Low frequency of HLA DRB1*03 - DQB1*02 and DQB1*0302 haplotypes in Romania is consistent with the country's low incidence of Type I diabetes

Association of HLA Haplotypes with Autoimmune Pathogenesis in Newly Diagnosed Type 1 Romanian Diabetic Children: A Pilot, Single-Center Cross-Sectional Study

BACKGROUND

The increasing incidence of autoimmune diseases in type 1 diabetes mellitus (T1DM) patients highlights the influence of human leukocyte antigen (HLA) haplotypes on their development. This study aims to determine genetic predisposition to autoimmune diseases in T1DM patients, including thyroid disease and celiac diseases, and explore its correlation with vitamin D deficiency.

METHODS

A cross-sectional study involving thirty-six T1DM children was conducted. Typing was performed for the HLA A, B, C, DP, DR, and DQ loci. Regression analysis linked DR-DQ haplotypes to T1DM and the associated conditions.

RESULTS

The most frequent predisposing alleles and haplotypes were HLA-DR3 (70.27%), DQ2 (70.27%), DR3-DQ2 (70.27%), DQB1*02:01 (70.27%), A02 (54.05%), whereas the most prevalent protecting allele was DPB1*04:01 (52.63%). Positive correlations were observed between positive anti-thyroid peroxidase antibodies and the absence of protective alleles (DPB1*04:02, p = 0.036; DPB1*04:01, p = 0.002). Associations were found between the absence of DPB1*04:01 and anti-thyroglobulin antibodies (p = 0.03). HLA allele DPB1*03:01 was linked with vitamin D deficiency (p = 0.021). Positive anti-transglutaminase antibodies correlated with C03:03 (p = 0.026) and DRB1*04:01-DQA1*03-DQB1*03:01 (p < 0.0001) and the lack of DQA1*01:03-DQB1*06:03-DRB1*13:01 (p < 0.0001).

CONCLUSIONS

The predisposing T1DM haplotypes were associated with the presence of anti-transglutaminase and anti-thyroid antibodies, indicating a genetic predisposition to autoimmune diseases.

The Association of Human Leukocyte Antigen Genotyping Among Sudanese Patients With Rheumatoid Arthritis: Reference to Ethnicity

INTRODUCTION

 Human leukocyte antigens (HLA) account for up to one-half of the total genetic contribution to rheumatoid arthritis (RA) risk. The study investigated the association of HLA class II genotyping with RA susceptibility in Sudanese ethnic groups.

METHODS

 The DRB1 and DQB1 alleles and haplotypes were determined in 122 RA patients (i.e., Gaalia = 54, Johayna = 24, Baggara = 17, Nile Nubian = 12, and others = 15) and 120 healthy controls of ethnic groups (i.e., Gaalia = 44, Johayna = 11, Baggara = 15, Nile Nubian = 9, and others = 21) using a polymerase chain reaction with sequence-specific primers method.

RESULTS

Susceptibility to RA was associated with a high frequency of DRB1*04 (P = 0.04), DRB1*10 (P = 0.04), and DQB1*03 (P = 2.2 x 10-8/Pc = 6.6 x 10-8) between study ethnic groups, while protective effects were shown with DRB1*07 (P = 0.01), DQB1*02 (P = 0.02), and DQB1*06 (P = 2.2 x 10-6/Pc = 6.6 x 10-6), with an inconsistent frequency between study ethnic groups. The HLA haplotypes that were high in frequency among RA ethnic groups and showed susceptibility associations were DRB1*03-DQB1*03, DRB1*04-DQB1*03, DRB1*08-DQB1*03, DRB1*13-DQB1*02, and DRB1*13-DQB1*03 (P = 0.00003/Pc = 0.0003, P = 0.0001/Pc = 0.0001, P = 0.03, P = 0.004/Pc = 0.03, and P = 3.79x10-8/Pc = 3.3x10-9, respectively). On the contrary, DRB1*03-DQB1*02, DRB1*07-DQB1*02, and DRB1*13-DQB1*06 were lower in frequency in the ethnic groups with RA and may confer protection (P = 0.004/Pc = 0.032, P = 0.002/Pc = 0.02, and P = 0.01, respectively).

CONCLUSIONS

Our findings indicate an association between HLA-DRB1 and DQB1 genotypes and the susceptibility to RA in the Sudanese population, with a moderate frequency between our ethnic groups.

Association of HLA-DQA1 and -DQB1 alleles with type I diabetes in Arabs: a meta-analyses

This study aimed at assessing the nature and significance of associations between various alleles of HLA-DQA1, HLA-DQB1, and type I diabetes (T1D) in Arab populations. Evidence from literature (published before 20 April 2015) was amassed and analysed through multiple meta-analyses, which yielded effect summary odds ratios and 95% confidence intervals for 24 alleles and 4 haplotypes. A total of 1273 cases and 1747 controls from 16 studies were analysed. High levels of significance were obtained to support higher T1D risk when harbouring DQA1*03:01. The alleles DQB1*02:01 and *03:02 and the haplotypes DR3 and DR4 were significant risk factors, albeit with high publication heterogeneity. The protective effects of DQA1*01:01, DQB1*05:03, *06:02, *06:03, and *06:04 were robustly suggested by all indicators of meta-analyses. The haplotypes DR7 and DR11 were strongly suggested to be protective in Arabs. A relatively small number of studies have emerged from Arab countries, mostly with inadequate power on an individual basis. This study fills the gap by providing significant size effect of human leukocyte antigen (HLA) alleles and completes the continuum of global ethnic differences in this context.

The Association between Human Leukocyte Antigen Class II DR3-DQ2 Haplotype and Type 1 Diabetes in Children of the East Azerbaijan State of Iran

Background:

Type 1 diabetes mellitus (T1D) is an autoimmune disease. Several associations between human leukocyte antigen (HLA) complex and T1D were found in various populations. Associations with various HLA types depend on the investigated populations. However, such associations have not yet been investigated in the East Azerbaijan state of Iran with Turkish ethnicity.

Objectives:

The aims of the current study was to describe T1D genetic susceptibility conferred by HLA class II alleles (DRB1*0301, DQA1*0501 and DQB1*0201) and to determine haplotype frequencies among T1D patients.

Patients and Methods:

This study was a case-control study. The number of samples was determined using the Cochran formula. Eighty unrelated T1D patients, including 42 (52.5%) females and 38 (47.5%) males, were randomly recruited from the East Azerbaijan state of Iran. Typing of HLA was performed by polymerase chain reaction-sequence-specific priming (PCR-SSP) on DNA extracted from peripheral blood mononuclear cells of 80 unrelated patients and 80 unrelated healthy control donors, who were selected randomly. For haplotype analysis, the logistic regression model was performed that allows joint estimation of Single-nucleotide polymorphisms (SNPs) via haplotypes.

Results:

The frequency of drb1*0301 (82.5% vs. 11.3%), dqa1*0501 (82.5% vs. 36.3%) and dqb1*0201 (81.3% vs. 35%) were significantly higher among patients compared with that of healthy subjects.

Conclusions:

Our investigation demonstrated that there is a highly significant association between the studied alleles and T1D. It can be construed that haplotype HLA-DR3-DQ2 has a very modest effect with respect to the risk of T1D.

Evaluation of Association Between HLA Class II DR4-DQ8 Haplotype and Type I Diabetes Mellitus in Children of East Azerbaijan State of Iran

PURPOSE

Association between HLA-DR4-DQ8 haplotype and type 1 Diabetes Mellitus (DM-1A) was investigated in children of East Azerbaijan state of Iran because such an association has not been previously studied in this population.

METHODS

HLA-typing was performed by polymerase chain reaction sequence-specific priming. For haplotype analysis, the logistic regression model was performed.

RESULTS

Of the three investigated alleles, the frequency of DRB1*0401 was significantly higher among patients compared with that in healthy subjects (76.74% vs. 23.26%).

CONCLUSION

The findings of the current study are consistent with those of previous studies and show that DRB1*0401 is associated with DM-1A; the frequencies of the two other alleles were also higher among patients, although the differences were not statistically significant. Two haplotypes associated with these alleles were also surveyed, and DRB1*0401--DQA1*0301-, and DRB1*0401--DQA1*0301--DQB1*0302- were the most frequent haplotypes among the patient group.

The influence of the HLA-DRB, HLA-DQB and polymorphic positions of the HLA-DRβ1 and HLA-DQβ1 molecules on risk of Iranian type 1 diabetes mellitus patients

Type 1 Diabetes mellitus (T1D) is an autoimmune and multifactorial disease. HLA-DRB1 and DQB1 loci have the strongest association with T1D. This study aimed at investigating (i) susceptibility or protection of alleles, genotypes and haplotypes of HLA-DRB1 and DQB1 loci; and (ii) highly polymorphic amino acid residues of HLA-DRβ1 and DQβ1 in 105 Iranian T1D patients and 100 controls. The results indicated that DRB1*04:01, 03:01, DQB1*03:02, 02:01 alleles, DRB1*03:01/04:01, 03:01/13:03, DQB1*02:01/03:02 genotypes, DRB1*04:01-DQB1*03:02, DRB1*03:01-DQB1*02:01, DRB1*07:01-DQB1*03:03 haplotypes had positive association with T1D. In contrast, HLA-DRB1*15:01, 13:01, DQB1*03:01, 06:01 alleles, DRB1*11:01/15:01, DQB1*03:01/06:01, 03:01/05:01 genotypes and DRB1*15:01-DQB1*06:01, DRB1*11:01-DQB1*03:01 haplotypes had negative association with T1D. Analysis of amino acid sequence of HLA-DRβ1 and DQβ1 revealed that DRβ1(Lys71+) and DQβ1(Asp57-) were significantly more frequent in patients than in controls and had a positive effect in the development of T1D. Haplotype analysis demonstrated that HLA-DRB1(Lys71+) allele provided major susceptibility for T1D, and DQβ1(Asp57-) had an additive effect. We designed an allele-specific primer to develop an easy, quick and cost-benefit method to detect the DRβ1(Lys71+) . This method can identify all 114 DRB1 alleles encoding DRβ1(Lys71+) by three PCR reactions. The PcPPV and PcNPV were also calculated to determine the impact of HLA genotype testing at amino acid positions. It showed that the DRβ1(Lys71+/+) genotype carrier had 1% absolute risk of developing T1D.

Autoimmune type 1 diabetes genetic susceptibility encoded by human leukocyte antigen DRB1 and DQB1 genes in Tunisia

Human leukocyte antigen (HLA) class II genes contribute to the genetic susceptibility to type 1 diabetes (T1D), and susceptible alleles and haplotypes were implicated in the pathogenesis of T1D. This study investigated the heterogeneity in HLA class II haplotype distribution among Tunisian patients with T1D. This was a retrospective case control study done in Monastir in central Tunisia. The subjects comprised 88 T1D patients and 112 healthy controls. HLA-DRB1 and -DQB1 genotyping was done by PCR-sequence-specific priming. Significant DRB1 and DQB1 allelic differences were seen between T1D patients and controls; these differences comprised DRB1*030101 and DQB1*0302, which were higher in T1D patients than in control subjects, and DRB1*070101, DRB1*110101, DQB1*030101, and DQB1*060101, which were lower in T1D patients than in control subjects. In addition, the frequencies of DRB1*030101-DQB1*0201 and DRB1*040101-DQB1*0302 were higher in T1D patients than in control subjects, and the frequencies of DRB1*070101-DQB1*0201 and DRB1*110101-DQB1*030101 haplotypes were lower in T1D patients than in control subjects. Multiple logistic regression analysis revealed the positive association of DRB1*030101-DQB1*0201 and DRB1*040101-DQB1*0302 and the negative association of only DRB1*070101-DQB1*0201 haplotypes with T1D. Furthermore, a significantly increased prevalence of DRB1*030101-DQB1*0201 homozygotes was seen for T1D subjects than for control subjects. Our results confirm the association of specific HLA-DR and -DQ alleles and haplotypes with T1D in Tunisians. The identification of similar and unique haplotypes in Tunisians compared to other Caucasians highlights the need for evaluating the contribution of HLA class II to the genetic susceptibility to T1D with regard to haplotype usage and also to ethnic origin and racial background.

Influence of common and specific HLA-DRB1/DQB1 haplotypes on genetic susceptibilities of three distinct Arab populations to type 1 diabetes

The contribution of HLA DRB-DQB to type 1 diabetes (T1D) in Bahrainis, Lebanese, and Tunisians was investigated. DRB1*030101-DQB1*0201 was a locus that conferred susceptibility in three populations, while DRB1*040101-DQB1*0302 was a locus that conferred susceptibility only in Tunisians and Bahrainis. The DRB1*100101-DQB1*050101 (Bahrainis) and DRB1*150101-DQB1*060101 (Lebanese) loci were largely protective. The contribution of HLA to T1D must be evaluated with regard to ethnic background.

T cell cytokine gene polymorphisms in canine diabetes mellitus

Insulin-deficiency diabetes in dogs shares some similarities with human latent autoimmune diabetes of adults (LADA). Canine diabetes is likely to have a complex pathogenesis with multiple genes contributing to overall susceptibility and/or disease progression. An association has previously been shown between canine diabetes and MHC class II genes, although other genes are also likely to contribute to the genetic risk. Potential diabetes susceptibility genes include immuno-regulatory TH1/TH2 cytokines such as IFNgamma, IL-12, IL-4 and IL-10. We screened these candidate genes for single nucleotide polymorphisms (SNPs) in a range of different dog breeds using dHPLC analysis and DNA sequencing. Thirty-eight of the SNPs were genotyped in crossbreed dogs and seven other breed groups (Labrador Retriever, West Highland White Terrier, Collie, Schnauzer, Cairn Terrier, Samoyed and Cavalier King Charles Spaniel), which demonstrated substantial intra-breed differences in allele frequencies. When SNPs were examined for an association with diabetes by case:control analysis significant associations were observed for IL-4 in three breeds, the Collie, Cairn Terrier and Schnauzer and for IL-10 in the Cavalier King Charles Spaniel. These results suggest that canine cytokine genes regulating the TH1/TH2 immune balance might play a contributory role in determining susceptibility to diabetes in some breeds.

The candidate genes TAF5L, TCF7, PDCD1, IL6 and ICAM1 cannot be excluded from having effects in type 1 diabetes

BACKGROUND

As genes associated with immune-mediated diseases have an increased prior probability of being associated with other immune-mediated diseases, we tested three such genes, IL23R, IRF5 and CD40, for an association with type 1 diabetes. In addition, we tested seven genes, TAF5L, PDCD1, TCF7, IL12B, IL6, ICAM1 and TBX21, with published marginal or inconsistent evidence of an association with type 1 diabetes.

METHODS

We genotyped reported polymorphisms of the ten genes, nonsynonymous SNPs (nsSNPs) and, for the IL12B and IL6 regions, tag SNPs in up to 7,888 case, 8,858 control and 3,142 parent-child trio samples. In addition, we analysed data from the Wellcome Trust Case Control Consortium genome-wide association study to determine whether there was any further evidence of an association in each gene region.

RESULTS

We found some evidence of associations between type 1 diabetes and TAF5L, PDCD1, TCF7 and IL6 (ORs = 1.05 - 1.13; P = 0.0291 - 4.16 x 10-4). No evidence of an association was obtained for IL12B, IRF5, IL23R, ICAM1, TBX21 and CD40, although there was some evidence of an association (OR = 1.10; P = 0.0257) from the genome-wide association study for the ICAM1 region.

CONCLUSION

We failed to exclude the possibility of some effect in type 1 diabetes for TAF5L, PDCD1, TCF7, IL6 and ICAM1. Additional studies, of these and other candidate genes, employing much larger sample sizes and analysis of additional polymorphisms in each gene and its flanking region will be required to ascertain their contributions to type 1 diabetes susceptibility.

Large-scale genetic fine mapping and genotype-phenotype associations implicate polymorphism in the IL2RA region in type 1 diabetes

Genome-wide association studies are now identifying disease-associated chromosome regions. However, even after convincing replication, the localization of the causal variant(s) requires comprehensive resequencing, extensive genotyping and statistical analyses in large sample sets leading to targeted functional studies. Here, we have localized the type 1 diabetes (T1D) association in the interleukin 2 receptor alpha (IL2RA) gene region to two independent groups of SNPs, spanning overlapping regions of 14 and 40 kb, encompassing IL2RA intron 1 and the 5' regions of IL2RA and RBM17 (odds ratio = 2.04, 95% confidence interval = 1.70-2.45; P = 1.92 x 10(-28); control frequency = 0.635). Furthermore, we have associated IL2RA T1D susceptibility genotypes with lower circulating levels of the biomarker, soluble IL-2RA (P = 6.28 x 10(-28)), suggesting that an inherited lower immune responsiveness predisposes to T1D.

Analysis of Candidate Susceptibility Genes in Canine Diabetes

Canine diabetes is a complex genetic disease of unknown aetiology. It affects 0.005-1.5% of the canine population and shows a clear breed predisposition with the Samoyed being at high risk and the Boxer being at low risk of developing the disease. Canine diabetes is considered to be a disease homologue for human type 1 diabetes (T1D). It results in insulin deficiency as a consequence of autoimmune destruction of islet beta-cells in the pancreas and is believed to be mediated by Th1 cytokines (IFNgamma, TNFalpha, and IL-2). A number of genes have been associated with type 1 diabetes in humans, including the human leukocyte antigen region, the insulin variable number tandem repeat, PTPN22, CTLA4, IL-4, and IL-13. As yet, these genes have not been evaluated in canine diabetes. In this study, 483 cases of canine diabetes and 869 controls of known breed were analyzed for association with IFNgamma, IGF2, IL-10, IL-12beta, IL-6, insulin, PTPN22, RANTES, IL-4, IL-1alpha and TNFalpha. Minor allele frequencies were determined for these genes in each breed. These data were used for comparative analyses in a case-control study, and clear associations with diabetes were identified in some breeds with certain alleles of candidate genes. Some associations were with increased susceptibility to the disease (IFNgamma, IL-10, IL-12beta, IL-6, insulin, PTPN22, IL-4, and TNFalpha), whereas others were protective (IL-4, PTPN22, IL-6, insulin, IGF2, TNFalpha). This study demonstrates that a number of the candidate genes previously associated with human T1D also appear to be associated with canine diabetes and identifies an IL-10 haplotype which is associated with diabetes in the Cavalier King Charles Spaniel. This suggests that canine diabetes is an excellent comparative and spontaneously occurring disease model of human T1D.

No evidence for a major effect of two common polymorphisms of the catalase gene in type 1 diabetes susceptibility

BACKGROUND

Type 1 diabetes (T1D) is a multifactorial disease, the genetic analysis of which has yielded few true positive linkage and association results. Replication of association in independent, large-sample studies is essential to further identify the genes involved in T1D. Two single nucleotide polymorphisms (SNPs) in the catalase gene have been reported to be associated with T1D.

METHODS

Major effects of two SNPs, C1167T (rs769217) and C(-262)T (rs1001179), of the catalase gene on T1D susceptibility have been reported previously in Russians from Moscow. We genotyped C1167T and C(-262)T in large family (1642 families) and British case-control (3530 cases and 3930 controls) collections and tested for association with T1D.

RESULTS

We found no evidence of an association between T1D and C1167T or C(-262)T in either the family or case-control collections, or for the D11S2008 microsatellite polymorphism in families. However, we did find limited statistical evidence of an association at C1167T in USA families (P = 0.033; RR for 1167C = 1.23, 95% CI = 1.02-1.49) and C(-262)T in UK families (P = 0.046; RR for (-262)C = 0.86, 95% CI = 0.75-0.99).

CONCLUSION

We found no evidence for a major effect of C1167T or C(-262)T on T1D susceptibility in two large sample collections. Limited statistical evidence of an association at C1167T in USA families and C(-262)T in UK families was found, but these results are likely to be false positives. The previously reported association of these SNPs may also have been a false positive, or a population specific association in Russians from Moscow.

No evidence for association of OAS1 with type 1 diabetes in unaffected siblings or type 1 diabetic cases

Type 1 diabetes is a common autoimmune disorder that is strongly clustered in families. As the sharing of alleles of the HLA class II genes cannot explain all of this aggregation, alleles of multiple other loci are involved. Recently, it was reported that an A/G splice-site single nucleotide polymorphism (SNP; rs10774671) in the OAS1 gene, encoding 2'5'-oligoadenylate synthetase, was associated with a protective effect against type 1 diabetes in unaffected siblings, and yet affected siblings showed random transmission. Since this finding is difficult to explain biologically, we genotyped the OAS1 SNP in 1,552 type 1 diabetic families from the U.K., U.S., Romania, and Norway and in 4,287 type 1 diabetic cases and 4,735 control subjects from the U.K. We found no evidence of association in either unaffected (relative risk 1.00; P = 0.94) or affected (1.00; P = 0.96) siblings or in the case-control study (odds ratio 0.99; P = 0.83). These results suggest that additional evidence of association of a low penetrance effect in common disease should be sought when the primary result comes from unaffected siblings in the absence of any effect in cases.

Genetic association of type 1 diabetes in an Azerbaijanian population: the HLA-DQ, -DRB1*04, the insulin gene, and CTLA4

BACKGROUND

Little is known on the genetic susceptibility to type 1 diabetes mellitus (T1DM) in the nations of the former Soviet part of south-west Asia.

OBJECTIVE

The aim of the study was to characterize the genetic association of T1DM in the Azeri, the majority population of Azerbaijan.

SUBJECTS AND METHODS

One hundred and sixty patients with childhood-onset T1DM, and 271 healthy unrelated controls were compared in a case-control study. All declared themselves as Azeri. The human leukocyte antigen (HLA)-DQB1, -DQA1 alelles, of DRB1*04 subtypes, and of insulin gene and cytotoxic T-lymphocyte-associated protein 4 (CTLA4) single nucleotide polymorphisms were determined using polymerase chain reaction (PCR) techniques, the association was tested from cross-tabulations, and quantified using odds ratios (OR). In the non-HLA factors, analyses were also stratified according to the HLA-conferred risk.

RESULTS

Risk for T1DM was associated with presence of the HLA-DQB1*02-DQA1*05, OR = 6.6 [95% confidence interval (CI) 4.3-10], the HLA-DQB1*0302-DQA1*03, OR = 3.9 (95% CI 2.6-6.0), and an unexpectedly high risk was observed for DQB1*0304, OR = 10.9, but the very wide CI (CI 95% 2.4-49) prompts careful interpretation. A negative association with diabetes was observed for the DQB1*0602, 0503, 0301, and 0601 alleles, as well as the DRB1*0403 subtype. A strong protection was also associated with the less frequent variant of the insulin gene (OR of the phenotypic positivity was 0.28, CI 95% 0.17-0.46), while the CTLA4 +49 A/G transition was not associated with T1DM.

CONCLUSIONS

We bring the first report on both HLA, and non-HLA association of T1DM from the majority Azeri population of Azerbaijan.

No evidence for association of the TATA-box binding protein glutamine repeat sequence or the flanking chromosome 6q27 region with type 1 diabetes

Susceptibility to the autoimmune disease type 1 diabetes has been linked to human chromosome 6q27 and, moreover, recently associated with one of the genes in the region, TATA box-binding protein (TBP). Using a much larger sample of T1D families than those studied by others, and by extensive re-sequencing of nine other genes in the proximity, in which we identified 279 polymorphisms, 83 of which were genotyped in up to 725 T1D multiplex and simplex families, we obtained no evidence for association of the TBP CAG/CAA (glutamine) microsatellite repeat sequence with disease, or for nine other genes, PDCD2, PSMB1, KIAA1838, DLL1, dJ894D12.4, FLJ25454, FLJ13162, FLJ11152, PHF10 and CCR6. This study also provides an exon-based tag single nucleotide polymorphism map for these 10 genes that can be used for analysis of other diseases.

Association analysis of the lymphocyte-specific protein tyrosine kinase (LCK) gene in type 1 diabetes

Prior data associating the expression of lymphocyte-specific protein tyrosine kinase (LCK) with type 1 diabetes, its critical function in lymphocytes, and the linkage of the region to diabetes in the nonobese diabetic (NOD) mouse model make LCK a premier candidate for a susceptibility gene. Resequencing of LCK in 32 individuals detected seven single nucleotide polymorphisms (SNPs) with allele frequencies >3%, including four common SNPs previously reported. These and six other SNPs from dbSNP were genotyped in a two-stage strategy using 2,430 families and were all shown not to be significantly associated with type 1 diabetes. We conclude that a major role for the common LCK polymorphisms in type 1 diabetes is unlikely. However, we cannot rule out the possibility of there being a causal variant outside the exonic, intronic, and untranslated regions studied.

Remapping the insulin gene/IDDM2 locus in type 1 diabetes

Type 1 diabetes susceptibility at the IDDM2 locus was previously mapped to a variable number tandem repeat (VNTR) 5' of the insulin gene (INS). However, the observation of associated markers outside a 4.1-kb interval, previously considered to define the limits of IDDM2 association, raised the possibility that the VNTR association might result from linkage disequilibrium (LD) with an unknown polymorphism. We therefore identified a total of 177 polymorphisms and obtained genotypes for 75 of these in up to 434 pedigrees. We found that, whereas disease susceptibility did map to within the 4.1-kb region, there were two equally likely candidates for the causal variant, -23HphI and +1140A/C, in addition to the VNTR. Further analyses in 2,960 pedigrees did not support the difference in association between VNTR lineages that had previously enabled the exclusion of these two polymorphisms. Therefore, we were unable to rule out -23HphI and +1140A/C having an etiological effect. Our mapping results using robust regression methods show how precisely a variant for a common disease can be mapped, even within a region of strong LD, and specifically that IDDM2 maps to one or more of three common variants in a approximately 2-kb region of chromosome 11p15.

An increasing trend in the incidence of type 1 diabetes mellitus in children aged 0-14 years in Romania--ten years (1988-1997) EURODIAB study experience

AIM

To assess the incidence of type 1 diabetes mellitus (DM1) in Romanian children aged 0-14 years using EURODIAB Study methodology.

METHODS

Data were collected for a 10-year interval (1988-1997) for the whole country, using the capture-recapture method.

RESULTS

We registered 1,418 newly diagnosed patients. The mean total incidence rate was 3.051/100,000/year. There was a wide geographic variation (6.71-fold) between the highest and the lowest incidence rates in different districts. We noticed a progressive increase of age-specific incidence rates from 1.43/100,000/year for the 0-4 year age subgroup to 4.37/100,000/year (10-14 years). The annual mean incidence rate rose from 1.91/100,000/year (1988) to 3.94/100,000/year (1996).

CONCLUSIONS

Romania is one of the European countries with the lowest incidence rates (3.051/100,000/year) for DM1 in children. There was an evident increasing trend of DM1 incidence in children between 1988 and 1997, with an annual increase of 7.57%.

Lack of association of the Ala(45)Thr polymorphism and other common variants of the NeuroD gene with type 1 diabetes

Variation in genes necessary for normal functioning and development of beta-cells, e.g., NEUROD1, which encodes a transcription factor for the insulin gene and is important in beta-cell development, causes maturity-onset diabetes of the young. Some studies have reported an association between a nonsynonymous Ala(45)Thr (+182G-->A) single nucleotide polymorphism (SNP) in NEUROD1 and type 1 diabetes, but this result has not been consistently found. To clarify this, we genotyped Ala(45)Thr in 2,434 type 1 diabetic families of European descent and Caucasian ethnicity from five different countries. Taking the allele frequency of 36% for Thr(45) and an odds ratio (OR) of 1.2, this sample provided >99% power to detect an association (P < 0.05). We could not confirm the association (P = 0.77). No evidence of population heterogeneity in the lack of association of Thr(45) with type 1 diabetes was observed. To evaluate the possibility that another NEUROD1 variant was associated with type 1 diabetes, we resequenced the gene in 32 U.K. affected individuals and identified and genotyped all common SNPs (minor allele frequency >10%; n = 5) in 786 families. We report no evidence of association of these common variants in NEUROD1 and type 1 diabetes in these samples.

Type 1 diabetes genetic susceptibility encoded by HLA DQB1 genes in Romania

Most cases of type 1 diabetes (T1DM) are due to an immune-mediated destruction of the pancreatic beta cells, a process that is conditioned by multiple genes and environmental factors. The main susceptibility genes are represented by the class II HLA-DRB1 and DQB1 alleles. The aim of our study was to reconfirm the contribution of HLA-DQB1 polymorphisms to T1DM genetic susceptibility for the Romanian population. For this, 219 Romanian T1DM families were genotyped at high resolution for HLA DQB1 using the PCR-SSOP method (Polymerase Chain Reaction - Sequence Specific Oligonucleotide Probes). Allele transmission to diabetics and unaffected siblings was studied using the Transmission Disequilibrium Test (TDT). We found an increased transmission of DQB1*02 (77.94% transmission, p(TDT) = 7.18 x 10(-11)) and DQB1*0302 (80.95% transmission, p(TDT) = 2.25 x 10(-10)) alleles to diabetics, indicating the diabetogenic effect of these alleles. Conversely, DQB1*0301, DQB1*0603, DQB1*0602, DQB1*0601 and DQB1*05 alleles are protective, being significantly less transmitted to diabetics. In conclusion, our results confirmed the strong effect of HLA-DQB1 alleles on diabetes risk in Romania, with some characteristics which can contribute to the low incidence of T1DM in this country.

Similar incidence of type 1 diabetes in two ethnically different populations (Italy and Slovenia) is sustained by similar HLA susceptible/protective haplotype frequencies

The incidence of type 1 diabetes (T1DM) seems to depend in part on the population frequencies of susceptible and protective HLA haplotypes. The present study aimed to (i): characterize the genetic susceptibility to T1DM in the Slovenian population, (ii) test the general hypothesis that T1DM incidence is related to the frequencies of susceptible/protective haplotypes, (iii) compare allele, haplotype and genotype frequencies in Slovenians and Italians that represent two white populations with a similar incidence of T1DM (7.9/100,000/year and 8.1/100,000/year, respectively). The haplotype found most frequently among Slovenian T1DM patients was DRB1*0301-DQA1*0501-DQB1*0201 (53%). The DR4-DQA1*0301-DQB1*0302 haplotypes conferring susceptibility to T1DM were those bearing DRB1*0401 (OR = 12), DRB1*0404 (OR = 4.7) and DRB1*0402 (OR = 4.5). Negative associations with the disease were found for the following haplotypes: DRB1*1501-DQA1*0102-DQB1*0602, DRB1*1301-DQA1*0102-DQB1*0603, DRB1*1101/1104-DQA1*0501-DQB1*0301, and DRB1*1401-DQA1*0101-DQB1*0503. Our findings indicate that the low frequencies of susceptible genotypes, in particular, DR3-DQA1*0501-DQB1*0201/DR4-DQA1*0301-DQB1*0302, together with a high frequency of protective haplotypes, could in part explain the low incidence of T1DM in the Slovenian population. The combined frequencies of susceptible genotypes were similar in the two populations (Slovenia = 19.2%, Italy = 17.6%), and the 95% confidence limits of the OR values for each genotype in the two populations overlapped, indicating no significant differences between the values. We conclude that the similar incidences of T1DM in Italian and Slovenian populations are in part a reflection of similar frequencies of HLA susceptible/protective haplotypes.

The study of CTLA-4 and vitamin D receptor polymorphisms in the Romanian type 1 diabetes population

Several studies suggested that part of the genetic susceptibility for Type 1 diabetes (T1DM) is encoded by some polymorphisms of CTLA-4 gene (2q33) and of Vitamin D Receptor gene (VDR; 12q12-14). Our aim was to assess their contribution to T1DM genetic susceptibility in the Romanian population. We typed CTLA-4 49 A/G and VDR FokI (F/f), ApaI (A/a) and TaqI (T/t) polymorphisms by Sequence Specific Primer PCR (SSP-PCR) in 204 Romanian diabetic families (756 individuals: 212 T1DM probands and 544 unaffected parents and siblings). We studied alleles transmission using the Transmission Disequilibrium Test (TDT). We found an increased transmission of CTLA-4 49G allele to diabetics (54.8%, p=0.11). The transmission of F (56.1%, p=0.063), a (55.7%, p=0.061) and T (51.8%, p=0.37) alleles of VDR gene to diabetics was increased but did not reach statistical significance. In conclusion we found the same increased transmission of CTLA-4 49 G allele to diabetics as previously reported. VDR FoqI F allele seems to be predisposing while TaqI T allele seems to be protective.