utilized to estimate the number of independent celiac disease loci present in the xMHC after accounting for the known effects. There was significant statistical evidence for four new independent celiac disease loci within the classic MHC region. This study is the first comprehensive association analysis of the xMHC in celiac disease that specifically accounts for the known HLA disease genotypes and the genetic complexity of the region.

European Society for Pediatric Gastroenterology, Hepatology, and Nutrition guidelines for the diagnosis of coeliac disease

OBJECTIVE

Diagnostic criteria for coeliac disease (CD) from the European Society for Paediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) were published in 1990. Since then, the autoantigen in CD, tissue transglutaminase, has been identified; the perception of CD has changed from that of a rather uncommon enteropathy to a common multiorgan disease strongly dependent on the haplotypes human leukocyte antigen (HLA)-DQ2 and HLA-DQ8; and CD-specific antibody tests have improved.

METHODS

A panel of 17 experts defined CD and developed new diagnostic criteria based on the Delphi process. Two groups of patients were defined with different diagnostic approaches to diagnose CD: children with symptoms suggestive of CD (group 1) and asymptomatic children at increased risk for CD (group 2). The 2004 National Institutes of Health/Agency for Healthcare Research and Quality report and a systematic literature search on antibody tests for CD in paediatric patients covering the years 2004 to 2009 was the basis for the evidence-based recommendations on CD-specific antibody testing.

RESULTS

In group 1, the diagnosis of CD is based on symptoms, positive serology, and histology that is consistent with CD. If immunoglobulin A anti-tissue transglutaminase type 2 antibody titers are high (>10 times the upper limit of normal), then the option is to diagnose CD without duodenal biopsies by applying a strict protocol with further laboratory tests. In group 2, the diagnosis of CD is based on positive serology and histology. HLA-DQ2 and HLA-DQ8 testing is valuable because CD is unlikely if both haplotypes are negative.

CONCLUSIONS

The aim of the new guidelines was to achieve a high diagnostic accuracy and to reduce the burden for patients and their families. The performance of these guidelines in clinical practice should be evaluated prospectively.

HLA-G 14 bp deletion/insertion polymorphism in celiac disease

OBJECTIVES

Nonclassical major histocompatibility class I HLA-G antigen is a tolerogenic molecule that inhibits lytic activity of natural killer (NK) cells and cytotoxic T lymphocytes. Because of its immunomodulatory and tolerogenic properties, HLA-G molecules may have a role in celiac disease (CD). We analyzed the HLA-G 14 bp deletion/insertion polymorphism, known to have a functional effect on mRNA stability, in a group of 522 CD patients, stratified for the presence of HLA-DQ2 genotype, and 400 healthy individuals to evaluate the possible effect of the polymorphism on the risk to develop the disease.

METHODS

HLA-G 14 bp deletion/insertion polymorphism (rs1704) was detected by polymerase chain reaction and double-checked by direct sequencing.

RESULTS

The 14 bp inserted (I) allele and the homozygous I/I genotype were significantly more frequent in CD patients than in healthy controls. The presence of I allele was associated with an increased risk of CD (OR 1.35) and the effect of I allele was consistent with a recessive genetic model (P<0.001).

CONCLUSIONS

Our results also indicate that the effect of the HLA-G D/I polymorphism is restricted for HLA-DQ2, and not simply due to the presence of linkage disequilibrium with the major known risk factor; moreover we found that the presence of the I allele confers an increased risk of CD in addition to the risk conferred by HLA-DQ2 alone and that subjects that carry both DQ2 and HLA-G I alleles have an increased risk of CD than subjects that carry DQ2 but not the I allele.

Cost-effective HLA typing with tagging SNPs predicts celiac disease risk haplotypes in the Finnish, Hungarian, and Italian populations

Human leukocyte antigen (HLA) genes, located on chromosome 6p21.3, have a crucial role in susceptibility to various autoimmune and inflammatory diseases, such as celiac disease and type 1 diabetes. Certain HLA heterodimers, namely DQ2 (encoded by the DQA1*05 and DQB1*02 alleles) and DQ8 (DQA1*03 and DQB1*0302), are necessary for the development of celiac disease. Traditional genotyping of HLA genes is laborious, time-consuming, and expensive. A novel HLA-genotyping method, using six HLA-tagging single-nucleotide polymorphisms (SNPs) and suitable for high-throughput approaches, was described recently. Our aim was to validate this method in the Finnish, Hungarian, and Italian populations. The six previously reported HLA-tagging SNPs were genotyped in patients with celiac disease and in healthy individuals from Finland, Hungary, and two distinct regions of Italy. The potential of this method was evaluated in analyzing how well the tag SNP results correlate with the HLA genotypes previously determined using traditional HLA-typing methods. Using the tagging SNP method, it is possible to determine the celiac disease risk haplotypes accurately in Finnish, Hungarian, and Italian populations, with specificity and sensitivity ranging from 95% to 100%. In addition, it predicts homozygosity and heterozygosity for a risk haplotype, allowing studies on genotypic risk effects. The method is transferable between populations and therefore suited for large-scale research studies and screening of celiac disease among high-risk individuals or at the population level.

HLA-DQB1*02 dose effect on RIA anti-tissue transglutaminase autoantibody levels and clinicopathological expressivity of celiac disease

OBJECTIVES

Celiac disease is an autoimmune enteropathy caused by gluten ingestion in genetically susceptible individuals. Anti-transglutaminase autoantibody (tTGAb) assay is useful to detect candidates undergoing intestinal biopsy. Our aim was to investigate whether the DQB1*02 allele could influence tTGAb titers and the clinicopathological expressivity of the disease.

METHODS

A total of 124 patients with celiac disease, tested for RIA tTGAb at diagnosis, were typed for HLA-DRB1, -DQA1, and -DQB1 genes and divided according to the number of DQB1*02 alleles: group 1, homozygous; group 2, heterozygous; group 3, negative.

RESULTS

The mean of tTGAb indexes was significantly higher in group 1 patients than in group 2 (P < 0.02) and group 3 patients (P < 0.01). Patients with at least 1 DQB1*02 allele showed more often a typical CD and diffuse histological lesions than did patients in the other groups.

CONCLUSIONS

The study demonstrates that tTGAb titers are HLA-DQB1*02 dose dependent, with significantly higher levels in homozygous individuals. Moreover, individuals with at least 1 HLA-DQB1*02 allele tend to have a more expressed clinical and histological form of celiac disease.

A one-step real-time PCR assay for detection of DQA1*05, DQB1*02 and DQB1*0302 to aid diagnosis of celiac disease

Celiac disease is an autoimmune disorder that develops after dietary exposure of the small intestine to gluten peptides in cereals. Celiac disease has a strong genetic component associated with HLA-DQ2 and HLA-DQ8, and testing for absence of these genetic markers is useful when serological tests and biopsies are indeterminate, as it renders celiac disease highly unlikely. We have developed a new real-time PCR assay, using sequence-specific primers (PCR-SSP) and TaqMan probes, for detection of DQB1*05, DQB1*02 (coding for DQ2) and DQB1*0302 (coding for DQ8). PCR amplification and detection of DQ2 and DQ8 was accurately and unambiguously performed from genomic DNA isolated from cell lines and human DNA. Amplification was scored digitally, without laboratory manipulation of amplified PCR products and with a higher accuracy than PCR-SSP. This assay should increase accuracy and throughput, and reduce risks of contamination in laboratories where testing for HLA DQ2 and DQ8 is performed as part of diagnosis of celiac disease.

What are the sensitivity and specificity of serologic tests for celiac disease? Do sensitivity and specificity vary in different populations?

A number of serologic tests are available commercially for identifying individuals who require an intestinal biopsy examination to diagnose celiac disease (CD). The aim of this study was to determine which test, or combination of tests, was most sensitive and specific for this purpose. We performed a literature review of studies that determined the sensitivity and specificity of serologic tests for CD. Studies that compared biopsy examination-confirmed cases of CD with controls with normal intestinal histology were selected for analysis. Sensitivities and specificities for the antigliadin tests were highly variable. Immunoglobulin (Ig)G-based antigliadin (AGA) tests generally were poor in both parameters whereas the IgA-based test was poorly sensitive but more specific. The IgA endomysium (EMA-IgA) and tissue transglutaminase (TTG-IgA) tests were both highly sensitive and specific with values for both parameters exceeding 95% in most studies. There were no identifiable differences between adults and children with respect to these tests. There was no evidence that a combination of tests was better than a single test using either the EMA IgA or TTG IgA. Either the EMA-IgA or TTG-IgA test is most useful for identifying individuals with CD. The variability and generally lower accuracy associated with the AGA tests make them unsuitable for screening purposes. There is no advantage to using a panel of tests as opposed to a single test. Because these data were obtained largely from studies conducted in a research setting, it is possible the tests will be less accurate when used in the clinical setting.

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.

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.

Genetic dissection between silent and clinically diagnosed symptomatic forms of coeliac disease in multiplex families

BACKGROUND

Coeliac disease has a large variation in clinical outcome. In addition to the classical disease with malabsorption, many individuals have a silent form, in which subject symptoms are missing but autoantibodies and mucosa lesions are identical to the symptomatic disease.

AIM

To investigate whether differences in HLA DR-DQ genes explain the variation in outcome.

MATERIALS AND METHODS

HLA DQ alleles were determined in 28 multiplex families with sibling pairs in which one had the symptomatic disease but the other had the silent form.

RESULTS

No differences in the distribution of HLA DR-DQ haplotypes could be observed. The clinically diagnosed coeliac disease seemed to have earlier onset than silent coeliac disease.

CONCLUSIONS

Results indicate that the major genetic susceptibility locus, HLA DQ, does not determine the exact clinical outcome of coeliac disease.

HLA in coeliac disease families: a novel test of risk modification by the 'other' haplotype when at least one DQA1*05-DQB1*02 haplotype is carried

Predisposition to coeliac disease (CD) involves HLA genes. We investigated whether any haplotypes modify risk when carried trans to a known high-risk haplotype, DQA1*05-DQB1*02. Earlier attempts to rank levels of risk contributed by the 'other' haplotype were burdened by use of case-control populations; haplotype frequencies were estimated and homozygosity was only presumed. In contrast, exact haplotypes can be determined and allele transmission can be traced in families. A similar study in narcolepsy reported strata of different degrees of predisposition, attributable to the 'other' haplotype. A gene dosage effect similar to that described for DQB1*02 in CD, has also been reported in narcolepsy. We genotyped 439 simplex/multiplex trios for DQA1 and DQB1. We designed a new statistic to test risk modulation by the trans haplotype, even if the affected offspring was homozygous. We tested for significant deviation in transmission of the 'other' haplotype, i.e., modification of DQA1*05-DQB1*02 risk. We also addressed the proposed difference in risk, between DQA1*05-DQB1*02 homozygotes and DQA1*05-DQB1*02/DQA1*0201-DQB1*02 heterozygotes, reported in Southern Europe. We confirmed a DQB1*02 gene dosage effect. However, no haplotypes were found to modify risk when carried trans to DQA1*05-DQB1*02, except DQA1*05-DQB1*02 and DQA1*0201-DQB1*02 which were already known. We did not find credible evidence for a difference in risk conferred by DQA1*05-DQB1*02 and DQA1*0201-DQB1*02, when carried with DQA1*05-DQB1*02. The new test, which directly inspects haplotype transmissions rather than estimated haplotype frequencies, was used to demonstrate that the 'other' haplotype (except DQA1*05-DQB1*02 and DQA1*0201-DQB1*02) does not modify risk conferred by DQA1*05-DQB1*02. The test is applicable to other diseases.

The role of hemochromatosis susceptibility gene mutations in protecting against iron deficiency in celiac disease

BACKGROUND & AIMS

Celiac disease and hereditary hemochromatosis are common HLA-defined conditions in northwestern Europe. We sought to determine whether there is a genetic relationship between the 2 diseases and if hemochromatosis susceptibility gene (HFE) mutations are protective against iron deficiency in celiac disease.

METHODS

Polymerase chain reaction amplification using sequence-specific primers capable of identifying the 2 HFE gene mutations (H63D and C282Y) and the HLA class I and II alleles was used to type 145 white patients with celiac disease and 187 matched controls. Hemoglobin and fasting serum iron levels in celiac patients were measured at diagnosis.

RESULTS

HFE gene mutations, H63D or C282Y, were identified in 70 celiac patients (48.3%) and 61 controls (32.6%) (P = 0.004). The C282Y mutation was associated with HLA-A*03 and B*07 alleles in controls and with A*01, A*03, B*08, and DRB1*0301 alleles in celiac patients; the H63D mutation was associated with HLA-A*25 and DRB1*03 alleles in controls and A*29 and DRB1*03 alleles in celiac patients. At diagnosis, celiac patients with the C282Y mutation had higher mean hemoglobin and fasting serum iron levels compared with the HFE wild type (P = 0.0002 and 0.006, respectively). This was not observed with the H63D mutation.

CONCLUSIONS

In celiac disease, HFE gene mutations are common and are in linkage disequilibrium with different HLA alleles compared with controls. A disease-specific haplotype that carries C282Y and DQB1*02 is suggested. We propose that HFE gene mutations provide a survival advantage by ameliorating the iron deficiency seen in celiac patients.

Genome-wide linkage analysis for celiac disease in North American families

Celiac disease (CD) is an autoimmune disease caused by sensitivity to the dietary protein gluten. It has a prevalence of 1 in 250 in the United States. Multiple-case families are common with a risk to siblings from 10-12%. Previous linkage studies have found no significant evidence for linkage other than to HLA. In this study, we performed a genome-wide search on 62 families with at least two cases of CD to identify non-HLA loci for CD. Two-point and multipoint parametric and nonparametric analyses were performed on the entire set of families and on sets stratified by the HLA genotype. Accounting for multiple testing, we found genome-wide intermediate linkage evidence at 18q (heterogeneity LOD (HLOD) = 3.6) and at 3p (HLOD = 3.2) and suggestive evidence at 5p (HLOD = 2.7). Good consensus between two-point and multipoint evidence was not found, and after genotyping with new markers in these regions, our results were inconclusive. The 18q region had intermediate two-point evidence, but weak multipoint evidence. At 3p and 5p, the addition of follow-up markers added flanking support, yet multipoint evidence was still lacking. Our results indicate that multipoint analyses may be hindered by the complexity of CD. Multipoint analyses are not robust to model misspecification, and further development of models is needed. Additional study of these and other families is necessary to validate or rule out the regions implicated in this study.

HLA DQA1-DQB1 genotypes in Bedouin families with celiac disease

Celiac disease (CD) has a strong genetic association with human leukocyte antigens (HLA). The primary susceptibility for CD is HLA-DQA1*05 DQB1*02 (also known as DQ2), with the remainder of cases primarily HLA-DQA1*03 DQB1*03 (also known as DQ8). In a set of nine Bedouin multiplex celiac disease families and one simplex, we genotyped DNA samples at HLA DQA1 and DQB1. Nineteen celiac disease patients had at least one DQA1*05 DQB1*02 genotype (= DQ2), 4 affecteds had the second most common genotype of DQA1*03 DQB1*0302 (= DQ8), 9 were DQ2 and DQ8, and 4 had at least one copy of DQB1*02 without the DQA1*05 genotype. Using transmission disequilibrium testing, we observed a significant over-representation in affecteds of the DQA1*05 DQB1*02 genotype (p = 0.0089), as well as over-representation of the DQA1*03 DQB1*0302 genotype (p = 0.078). The HLA DQA1 DQB1 high-risk genotypes associated with celiac disease are similar in these Bedouin families with CD to what is observed in Northern and Southern Europeans.

Use of closely related affected individuals for the genetic study of complex diseases in founder populations

We propose a method, the maximum identity length contrast (MILC) statistic, to locate genetic risk factors for complex diseases in founder populations. The MILC approach compares the identity length of parental haplotypes that are transmitted to affected offspring with the identity length of those that are not transmitted to affected offspring. Initially, the statistical properties of the method were assessed using randomly selected affected individuals with unknown relationship. Because both nuclear families with multiple affected sibs and large pedigrees are often available in founder populations, we performed simulations to investigate the properties of the MILC statistic in the presence of closely related affected individuals. The simulation showed that the use of closely related affected individuals greatly enhances the power of the statistic. For a given sample size and type I error, the use of affected sib pairs, instead of affected individuals randomly selected from the population, could increase the power by a factor of two. This increase was related to an increase of kinship-coefficient contrast between haplotype groups when closely related individuals were considered. The MILC approach allows the simultaneous use of affected individuals from a founder population and affected individuals with any kind of relationship, close or remote. We used the MILC approach to analyze the role of HLA in celiac disease and showed that the effect of HLA may be detected with the MILC approach by typing only 11 affected individuals, who were part of a single large Finnish pedigree.

Celiac disease--a worldwide problem

Celiac disease and dermatitis herpetiformis are caused by the alcohol soluble fractions of wheat, barley, and rye. Reliable serological tests are available for both mass and risk group screening and recent epidemiological studies on celiac disease suggest that the prevalence varies between 1:100-300 in different continents. The clinical manifestations of the disease has changed in the West and the classical symptomatic cases represent only approximately 1/7th of all diagnosed cases. Symptoms such as, anemia, short stature, dental enamel defect or osteoporosis can be the only manifestations of the atypical disease. There is an increased prevalence of celiac disease in patients with autoimmune diseases. Recent data suggest that there is a correlation between the prevalence of autoimmune diseases and the number of years that an individual consumes gluten-containing foods. Genetic studies revealed a high prevalence of certain HLA antigens in celiac patients, however, there is likelihood that non-HIA genes are also important in the pathomechanism. An interesting new development is the recognition of tissue transglutaminase (tTG), an enzyme that probably forms an autoantigen with gluten. It is generally accepted that antibodies to tTG are identical to the previously described antiendomysium antibodies. Whether or not tTG is responsible for the initiation of an immunoreaction against prolamines or just exacerbates the immune response is a subject of further investigations.

Molecular basis of celiac disease

Celiac disease (CD) is an intestinal disorder with multifactorial etiology. HLA and non-HLA genes together with gluten and possibly additional environmental factors are involved in disease development. Evidence suggests that CD4(+) T cells are central in controlling an immune response to gluten that causes the immunopathology, but the actual mechanisms responsible for the tissue damage are as yet only partly characterized. CD provides a good model for HLA-associated diseases, and insight into the mechanism of this disease may well shed light on oral tolerance in humans. The primary HLA association in the majority of CD patients is with DQ2 and in the minority of patients with DQ8. Gluten-reactive T cells can be isolated from small intestinal biopsies of celiac patients but not of non-celiac controls. DQ2 or DQ8, but not other HLA molecules carried by patients, are the predominant restriction elements for these T cells. Lesion-derived T cells predominantly recognize deamidated gluten peptides. A number of distinct T cell epitopes within gluten exist. DQ2 and DQ8 bind the epitopes so that the glutamic acid residues created by deamidation are accommodated in pockets that have a preference for negatively charged side chains. Evidence indicates that deamidation in vivo is mediated by the enzyme tissue transglutaminase (tTG). Notably, tTG can also cross-link glutamine residues of peptides to lysine residues in other proteins including tTG itself. This may result in the formation of complexes of gluten-tTG. These complexes may permit gluten-reactive T cells to provide help to tTG-specific B cells by a mechanism of intramolecular help, thereby explaining the occurrence of gluten-dependent tTG autoantibodies that is a characteristic feature of active CD.

Synergistic effect of two HLA heterodimers in the susceptibility to celiac disease in Tunisia

The DR and DQ HLA genotypes of 94 Tunisian children affected with celiac disease are analyzed so that we can gain a better understanding of the HLA component of this disease. All of them carry at least one of two specific heterodimers: a DQ heterodimer, encoded by DQA1*0501, DQB1*0201 and/or a DR heterodimer, encoded by the nonpolymorphic gene DRA and the DRB4 gene. Quantifying the relative penetrances of all susceptible genotypes gives evidence for a synergistic effect of these two heterodimers and for a dose effect of the alleles encoding the beta chains of these two heterodimers. The DR3DR7 individuals have the greatest risk. They present the two kinds of heterodimers and carry two DQB1*0201 alleles. Celiac disease is the first HLA-associated disease for which the at-risk genotypes are so well delineated.

Linkage and association study of the CTLA-4 region in coeliac disease for Italian and Tunisian populations

Coeliac disease (CD) is a multifactorial disease for which there is an intensive search for genetic risk factors. Some authors found an association between the CTLA-4 region and CD. In the present work, we investigate the possible implication of the CTLA-4 region as a genetic risk factor for CD, through two statistical approaches: the maximum likelihood score (MLS) test in a large Italian sample of affected sib-pairs using polymorphic genetic markers on chromosome 2, and the transmission disequilibrium test (TDT) in continental Italian and Tunisian families using the CTLA-4 exon 1 49 A/G polymorphism. None of these approaches provides evidence for linkage or association between the CTLA-4 region and CD. This might result from a difference in the CTLA-4 region from population to population, either in its involvement as a risk factor or in the strength of linkage disequilibrium.

A gene telomeric of the HLA class I region is involved in predisposition to both type 1 diabetes and coeliac disease

We have recently shown that an as yet unidentified gene within or in the vicinity of the HLA complex, in linkage disequilibrium with microsatellite D6S2223, modifies the risk to develop type 1 diabetes independently of HLA-DR and -DQ genes. This microsatellite is located 2.5 Mb telomeric to HLA-F and particular alleles at this microsatellite modifies the risk encoded by the high-risk DRB1*03-DQA1*0501-DQB1*0201 (hereafter called DR3) haplotype. Coeliac disease and type 1 diabetes share some susceptibility HLA class II haplotypes, in Scandinavia particularly the DR3 haplotype. We therefore investigated whether the marker D6S2223 might also be associated with coeliac disease. In order to keep the contributions from the DRB1-DQA1-DQB1 genes constant (i.e., eliminate the effects of linkage disequilibrium to disease associated DR and/or DQ alleles), we only used cases and controls being homozygous for DR3. We found the frequency of allele 3 at D6S2223 to be reduced among patients with coeliac disease compared to controls, to a similar extent as seen in type 1 diabetes, which could not be explained by a different distribution of HLA-B alleles (as ascertained by typing for the MIB microsatellite). This negatively associated allele 3 at D6S2223 occurred in a homozygous combination at a significantly lower frequency among patients than controls. Thus, allele 3 at D6S2223 on DR3 haplotypes is associated with reduced susceptibility for development of both type 1 diabetes and coeliac disease. This suggests that a gene(s) in the vicinity of D6S2223 is involved in the pathogenesis of both of these immune-mediated diseases.

Absolute linkage of celiac disease and dermatitis herpetiformis to HLA-DQ

This report shows the absolute genetic linkage of celiac disease (CD) to the HLA-DQ region, and supports the fact that dermatitis herpetiformis (DH) follows the same pattern of HLA-mediated susceptibility in extensive series of Caucasian Spanish patients. Ninety-five percent of CD (201 of 212) and 100% of DH (55) patients could produce DQ alpha 1*0501-DQ beta 1*02 heterodimers. Negative CD patients for this combination were mostly DR4-DQ8 (DQA1*03-DQB1*0302) (9 OF 11), along with a restricted number of complementary chromosomes. Comparison of observed and expected DQA1-DQB1 genotype distributions (Hardy-Weinberg equilibrium) showed that the excess of patients with DQB1*02 in double doses would be the consequence for which this allele should be complemented by DQA1*0501. Homozygosity for DQA1*0501 would restrain susceptibility to CD and DH.

Is celiac disease due to molecular mimicry between gliadin peptide-HLA class II molecule-T cell interactions and those of some unidentified superantigen?

This paper presents a new hypothesis for the etiology and pathogenesis of celiac disease (CD). It is our contention that CD is triggered by the binding of one or more gliadin peptides to CD-associated HLA class II molecules. Furthermore, we propose that these putative CD peptides bind to oligosaccharide residues on HLA class II molecules distal to the peptide-binding groove invoking recognition and binding by specialized subsets of gamma delta T cell receptor-bearing lymphocytes. The binding of these gamma delta T cells serves as a signal for abrogation of oral tolerance to ingested proteins setting in motion a series of immune responses directed against the small intestinal epithelium of CD patients. CD patients are victimized by this self-distructed immune response because of inheritance of certain combinations of HLA-DQ and DR haplotypes. Dimers encoded by HLA-DR haplotypes may be the primary restriction elements for lectin-like, gliadin peptides while the degree of immune suppression (or lack thereof) to ingested gliadins is governed by inherited HLA-DQ haplotypes. Finally, we speculate that molecular mimicry between one or more gliadin peptides and some, as yet unidentified, bacterial or viral superantigen plays a role in disease pathogenesis.

Association of HLA-DQ7 antigen with cow milk protein allergy in Italian children

In this study we investigated the HLA association with cow milk allergy. Thirty-seven Italian children with cow milk allergy and 35 randomly selected age-matched healthy children as control group were included in the study. DNA typing was performed by restriction fragment length polymorphism (RFLP) technique. We show the first statistically significant positive association between the expression of the HLA-DQ7 antigen and cow milk allergy. Several immunological tests (skin prick test, RIA, radioallergosorbent test (RAST) and ELISA) were performed to evaluate the humoral immune responses of DQ7 positive and DQ7 negative allergic patients. Our results show that among the DQ7 positive patients the majority presented a high humoral response. Furthermore, the in vitro proliferative response of patients to the beta-lactoglobulin antigen was performed to evaluate their cell-mediated immune response. We observed that the number of the nonresponders was higher in the DQ7 positive patients when compared to the DQ7 negative patients. Our data indicate an association of HLA-DQ7 antigen with cow milk protein allergy and that the DQ7 positive patients had a prevalence of humoral rather than cellular responses.

[Dermatitis herpetiformis occuring in patients with celiac disease in childhood]

BACKGROUND

Dermatitis herpetiformis (DH) is a chronic papulovesicular immune-mediated disorder associated with gluten-sensitive enteropathy. We report eight cases in which DH appeared many years after celiac disease (CD) in child.

PATIENTS AND METHODS

The diagnosis of CD was based on histological features of total or subtotal villous atrophy, full remission after withdrawal of gluten from the diet, and eventually circulating antibodies (IgA gliadin, antireticulin and antiendomysium) at the time of diagnosis and their disappearance under gluten-free diet. The diagnosis of DH was made from clinical findings, histological examination of the involved skin and direct immunofluorescence microscopy of normal or perilesional skin. HLA class II typing was performed in five patients. DRB1, DQA1, DQB1 and DBP1 alleles were studied.

RESULTS

DH appeared between 3 and 22 years after the initial diagnosis of CD. Five patients did not show at that time any digestive symptoms. In three cases, a break in the gluten-free diet or a recent revival of the normal diet preceded the rash. In only one case, DH appeared while the patient was under gluten-free diet. In three patients, the rash appeared many years after the gluten-free diet had been stopped. Phenotype DR3 and/or DR7 of the celiac disease could be found in four of the five patients studied; three of them were found to bear DQW2. The DR2 allele was not found in any of the five tested patients.

DISCUSSION

These eight cases illustrate the absence of precise nosological barrier between gluten-sensitive enteropathy of the DH and that observed in CD. The presence of the DR7 allele, and especially the absence of the DR2 allele, could explain the particularly severe and symptomatic course of the enteropathy in these patients. The delay in the appearance of DH, after a very variable period of normal diet, could correspond to the necessary time for progressive accumulation of IgA (or immune complex IgA-gluten) in the skin after a digestive sensitization to gluten. The preventive role of gluten-free diet is thus probable.

CONCLUSION

CD and DH likely correspond to two different stages of the same disease, thus requiring a prolonged follow-up of both digestive and skin tissues. Long-term eviction of gluten to prevent eventual DH must be balanced with the demand and the cost of such a diet.

Reevaluation of the relative risk for susceptibility to celiac disease of HLA-DRB1, -DQA1, -DQB1, -DPB1, and -TAP2 alleles in a French population

In a population of 46 children with CD recruited in the Paris area of France, an excess of DRB1*03 and DRB1*07 alleles and of DR3/DR7, DR3/DR3 and DR11(or 12)/DR7 phenotypes was found (RRs of 6.3, 9.3, 24.6, 15, and 15.1, respectively), which is reminiscent of the markers of susceptibility observed in southern rather than in northern European celiac patients. More importantly, the highest association with CD was not found in individuals expressing the DQA1*0501-DQB1*0201 heterodimer in single dosage (RR = 24.9) or in homozygous state, but in people co-expressing one copy of DQA1*0501-DQB1*0201 on one haplotype and a second copy of DQB1*0201 on the second haplotype (RR = 35.7). This suggests that in our population either DQB1*0201 or a gene closely linked to DQB1*0201 influences the susceptibility to CD conferred by the DQA1*0501-DQB1*0201 heterodimer. Significant positive or negative RRs conferred by some TAP2 or DPB1 alleles were found. However, they were moderate compared to the RR conferred by the expression of a second copy of DQB1*0201. Moreover, they were no longer significant when patients were compared with HLA-DR matched controls. This suggests that associations of CD with TAP2 and DPB1 alleles are secondary to linkage disequilibria and argues against the contribution of these alleles in resistance and/or susceptibility to CD. Thus the "raison d'être" of a "DQB1*0201 second haplotype effect" in susceptibility to CD remains to be elucidated.

T cells from the small intestinal mucosa of a DR4, DQ7/DR4, DQ8 celiac disease patient preferentially recognize gliadin when presented by DQ8

CD is an immunologic disease of the small intestine which is precipitated by ingestion of wheat gliadin. Most patients carry the HLA-DQ (alpha 1*0501, beta 1*0201) (DQ2) heterodimer. We recently reported that a preponderance of gliadin-specific T cells from the small intestinal mucosa of DQ2-positive CD patients were restricted by this DQ heterodimer. However, a small percentage of CD patients do not carry this DQ heterodimer, and most of them instead carry DQ (alpha 1*0301, beta 1*0302) (DQ8). Here we report that a majority of gliadin-specific T cells from the small intestinal mucosa of a DR4,DQ7/DR4,DQ8 heterozygous CD patient are restricted by DQ8. Thus, preferential presentation of gliadin-derived peptides to T cells by the CD-associated DQ2 and DQ8 molecules may be an initial and important immunopathogenic step in CD.

Coeliac disease, enamel defects and HLA typing

The presence of dental enamel defects in coeliac disease and their relation to hypocalcaemia or a particular HLA class in 82 Italian children with coeliac disease was studied. Demarcated opacities or hypoplasia were detected in 23 subjects (group 1) while minimal or no dental lesions were found in the remaining 59 patients (group 2); in 189 normal controls, enamel lesions were significantly less frequent than in patients with coeliac disease (14.8% versus 28.0%; p < 0.005). No statistically significant differences were found for age at diagnosis and calcium concentrations between groups 1 and 2. Regression analysis showed a correlation between age at diagnosis and number of teeth with enamel defects. In our patients, the presence of HLA DR3 antigen significantly increased the risk of dental lesions, while genotype DR5,7 seemed to protect against enamel defects. A logistic regression analysis of the variables age, serum calcium concentrations, number of affected teeth, type of enamel defect and DR antigens showed that only DR antigens discriminated coeliac disease patients with from those without enamel defects.

A gene dosage effect of the DQA1*0501/DQB1*0201 allelic combination influences the clinical heterogeneity of celiac disease

This study reports the HLA-DR and DQ molecular characterization of 62 CD patients of Sardinian descent. Patients were divided in two groups (36 in group I and 26 in group II) according to the clinical features at the disease onset. Among the patients of group I, having the fully expressed form of CD and a mean age of 3 years at disease onset, a significant increase of DRB1*0301, DQA1*0501, DQB1*0201 homozygotes, encoding in cis two DQ (alpha 1*0501, beta 1*0201) susceptibility heterodimers, was observed when compared either with the patients of group II (pIII < 0.012) or with healthy individuals (pI < 10(-6)). On the other hand, in the patients of group II, presenting oligosymptomatic forms and a mean age of 5.7 years at the disease onset, the haplotype combinations encoding in cis or in trans only one DQ (alpha 1*0501, beta 1*0201) heterodimer were significantly increased in comparison either with the patients of group I (pIII < 0.026) or with controls (pII < 10(-6)). These findings suggest that a double dose of DQA1*0501, DQB1*0201 genes may predispose a person to an earlier onset and to more severe disease manifestations. Genotype analysis showed that only three patients (all in group I) failed to form in trans or in cis the DQ (alpha 1*0501, beta 1*0201) heterodimer and carried the DQA1*0101,DQB1*0501 haplotype, suggesting its possible role in CD susceptibility. In addition, a significant increment of DQB1*0501 gene (pc < 0.0065) was found comparing the frequency of DQB1 alleles in CD patients and healthy controls, after exclusion of DQB1*0201 chromosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Polymorphism of antigen processing (TAP, LMP) and HLA class II genes in celiac disease

Susceptibility to CD is strongly associated with particular HLA class II molecules. However, additive genetic factors are likely to be required for the development of the disease. The polymorphic TAP and LMP genes, located within the HLA class II region, are involved in the antigen presentation pathway and thus represent candidate susceptibility genes. HLA class II DRB1, DRB3, DQA1, DQB1, and DPB1 as well as TAP1, TAP2, and LMP2 polymorphism was studied in 80 Caucasian CD patients and 213 normal controls by DNA oligotyping. The DQB1*0201 allele was found in 96.3% of CD patients and provided the highest risk (RR = 50), whereas only 89% of CD patients carried the DQ alpha 501/beta 201 heterodimer (RR = 30). The participation of the DRB3 and DPB1 locus was ruled out as it was attributed to a linkage disequilibrium on the DR3 haplotype. TAP1 and LMP2 allelic distribution was not significantly different among CD patients and controls. The TAP2-C allele was completely absent from the CD population, while it was found in 22.5% of controls. Although linkage disequilibrium between TAP2 and class II loci clearly exists in some haplotypes, TAP could act as additional susceptibility genes.

T cells recognize a peptide derived from alpha-gliadin presented by the celiac disease-associated HLA-DQ (alpha 1*0501, beta 1*0201) heterodimer

CD is unique among the HLA-associated diseases since (a) the disease-promoting agent (gliadin) is known and (b) the disease is precipitated mainly in individuals carrying a particular cis- or trans-encoded HLA-DQ heterodimer; i.e., DQ(alpha 1*0501, beta 1*0201). Further, a preponderance of gliadin-specific T cells derived from the small intestinal mucosa of CD patients are restricted by this DQ heterodimer. T-cell recognition of gliadin peptides presented by the DQ(alpha 1*0501, beta 1*0201) heterodimer may thus be of importance in CD. Here we report that a T-cell clone from a patient with CD recognizes a synthetic alpha-gliadin peptide, when presented by the cis- or trans-encoded CD-associated DQ(alpha 1*0501, beta 1*0201) heterodimer. The minimal peptide recognized by the T-cell clone corresponds to residues 31-47 of alpha-gliadin, which is included in the part of alpha-gliadin previously shown to have disease-promoting activity. When testing analogue peptides derived from other alpha-gliadin sequences, one peptide differing by one amino acid was recognized by the T-cell clone, whereas the other peptide differing by two amino acids was not recognized. Our findings demonstrate that the CD-associated DQ(alpha 1*0501, beta 1*0201) heterodimer may serve as an antigen-presenting molecule to T cells for certain gliadin peptides.

HLA susceptibility genes in celiac disease: genetic mapping and role in pathogenesis

The overrepresentation of particular HLA alleles in patients with celiac disease was first noted two decades ago. Several lines of evidence obtained during the last years strongly suggest that a particular HLA-DQ heterodimer, encoded by the DQA1*0501 and DQB1*0201 genes in cis or trans configuration, confers the primary disease susceptibility. This paper reviews the evidence behind this concept and discusses how this particular DQ molecule may be involved in the pathogenesis.

Combinations of specific DRB1, DQA1, DQB1 haplotypes are associated with insulin-dependent diabetes mellitus in Sardinia

The Sardinian population has an extremely high incidence of IDDM (30.2 of 100.000 in the age group of 0-14 years). This study reports the molecular characterization of HLA class II genes in 120 IDDM sporadic patients and 89 healthy subjects of Sardinian origin. Compared with other Caucasians, both Sardinian patients and controls had an unusual distribution of haplotypes and genotypes. In particular, there was a high gene frequency of the DRB1*0301, DQA1*0501, DQB1*0201 susceptibility haplotype both in patients (0.58) and controls (0.23) while a reduction of the DRB1*1501, DQA1*0102, DQB1*0602 protective haplotype (0.03) was observed in the healthy population. This distribution may partially explain the high incidence of IDDM reported in Sardinia. The analysis of the DQ beta 57 and DQ alpha 52 residues showed that the absence of Asp 57 and the presence of Arg 52 were associated with IDDM in a dose-response manner. On the other hand, we found that (a) a very similar distribution of these residues was found when comparing Sardinians with another healthy Caucasian population from the same latitude but with a lower rate of IDDM incidence; (b) several genotypes encoding the identical DQ alpha 52/DQ beta 57 phenotype carried very different relative risks; and (c) the DRB1*0403, DQA1*0301, DQB1*0304 haplotype (DQ beta 57 Asp-neg and DQ alpha 52 Arg-pos) was found in 40% of the DR4-positive controls but not in patients (p = 0.00034), while the DRB1*0405, DQA1*0301, and DQB1*0302 haplotype carrying the same residues at the same positions was found in 70% of the DR4-positive patients and in only one control (p = 0.00003). These findings suggest that IDDM susceptibility cannot be completely explained by the model in which only DQ alpha 52 and DQ beta 57 residues are taken into account.

Linkage disequilibrium between TAP2 variants and HLA class II alleles; no primary association between TAP2 variants and insulin-dependent diabetes mellitus

The TAP1 and TAP2 genes, located in the HLA class II region, encode subunits of a peptide transporter. Both genes display limited genetic variability; four different nucleotide substitutions have been found in the TAP2 gene. Here studies on linkage disequilibrium between TAP2 variants and HLA class II alleles are reported, in an attempt to evaluate whether TAP2 variants are associated with insulin-dependent diabetes mellitus (IDDM). As reported previously, a significant decrease of homozygosity for TAP2 alleles encoding alanine at residue 665 (665 Ala) and glutamine at 687 (687 Gln) paralleled by an increase in homozygosity for TAP2 alleles encoding threonine at residue 665 (665 Thr) and a stop codon at 687 (687 Stop), was found in both Finnish and Norwegian IDDM patients compared to random controls. However, a strong linkage disequilibrium between these TAP2 polymorphisms and given HLA-DR and -DQ genes was observed among healthy controls. The frequent 665 Thr and 687 Stop variants were in linkage disequilibrium both with the DR4-DQ8 and the DR3-DQ2 haplotypes, haplotypes which are strongly associated with IDDM. In contrast, the DR1-DQ5 and DR13-DQ6 (e.g. DQB1*0603) haplotypes, which are decreased among IDDM patients, were associated with the 665 Ala and 687 Gln variants. Thus, when DR- and DQ-matched patients and controls were compared, associations of the investigated TAP2 variants and IDDM were no longer detectable. These data, therefore, indicate that the associations previously found between certain TAP2 variants and IDDM are secondary to a primary association between this disease and particular DQ alpha beta heterodimers.