Association analysis of MYO9B gene polymorphisms with celiac disease in a Swedish/Norwegian cohort

Understanding the Genetic Basis of Celiac Disease: A Comprehensive Review

Celiac disease is an immune-mediated enteropathy with typical symptoms of weight loss, abdominal bloating, diarrhea, vomiting, or constipation. Many shreds of evidence show that CeD is hereditary in origin and various biochemical pathways have been connected to its etiology. Numerous genes from different physiological pathways have been investigated in the last few decades, however a comprehensive analysis is required to address the gaps and provide a more integrated understanding of how these genetic factors contribute to the pathogenesis of disease. Present study attempts to summarize the historical and up-to-date findings to understand the role of genetics in Celiac disease. The literature was searched from sources such as PubMed and Google Scholar to analyze studies conducted on celiac disease from the years 1995 to 2024. Term maps were created to examine the frequency of studies related to various terms to understand the major focus of the studies till date. The study also concise the different genetic polymorphisms studied in a table to understand the role of genetics in celiac diseases. Early studies on celiac disease primarily focused on its pathophysiology, prevalence, and general aspects, with limited attention to genetics. However, recent studies have increasingly emphasized the genetic basis of the disease and highlighting the involvement of various pathways like inflammation, T-cell differentiation and activation, epithelial barrier function, stress and apoptosis pathways. However, present study indicate that most current research predominantly focus on cytokines, specifically the TNF alpha gene. Consequently, there is a need for additional research to gain a more comprehensive understanding of the genetics of celiac disease.

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.

MAGI2 Gene Region and Celiac Disease

Celiac disease (CD) patients present a loss of intestinal barrier function due to structural alterations in the tight junction (TJ) network, the most apical unions between epithelial cells. The association of TJ-related gene variants points to an implication of this network in disease susceptibility. This work aims to characterize the functional implication of TJ-related, disease-associated loci in CD pathogenesis. We performed an association study of 8 TJ-related gene variants in a cohort of 270 CD and 91 non-CD controls. The expression level of transcripts located in the associated SNP region was analyzed by RT-PCR in several human tissues and in duodenal biopsies of celiac patients and non-CD controls. (si)RNA-driven silencing combined with gliadin in the Caco2 intestinal cell line was used to analyze the implication of transcripts from the associated region in the regulation of TJ genes. We replicated the association of rs6962966^*A variant [p = 0.0029; OR = 1.88 (95%1.24–2.87)], located in an intron of TJ-related MAGI2 coding gene and upstream of RP4-587D13.2 transcript, bioinformatically classified as a long non-coding RNA (lncRNA). The expression of both genes is correlated and constitutively downregulated in CD intestine. Silencing of lncRNA decreases the levels of MAGI2 protein. At the same time, silencing of MAGI2 affects the expression of several TJ-related genes. The associated region is functionally altered in disease, probably affecting CD-related TJ genes.

The intestinal epithelial barrier: a therapeutic target?

A fundamental function of the intestinal epithelium is to act as a barrier that limits interactions between luminal contents such as the intestinal microbiota, the underlying immune system and the remainder of the body, while supporting vectorial transport of nutrients, water and waste products. Epithelial barrier function requires a contiguous layer of cells as well as the junctions that seal the paracellular space between epithelial cells. Compromised intestinal barrier function has been associated with a number of disease states, both intestinal and systemic. Unfortunately, most current clinical data are correlative, making it difficult to separate cause from effect in interpreting the importance of barrier loss. Some data from experimental animal models suggest that compromised epithelial integrity might have a pathogenic role in specific gastrointestinal diseases, but no FDA-approved agents that target the epithelial barrier are presently available. To develop such therapies, a deeper understanding of both disease pathogenesis and mechanisms of barrier regulation must be reached. Here, we review and discuss mechanisms of intestinal barrier loss and the role of intestinal epithelial barrier function in pathogenesis of both intestinal and systemic diseases. We conclude with a discussion of potential strategies to restore the epithelial barrier.

IBD candidate genes and intestinal barrier regulation

Technological advances in the large scale analysis of human genetics have generated profound insights into possible genetic contributions to chronic diseases including the inflammatory bowel diseases (IBDs), Crohn's disease and ulcerative colitis. To date, 163 distinct genetic risk loci have been associated with either Crohn's disease or ulcerative colitis, with a substantial degree of genetic overlap between these 2 conditions. Although many risk variants show a reproducible correlation with disease, individual gene associations only affect a subset of patients, and the functional contribution(s) of these risk variants to the onset of IBD is largely undetermined. Although studies in twins have demonstrated that the development of IBD is not mediated solely by genetic risk, it is nevertheless important to elucidate the functional consequences of risk variants for gene function in relevant cell types known to regulate key physiological processes that are compromised in IBD. This article will discuss IBD candidate genes that are known to be, or are suspected of being, involved in regulating the intestinal epithelial barrier and several of the physiological processes presided over by this dynamic and versatile layer of cells. This will include assembly and regulation of tight junctions, cell adhesion and polarity, mucus and glycoprotein regulation, bacterial sensing, membrane transport, epithelial differentiation, and restitution.

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.

Myo9B is associated with an increased risk of Barrett's esophagus and esophageal adenocarcinoma

BACKGROUND

Reflux esophagitis (RE) and Barrett's esophagus (BE) are predisposing factors for development of esophageal adenocarcinoma (EAC), the solid tumor with the fastest rising incidence in the Western world. This RE-BE-EAC cascade involves multiple host factors and consequently multiple genes. Polymorphisms in the 3' region of myosin IXB (Myo9B) are associated with chronic inflammatory gastrointestinal disorders like celiac disease and ulcerative colitis, assuming that variation in Myo9B influences the intestinal permeability.

AIM

To determine esophageal expression and the genetic variation of the Myo9B gene in the RE-BE-EAC cascade.

METHODS

DNA from 886 Caucasian participants (198 non-reflux controls, 305 RE, 254 BE, 129 EAC) was collected for the determination of the Myo9B gene polymorphism (rs2305764). Esophageal Myo9B expression was determined on biopsies from normal, RE, BE and EAC epithelium.

RESULTS

Genotype G/G was more common in BE (p = 0.032) and EAC (p = 0.046), but not in RE (p = 0.126) compared with the control group. Cytoplasmic Myo9B expression was determined in RE, BE and EAC, but most prominent in epithelial cells of BE and EAC.

CONCLUSIONS

Genetic variation of Myo9B may play a role in the etiology of BE and EAC by increasing the permeability of the epithelial barrier.

No association observed between schizophrenia and non-HLA coeliac disease genes: integration with the initial MYO9B association with coeliac disease

Schizophrenia is a severe psychotic illness with a heterogeneous presentation and a devastating impact on social and occupational function. Worldwide variations in schizophrenia incidence rates suggest that local conditions may modify disease risk. The human leukocyte antigen (HLA) region has been confirmed to be associated with schizophrenia by genome-wide association studies in populations across the world. While the presence of autoimmune processes in a subgroup of schizophrenia cases is contentious, the immune system could allow environmental exposures to lead to schizophrenia by generating improper immune response. To investigate this topic, we reviewed the current evidence of the relationship between schizophrenia and coeliac disease. Based on this review, we performed genetic analysis of the MYO9B gene and the IL-2/IL-21 locus by genotyping SNPs that have been previously associated with coeliac disease or schizophrenia in 223 families, 108 unrelated individuals with schizophrenia and 120 controls. Finding no evidence for association with these two loci in our study samples, we applied meta-analytic techniques to combine our findings with previous reports. This synthesis, in light of our review of previous reports, suggests a differing developmental trajectory for schizophrenia and coeliac disease. It is possible that these two conditions do not share any functional overlap.

Dermatitis herpetiformis. Part I. Epidemiology, pathogenesis, and clinical presentation

Dermatitis herpetiformis (DH) is an autoimmune disease that is linked to gluten sensitivity and has a clear relationship to celiac disease. Both conditions are mediated by the IgA class of autoantibodies and the diagnosis of DH is dependent on detection of granular deposits of IgA in the skin. There is an underlying genetic predisposition to the development of DH but environmental factors are also important. Typically, young adults present with excoriations only, as the severe pruritus effectively destroys any primary lesions. Based upon our experience with DH and a comprehensive literature review, we provide an update of DH epidemiology, pathophysiology, and clinical presentation.

The R30Q DLG5 variant is not associated with celiac disease or inflammatory bowel disease in the Spanish population

Alterations in intestinal epithelial permeability could underlie inflammatory bowel disease (IBD) and celiac disease (CeD) etiology, as supported by previous association studies. One related gene, DLG5 [discs, large homologue 5 (Drosophila)], has been associated with IBD in several populations and with CeD in the Dutch population. We tried to confirm the involvement of DLG5 in CeD performing a case-control study (725 CeD patients and 803 controls) by analysing the R30Q variant (rs1248696). Genetic frequencies did not significantly differ between groups (P > 0.80) and the meta-analysis with the Dutch data did not show any association. Additionally, we evaluated the effect of R30Q in IBD risk (858 patients), as discordant results were previously obtained. No association was detected. Our study does not support the effect of the R30Q DLG5 variant in CeD or IBD predisposition in the Spanish population.

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.

Association between genetic variants in myosin IXB and Crohn's disease

BACKGROUND

Genetic variation in myosin IXB (MYO9B) was found to be associated with ulcerative colitis (UC) in a recent collaborative study. A nonsynonymous single nucleotide polymorphism (SNP) rs1545620 at the 3' end of the gene was found to be significantly associated with UC and weakly associated with Crohn's disease (CD). The aim of our current study was to replicate these findings in an independent UC cohort and to investigate association with CD. We also investigated subphenotype association and interactions with CARD15, IL23R, ATG16L1, and the IBD5 risk haplotype.

METHODS

In all, 652 CD patients, 650 UC patients, and 1190 controls were genotyped for 8 MYO9B SNPs. Haplotype testing, epistasis testing with known polymorphisms, and subphenotype analysis were performed.

RESULTS

An intronic SNP rs2305767 in the MYO9B gene was associated with inflammatory bowel disease (IBD) overall (corrected P-value 0.002, odds ratio [OR] 0.76, 95% confidence interval [CI] 0.67-0.86). On individual disease analysis an association was found with CD (corrected P-value 0.001, OR 0.62, 95% CI 0.53-0.73) but not with UC. Analysis of the common MYO9B haplotypes showed significant association for CD and UC alone and IBD overall. No subphenotypic association was found. These data support an association between CD and SNPs in MYO9B independent of the established effects of SNPs in CARD15, IL23R, ATG16L1, and the IBD5 haplotype. There was no evidence of epistasis between SNPs in MYO9B and these established genes.

CONCLUSIONS

MYO9B variants may be involved in IBD pathogenesis.

Translational mini-review series on the immunogenetics of gut disease: immunogenetics of coeliac disease

Recent advances in immunological and genetic research in coeliac disease provide new and complementary insights into the immune response driving this chronic intestinal inflammatory disorder. Both approaches confirm the central importance of T cell-mediated immune responses to disease pathogenesis and have further begun to highlight other relevant components of the mucosal immune system, including innate immunity and the control of lymphocyte trafficking to the mucosa. In the last year, the first genome wide association study in celiac disease led to the identification of multiple new risk variants. These risk regions implicate genes involved in the immune system. Overlap with autoimmune diseases is striking with several of these regions being shown to confer susceptibility to other chronic immune-mediated diseases, particularly type 1 diabetes.

Combined functional and positional gene information for the identification of susceptibility variants in celiac disease

BACKGROUND & AIMS

Celiac disease is a complex, immune-mediated disorder of the intestinal mucosa with a strong genetic component. HLA-DQ2 is the major determinant of risk, but other minor genes, still to be identified, also are involved.

METHODS

We designed a strategy that combines gene expression profiling of intestinal biopsy specimens, linkage region information, and different bioinformatics tools for the selection of potentially regulatory single-nucleotide polymorphisms (SNPs) involved in the disease. We selected 361 SNPs from 71 genes that fulfilled stringent functional (changes in expression level) and positional criteria (located in regions that have been linked to the disease, other than HLA). These polymorphisms were genotyped in 262 celiac patients and 214 controls.

RESULTS

We detected strong evidence of association with several SNPs (the most significant were rs6747096, P = 2.38 x 10(-5); rs7040561, P = 6.55 x 10(-5); and rs458046, P = 1.35 x 10(-4)) that pinpoint novel candidate determinants of predisposition to the disease in previously identified linkage regions (eg, SERPINE2 in 2q33, and PBX3 or PPP6C in 9q34).

CONCLUSIONS

Our study shows that the combination of function and position is a valid strategy for the genetic dissection of complex traits.

Genetic background of celiac disease and its clinical implications

Celiac disease (CD) 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 identified are HLA-DQ2 and HLA-DQ8, which are necessary but not sufficient to predispose to CD. The associations found in non-HLA genomewide linkage and association studies are much weaker. This might be because a large number of non-HLA genes contributes to the pathogenesis of CD. Hence, the contribution of a single predisposing non-HLA gene might be quite modest. Practically all CD patients carry HLA-DQ2 or HLA-DQ8, while the absence of these molecules has a negative predictive value for CD close to 100%. Genetic risk profiles for CD would be helpful in clinical practice for predicting disease susceptibility and progression.

The MYO9B gene is a strong risk factor for developing refractory celiac disease

BACKGROUND & AIMS

Celiac disease (CD) is associated with HLA-DQ2 and HLA-DQ8 and has been linked to genetic variants in the MYO9B gene on chromosome 19. HLA-DQ2 homozygosity is associated with complications of CD such as refractory celiac disease type II (RCD II) and enteropathy-associated T-cell lymphoma (EATL). We investigated whether MYO9B also predisposes to RCD II and EATL.

METHODS

Genotyping of MYO9B and molecular HLA-DQ2 typing were performed on 62 RCD II and EATL patients, 421 uncomplicated CD patients, and 1624 controls.

RESULTS

One single nucleotide polymorphism in MYO9B showed a significantly different allele distribution in RCD II and EATL patients compared with controls (P = .00002). The rs7259292 T allele was significantly more frequent in RCD II and EATL patients compared with CD patients (P = .0003; odds ratio [OR], 3.61; 95% confidence interval [CI], 1.78-7.31). The frequency of the haplotype carrying the T allele of this single nucleotide polymorphism was significantly increased in RCD II and EATL patients (11%), compared with controls (2%) and CD patients (3%) (OR, 6.76; 95% CI, 3.40-13.46; P = 2.27E-09 and OR, 4.22; 95% CI, 1.95-9.11; P = .0001, respectively). Both MYO9B rs7259292 and HLA-DQ2 homozygosity increase the risk for RCD II and EATL to a similar extent when compared with uncomplicated CD patients (OR, 4.3; 95% CI, 1.9-9.8 and OR, 5.4; 95% CI, 3.0-9.6, respectively), but there was no evidence for any interaction between these 2 risk factors.

CONCLUSIONS

We show that both MYO9B and HLA-DQ2 homozygosity might be involved in the prognosis of CD and the chance of developing RCD II and EATL.

Genetic analyses of celiac disease in a Spanish population confirm association with CELIAC3 but not with CELIAC4

Genetic predisposition to celiac disease (CD) is determined primarily by the human leukocyte antigen (HLA) genes (CELIAC1 region; 6p21), although many loci are involved in disease susceptibility. First, we have analysed a large series of CD patients from the Spanish Mediterranean region who had previously been characterised for the HLA complex. We have investigated how relevant regions contribute to CD susceptibility: CELIAC3 (CD28/CTLA4/ICOS region on 2q33) and CELIAC4 (19p13) as well as the tumour necrosis factor alpha (TNF-alpha) and the linfotoxin loci by case-control and association analyses. We highlight the association with the +49*A allele of cytotoxic T-lymphocyte-associated antigen 4 locus (P = 0.01), and the -308*A of TNF-alpha locus (P = 0.0008) in DQ2 individuals, although an independent role for TNF-alpha as risk factor has not been proven. Moreover, we do not confirm the association with the CELIAC4 region polymorphisms described in other populations.

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.

MYO9B gene polymorphisms are associated with autoimmune diseases in Spanish population

The aim of the study was to test MYO9B gene polymorphisms for association with three autoimmune diseases, systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and celiac disease (CD), in a Spanish population. We analyzed three SNPs (rs2305767, rs1457092, and rs2305764) in a case-control cohort composed of 349 SLE patients, 356 RA patients, 90 CD patients, and 345 healthy controls. All three SNPs showed a consistent increased frequency of the A allele in SLE, RA, and CD patients compared with healthy controls. An association was observed between CD and rs2305764 (p=0.01, OR=2.3), between SLE and rs1457092 (p=0.002, OR=1.4), and between RA and rs1457092 (p=0.02, OR=1.3). The three autoimmune diseases combined showed significant association with rs1457092 and rs2305764 and with the AAA haplotype (p haplotype=0.005, OR=1.3). Our data demonstrate consistent association with the A allele and AAA haplotype of three SNPs in the MYO9B gene, which were previously reported to be associated with CD in the Dutch population. This suggests that genetic variation in MYO9B is associated with CD, SLE, and RA and that MYO9B is a general risk factor for autoimmunity.

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.

Genetics of the innate immune response in inflammatory bowel disease

The discovery of nucleotide-binding oligomerization domain 2/caspase recruitment domain-containing protein 15 (NOD2/CARD15) as the first susceptibility gene in Crohn's disease (CD) has shifted the focus of research into the pathogenesis of inflammatory bowel disease (IBD) firmly to the innate immune response and the integrity of the epithelial barrier. The subsequent implication in IBD of variant alleles of OCTN, DLG5, MDR1, and TLRs has provided further support for a new, more complex model of innate immunity function in the gastrointestinal tract. In this review, we examine the recent advances in our understanding of the influence of genetics of the innate immune response on IBD. We will focus on germline variation of genes encoding pathogen-recognition receptors, proteins involved in epithelial homeostasis and secreted antimicrobial proteins.

Do MYO9B genetic variants predispose to coeliac disease? An association study in a cohort of South Italian children

BACKGROUND

Coeliac disease is a complex disorder influenced by environmental and genetic factors. A genome wide linkage study identified the myosin IXB (MYO9B) as a gene possibly associated with coeliac disease. Recently, a Dutch study reported a strong association of a single SNP, rs 2305764, of MYO9B with coeliac disease. However, two successive studies carried out on British and Swedish/Norwegian cohorts reported lack of association of the MYO9B variant with coeliac disease.

AIMS

The aim of the present study is to verify the effects of the MYO9B rs 2305764 polymorphism on disease risk in a Mediterranean population of coeliac children.

PATIENTS AND METHODS

To address this issue, an association study was performed in 223 (127 females) Italian coeliac children and adolescents and in 600 controls.

RESULTS

The allelic frequencies of the MYO9B rs 2305764 polymorphism found in our patients and in the population control were not statistically different (P=0.46).

CONCLUSION

The MYO9B gene rs 2305764 polymorphism is not associated to coeliac disease in coeliac children from Southern Italy. This is in accordance with the most recent reports. Ethnic differences or a false positive result might explain the discrepancy with the Dutch study.

Mechanisms of disease: immunopathogenesis of celiac disease

Celiac disease is a genetic inflammatory disorder with autoimmune components that is induced by the ingestion of dietary gluten. Refractory sprue and enteropathy-associated T-cell lymphoma are rare but distinctive complications of the disease. Although the importance of the adaptive immune response to gluten has been well established, observations now also point towards a central role for the gluten-induced innate stress response in the pathogenesis of celiac disease and its malignant complications.

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.

Genome-wide linkage analysis of 160 North American families with celiac disease

Celiac disease (CD) is a common autoimmune disease caused by exposure to the protein gliadin in wheat, and related prolamins in barley and rye. The prevalence of the disease in the US is 1:133. The aim of this study was to identify non-human leukocyte antigen (HLA) loci that predispose to CD. A genome-wide search of 405 microsatellite markers was performed on DNA samples from 160 families with a minimum of two cases of CD. Multipoint, parametric and non-parametric linkage (NPL) analyses were performed. Locations on chromosomes 1q, 3q, 6p, 6q, 7q, 9q and 10q showed linkage statistics (NPL scores or heterogeneity logarithm of the odds (HLOD) scores) of approximately 2.0 or larger. The greatest evidence for linkage outside of chromosome 6 was on 7q and 9q. An NPL score of 2.60 occurred at position 151.0 on 7q and a HLOD score of 2.47 occurred at position 144.8 on 9q under a recessive model. As expected, there was highly significant linkage to the HLA region on 6p, with NPL and HLOD scores exceeding 5.50. In conclusion, this genome-wide linkage analysis represents one of the largest such studies of CD. The most promising region is a putative locus on 7q, a region reported independently in previous genome-wide searches.

Association analysis of MYO9B gene polymorphisms and inflammatory bowel disease in a Norwegian cohort

Association between single nucleotide polymorphisms (SNPs) within the MYO9B gene and celiac disease was recently reported. The role of MYO9B in celiac disease was suggested to relate to an epithelial barrier defect. The region to which MYO9B localize is also linked with inflammatory bowel disease (IBD). For these reasons, we hypothesize that MYO9B could also be a susceptibility gene in IBD. To address this, we performed an association study of a Norwegian IBD cohort (149 patients with Crohn's disease, 308 patients with ulcerative colitis and 562 healthy controls) using SNPs, which tagged the celiac disease associated MYO9B haplotype. No association between these SNPs and IBD was observed. Our results failed to support the notion that MYO9B is a susceptibility gene in IBD.

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.

Understanding the molecular basis of celiac disease: what genetic studies reveal

Celiac disease (CD) is characterized by a chronic immune reaction in the small intestine to the gluten proteins that are present in a (Western) daily diet. Besides the well known involvement of the HLA class II histocompatibility antigen (HLA)-DQ2.5 and -DQ8 heterodimers (encoded by particular combinations of the HLA-DQA1 and -DQB1 gene) in CD and the minor contribution of the CTLA-4 gene, recently the myosin IXB (MYO9B) gene has also been found to be genetically associated. This review covers the general aspects of CD as well as current insight into important molecular aspects. We evaluate the role of susceptibility genes in CD by following gluten along its path from ingestion to uptake in the body, which leads us through the three aspects of CD's pathology. The first is the presence of gluten in the lumen of the intestine, where it is broken down by several enzymes. The second is the intestinal barrier through which gluten peptides pass. The third is the reaction of the immune system in response to gluten peptides, in which both the innate and the adaptive immune systems play a role. Our main conclusion, based on the current genetic and functional studies, is that we should look for causal genes in the barrier function as well as in the immune systems.