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.

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.

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.

FOXP3 polymorphisms in type 1 diabetes and coeliac disease.

The FOXP3 gene encodes a transcription factor thought to be essential for the development and function of T regulatory cells. Two previous studies have tested common polymorphisms in FOXP3 for association with type 1 diabetes (T1D) with conflicting results. The aim of our study was to see whether there is any evidence of association between the FOXP3 polymorphisms previously reported to be associated with T1D, in a Caucasian population regarding T1D and coeliac disease (CD). We further looked for evidence of interaction between FOXP3 polymorphisms and HLA-DR3 in conferring susceptibility to T1D. Initially, we analysed two microsatellites in the FOXP3 gene in 363 T1D nuclear families. Our results indicated an association between FOXP3 and T1D (global p=0.004) and a possible interaction between FOXP3 and the HLA-DR3-DQ2 susceptibility haplotype. We then genotyped an additional independent set of 826 T1D patients and 1459 controls as well as one CD dataset consisting of 325 families. A similar tendency was revealed in the CD family material (pnc=0.055 for the associated allele). On the other hand, we were unable to reproduce our initial findings in the T1D case-control dataset (global p=0.6). Our results suggest that the tested FOXP3 markers do not have any major impact on susceptibility for these diseases.

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

Association between myosin IXB (MYO9B) gene variants and celiac disease (CD) has been reported in a study of a Dutch cohort. Six single nucleotide polymorphisms (SNPs) within the 3' part of the MYO9B gene showed significant genetic association and formed an associated haplotype. The current study aimed to replicate these findings in a Swedish/Norwegian cohort. Genotyping of the three SNPs which tagged the associated haplotype was performed in a CD family dataset (n = 326) and in an additional set of healthy controls (n = 562). Although our material provided reasonable power to detect the previously observed association, we were unable to replicate association with these SNPs. Lack of reproducibility could be explained by no or negligible contribution of MYO9B to the genetic predisposition to CD in the Swedish/Norwegian population. Alternatively, it might be due to variable linkage disequilibria in distinct populations in the tested SNPs and a causative mutation yet to be identified or to false positive findings (type I error) in the Dutch study.

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.

Coeliac disease patients carry conserved HLA-DR3-DQ2 haplotypes revealed by association of TNF alleles.

Certain HLA-DQ alleles are known to contribute to predisposition to coeliac disease (CD). The existence of additional independent risk-modifying loci in the HLA complex is still being debated. The DR3-DQ2 haplotype has been studied most, but the evidence is conflicting. The discrepancies may stem from the absence of such an effect, insufficient statistical power to detect an effect (i.e. small studies) and/or incomplete control of linkage disequilibrium (LD) to the neighbouring DQ-loci, known to elicit a strong effect. In the present study, we aimed to undertake a statistically high-powered family-based analysis, fully controlling effects of LD between the major DQ-risk haplotypes and neighbouring candidate loci. We investigated five markers on DR3-DQ2, DR5-DQ7 and DR7-DQ2 haplotypes in 327 Norwegian and Swedish families. Our primary finding was that TNF-308A ( TNF2) was significantly associated on the DR3-DQ2 haplotype [stratum specific odds ratio (OR) = 2.40 (1.25-4.48), Pc = 0.009, where P(c) = Pn and n = number of tests performed]. Furthermore, we confirmed earlier indications that LD between TNF2 and DQA1*05-DQB1*02 on the DR3 haplotype is more strongly maintained in family-based cases than family-based controls. In conclusion, we confirmed in this study, the largest of its kind, that additional CD risk factors independent of DQ2 alleles do exist on the DR3 haplotype.