Genome-wide linkage analysis of Scandinavian affected sib-pairs supports presence of susceptibility loci for celiac disease on chromosomes 5 and 11

An updated overview on celiac disease: from immuno-pathogenesis and immuno-genetics to therapeutic implications

INTRODUCTION

Celiac disease (CD) is an autoimmune enteropathy triggered by ingestion of gluten. While presenting many similarities with other autoimmune diseases, celiac disease is unique in that the external trigger, gluten, and the genetic background necessary for disease development (HLA DQ2/DQ8) are well described. The prevalence of celiac disease is dramatically increasing over the years and new epidemiologic data show changes regarding age of onset and symptoms. A better understanding of CD-pathogenesis is fundamental to highlight the reasons of this rise of celiac diagnoses.

AREAS COVERED

In this review we describe CD-pathogenesis by dissecting all the components necessary to lose tolerance to gluten (ingestion of gluten, genetic predisposition, loss of barrier function and immune response). Additionally, we also highlight the role that microbiome plays in celiac disease as well as new proposed therapies and experimental tools.

EXPERT OPINION

Prevalence of autoimmune diseases is increasing around the world. As a result, modern society is strongly impacted by a social and economic burden. Given the unique characteristics of celiac disease, a better understanding of its pathogenesis and the factors that contribute to it may shed light on other autoimmune diseases for which external trigger and genetic background are not known.

A family-based genome-wide association study of recurrent aphthous stomatitis

OBJECTIVES

The aetiology of recurrent aphthous stomatitis (RAS) remains unknown. Individuals may share features of genetic susceptibility, and there may also be a hereditary component. The aim was to identify patterns of association and segregation for genetic variants and to identify the genes and signalling pathways that determine the risk of developing RAS, through a family-based genome-wide association study (GWAS).

SUBJECTS AND METHODS

DNA was extracted from buccal swabs of 91 individuals in 16 families and analysed in an Illumina core exome single nucleotide polymorphism (SNP) array. A family-based association test (dFAM) was used to derive SNP association values across all chromosomes.

RESULTS

None of the final 288,452 SNPs reached the genome-wide significant threshold of 5 × 10^-8 . The most significant pathways were the Ras and PI3K-Akt signalling pathways, pathways in cancer, circadian entrainment and the Rap 1 signalling pathway.

CONCLUSIONS

This confirms that RAS is not monogenic but results as a consequence of interactions between multiple host genes and possibly also environmental factors. The present approach provides novel insights into the mechanisms underlying RAS and raises the possibility of identifying individuals at risk of acquiring this condition.

Study Designs for Exploring the Non-HLA Genetics in Celiac Disease

Since the breakthrough of genome-wide association studies and genetic studies of common complex diseases like celiac disease have been able to finally identify reproducible gene regions affecting risk of developing disease. Before it was possible to perform genome-wide association analysis, the field struggled with genome-wide linkage analysis to identify gene regions. Genome-wide linkage had been very successful in identifying genes underlying monogenic diseases, but common complex polygenic diseases did not prove so tractable. This chapter will describe the genome-wide methods available for genetic analyses of families today and compare these with the previous analyses performed in the 1990s and early twenty-first century.

Interleukin-18 gene promoter polymorphisms and celiac disease in Italian patients

Celiac disease (CD) is the most common food-sensitive enteropathy in genetically susceptible individuals. The major genetic risk factors known are specific human leukocyte antigen (HLA)-DQ haplotypes, but other genetic factors are supposed to be involved. Interleukin-18 (IL-18) is a pro-inflammatory cytokine that has an important role in the immune defense and it has the potential to influence inflammatory disorders. IL-18 is able to promote Th1 cell development and it is expressed in the mucosa of the small intestine in celiac patients. Given the IL-18 biological role, and since a few studies have previously suggested its involvement in CD, in order to investigate the role of IL18 gene in the susceptibility to CD we have performed a case-control study, analyzing two IL18 gene promoter polymorphisms, previously reported to impair the transcriptional activity of the gene, (-137G > C and -607C > A, rs187238 and rs1946518 respectively). A total of 556 CD Italian patients and 582 controls, further stratified for HLA class II (DQ) CD risk haplotypes were enrolled. The -607A > C A allele and A/A genotype, as well as the combination of this allele with the -137G allele in the AG haplotype, were associated with an increased risk towards CD development, in particular in HLA-DQ2.2 patients. Although the association was very moderate, our results indicate the possible involvement of IL18 gene in the susceptibility to CD, and for this reason we do think it should deserve further investigation.

A possible mechanism behind autoimmune disorders discovered by genome-wide linkage and association analysis in celiac disease

Celiac disease is a common autoimmune disorder characterized by an intestinal inflammation triggered by gluten, a storage protein found in wheat, rye and barley. Similar to other autoimmune diseases such as type 1 diabetes, psoriasis and rheumatoid arthritis, celiac disease is the result of an immune response to self-antigens leading to tissue destruction and production of autoantibodies. Common diseases like celiac disease have a complex pattern of inheritance with inputs from both environmental as well as additive and non-additive genetic factors. In the past few years, Genome Wide Association Studies (GWAS) have been successful in finding genetic risk variants behind many common diseases and traits. To complement and add to the previous findings, we performed a GWAS including 206 trios from 97 nuclear Swedish and Norwegian families affected with celiac disease. By stratifying for HLA-DQ, we identified a new genome-wide significant risk locus covering the DUSP10 gene. To further investigate the associations from the GWAS we performed pathway analyses and two-locus interaction analyses. These analyses showed an over-representation of genes involved in type 2 diabetes and identified a set of candidate mechanisms and genes of which some were selected for mRNA expression analysis using small intestinal biopsies from 98 patients. Several genes were expressed differently in the small intestinal mucosa from patients with celiac autoimmunity compared to intestinal mucosa from control patients. From top-scoring regions we identified susceptibility genes in several categories: 1) polarity and epithelial cell functionality; 2) intestinal smooth muscle; 3) growth and energy homeostasis, including proline and glutamine metabolism; and finally 4) innate and adaptive immune system. These genes and pathways, including specific functions of DUSP10, together reveal a new potential biological mechanism that could influence the genesis of celiac disease, and possibly also other chronic disorders with an inflammatory component.

Molecular diagnosis of celiac disease: are we there yet?

BACKGROUND

Celiac disease (CD) is a complex genetic disorder of the small intestine resulting from aberrant cellular responses to gluten peptides. It may affect as much as 1% of the Western population and the only treatment is a lifelong gluten-free diet. Allelic variants of the HLA-DQ locus, coding for the HLA-DQ2 and HLA-DQ8 molecules, contribute to ∼ 40% of CD etiology, whereas other genes, such as MYO9B, CTLA4, IL2, IL21, PARD3 and MAGI2, have only a modest effect. Most of these genes have shown varied association among different populations and an overlap with other autoimmune or inflammatory disorders, indicating that such disorders may share common pathways.

OBJECTIVES

In this review, a molecular approach into diagnostics of celiac disease is shown.

CONCLUSIONS

Genome-wide association studies will allow more genes to be identified, and knowing how risk variants combine will help to predict better the risk for the individual. HLA typing can already be used to identify high-risk individuals.

Prevalence of celiac disease and gluten sensitivity in the United States clinical antipsychotic trials of intervention effectiveness study population

Celiac disease (CD) and schizophrenia have approximately the same prevalence, but epidemiologic data show higher prevalence of CD among schizophrenia patients. The reason for this higher co-occurrence is not known, but the clinical knowledge about the presence of immunologic markers for CD or gluten intolerance in schizophrenia patients may have implications for treatment. Our goal was to evaluate antibody prevalence to gliadin (AGA), transglutaminase (tTG), and endomysium (EMA) in a group of individuals with schizophrenia and a comparison group. AGA, tTG, and EMA antibodies were assayed in 1401 schizophrenia patients who were part of the Clinical Antipsychotic Trials of Intervention Effectiveness study and 900 controls. Psychopathology in schizophrenia patients was assessed using the Positive and Negative Symptoms Scale (PANSS). Logistic regression was used to assess the difference in the frequency of AGA, immunoglobulin A (IgA), and tTG antibodies, adjusting for age, sex, and race. Linear regression was used to predict PANSS scores from AGA and tTG antibodies adjusting for age, gender, and race. Among schizophrenia patients, 23.1% had moderate to high levels of IgA-AGA compared with 3.1% of the comparison group (χ(2) = 1885, df = 2, P < .001.) Moderate to high levels of tTG antibodies were present in 5.4% of schizophrenia patients vs 0.80% of the comparison group (χ(2) = 392.0, df = 2, P < .001). Adjustments for sex, age, and race had trivial effects on the differences. Regression analyses failed to predict PANSS scores from AGA and tTG antibodies. Persons with schizophrenia have higher than expected titers of antibodies related to CD and gluten sensitivity.

Evaluation of 6 candidate genes on chromosome 11q23 for coeliac disease susceptibility: a case control study

Background

Recent whole genome analysis and follow-up studies have identified many new risk variants for coeliac disease (CD, gluten intolerance). The majority of newly associated regions encode candidate genes with a clear functional role in T-cell regulation. Furthermore, the newly discovered risk loci, together with the well established HLA locus, account for less than 50% of the heritability of CD, suggesting that numerous additional loci remain undiscovered. Linkage studies have identified some well-replicated risk regions, most notably chromosome 5q31 and 11q23.

Methods

We have evaluated six candidate genes in one of these regions (11q23), namely CD3E, CD3D, CD3G, IL10RA, THY1 and IL18, as risk factors for CD using a 2-phase candidate gene approach directed at chromosome 11q. 377 CD cases and 349 ethnically matched controls were used in the initial screening, followed by an extended sample of 171 additional coeliac cases and 536 additional controls.

Results

Promotor SNPs (-607, -137) in the IL18 gene, which has shown association with several autoimmune diseases, initially suggested association with CD (P < 0.05). Follow-up analyses of an extended sample supported the same, moderate effect (P < 0.05) for one of these. Haplotype analysis of IL18-137/-607 also supported this effect, primarily due to one relatively rare haplotype IL18-607C/-137C (P < 0.0001), which was independently associated in two case-control comparisons. This same haplotype has been noted in rheumatoid arthritis.

Conclusion

Haplotypes of the IL18 promotor region may contribute to CD risk, consistent with this cytokine's role in maintaining inflammation in active CD.

Fine mapping of the CELIAC2 locus on chromosome 5q31-q33 in the Finnish and Hungarian populations

Celiac disease is a chronic inflammation of the small intestine, arising in genetically predisposed individuals as a result of ingestion of dietary gluten. The only confirmed and functionally characterised genetic risk factors for celiac disease are the DQ2 or DQ8 heterodimers at the major histocompatibility complex (MHC) class II locus (CELIAC1). These genes are necessary but alone not sufficient for disease onset. Genome-wide linkage scans have suggested chromosome 5q31-q33 (CELIAC2) as an important risk locus for celiac disease. This region has also been associated to other inflammatory disorders, although as yet, no clear gene associations have been found. In the current study, 11 celiac disease candidate loci were screened for genetic linkage in the Hungarian population. As the CELIAC2 locus showed the strongest evidence for linkage, this locus was selected for follow-up. Seventeen candidate genes were selected from the CELIAC2 locus, and genotyped using 48 haplotype tagging single nucleotide polymorphisms (SNPs) in large Finnish and Hungarian family materials. A subset of these, 40 tagging SNPs in 15 genes, were genotyped in an independent set of Finnish and Hungarian cases and controls. We confirmed linkage of this region with celiac disease and report strong linkage in both the Finnish and Hungarian populations. The association analysis showed modest associations throughout the whole region. These association findings were not replicated in the case-control datasets. Our study strongly supports the role of the CELIAC2 locus in celiac disease, but it also highlights the need for a more powerful study design in the region, to locate the true disease risk variants.

Celiac disease: from pathogenesis to novel therapies

Celiac disease has become one of the best-understood HLA-linked disorders. Although it shares many immunologic features with inflammatory bowel disease, celiac disease is uniquely characterized by (1) a defined trigger (gluten proteins from wheat and related cereals), (2) the necessary presence of HLA-DQ2 or HLA-DQ8, and (3) the generation of circulating autoantibodies to the enzyme tissue transglutaminase (TG2). TG2 deamidates certain gluten peptides, increasing their affinity to HLA-DQ2 or HLA-DQ8. This generates a more vigorous CD4(+) T-helper 1 T-cell activation, which can result in intestinal mucosal inflammation, malabsorption, and numerous secondary symptoms and autoimmune diseases. Moreover, gluten elicits innate immune responses that act in concert with the adaptive immunity. Exclusion of gluten from the diet reverses many disease manifestations but is usually not or less efficient in patients with refractory celiac disease or associated autoimmune diseases. Based on the advanced understanding of the pathogenesis of celiac disease, targeted nondietary therapies have been devised, and some of these are already in phase 1 or 2 clinical trials. Examples are modified flours that have been depleted of immunogenic gluten epitopes, degradation of immunodominant gliadin peptides that resist intestinal proteases by exogenous endopeptidases, decrease of intestinal permeability by blockage of the epithelial ZOT receptor, inhibition of intestinal TG2 activity by transglutaminase inhibitors, inhibition of gluten peptide presentation by HLA-DQ2 antagonists, modulation or inhibition of proinflammatory cytokines, and induction of oral tolerance to gluten. These and other experimental therapies will be discussed critically.

Association between genotypes and phenotypes in coeliac disease

BACKGROUND

Coeliac disease (CD) is a genetically driven immunological intolerance to dietary gluten with a wide range of clinical presentations. The aim of this study was to investigate the heritability of the phenotype in CD and the influence on the phenotype of different genes associated with the disease.

PATIENTS AND METHODS

One hundred and seven families with at least 2 siblings with CD were collected. The patients were grouped in symptom grades on the basis of the clinical presentation, the age at diagnosis, and sex. Stratification analyses of the human leucocyte antigen-DQA1 and human leucocyte antigen-DQB1 genotypes, the CTLA4 +49A/G polymorphism, the CTLA4 haplotype MH30*G:-1147*T:+49*A:CT60*G:CT61*A, and the 5q31-33 loci were done.

RESULTS

The heritability of the phenotype was estimated to be 0.45. Significant association and linkage was found between the clinical presentation and the CTLA4 +49A/G polymorphism but not for the other genotypes. No correlation was found between genotypes and age at diagnosis or sex.

CONCLUSIONS

Our results indicate that the heritability is determiner of the phenotype in CD. The CTLA4 +49A/G polymorphism is correlated to the clinical presentation: the AA genotype is associated with clinically silent disease.

Meta-analysis of genome-wide linkage studies in celiac disease

OBJECTIVE

A meta-analysis of genome-wide linkage studies allows us to summarize the extensive information available from family-based studies, as the field moves into genome-wide association studies.

METHODS

Here we apply the genome scan meta-analysis (GSMA) method, a rank-based, model-free approach, to combine results across eight independent genome-wide linkages performed on celiac disease (CD), including 554 families with over 1,500 affected individuals. We also investigate the agreement between signals we identified from this meta-analysis of linkage studies and those identified from genome-wide association analysis using a hypergeometric distribution.

RESULTS

Not surprisingly, the most significant result was obtained in the HLA region. Outside the HLA region, suggestive evidence for linkage was obtained at the telomeric region of chromosome 10 (10q26.12-qter; p = 0.00366), and on chromosome 8 (8q22.2-q24.21; p = 0.00491). Testing signals of association and linkage within bins showed no significant evidence for co-localization of results.

CONCLUSION

This meta-analysis allowed us to pool the results from available genome-wide linkage studies and to identify novel regions potentially harboring predisposing genetic variation contributing to CD. This study also shows that linkage and association studies may identify different types of disease-predisposing variants.

Evidence for aberrant regulation of MAP kinase signal transduction pathway in peripheral blood mononuclear cells in patients with active celiac disease

BACKGROUND

Aberrant signaling via the p21/mitogen-activated proteins (MAP) kinase pathway has been described in lymphocytes of patients with various autoimmune diseases. There is little published data about the intracellular mediators and signals that regulate expression and activity of transcription factors and their effect on celiac disease induction and progression.

AIM

To investigate the possible involvement of MAP kinase pathway in peripheral blood mononuclear cells (PBMC) in celiac disease and its correlation with disease activity.

METHODS

Expression of the total and activated forms of two MAP kinases [extracellular response kinase (ERK) and c-Jun amino terminal kinase (JNK)] were studied by Western blots in PBMC of 17 untreated and 19 treated celiac patients, and 17 controls. Seven of these untreated celiac patients were studies before and after 6 months of gluten-free diet.

RESULTS

Phosphorylated ERK of active celiac disease patients was significantly lower compared with controls (P < 0.01) and was increased towards normal after 6 month of gluten-free diet (P < 0.01). Phosphorylated JNK was increased significantly in the untreated celiac group (P < 0.01) and normalized towards the control level after 6 months of gluten-free diet (P < 0.04).

CONCLUSIONS

Aberrant MAP-kinase pathway activity is associated with active celiac disease (CD). Further studies should examine the potential role of this aberration in pathogenesis of CD.

Variants within protectin (CD59) and CD44 genes linked to an inherited haplotype in a family with coeliac disease

Coeliac disease (CD) is an autoimmune disorder characterised by inflammation, villous atrophy and hyperplasia of the small intestinal mucosa that affects genetically susceptible individuals. A genome-wide scan was performed in 17 family members with high incidence of CD. Highest nonparametric linkage (NPL) and logarithm of odds (LOD) scores were of 6.21 (P = 0.0107) and 2.57, respectively, to a region on chromosome 11p13-12. Following fine mapping, NPL and LOD scores did not change, but the linkage interval on chromosome 11 was narrowed to a region that is approximately 50.94 cM from pTer. Two inherited haplotypes on chromosomes 11p13-12 and 9q21 were observed in all affected members but not in the majority of clinically normal individuals. Sequencing of genes at region 11p13-12 showed a number of sequence variants, two of which were linked with the inherited haplotype. One of these variants in the CD59 gene was found at a very low frequency in the population and could possibly affect pre-messenger RNA splicing. This study is of particular importance for the identification of novel genes that might be responsible for CD other than human leukocyte antigen.

Meta-analysis of genome-wide linkage studies across autoimmune diseases

Autoimmune diseases are chronic disorders initiated by a loss of immunologic tolerance to self-antigens. They cluster within families, and patients may be diagnosed with more than one disease, suggesting pleiotropic genes are involved in the aetiology of different diseases. To identify potential loci, which confer susceptibility to autoimmunity independent of disease phenotype, we pooled results from genome-wide linkage studies, using the genome scan meta-analysis method (GSMA). The meta-analysis included 42 independent studies for 11 autoimmune diseases, using 7350 families with 18 291 affected individuals. In addition to the HLA region, which showed highly significant genome-wide evidence for linkage, we obtained suggestive evidence for linkage on chromosome 16, with peak evidence at 10.0-19.8 Mb. This region may harbour a pleiotropic gene (or genes) conferring risk for several diseases, although no such gene has been identified through association studies. We did not identify evidence for linkage at several genes known to confer increased risk to different autoimmune diseases (PTPN22, CTLA4), even in subgroups of diseases consistently found to be associated with these genes. The relative risks conferred by variants in these genes are modest (<1.5 in most cases), and even a large study like this meta-analysis lacks power to detect linkage. This study illustrates the concept that linkage and association studies have power to identify very different types of disease-predisposing variants.

Fine mapping study in Scandinavian families suggests association between coeliac disease and haplotypes in chromosome region 5q32

The previous genome-wide scan in Scandinavian families supported earlier evidence for linkage of a region on chromosome 5 (5q31-33) to coeliac disease. This study deals with further genetic mapping of an 18 cM region, spanning from marker GAh18A (131.87 Mb) to D5S640 (149.96 Mb). Linkage and association analyses were performed in a two-step approach. First, seven microsatellites were added. Strong evidence for linkage was obtained with a Zlr score of 3.96, P(nc) = 4 x 10(-5) at marker D5S436. The strongest association was with a haplotype consisting of the markers D5S2033 and D5S2490 (P(nc) < 0.001). In the second step, we added 17 microsatellites and 69 single nucleotide polymorphisms (SNPs) to the analysis. These markers were located close to or within candidate genes across the region of approximately 7 Mb beneath the linkage peak marked by D5S2017 and D5S812. A substantial increase of the linkage signal with a maximum Zlr score of 4.6 at marker rs1972644 (P(nc) = 2 x 10(-6)) was obtained and several SNPs showed association. Seven SNPs that individually showed the strongest association were genotyped in a second independent family sample set (225 trios). In the trio family sample as well as in the multiplex family sample, the strongest association was found with SNPs within the region flanked by the associated microsatellites D5S2033 and D5S2490 at 5q32.

An autosomal genome-wide screen for celiac disease in Bedouin families

Celiac disease is a common, familial autoimmune disease caused by exposure to gliadin in wheat, and related prolamins in barley and rye. The prevalence of the disease is approximately 1:133. Celiac disease can cause significant morbidity. The only treatment is a gluten-free diet. A genome-wide search of 405 microsatellite markers was performed on samples from 18 Bedouin families with a minimum of two cases of celiac disease. Non-parametric and parametric (including both dominant and recessive models of inheritance) linkage analyses were performed. The most significant genome-wide linkage evidence was at chromosome 3p26 with an HLod of 3.21, under the dominant model. The only other HLod or NPL greater than 2 was at 4q35, with an HLod of 2.15 under a dominant model. The region at 3p26, previously reported in two linkage analyses, harbors interleukin receptor genes, plausible candidates for celiac disease.

Searching for genes influencing a complex disease: the case of coeliac disease

Recently, a few genes have been reported to be causative in inflammatory diseases. Still, we are waiting for the vast majority to be discovered. New tools for genotyping and statistical analysis have been developed and emphasis has been put on study design. Coeliac disease (CD) is a disorder, where prolamins in dietary wheat gluten and related proteins from rye or barley are not tolerated. It is one of the most common chronic diseases in humans exceeding a population prevalence of 1%. In this article, we will summarise what is currently known about the genetics influencing CD with the emphasis on the non-HLA genetic component. We will discuss some difficulties when searching for susceptibility genes in disorders with complex inheritance patterns.

Analysis of candidate genes on chromosomes 5q and 19p in celiac disease

BACKGROUND AND AIM

Celiac disease (CD) is a multifactorial disease with involvement of both environmental and genetic susceptibility factors. The HLA-DQ loci account for <40% of CD heritability, but linkage studies have delineated other loci at the 5q31-33 (CELIAC2), and 19p13 regions (CELIAC4), similarly as in inflammatory bowel diseases. However, data in association studies are contradictory. To evaluate whether single nucleotide polymorphisms (SNPs) tagging the MYO9B susceptibility haplotype and the IBD5 locus (5q31-33) are involved in CD predisposition, we performed case-control and family-based analyses. Additionally, any possible correlation with the HLA-DQ status was investigated. Finally, our data were pooled with the results of other studies by a meta-analysis.

PATIENTS AND METHODS

In all, 337 unrelated patients with CD, 424 parents (212 sets), and 452 healthy individuals were genotyped for the IGR2198a_1, rs12521868, rs1050152, and rs2631367 SNPs (IBD5 locus) and the rs962917, rs2305764, and rs1545620 SNPs of the MYO9B gene by the restriction enzyme method and the TaqMan system ABI PRISM 7700, respectively.

RESULTS

In comparison with healthy control individuals, the allele, genotype, and haplotype frequencies of all investigated SNPs were not different in the CD patients, nor was any correlation observed with the HLA-DQ status or clinical presentation. The transmission disequilibrium test did not show a transmission distortion. Five other studies were available for meta-analysis on MYO9B variants; by pooling of data, no significant association was demonstrated by the random effect model. A significant heterogeneity (P < 0.002) among the studies was present, mainly explained by a single study in the Dutch population.

CONCLUSIONS

Our results and those of the meta-analysis (>2000 CD patients and 4000 control individuals) question the role of MYO9B at the CELIAC4 locus as a disease-causing gene. Moreover, none of the investigated SNPs explain the linkage at the CELIAC2 locus.

A comprehensive screen for SNP associations on chromosome region 5q31–33 in Swedish/Norwegian celiac disease families

Celiac disease (CD) is a gluten-induced enteropathy, which results from the interplay between environmental and genetic factors. There is a strong human leukocyte antigen (HLA) association with the disease, and HLA-DQ alleles represent a major genetic risk factor. In addition to HLA-DQ, non-HLA genes appear to be crucial for CD development. Chromosomal region 5q31-33 has demonstrated linkage with CD in several genome-wide studies, including in our Swedish/Norwegian cohort. In a European meta-analysis 5q31-33 was the only region that reached a genome-wide level of significance except for the HLA region. To identify the genetic variant(s) responsible for this linkage signal, we performed a comprehensive single nucleotide polymorphism (SNP) association screen in 97 Swedish/Norwegian multiplex families who demonstrate linkage to the region. We selected tag SNPs from a 16 Mb region representing the 95% confidence interval of the linkage peak. A total of 1,404 SNPs were used for the association analysis. We identified several regions with SNPs demonstrating moderate single- or multipoint associations. However, the isolated association signals appeared insufficient to account for the linkage signal seen in our cohort. Collective effects of multiple risk genes within the region, incomplete genetic coverage or effects related to copy number variation are possible explanations for our findings.

Celiac disease: pathogenesis of a model immunogenetic disease

Celiac disease is characterized by small-intestinal mucosal injury and nutrient malabsorption in genetically susceptible individuals in response to the dietary ingestion of wheat gluten and similar proteins in barley and rye. Disease pathogenesis involves interactions among environmental, genetic, and immunological factors. Although celiac disease is predicted by screening studies to affect approximately 1% of the population of the United States and is seen both in children and in adults, 10%-15% or fewer of these individuals have been diagnosed and treated. This article focuses on the role of adaptive and innate immune mechanisms in the pathogenesis of celiac disease and how current concepts of immunopathogenesis might provide alternative approaches for treating celiac disease.

No evidence of association of the MYO9B polymorphisms with celiac disease in the Spanish population

Inconsistent results concerning the association of polymorphisms in the MYO9B gene with celiac disease (CD) have been recently published. This gene encodes a myosin with a guanosine-triphosphatase (GTPase)-activating protein domain for the Rho-family of small G proteins, which are involved in cytoskeleton remodeling and therefore potentially involved in intestinal permeability. Functional and positional reasons led us to investigate the role of MYO9B polymorphisms in the Spanish CD population. A case-control study, including 415 CD patients and 433 ethnically matched healthy controls, and a familial study, including parents of 145 of those CD patients, was performed. Six MYO9B variants previously associated with CD were analyzed: rs2305767, rs2279003, rs962917, rs1457092, rs2305765 and rs2305764. No MYO9B variants or MYO9B haplotypes were found associated with CD, either before or after stratification of the patients for the human leucocyte antigen (HLA)-DQ2-positive risk factor. The family study revealed no distorted transmission of the aforementioned MYO9B polymorphisms or haplotypes. Our results support a negligible influence of this gene on CD predisposition.

HLA genotyping is useful in the evaluation of the risk for coeliac disease in the 1st-degree relatives of patients with coeliac disease

OBJECTIVE

Coeliac disease (CD) is a common disease with a strong heredity. About 10-20% of 1st-degree relatives of probands develop CD. Relatives should be screened for CD, because if not treated, CD exposes patients to numerous complications. The heterogeneity of symptoms and the lifetime-spanning risk of CD render the timing of CD antibody and/or gastroscopy screenings difficult. As CD susceptibility has been shown to be strongly associated with the HLA alleles DQA1*0501 and DQB1*0201 (together encoding the DQ2 heterodimer) and DRB1*04 (associated with the DQ8 heterodimer), our aim was to investigate whether HLA genotyping might be useful in the identification of 1st-degree relatives of CD patients who do not need further screening for CD.

MATERIAL AND METHODS

The study comprised 54 Finnish CD families including 54 CD probands and 382 living 1st-degree relatives. All subjects who were willing to participate were screened for CD (duodenal and skin biopsies; endomysial, reticulin and gliadin antibodies). The DQA1*0501, DQB1*0201 and DRB1*04 allele frequencies of CD patients and the 1st-degree relatives were determined.

RESULTS

Altogether 17.6% (5.9% of the parents, 15.7% of the siblings, 25.8% of the offspring) of the investigated 1st-degree relatives (n = 245) did not carry any of the alleles studied. All of the CD patients (n = 136) with the exception of one (0.7%) carried at least one of the alleles investigated.

CONCLUSIONS

By using the HLA genotyping a considerable proportion of 1st-degree relatives of CD probands could be excluded from further screening for CD.

Celiac disease and HLA in a Bedouin kindred

We report the prevalence of celiac disease (CD) and its relationship with other autoimmune diseases and HLA haplotypes in a Bedouin kindred. Of 175 individuals sampled and typed for autoantibodies and HLA class II genotypes, six (3.4%) members had CD, and an additional 10 (5.7%) members tested positive for autoantibodies to transglutaminase (TgAA+). Several CD/TgAA+ relatives also had islet cell antigen or adrenal autoimmunity. Affected relatives are more closely related than expected from the pedigree relationships of all family members and were more often the offspring of consanguineous marriages. Individuals with CD or TgAA+ were enriched for DRB1*0301-DQA1*0501-DQB1*0201, a haplotype previously reported as high risk for CD. There was also an increased frequency of DQB1*0201/DQB1*0201 homozygotes among affected relatives. We found no evidence that DRB1*0701-DQA1*0201-DQB1*0201/DRB1*11-DQA1*0501-DQB1*0301 is a high-risk genotype, consistent with other studies of Arab communities. In addition, a nonparametric linkage analysis of 376 autosomal markers revealed suggestive evidence for linkage on chromosome 12p13 at marker D12S364 (NPL = 2.009, p = 0.0098). There were no other significant results, including the HLA region or any other previously reported regions. This could reflect the reduced power of family-based linkage and association analyses in isolated inbred populations.

A family-based study does not confirm the association of MYO9B with celiac disease in the Italian population

Association between Myosin IXB (MYO9B) gene polymorphisms and celiac disease (CD) was recently detected by a case-control association study in the Dutch, but not confirmed in the British and Swedish/Norwegian populations. We tested the association between CD and the three most associated single nucleotide polymorphisms (SNPs) in the Dutch study by the transmission disequilibrium test in the Italian population. A total of 252 pediatric patients and 504 parents were genotyped. No transmission distortion was detected either for the single SNPs or for their haplotypic combinations. Control allele frequencies, calculated from untransmitted alleles, were significantly different from those of the Dutch control population. Conversely, allele frequencies were very similar in Italian, British, Swedish/Norwegian and Dutch patients. In conclusion, MYO9B is not involved in CD susceptibility in the Italian population. The difference with the Dutch result might be explained by an imperfect selection of the Dutch controls.

Celiac disease

Celiac disease is an autoimmune disease that occurs in genetically predisposed individuals as the result of an immune response to gluten. This immune response occurs in both the lamina propria and the epithelium of the small intestine. There is a close link to HLA DQ2 and DQ8, although these HLA genes account for only 40% of the genetic influence. Environmental factors, such as the amount and timing of gluten administration in infancy, as well as breastfeeding, influence the disease. Serologic screening studies that use sensitive and specific antibody tests have revealed the disease to be common, occurring in approximately 1% of the population. Clinical presentations are diverse and atypical; the majority of patients lack diarrhea. Therapy is a gluten-free diet that requires avoidance of wheat, rye, and barley, although there is potential for other therapies based on our understanding of the pathophysiology of the disease.

Immunomodulatory strategies for celiac disease

Celiac disease (CD) is the most common food-sensitive enteropathy in humans and is caused by the lack of immune tolerance (oral tolerance) to gluten. The identification of gluten-specific T cells in the lamina propria of celiacs and the strong association with HLA-DQ2 and -DQ8 genes support a central role of CD4(+) T cells in CD pathogenesis. Studies focused on the modulation of autoimmunity in different experimental models highlighted possible immune therapeutic protocols useful also for the management of CD. On the basis of these observations, a series of strategies have been designed: some of them are based on the identification of immunogenic epitopes and their suppression via enzymatic treatment or by using peptide analogues; others rely on the delivery of unmodified antigen through the nasal route or coadministered with downregulatory cytokines. studies are generally early stage but encouraging in paving a way for an alternative treatment for celiac disease.

The gluten connection: the association between schizophrenia and celiac disease

OBJECTIVE

Schizophrenia affects roughly 1% of the population and is considered one of the top 10 causes of disability worldwide. Given the immense cost to society, successful treatment options are imperative. Based on initial findings, gluten withdrawal may serve as a safe and economical alternative for the reduction of symptoms in a subset of patients.

METHOD

A review of the literature relevant to the association between schizophrenia and celiac disease (gluten intolerance) was conducted.

RESULTS

A drastic reduction, if not full remission, of schizophrenic symptoms after initiation of gluten withdrawal has been noted in a variety of studies. However, this occurs only in a subset of schizophrenic patients.

CONCLUSION

Large-scale epidemiological studies and clinical trials are needed to confirm the association between gluten and schizophrenia, and address the underlying mechanisms by which this association occurs.

Gene dose effect of the DQB1*0201 allele contributes to severity of coeliac disease

OBJECTIVE

Coeliac disease (CD) susceptibility has been shown to be associated with the HLA alleles DQA1*0501 and DQB1*0201. This HLA-associated risk has been estimated to account for 29-40% of the genetic component of CD. Conflicting data have been published on the gene dose effect of these HLA alleles on the risk and severity of CD. In this study the aim was to investigate the association between the number of HLA risk alleles and the severity of CD.

MATERIAL AND METHODS

Fifty-four Finnish CD families, including 144 CD patients mainly diagnosed in adulthood (94.4%), were enrolled in the study. The association between the number of DQA1*0501 and DQB1*0201 alleles and villous atrophy, symptoms and laboratory parameters at the time of diagnosis, and the association with villous atrophy after one year of treatment on a gluten-free diet were studied.

RESULTS

The homozygosity for the DQB1*0201 allele was associated with a more severe form of CD assessed by more severe villous atrophy (p=0.011), younger age (p=0.036), more severe diarrhoea (p=0.048) and a lower level of blood haemoglobin at the time of diagnosis (p=0.010). Furthermore, the homozygosity for the DQB1*0201 allele was associated with a slower recovery of villous atrophy after a gluten-free diet (p=0.041). In contrast, the DQA1*0501 allele did not have a significant association with the severity of CD.

CONCLUSIONS

Our results demonstrate a gene dose effect of the DQB1*0201 allele on the clinical heterogeneity of CD and on the rate of recovery from villous atrophy in patients on a gluten-free diet.

"Coelionomics": towards understanding the molecular pathology of coeliac disease

Coeliac disease (CD) is an inflammatory disorder of the small intestine characterised by a permanent intolerance to gluten-derived peptides. When gluten-derived peptides reach the lamina propria in CD patients, they provoke specific changes in the mucosa of their small intestine. Although the susceptibility to CD is strongly determined by environmental gluten, it is clearly a common genetic disorder. Important genetic factors for CD are the HLA-DQ genes located in the MHC region on chromosome 6 [HLA-DQ2 (95%) or HLA-DQ8 ( approximately 5%) heterodimers]. So far, the only treatment for CD consists of a life-long gluten-free diet. A key question in CD is why the gluten-derived peptides are resistant to further breakdown by endogenous proteases and how, in turn, they can activate a harmful immune response in the lamina propria of genetically predisposed individuals. Four mechanisms, namely apoptosis, oxidative stress, matrix metalloproteinases and dysregulation of proliferation and differentiation, are thought to play a role in the pathophysiology of CD. Whether the genes involved in these four mechanisms play a causative role in the development of the villous atrophy or are, in fact, a consequence of the disease process is unknown. In this review we summarise these mechanisms and discuss their validity in the context of current insights derived from genetic, genomic and molecular studies. We also discuss future directions for research and the therapeutic implications for patients.

Haplotypes in the CTLA4 region are associated with coeliac disease in the Irish population

Chromosomal region 2q33 encodes the immune regulatory genes, CTLA4, ICOS and CD28, which are involved in regulation of T-cell activity and has been studied as a candidate gene locus in autoimmune diseases, including coeliac disease (CD). We have investigated whether an association exists between this region and CD in the Irish population using a comprehensive analysis for genetic variation. Using a haplotype-tagging approach, this gene cluster was investigated for disease association in a case-control study comprising 394 CD patients and 421 ethnically matched healthy controls. Several SNPs, including CTLA4_CT60, showed association with disease; however, after correction for multiple-testing, CTLA4-658C/T was the only polymorphism found to show significant association with disease when allele, genotype, or carrier status frequency were analysed (carrier status (Allele C), P = 0.0016). Haplotype analysis revealed a haplotype incorporating the CD28/CTLA4 and two 5' ICOS polymorphisms to be significantly associated with disease (patients 24.1%; controls 31.5%; P = 0.035), as was a shorter haplotype composed of the CTLA4 markers only (30.9 vs 34.9%; P = 0.042). The extended haplotype incorporating CD28/CTLA4 and 5' ICOS is more strongly associated with disease than haplotypes of individual genes. This suggests a causal variant associated with this haplotype may be associated with disease in this population.

Innate and adaptive immunity: the yin and yang of celiac disease

Celiac disease is a multigenetic complex inflammatory disorder with an autoimmune component, induced by gluten, a protein found in wheat. It is a unique human disease model to dissect the innate and adaptive immune mechanisms underlying T-cell-mediated tissue destruction and the development of T-cell lymphoma in conditions of chronic T-cell activation.

Gluten: a two-edged sword. Immunopathogenesis of celiac disease

Celiac disease (CD) is a small intestinal disorder caused by adaptive and innate immune responses triggered by the gluten proteins present in wheat. In the intestine, gluten is partially degraded and modified, which results in gluten peptides that bind with high affinity to HLA-DQ2 or HLA-DQ8 and trigger an inflammatory T cell response. Simultaneously, gluten exposure leads to increased production of IL15, which induces the expression of NKG2D on intraepithelial lymphocytes and its ligand MICA on epithelial cells, leading to epithelial cell destruction. The gluten-specific T cell response results in the production of antibodies against tissue transglutaminase and these are specific indicators of disease. CD is one of the most common inherited diseases, the HLA-DQ locus being the major contributing genetic factor. However, as the inheritance does not follow a Mendelian segregation pattern, multiple other genes, each with relative weak effect, contribute to disease development. An important role for environmental factors, however, can not be ignored as the concordance rate in monozygous twins is considerably less than 100%. The identification of these environmental factors and susceptibility genes may allow a better understanding of disease etiology and provide diagnostic and prognostic markers. The current treatment for CD consists of a life-long gluten-free diet. Although long thought to be impossible, recent results suggest that the development of nontoxic wheat varieties may be feasible, which would aid disease prevention and provide an alternative food source for patients.

Gene, gut and schizophrenia: the meeting point for the gene-environment interaction in developing schizophrenia

Both schizophrenia and celiac disease involve a genetic component. Several lines of evidence have shown a genetic relationship between these two conditions. Celiac disease is characterized by damage to the microscopic finger-like projections called villi, which line the small intestine and play a significant role in digestion, due to an inflammatory condition caused by a reaction to wheat gluten or related rye and barley proteins. Celiac disease represents not only malabsorption leading to a poor nutritional condition but also an alteration of gut permeability. Individuals with a history of a childhood celiac condition have a raised risk of developing schizophrenia. Psychotic symptoms often occur in adult celiac disease. It can be hypothesized that apart from malnutrition, the meeting point for the gene-environment interaction may be an alteration in gut permeability, in which the gut may lose its capacity to block exogenous psychosis-causing substances that may enter the body thus causing the development of schizophrenia and other mental conditions. To support this hypothesis, the conditional test was conducted to look at the combined effect of the CLDN5 gene involved in forming permeability barriers and the DQB1 gene that has been found to be associated with celiac disease. The results demonstrate that these two genes possibly work together in conferring a susceptibility to schizophrenia.

Association of the Matrix Metalloproteinase-3 (MMP-3) Promoter Polymorphism With Celiac Disease in Male Subjects

Matrix metalloproteinases (MMPs), such as stromelysin-1 (MMP-3), are a family of enzymes important in resorption and remodeling of the extracellular matrix whose degradation may play a role in the villous atrophy characteristic of celiac disease (CD). We investigated the association between the polymorphism at position -1171 of the MMP-3 gene and susceptibility to CD in 225 Italian patients and 170 controls previously typed for human leukocyte antigen (HLA) class II genes. We also evaluated sex differences in the effect of this polymorphism on disease risk. A male-specific association of the 5A/6A polymorphism with CD was observed. The frequencies of 6A allele and 6A/6A genotype in affected male subjects were significantly above those observed both in male controls (p = 4.1 x 10(-3) and p = 3.4 x 10(-3); odds ratio = 2.4, 95% confidence interval 1.3-4.3) and in female patients (p = 2.7 x 10(-4) and p = 6.2 x 10(-4)). This is the first demonstration of a sex-specific association between the MMP-3 promoter polymorphism and CD. Homozygosity for the 6A allele appears as a risk factor for CD only in men, which is different from the HLA susceptibility alleles that confer a higher risk in women.

Genetics in coeliac disease

Coeliac disease has a strong genetic component, higher than for many other common complex diseases. Possession of the HLA-DQ2 variant is required for presentation of disease causing dietary antigens to T cells, although this is also common in the healthy population. Non-HLA genetic factors account for the majority of heritable risk. Linkage studies have identified promising regions on chromosomes 5 and 19, with multiple other loci awaiting definitive confirmation in independent studies. Inherited variants in the tightly clustered chromosome 2q CD28-CTLA4-ICOS region are associated with disease, although of weak effect size. Larger sample sizes are necessary in coeliac disease genetic studies to detect small effects, alternatively meta-analysis offers promise. Newer methods including gene expression analysis and genome wide association studies will advance understanding of genetic susceptibility. Identification of coeliac disease genes may improve diagnostic/prognostic markers, basic understanding of disease aetiology, permit development of novel therapeutics and provide insight into other autoimmune disorders.

Chromosome 5q candidate genes in coeliac disease: Genetic variation at IL4, IL5, IL9, IL13, IL17B and NR3C1

Genetic predisposition to coeliac disease (CD) is determined primarily by alleles at the HLA-DQB locus, and evidence exists implicating other major histocompatibility complex-linked genes (6p21) and the CTLA4 locus on chromosome 2q33. In addition, extensive family studies have provided strong, reproducible evidence for a susceptibility locus on chromosome 5q (CELIAC2). However, the gene responsible has not been identified. We have assayed genetic variation at the IL4, IL5, IL9, IL13, IL17B and NR3C1 (GR) loci, all of which are present on chromosome 5q and have potential or demonstrated involvement in autoimmune and/or inflammatory disease, in a sample of 409 CD cases and 355 controls. Thirteen single nucleotide polymorphisms were chosen on the basis of functional relevance, prior disease association and, where possible, prior knowledge of the haplotype variation present in European populations. There were no statistically significant allele or haplotype frequency differences between cases and controls. Therefore, these results provide no evidence that these loci are associated with CD in this sample population.

A second-generation genomic screen for multiple sclerosis

Multiple sclerosis (MS) is a debilitating neuroimmunological and neurodegenerative disorder. Despite substantial evidence for polygenic inheritance of the disease, the major histocompatibility complex is the only region that clearly and consistently demonstrates linkage and association in MS studies. The goal of this study was to identify additional chromosomal regions that harbor susceptibility genes for MS. With a panel of 390 microsatellite markers genotyped in 245 U.S. and French multiplex families (456 affected relative pairs), this is the largest genomic screen for MS conducted to date. Four regions met both of our primary criteria for further interest (heterogeneity LOD [HLOD] and Z scores >2.0): 1q (HLOD=2.17; Z=3.38), 6p (HLOD=4.21; Z=2.26), 9q (HLOD; Z=2.71), and 16p (HLOD=2.64; Z=2.05). Two additional regions met only the Z score criterion: 3q (Z=2.39) and 5q (Z=2.17). Further examination of the data by country (United States vs. France) identified one additional region demonstrating suggestive linkage in the U.S. subset (18p [HLOD=2.39]) and two additional regions generating suggestive linkage in the French subset (1p [HLOD=2.08] and 22q [HLOD=2.06]). Examination of the data by human leukocyte antigen (HLA)-DR2 stratification identified four additional regions demonstrating suggestive linkage: 2q (HLOD=3.09 in the U.S. DR2- families), 6q (HLOD=3.10 in the French DR2- families), 13q (HLOD=2.32 in all DR2+ families and HLOD=2.17 in the U.S. DR2+ families), and 16q (HLOD=2.32 in all DR2+ families and HLOD=2.13 in the U.S. DR2+ families). These data suggest several regions that warrant further investigation in the search for MS susceptibility genes.

Genetic association of coeliac disease susceptibility to polymorphisms in the ICOS gene on chromosome 2q33

An interesting candidate gene region for coeliac disease (CD), a common multifactorial disease, is a segment on 2q33-37 harbouring the genes for the CD28, cytotoxic T-lymphocyte-associated antigen-4 (CTLA4), inducible costimulator (ICOS), and programmed death-1 (PD-1), all receptors that regulate lymphocyte activation. Several studies have suggested a role for this locus in immune-mediated diseases. To study further our previous finding of genetic linkage of this region to CD, we studied 25 polymorphic markers to identify the putative disease-associated polymorphism. Transmission/disequilibrium test in 106 Finnish families with CD indicated that only four polymorphisms, all located in the ICOS gene, showed evidence for genetic association. Strong linkage disequilibrium (LD), based on the analysis of 424 haplotypes, encompassed not only the associated ICOS markers but also many polymorphisms in the CTLA4 gene. Our results demonstrate that due to LD, it appears not easy to identify the genuine susceptibility factor in this region without larger multipopulation studies. Furthermore, the results did not support the evidence that polymorphisms in CTLA4 were the major susceptibility locus for CD.

[Genetics and immunopathogenics aspects of the celiac disease: a recent vision]

BACKGROUND

Celiac disease, or gluten-sensitive enteropathy, is a strongly inherited condition. Although the genetic association of CD with the DQ2 and DQ8 HLA haplotypes has been known for long, others HLA and non-HLA genes are also important in the development of the disease. Celiac disease results of the combined effect of different normally functioning genes' products. The tissue damage in celiac disease is immunologically mediated and several effector mechanisms are responsible for the disease expression. The interplay between genetic, immunological and environmental factors explains the large spectrum of clinical, histological and serological alterations observed in the different stages of the disease development, pointing out to the polygenic nature of celiac disease.

CONCLUSION

The recent advances in the understanding of the immunopathogenesis, genetics and diagnoses of celiac disease have allowed the revision of strict concepts and previous criteria and their adequation to the new evidences, aiming a better diagnostic and orientation to celiac patients and relatives.

Emerging concepts in celiac disease

PURPOSE OF REVIEW

There has been an explosion in knowledge about celiac disease (CD) in the last decade based on the availability of serologic screening tests and the elucidation of some of the important disease susceptibility genes. What has been discovered is that CD is among the most common inherited diseases with a worldwide prevalence of almost 1% of the population. Also, there has been a tremendous expansion of the possible clinical presentations in patients with CD, many of them predominantly or even exclusively extraintestinal. Over the last year, both the North American Society of Pediatric Gastroenterology and Nutrition, and the NIH, through the mechanism of a consensus development conference held in May 2004, have published guidelines outlining the current state of knowledge and the areas where more research is needed.

RECENT FINDINGS

This review will stress the most recent findings in CD in the areas of genetics, pathogenesis, epidemiology, screening and diagnosis, and natural history. It will stress the importance of HLA DQ2 and DQ8 as disease susceptibility genes, and the interaction of the environmental triggers (gliadins and glutenins) with these gene products to trigger the immunologic response in the gut that is responsible for the pattern of injury. Recent reports that stress the importance of screening high-risk groups (i.e. siblings of index cases and first degree relatives, patients with Type I diabetes, patients with Downs syndrome, patients with IgA deficiency) will be highlighted. The identification of the most sensitive and specific screening tests will be summarized with an explanation of special situations that affect the interpretation of these tests. Finally, the long-term morbidities associated with CD will be characterized supporting the case for early diagnosis and treatment.

SUMMARY

The implications of these recent findings are of tremendous importance for both pediatricians and internists. Screening of high-risk groups, and of patients with the common symptoms of irritable bowel syndrome, iron deficiency anemia, unexplained arthritis, and even chronic elevations of aminotransferases is becoming the accepted standard of practice. Much research remains to be done to further refine our understanding of CD, and to devise more effective strategies for treatment, compliance, and prevention of long-term complications.

Candidate gene region 2q33 in European families with coeliac disease

Chromosome region 2q33 harbours a cluster of genes, CTLA-4, CD28, ICOS and closely located PD-1, all related to immune activation and considered as promising candidate genes for susceptibility to coeliac disease (CD). We present here the results of a genetic linkage and association analysis of nine markers located in this gene region in a large combined European material of 796 families with CD from Finland, Sweden, Norway, UK, France and Italy. The joint analysis supports earlier findings that this susceptibility locus, assigned as CELIAC3, merits further studies. Nominally significant linkage to CD was found in 314 families including affected sib pairs. Each of the five populations showed weak associations to several marker alleles, but the analysis revealed, however, no conclusive evidence for a primary functional gene or gene variant present in the total set of families. The results suggest that the CD risk due to 2q33 gene region is complex and may involve more than one susceptibility allele, which possibly differ from other autoimmune diseases.

Haplotype variation at the IBD5/SLC22A4 locus (5q31) in coeliac disease in the Irish population

In addition to the well-established association of coeliac disease (CD) with HLA-DQ (6p21) and possibly CTLA4 (2q33), there is considerable evidence for a susceptibility locus on chromosome 5q, which contains many potential candidates for inflammatory disease, including a cluster of cytokine genes in 5q31. CD cases and controls were genotyped for four single-nucleotide polymorphism (SNP) markers that together characterize >90% of the haplotype variation at the IBD5 locus encoding, among others, the SLC22A4 gene. IBD5 and SLC22A4 map to 5q31 and have recently been associated with Crohn's disease and rheumatoid arthritis. Haplotype frequencies do not differ significantly between CD cases and controls in the Irish population, and therefore the chromosome 5 CD susceptibility locus most likely lies elsewhere on 5q.

Meta and pooled analysis of European coeliac disease data

Four full genome scans have been carried out by the partners of the European cluster on coeliac disease as well as follow-up studies of candidate regions. No region outside HLA showed significant linkage to the disease in any single study. We first applied a meta-analysis based on a modification of Genome Screen Meta-Analysis to take into account the different linkage statistics, the arbitrariness of bin cutoff points, as well as the sample size of each study. We then performed a pooled linkage analysis of all families and raw genotypes. Besides the HLA region, already known to harbour a risk factor for coeliac disease, both approaches leave very little doubt on the presence of a genetic risk factor in the 5q31-33 region. This region was suggested by several individual studies, but did not reach statistical values high enough to be conclusive when data sets were analysed separately.

cDNA microarray analysis of gene expression in coeliac disease jejunal biopsy samples

In coeliac disease in the jejunum of a genetically susceptible person wheat gliadin and related prolamins from rye and barley trigger an immunological reaction, which induces small-bowel mucosal transformations, villous atrophy and crypt hyperplasia. Though CD4+ specific T cells, intraepithelial lymphocytes, infiltrating plasma cells and autoantibodies are known to have an effect on the coeliac disease, the pathogenic mechanisms leading to the tissue injury remain to be elucidated. Our aim was to find novel gene transcripts, which might have a role in coeliac disease pathogenesis. The gene expression in duodenal biopsy samples from untreated coeliac patients (n=4), patients on gluten-free diet (n=4) and healthy controls (n=4) was studied by cDNA microarray analysis. The method allows monitoring of the expression of thousands of genes simultaneously. Compared to healthy controls, the expression of 156 and 60 genes was changed in untreated and treated coeliac disease, respectively. Between treated and untreated coeliac disease, 98 genes had altered expression. Of the 5184 genes or expressed sequence tags, altogether 263 were affected. Many of these genes are directly or indirectly connected to T-cell activation, B-cell maturation or epithelial cell differentiation. By the microarray method, numerous genes were found to evince altered mRNA expression in coeliac disease. The method holds promise in exploring the pathogenetic mechanisms in the small bowel and may reveal new target genes for the therapy of coeliac disease.

The risk of celiac disease in 107 families with at least two affected siblings

OBJECTIVES

Screening for celiac disease (CD) in the apparently healthy members of 107 nuclear families with two affected siblings (sib pair) and estimating the risk of CD in siblings and parents.

METHODS

One hundred seven families from Sweden and southern Norway with at least two affected children were investigated. Frozen sera from 187 of the 192 healthy parents and from 94 of 95 siblings without diagnosed CD were examined for total immunoglobulin A (IgA) and anti-endomysial antibodies (EMA). Individuals with positive antibody titers underwent small intestinal biopsy.

RESULTS

Positive test for EMA was found in 6 of 94 (6.3%) siblings without previously diagnosed CD and in 8 of 189 (4.2%) parents. CD was confirmed by small intestinal biopsy in all siblings and seven parents. The estimated risk for CD in multiply affected families was 26.3% for siblings and 12.9% for parents. An unexpected male preponderance was found among the new CD cases (10 males, 3 females).

CONCLUSION

The risk of CD in the members of nuclear families with two affected children is approximately three times higher than that when only one child is affected. The high male preponderance of new cases is unexpected and could not be explained fully by more silent disease in males as compared with females. Considering the high level of knowledge about CD in these families, the number of undiagnosed cases is surprisingly high. The authors suggest that serologic screening should be offered to all first-degree relatives of patients with CD.

A genomewide screen in a four-generation Dutch family with celiac disease: evidence for linkage to chromosomes 6 and 9

OBJECTIVES

Celiac disease is caused by the interaction of multiple genes and environmental factors. Inheritance of the disease shows a complex pattern with a 10% sibling recurrence risk. The HLA-region is a major genetic risk locus in celiac disease, but genes outside this region are expected to contribute to the disease risk as well. The aim of this study was to identify the loci causing celiac disease in one large Dutch family with apparent dominant transmission of the disease.

METHODS

The family comprised 17 patients in four generations, with possible transmission of the disease by both grandparents. Microsatellite markers evenly spread over all chromosomes were genotyped and linkage analysis was performed using both dominant and recessive disease models and a model-free analysis.

RESULTS

Disease susceptibility in the family was linked to the HLA-region (lod score of 2.33) and all patients were HLA-DQ2. A dominantly inherited non-HLA locus with a maximum lod score of 2.61 was detected at 9p21-13, which was shared by 16 patients. Model-free analysis identified another possible non-HLA locus, at 6q25.3, which was shared by 14 patients (p = 0.01). Neither of these regions was detected in a genomewide screen in Dutch affected sibpairs, but the 9p21 locus has been implicated in Scandinavian families.

CONCLUSIONS

Two potential non-HLA loci for celiac disease were identified in this large Dutch family. Our results provide replication of the Scandinavian 9p21 locus, and suggest that this locus plays a role in celiac disease patients from different Caucasian populations.