HLA and celiac disease susceptibility: new genetic factors bring open questions about the HLA influence and gene-dosage effects.

Celiac disease (CD) is a chronic inflammatory disorder triggered after gluten ingestion in genetically susceptible individuals. The major genetic determinants are HLA-DQA1*05 and HLA-DQB1*02, which encode the DQ2 heterodimer. These alleles are commonly inherited in cis with DRB1*03∶01, which is associated with numerous immune-related disorders, in some cases contributing with a different amount of risk depending on the haplotype context. We aimed at investigating those possible differences involving DRB1*03∶01-carrying haplotypes in CD susceptibility. A family (274 trios) and a case-control sample (369 CD cases/461 controls) were analyzed. DRB1*03∶01-carrying individuals were classified according to the haplotype present (ancestral haplotype (AH) 8.1, AH 18.2 or non-conserved haplotype) after genotyping of HLA-DRB1, -DQA1, -DQB1, -B8, TNF -308, TNF -376 and the TNFa and TNFb microsatellites. We observe that the AH 8.1 confers higher risk than the remaining DRB1*03∶01-carrying haplotypes, and this effect only involves individuals possessing a single copy of DQB1*02. CD risk for these individuals is similar to the one conferred by inherit DQA1*05 and DQB1*02 in trans. It seems that an additional CD susceptibility factor is present in the AH 8.1 but not in other DRB1*03∶01-carrying haplotypes. This factor could be shared with individuals possessing DQ2.5 trans, according to the similar risk observed in those two groups of individuals.

Th17-related genes and celiac disease susceptibility.

Th17 cells are known to be involved in several autoimmune or inflammatory diseases. In celiac disease (CD), recent studies suggest an implication of those cells in disease pathogenesis. We aimed at studying the role of genes relevant for the Th17 immune response in CD susceptibility. A total of 101 single nucleotide polymorphisms (SNPs), mainly selected to cover most of the variability present in 16 Th17-related genes (IL23R, RORC, IL6R, IL17A, IL17F, CCR6, IL6, JAK2, TNFSF15, IL23A, IL22, STAT3, TBX21, SOCS3, IL12RB1 and IL17RA), were genotyped in 735 CD patients and 549 ethnically matched healthy controls. Case-control comparisons for each SNP and for the haplotypes resulting from the SNPs studied in each gene were performed using chi-square tests. Gene-gene interactions were also evaluated following different methodological approaches. No significant results emerged after performing the appropriate statistical corrections. Our results seem to discard a relevant role of Th17 cells on CD risk.

Lack of association of NKX2-3, IRGM, and ATG16L1 inflammatory bowel disease susceptibility variants with celiac disease.

Evidence about the presence of susceptibility factors shared among different autoimmune diseases is increasing. Based on this idea, NKX2-3, ATG16L1, and IRGM which are well-established inflammatory bowel disease risk factors, could be new celiac disease (CD) candidate genes. NKX2-3 encodes a transcription factor that in mice seems to be involved in gut development. The ATG16L1 and IRGM genes act in autophagy, a process related to innate and adaptive immunity. We aimed to study the implication of five polymorphisms in these genes in CD susceptibility: rs10883365 and rs888208 in the NKX2-3 gene, rs2241880 in ATG16L1, and rs10065172 and rs4958847 in IRGM. Association studies were performed using 725 Spanish CD patients and 956 ethnically matched healthy controls, as well as 309 parent-child trios. Genetic frequencies were compared with the chi(2) test and the familial study used the transmission disequilibrium test. Differences between CD patients and controls did not reach significance when genotypic and allelic frequencies were compared. No differential transmission of alleles or haplotypes from heterozygous parents to affected children was observed in the familial study. In conclusion, no evidence of association with CD has been reported for the Crohn's disease susceptibility polymorphisms studied in the NKX2-3, ATG16L1, and IRGM genes.

The IL6-174G/C polymorphism is associated with celiac disease susceptibility in girls.

The aim of this paper was to study the role of IL6 and IL6R polymorphisms in celiac disease (CD) susceptibility. Because previous literature describes IL-6-related gender differences, sex-stratified analyses were performed. We undertook a case-control study with 374 pediatric CD patients and 853 healthy controls, all white Spaniards, and a family study using an independent sample including 303 trios for replication purposes. Three single-nucleotide polymorphisms tagging most of the variability of the IL6 gene (rs2069827, rs1800795 [-174G/C], and rs2069840) and one functional polymorphism in IL6R (rs8192284, Asp358Ala) were genotyped using TaqMan technology. Case-control comparisons were performed with the chi2 test and family data were analyzed with the transmission disequilibrium test. No association was observed between any tested polymorphism and overall CD. However, after sex stratification, we found that the IL6 promoter variant -174C increases the risk of developing CD specifically in female patients. This effect was observed both in the case-control and in the family studies (considering girls included in both studies vs boys: p = 0.021, odds ratio [OR] = 1.31, 95% confidence interval [CI] 1.03-1.66; and vs controls: p = 0.003, OR = 1.30, 95% CI 1.09-1.55). The functional -174G/C IL6 polymorphism seems to influence CD susceptibility in girls. The gender-specific role of IL-6 in this pathology must be further investigated.

ICAM1 R241 is not associated with celiac disease in the Spanish population.

Celiac disease (CD) is a chronic intestinal inflammatory disease that develops in genetically susceptible individuals after gluten ingestion. The ICAM1 gene, located in the CD linkage region 19p13, encodes an intercellular adhesion molecule (ICAM-1) involved in inflammatory processes. Increased levels of ICAM-1 were observed in intestinal biopsies and in sera of CD patients. In addition, an association between the ICAM1 polymorphism G241R and CD patients has been recently described in a French population. Our aim in this study was to analyze the role of ICAM1 polymorphisms in CD susceptibility in the Spanish population. We performed a case-control study with 608 CD patients and 537 healthy control individuals and a family study including 231 trios. Four ICAM1 single nucleotide polymorphisms (SNPs) were analyzed: three nonsynonymous, R478W (rs5030400), P352L (rs1801714) and G241R (rs1799969); and one intronic, rs281432. Despite having above 98% statistical power to detect the association described in the French population (odds ratio = 1.7), we did not find any differences in genotypic or allelic frequencies of the G241R polymorphism between our CD patients and controls, and no differences were observed when the other SNPs were analyzed. Therefore, in our population our results discard the important previously described role of ICAM1 G241R in celiac disease.

Interleukin-10 haplotypes in Celiac Disease in the Spanish population.

BACKGROUND: Celiac disease (CD) is a chronic disorder characterized by a pathological inflammatory response after exposure to gluten in genetically susceptible individuals. The HLA complex accounts for less than half of the genetic component of the disease, and additional genes must be implicated. Interleukin-10 (IL-10) is an important regulator of mucosal immunity, and several reports have described alterations of IL-10 levels in celiac patients. The IL-10 gene is located on chromosome 1, and its promoter carries several single nucleotide polymorphisms (SNPs) and microsatellites which have been associated to production levels. Our aim was to study the role of those polymorphisms in susceptibility to CD in our population. METHODS: A case-control and a familial study were performed. Positions -1082, -819 and -592 of the IL-10 promoter were typed by TaqMan and allele specific PCR. IL10R and IL10G microsatellites were amplified with labelled primers, and they were subsequently run on an automatic sequencer. In this study 446 patients and 573 controls were included, all of them white Spaniards. Extended haplotypes encompassing microsatellites and SNPs were obtained in families and estimated in controls by the Expectation-Maximization algorithm. RESULTS: No significant associations after Bonferroni correction were observed in the SNPs or any of the microsatellites. Stratification by HLA-DQ2 (DQA1*0501-DQB1*02) status did not alter the results. When extended haplotypes were analyzed, no differences were apparent either. CONCLUSION: The IL-10 polymorphisms studied are not associated with celiac disease. Our data suggest that the IL-10 alteration seen in patients may be more consequence than cause of the disease.

Type 1 diabetes in the Spanish population: additional factors to class II HLA-DR3 and -DR4.

BACKGROUND: The Major Histocompatibility Complex is the main genetic contributor to susceptibility to type 1 diabetes (T1D); genome-wide scans have consistently mapped increased predisposition to this region. The highest disease risk has been associated with HLA-DR3 and HLA-DR4. In particular, the DR3-positive ancestral haplotype 18.2 was reported as highly diabetogenic. We aimed to corroborate whether this haplotype increases the susceptibility conferred by the DQ2-DR3 alleles in a Mediterranean population. We also searched for additional susceptibility factors to the classic DQ2-DR3 and DQ8-DR4. RESULTS: Genetic MHC markers were analysed in a case-control study with 302 T1D patients and 529 ethnically matched controls. DR3-TNFa1b5 carrier rate was significantly higher in DR3-positive heterozygous T1D patients than in DR3-positive heterozygous controls (p = 0.0019; odds ratio OR [95% confidence interval CI] = 2.26 [1.3-3.93]). This data was confirmed analysing the allelic frequency, which includes the information corresponding to the DR3-homozygous individuals (p = 0.001; OR = 2.09) and by using the Arlequin software to check the DR3-positive haplotypes (p = 0.004;OR = 1.93). The present results provide strong evidence of a second susceptibility region in the ancestral haplotype 18.2 in the Spanish population. Moreover, we searched for T1D susceptibility factors in addition to the MHC classical ones, within the DR2-DQ6/DR3-DQ2/DR4-DQ8 negative population. Several genetic markers in both MHC class II (DQA1*0101-DQB1*0501 [p = 0.007;OR = 2.81], DQA1*0201-DQB1*0202 [p = 0.03; OR = 2.35]) and III (TNFa2b1 [p = 0.01 OR = 2.74], BAT-2*2 [p = 0.004; OR = 3.19]) were found. These different alleles associated with T1D were not independent and we observed linkage disequilibrium among them leading us to describe two new risk haplotypes (DQA1*0101-DQB1*0501-TNFa2b1 and DQA1*0201-DQB1*0202- BAT-2*2). Finally, we studied a T1D susceptibility/protection marker located in extended class I, D6S2223; however, no association was observed in our population. CONCLUSION: Our results suggest that other associated MHC haplotypes might present susceptibility factors in loci different from HLA-class II and that the class II molecules are not necessarily the universal etiologic factor in every MHC haplotype.