Association of IL-2RA/CD25 with type 1 diabetes in the Belgian population.

Our goals were to study the proposed association of IL-2RA /CD25 with type 1 diabetes in the Belgian population over a broad age range, and to explore possible correlations with disease phenotypes, immune markers, HLA-DQ, INS, and PTPN22. Patients (n = 1954), healthy controls (n = 2082), and families (n = 420) were genotyped for IL-2RA/CD25 rs41295061(C>A), HLA-DQ, INS-VNTR and PTPN22. IL-2RA/CD25 was associated with type 1 diabetes (χ(2) = 26.8, p < 0.001 for alleles and χ(2) = 29.6, p < 0.001 for genotypes). The C allele (odds ratios [OR] = 1.59) and C/C genotype (OR = 1.56) were identified as susceptibility variants, whereas the A allele (OR = 0.63), A/A genotype (OR = 0.14), and A/C genotype (OR = 0.69) as protective variants. IL-2RA/CD25 is associated with both early-onset and late-onset type 1 diabetes, but with a larger effect size in early-onset disease. There was a nonsignificant tendency toward transmission distortion (p = 0.063). Except a tendency toward younger age at onset in carriers of the C/C genotype, no correlations with disease phenotype, immune markers, HLA-DQ, INS and PTPN22 were observed. Also, the frequency of the susceptible genotype was higher in early-onset compared with late-onset TID patients (p = 0.015). In conclusion, IL-2RA/CD25 is associated with type 1 diabetes in the Belgian population, independently of disease phenotype and other biologic markers.

IFIH1 gene polymorphisms in type 1 diabetes: genetic association analysis and genotype-phenotype correlation in the Belgian population.

The evaluation of susceptibility loci in a registry-based setting could be an important addition to the current predictive and screening models in T1D. Therefore, the aim of this study was to evaluate the importance of one of these loci, IFIH1. T1D patients (n=1981), control subjects (n=2092) and 430 families were genotyped for HLA-DQ and IFIH1 nsSNP rs1990760 (Ala946Thr). In the association analysis, the allelic frequencies, A (62.4% vs. 61.3%) and G (37.6% vs. 38.7%) were similar in cases and controls (chi(2) = 0.98, p = 0.32), the genotypic frequencies reveals a weak association with T1D (chi(2) = 6.79, p = 0.03), no significant transmission distortions in families (%T; A = 51.4%, G = 48.0 %, chi(2) = 1.76, p = 0.19) and no interaction with HLA-DQ-linked risk. Furthermore, no genotype-phenotype correlation was observed. In conclusion, IFIH1 has no important role in T1D risk assessment in a registry-based Belgian population.

TNFa microsatellite polymorphism modulates the risk of type 1 diabetes in the Belgian population, independent of HLA-DQ.

To determine the contribution of the tumor necrosis factor alpha gene (TNFA) to the immunogenetic risk prediction of type 1 diabetes (T1D) in the Belgian population, well-characterized antibody-positive patients with type 1 diabetes (T1D), nondiabetic control subjects, and nuclear families were analyzed for HLA-DQA1-DQB1, TNFA -308 G/A promoter single nucleotide polymorphism (SNP) and TNFa microsatellite markers in both case-control and transmission studies. A total of 1,029 patients (mean age at onset, 18 years; male/female ratio, 1.2), 575 control subjects and 179 nuclear families were analyzed for the -308 SNP and 1,082 patients (mean age at onset, 17 years; and male/female ratio, 1.3), 606 control subjects, and 261 nuclear families were analyzed for the TNFa microsatellite marker. All subjects were typed initially for HLA-DQ. No primary association was detected with the -308 G/A promoter SNP. In contrast, we found evidence of a contribution of TNFa1 allele to susceptibility for T1D independently of HLA-DQ. We observed that the conserved HLA-DQ-TNFa extended haplotype, HLA-DQA1 0501-DQB1 0201-TNFa1 is a diabetogenic haplotype in the Belgian population and is independent of age at onset and gender and confers an estimated relative risk of 4.55 and an absolute risk of 1.7%. In conclusion, our observations suggest that the-308 G/A promoter SNP is not a genetic marker for T1D, but that the TNFa microsatellite may have an added value to further refine the immunogenetic risk conferred by the HLA-DQ region in the Belgian population.

MICA is associated with type 1 diabetes in the Belgian population, independent of HLA-DQ.

To ascertain association of MICA with type 1 diabetes (T1D) in the Belgian population, well-characterized antibody-positive patients were analyzed for MICA transmembrane gene polymorphism in both an association study and a nuclear family study. The frequency of MICA5 was significantly increased in the T1D patient group (18%) compared with the control population (12%, OR=1.6, pc<10(-3)), whereas MICA9 was decreased (11% versus 16%, OR=0.7, pc<0.01). A p value<10(-3) for the association of MICA conditional on HLA class II and p=0.01 for the conditional extended transmission disequilibrium test were obtained, indicating that MICA is associated with type 1 diabetes, independent of HLA-DQ. Analysis of estimated extended HLA-DQ-MICA haplotypes revealed individual effects of MICA alleles. The most significant effect was seen for MICA5 on the HLA-DQA1*03-DQB1*0302-MICA haplotype (OR=2.5, p<10(-3)). A significant protective effect was seen for the combination of DQA1*01-DQB1*0602/3 and MICA5.1 (OR=0.3, p<10(-3)). However, patients stratified according to the presence or absence of the different MICA alleles did not differ in terms of age at onset, sex, or other diabetes-related clinical and epidemiological data. In conclusion, MICA is associated with type 1 diabetes in the Belgian population and the observed association does not result from the HLA-DQ associated risk.

The rare HLA-DQA1*03-DQB1*02 haplotype confers susceptibility to type 1 diabetes in whites and is preferentially associated with early clinical disease onset in male subjects.

The heterozygous combination of DQA1*03-DQB1*0302 (DQ8) and DQA1*05-DQB1*0201 (DQ2) confers the highest known HLA-DQ-linked risk for type 1 diabetes, suggesting a role for transcomplementation. The trans-heterodimer encoded by DQA1*03 and DQB1*02 is also rarely observed in cis in whites. Islet antibody-positive diabetic patients (P; n = 2,238) and control subjects (C; n = 2,223) of white descent were genotyped by a HLA-DQA1-DQB1 dot-blot method. The presence of the DQA1*03-DQB1*02 haplotype was observed in 22 patients (1%) versus 6 controls (0.3%) (odds ratio [OR] = 3.7, p = 0.005). It was more prevalent in whites of Northern African descent, but both in European (n = 3,813) and in Northern African whites (n = 648), the DQA1*03-DQB1*02 haplotype tended to be associated with diabetes (respectively, P 0.3% vs. C 0.03%, OR = 12.2, p = 0.005; and P 2.1% vs. C 0.6%, OR = 3.8, p = 0.03). DRB1 typing revealed that DQA1*03-DQB1*02 is usually associated with the DRB1*0405 risk allele in European patients and with DRB1*0405, DRB1*07 and DRB1*09 in Northern African whites. Like in DQ2/DQ8-positive patients, the presence of DQA1*03-DQB1*02 is preferentially associated with younger age at clinical onset than in other genotypes, but unlike in subjects carrying DQ2/DQ8, earlier clinical manifestation was mostly restricted to male subjects, often carrying DR3 and/or DQB1*02 on the other chromosome. These results are compatible with an effect of cis-encoded heterodimers or with previously suggested interactions of X-linked genetic factors with (DR3-)DQB1*02 haplotypes.

Relative and absolute HLA-DQA1-DQB1 linked risk for developing type I diabetes before 40 years of age in the Belgian population: implications for future prevention studies.

HLA-DQ genotyping remains the cornerstone of genetic risk stratification in type I diabetes prediction and prevention studies. We developed a genetic screening strategy for predisposition to type I diabetes in the Belgian population based upon HLA-DQA1-DQB1 typing and taking into account the age at clinical onset. A group of 1866 autoantibody-positive type I patients below age 40 years recruited by the Belgian Diabetes Registry and a group of 750 control subjects were DQA1-DQB1 genotyped. In the total study population 16 different DQA1-DQB1 haplotypes were revealed, allowing the stratification of 81 genotypes in ten different genotype groups. Apart from the highest risk DQA1*-DQB1* genotype 0301-0302/0501-0201 (odds ratio 21; absolute risk 6%), three other genotype groups conferred a highly significant disease risk (p < 10(-6)). Altogether, these susceptibility genotypes were carried by 9% of the control subjects versus 60% of the patients diagnosed before age 40 years and up to 70% of those under age 5 years. All other genotypes were protective, neutral, infrequent or associated with a moderate protection or susceptibility. A strong, although not absolute protection was conferred by DQB1*0602-positive haplotypes (odds ratio = 0.03). This study in a large cohort of autoantibody-positive patients shows that a DQA1-DQB1-based genotyping strategy allows the identification of a subgroup representing less than 10% of the Belgian population but harbouring the majority of future type I patients arising in childhood or early adulthood. Future prediction and prevention studies should take into account the age dependency of this HLA-DQ associated risk.