Primary association of HLA-DQw8 with type I diabetes in DR4 patients

Population genetics and external proficiency testing for HLA disease associations

Numerous associations of HLA variants with susceptibility to diseases, namely, those with an immunopathological component, have been described to date. The strongest HLA associations were incorporated into the standard algorithms for the diagnostics. Disease-associated HLA variants are routinely detected by various techniques including DNA-based assays. For the identification of HLA markers or their combinations with the highest diagnostic value and those with frequent clinical indications (e.g., HLA-B*27, -B*57:01, -DQ2/-DQ8, -DQB1*06:02), diagnostic tests that focus on a single or limited number of specific HLA antigens/alleles, have already been developed; the use of complete typing for particular HLA loci is a relevant alternative. Importantly, external proficiency testing (EPT) became an integral part of good laboratory practice for HLA disease associations in accredited laboratories and not only supports correct "technical" identification of the associated HLA variants, but also adequate interpretation of the results to the clinicians. In the present article selected aspects of EPT for HLA disease associations related to population genetics are reviewed and discussed with the emphasis on the optimal level of HLA typing resolution, population-based differences in disease associated HLA alleles within the allelic group, distribution and linkage disequilibrium of HLA alleles in particular populations and interpretation of the presence of less common HLA variants/haplotypes. In conclusion, the laboratories that perform and interpret the tests to the clinicians, producers of the certified diagnostics and EPT providers should consider, among others, the genetic characteristics of the populations in order to optimise the diagnostic value of the tests for disease-associated HLA variants.

Increased islet antigen-specific regulatory and effector CD4+ T cells in healthy individuals with the type 1 diabetes-protective haplotype

The DRB1*15:01-DQB1*06:02 (DR1501-DQ6) haplotype is linked to dominant protection from type 1 diabetes, but the cellular mechanism for this association is unclear. To address this question, we identified multiple DR1501- and DQ6-restricted glutamate decarboxylase 65 (GAD65) and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific T cell epitopes. Three of the DR1501/DQ6-restricted epitopes identified were previously reported to be restricted by DRB1*04:01/DRB1*03:01/DQB1*03:02. We also used specific class II tetramer reagents to assess T cell frequencies. Our results indicated that GAD65- and IGRP-specific effector and CD25⁺CD127^-FOXP3⁺ regulatory CD4⁺ T cells were present at higher frequencies in individuals with the protective haplotype than those with susceptible or neutral haplotypes. We further confirmed higher frequencies of islet antigen-specific effector and regulatory CD4⁺ T cells in DR1501-DQ6 individuals through a CD154/CD137 up-regulation assay. DR1501-restricted effector T cells were capable of producing interferon-γ (IFN-γ) and interleukin-4 (IL-4) but were more likely to produce IL-10 compared with effectors from individuals with susceptible haplotypes. To evaluate their capacity for antigen-specific regulatory activity, we cloned GAD65 and IGRP epitope-specific regulatory T cells. We showed that these regulatory T cells suppressed DR1501-restricted GAD65- and IGRP-specific effectors and DQB1*03:02-restricted GAD65-specific effectors in an antigen-specific fashion. In total, these results suggest that the protective DR1501-DQ6 haplotype confers protection through increased frequencies of islet-specific IL-10-producing T effectors and CD25⁺CD127^-FOXP3⁺ regulatory T cells.

HLA DR phenotypic frequencies and genetic risk of Type 1 diabetes in west region of Algeria, Tlemcen

Background

The main genomic region controlling the predisposition to type 1 diabetes is the Human Leukocyte Antigens (HLA) class II of the major histocompatibility complex. Association with different HLA types depends also on the studied populations. In our investigation, we tried to measure the phenotypic HLA class II association frequencies of DR3 and/or DR4 antigens, using a serologic method called microlymphocytotoxicity analysis, in diabetic and nondiabetic (ND) subjects originating from the west-Algerian region of Tlemcen. The aim of the present study was to determine which HLA DR antigens represent a high susceptibility to develop the disease in this area. Using a case-control retrospective study design, we randomly recruited ninety-one related subjects, 39 type 1 diabetics and 52 ND as controls, at the Internal Medicine Board of Medical Centre University of Tlemcen.

Results

DR3 antigen frequencies were comparable between the type 1 diabetics and the ND subjects and showed no association with the disease (p = 1.000, OR = 0.95), whereas DR4 and DR3DR4 antigens were associated with susceptibility to develop type 1 diabetes (DR4; OR = 2.10, DR3DR4; OR = 1.30). Also, no incidence for DR3 (p = 0.2646) or DR3DR4 (p = 0.0699) antigen frequencies was related to the sex ratio. However, significant differences in HLA DR4 frequencies between type 1 diabetics and ND were found to be related to sex (p = 0.0085).

Conclusion

Taken together, our investigation showed that the strongest association with type 1 diabetes was noticed in the presence of HLA DR4 antigens followed by DR3DR4 antigens. This study highlighted a characteristic of Tlemcen population; a history of consanguineous marriages. Association studies between the disease and genetic polymorphisms should be undertaken in a population where consanguinity is more limited to reduce confounding in result interpretations.

Ketosis-prone diabetes: dissection of a heterogeneous syndrome using an immunogenetic and beta-cell functional classification, prospective analysis, and clinical outcomes

Ketosis-prone diabetes is heterogeneous. Its causes could include novel beta-cell functional defects. To characterize such defects, 103 patients with diabetic ketoacidosis were evaluated for beta-cell autoimmunity and human leukocyte antigen (HLA) class II alleles, with longitudinal measurements of beta-cell function and biochemical and clinical parameters. They were classified into four A beta groups, based on the presence of glutamic acid decarboxylase (GAD)65, GAD67, or IA-2 autoantibodies (A+ or A-) and beta-cell functional reserve (beta+ or beta-). The group distribution was: 18 A+beta-, 23 A-beta-, 11 A+beta+, and 51 A-beta+. Collectively, the two beta- groups differed from the two beta+ groups in earlier onset and longer duration of diabetes, lower body mass index, less glycemic improvement, and persistent insulin requirement. HLA class II genotyping showed that the A-beta- group differed from the A+beta- group in having lower frequencies of two alleles strongly associated with autoimmune type 1 diabetes susceptibility: DQA*03 and DQB1*02. Similarly, the A-beta+ group differed from the A+beta+ group in having a lower frequency of DQB1*02. Ketosis-prone diabetes comprises at least four etiologically distinct syndromes separable by autoantibody status, HLA genotype, and beta-cell functional reserve. Novel, nonautoimmune causes of beta-cell dysfunction are likely to underlie the A-beta+ and A-beta- syndromes.

Analysis of the phenotypic distribution of HLA class I and class II in atopic and non-atopic asthma patients

In several studies the HLA system has been implicated in the development of asthma, but the importance of the associations between HLA genes and asthma remains unclear. The aim of this study was to determine the HLA class I and II phenotypic frequencies in a population of asthmatics, and to analyse the relationship between these phenotypes and any type of asthma. We typed HLA class I and II antigens in a series of 189 asthmatic individuals (102 atopic and 87 non-atopic), and in a control population of 150 unrelated healthy Caucasoid donors. When the HLA phenotypic frequencies were compared, no statistical differences were found. Therefore, no definitive HLA association could be established with atopic or non-atopic asthma in the studied population. Abbreviations AA, atopic asthma; FEV1, forced expiratory volume in 1 s; NAA, non-atopic asthma; PCR, polymerase chain reaction; SSOP, sequence-specific oligonucleotide probes; SPT, skin prick test.

Complex interaction between HLA DR and DQ in conferring risk for childhood type 1 diabetes

Type 1 (insulin-dependent) diabetes mellitus is associated with HLA DR and DQ factors, but the primary risk alleles are difficult to identify because recombination events are rare in the DQ-DR region. The risk of HLA genotypes for type 1 diabetes was therefore studied in more than 420 incident new onset, population-based type 1 diabetes children and 340 age, sex and geographically matched controls from Sweden. A stepwise approach was used to analyse risk by relative and absolute risks, stratification analysis and the predispositional allele test. The strongest relative and absolute risks were observed for DQB1*02-DQA1*0501/DQB1*0302-DQA1*0301 heterozygotes (AR 1/46, P < 0.001) or the simultaneous presence of both DRB1*03 and DQB1*0302 (AR 1/52, P < 0.001). Stratification analysis showed that DQB1*0302 was more frequent among DRB1*04 patients than DRB1*04 controls (P < 0.001), while DRB1*03 was more frequent among both DQA1*0501 (P < 0.001) and DQB1*02 (P < 0.001) patients than respective controls. The predispositional allele test indicated that DRB1*03 (P < 0.001) would be the predominant risk factor on the DRB1*03-DQA1*0501-DQB1*02 haplotype. In contrast, although DQB1*0302 (P < 0.001) would be the predominant risk factor on the DRB1*04-DQA1*0301-DQB1*0302 haplotype, the predispositional allele test also showed that DRB1*0401, but no other DRB1*04 subtype, had an additive risk to that of DQB1*0302 (P < 0.002). It is concluded that the association between type 1 diabetes and HLA is due to a complex interaction between DR and DQ since (1) DRB1*03 was more strongly associated with the disease than DQA1*0501-DQB1*02 and (2) DRB1*0401 had an additive effect to DQB1*0302. The data from this population-based investigation suggest an independent role of DR in the risk of developing type 1 diabetes, perhaps by providing diseases-promoting transcomplementation molecules.

The minisatellite in the diabetes susceptibility locus IDDM2 regulates insulin transcription

Genetic susceptibility to insulin-dependent diabetes mellitus (IDDM) is inherited as a polygenic trait. One of the loci implicated in IDDM is a polymorphic minisatellite 5' of the human insulin (INS) gene on chromosome 11. This insulin-linked polymorphic region (ILPR) is composed of tandemly repeated sequences, which fall into three size classes: IDDM is strongly associated with short ILPR alleles. We now show that the ILPR is capable of transducing a transcriptional signal in pancreatic beta-cells, with a long ILPR possessing greater activity than a short ILPR. The ILPR contains numerous high-affinity binding sites for the transcription factor Pur-1, and transcriptional activation by Pur-1 is modulated by naturally occurring sequences in the ILPR. Our results demonstrate a possible function for this unique minisatellite, which may have implications for type 1 diabetes.

Pathogenesis of insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus is strongly associated with certain HLA types and the presence of islet cell-specific autoantibodies. The pathogenesis is a specific loss of pancreatic beta cells. The dissection of IDDM genes is complicated by the low recurrence rate of the disease among first-degree relatives. HLA-DQ2 and 8 are closest to IDDM with a marked synergistic effect of DQ2/8 heterozygotes. The associations with other HLA genes are often explained by linkage disequilibrium. Genetic factors on other chromosomes which influence the pathogenesis are still to be fully identified but candidates are on chromosomes 11 (insulin gene polymorphisms) and 7 (TCR gene polymorphisms). The autoreactivity against the GAD65 isoform is pronounced both before and at the clinical onset of IDDM. GAD65 autoantibodies show the highest predictive value and may represent an initiating autoantigen. Autoantibodies to numerous other beta cell autoantigens are detected at the clinical onset but may represent a secondary response and antigen spreading during a sustained autoimmune attack on the beta cells. The role of T cells in human IDDM is yet to be defined. GAD65 and other islet autoantibodies have a low positive predictive value for IDDM and further investigations are needed to clarify ways to predict IDDM in the general population.

Particular HLA-DQ molecules play a dominant role in determining susceptibility or resistance to type 1 (insulin-dependent) diabetes mellitus

Genes in the HLA complex are by far the most important in determining genetic predisposition or resistance to Type 1 (insulin-dependent) diabetes mellitus. In this review evidence is presented that the HLA genes mainly involved are those encoding some particular HLA-DQ molecules. Both among Black, Caucasian and Japanese subjects particular cis or trans encoded DQ molecules are significantly associated with susceptibility, while others are associated with resistance. A varying degree of susceptibility or resistance seems to be conferred by these DQ molecules, where those determining resistance are dominant over those determining susceptibility. The degree of genetic predisposition to develop Type 1 diabetes carried by an individual would therefore be the result of his or her particular combination of DQ molecules. A primary association to particular DQ molecules explains previously found associations to other HLA complex genes by linkage disequilibrium. Some mechanisms by which particular DQ molecules may determine susceptibility or resistance are also discussed. Potential islet beta-cell reactive CD4+ T-cells may escape negative selection (deletion) in the thymus, but normally become anergized or remain ignorant extra-thymically. However, under particular circumstances they may be triggered. The DQ molecules associated with Type 1 diabetes susceptibility may preferentially bind and present triggering and/or beta-cell derived peptides to such T cells, causing beta-cell destruction. The finding that particular DQ molecules determine susceptibility may lead to new methods of preventing development of Type 1 diabetes in susceptible individuals.

Role of HLA genes in predisposition to develop insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM), or type I diabetes, is the end result mainly of a T-cell mediated autoimmune destruction of pancreatic islet beta cells. Genetical and environmental factors are both of importance in the pathogenesis. Genes in the HLA complex seem to be the most important genetical factors. Among Blacks, Caucasoids and Orientals, IDDM susceptibility is associated with some particular combinations of DQA1 and DQB1 genes in cis or trans position. This strongly argues that susceptibility is primarily associated to the corresponding HLA-DQ molecules themselves. However, weaker contributions by other genes in the HLA complex cannot be excluded. Similarly, a dominant protection is strongly associated with some other DQ molecules, in particular HLA-DQ6, in all three ethnic groups. The function of HLA-DQ (and other class II) molecules is to present peptide-fragments of antigens to CD4+ T cells (mainly helper T cells). Thus, the recognition of certain islet beta cell derived peptides by self-reactive CD4+ T cells, may be an initial event in the pathogenesis. The DQ molecules involved in IDDM susceptibility or protection may exert their function either during thymic development of potential self-reactive CD4+ T cells, or by preferential presentation of certain beta-cell derived peptides to CD4+ T cells, or both. The finding that certain DQ molecules as such confer IDDM susceptibility may lead to new methods to prevent IDDM, for example by using blocking peptide analogues.

HLA DQA tissue typing of cadaveric eye bank donor material with polymerase chain reaction

It has been suggested that the provision of HLA matched tissue for corneal transplantation would be beneficial for graft survival especially in high risk patients. In this study we report the application of a polymerase chain reaction (PCR) based tissue typing procedure to type cadaveric donor material. Using beta-globin gene amplification as a test system we found that cornea, corneal rim, conjunctiva, sclera, rectus muscle, optic nerve and neural retina were all suitable for PCR amplification but DNA extracted from pigment epithelial cells and from the iris could not be amplified. HLA DQA typing results of 9 samples identified 5 alleles and 7 genotypes. In two cases the antigens detected by serology reflected the alleles detected by PCR. In a third case in which the class II serological typing was inconclusive we detected two DQA alleles by PCR. These alleles were consistent with those which would be predicted to be present on the basis of known linkage disequilibrium between HLA-Cw, B, DR and DQ. In this study we have shown that PCR based tissue typing is more sensitive and gives more detailed typing results than serology and would be suitable to type cadaveric donor material on a routine basis.

Association of polar amino acids at position 26 of the HLA-DQB1 first domain with the anticentromere autoantibody response in systemic sclerosis (scleroderma)

HLA class II alleles (detected by DNA typing) were determined in 116 Caucasians with systemic sclerosis positive and negative for anticentromere autoantibodies (ACA). Significantly increased frequencies of HLA-DR5(DRw11) (P = 0.009) and the Dw13(DRB1*0403, *0407) subtypes of DR4 (probability corrected, Pc = 0.005) were seen in ACA positive patients, and HLA-DR1 and DRw8 were also increased. These findings appeared to reflect linkage disequilibrium of DR5(DRw11) and many DR4(Dw13) haplotypes with HLA-DQw7 and DR1 with DQw5. In fact, the presence of a DQB1 allele having a polar glycine or tyrosine at position 26 of the DQB1 first domain versus a hydrophobic leucine accounted for 100% of ACA positive Caucasian systemic sclerosis patients compared to 69% of the ACA negative SS patients (P = 0.0008) and 71% of Caucasian controls (P = 0.0003) as well as all 7 ACA patients of non-Caucasian background. Furthermore, the genotype frequency of DQB1 alleles lacking leucine at position 26 was 73% in ACA positive SS patients, compared to 42% of ACA negative patients (P = 1.2 x 10(-5)) and 38% of controls (P = 5.8 x 10(-7)). These data, then, suggest that the second hypervariable region of the HLA-DQB1 chain may form the candidate epitope associated with the ACA response.

Allele-specific gene probing supports the DQ molecule as a determinant of inherited susceptibility to type 1 (insulin-dependent) diabetes mellitus

Trans-racial analysis of disease associations has improved mapping of MHC-linked susceptibility to Type 1 (insulin-dependent) diabetes mellitus. In this study the contributions of the MHC class II DQA1 and DQB1 genes were investigated. Sequence-specific oligonucleotide gene probing in Type 1 diabetic and control subjects of North Indian origin supported the DQw1.18 allele of the DQB1 gene as a determinant of inherited protection against Type 1 diabetes (RR = 0.12, pc less than 0.05). The A3 allele of the DQA1 gene was positively associated with the disease, (RR = 3.6, pc less than 0.05), as was the DQw2 allele of the DQB1 gene (RR = 4.6, pc less than 0.01). Trans-racial comparison of these disease associations indicates that DQ alleles may directly determine an element of inherited susceptibility to Type 1 diabetes.

The polymerase chain reaction: miracle or mirage? A critical review of its uses and limitations in diagnosis and research

Since publication of the polymerase chain reaction (PCR) technique in 1985 (Saiki et al. Science 1985; 230: 1350-1354), there has been an explosion of reports on its use in medicine and science. We critically review its use both as a diagnostic technique and as a research tool, and show the pathologist how to evaluate PCR data and how to avoid the pitfalls of overinterpretation. We discuss the value of PCR in the characterization of genetic defects, prenatal diagnosis, carrier testing, HLA typing, detecting micro-organisms, identifying activated oncogenes, and in the characterization of leukaemias and lymphomas, and summarize the main applications in biomedical research.

Identification of susceptibility loci for type 1 (insulin-dependent) diabetes by trans-racial gene mapping

A major component of inherited susceptibility to Type 1 (insulin-dependent) diabetes mellitus has been mapped to the major histocompatibility complex. Certain gene alleles in this region determine susceptibility and resistance to the disease. Mapping of susceptibility is hindered by the limitations of conventional tissue typing techniques, and by strong linkage disequilibrium within this part of the genome. Recombinant DNA technology and trans-racial studies have been used to allow finer mapping of genetic predisposition to Type 1 diabetes. These techniques have localised alleles encoding susceptibility and resistance to the DQ region. Other alleles determining disease susceptibility remain poorly localised.

The A3 allele of the HLA-DQA1 locus is associated with susceptibility to type 1 diabetes in Japanese

Analysis of the frequencies of class II HLA-DR and HLA-DQ alleles by serological and DNA typing in 49 Japanese patients with type 1 (insulin-dependent) diabetes and 31 Japanese controls indicates the following. (i) Susceptibility is more strongly associated with the HLA-DQ subregion than with the HLA-DR subregion. (ii) Of the class II alleles detected, the A3 allele of the DQA1 locus was the most strongly associated with disease. Ninety-six percent of the patients were positive for the A3 allele compared to 53% of the controls (P = 0.001; relative risk = 19.7; confidence limits = 3.72-188.64). (iii) The DQw8 allele of the DQB1 locus, which is associated with susceptibility to type 1 diabetes in Caucasians and Blacks, was not increased in frequency in Japanese patients (22%) versus controls (19%). (iv) Asp-57-encoding DQB1 alleles are associated with reduced susceptibility to type 1 diabetes in Caucasians. The major predisposing haplotypes in Japanese are DR4 and DR9. By DNA sequence analysis, both of these Japanese haplotypes have Asp-57-encoding DQB1 alleles. Oligonucleotide dot blot analysis showed that all, except 1, of the 49 Japanese patients and all of the 31 controls have at least one Asp-57-encoding DQB1 allele. In addition, 40% of the patients were homozygous for Asp-57-encoding DQB1 alleles versus 35% of the controls. The high frequencies of Asp-57-encoding DQB1 alleles in this ethnic group may account for the rarity of type 1 diabetes in Japan.