TUMOR NECROSIS FACTOR ALPHA (TNF) PROMOTER HAPLOTYPE CONCURS WITH HLADQA1- DQB1 IN DETERMINING CELIAC DISEASE RISK

The rare A alleles at -308 and -238 positions of the TNFa gene have been associated with CD. Although they may be candidate disease susceptibility factors, it is likely that they act as part of TNFa haplotypes resulting from the combination of more SNPs of the promoter. The scopes of this study were to ascertain whether five SNPs in the TNFa promoter (-1031T>C,-857C>T,-376G>A,-308G>A,-238G>A) are associated singly or as haplotypes with CD and whether their effect is HLA-DQA1/–DQB1 dependent or independent. 527 children (250 CD, 277 controls) were studied. TNFa gene polymorphisms and HLADQA1 and –DQB1 alleles were analysed by RTPCR. The TNFa-1031C (OR=2.540,95%CI:1.157-5.575), -857T (OR=0.421,95%CI:0.282-0.627), -376A (OR=2.037,95%CI:1.109-3.741) and -308A (OR=4.486,95%CI:3.076-6.541), but not -238 alleles, were significantly CD-associated, this finding being confirmed at multivariate logistic regression analysis. The possible haplotypes derived from the combination of these four SNPs were estimated using the Arlequin statistical software. Six haplotypes were obtained: two (CCGG,TTGG) were more frequent in controls; three (CCAG,TCGA,CCGA) were more frequent in CD; one (TCGG) was equally found in controls and CD. TNFa promoter genotypes inferred from haplotypes were classified in six categories: 1)CD-associated/CD-associated; 2)CDassociated/ TCGG; 3)CD-associated/control-associated; 4)control-associated/TCGG; 5)TCGG/TTG; 6)controlassociated/ control-associated. A strong correlation was found between the first two categories and CD and between the last category and controls not only considering all cases, but also considering only those bearing HLA-DQA1/–DQB1 risk alleles. Binary logistic regression analysis performed by including among predictors TNFa promoter genotypes and HLA-DQ haplotype, documented a strong association between CD and homozygous HLA-DQ2 (OR=481;95%CI:112-2068), heterozygous HLA-DQ2 (OR=73;95%CI:26-208) or HLA-DQ8 (OR=14;95%CI:5-45), but also an HLAindependent correlation with CD-associated TNFa promoter homozygous (OR=7;95%CI:1,48-34,31) or heterozygous (OR=5;95%CI:1,56-16,59) genotypes. In conclusion the TNFa promoter haplotypes CCAG, TCGA and CCGA was shown to increase CD risk independently from HLA-DQ alleles suggesting the pivotal role of TNFa in the disease pathogenesis