The genetics of susceptibility to diabetes

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.

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.

The genetics of type 1 diabetes: lessons learned and future challenges

It has been more than 30 years since the first evidence was published suggesting the involvement of a specific chromosomal region, HLA, in modulating the risk for type 1 diabetes (T1D). In the intervening years, what have we learned regarding the identities of specific loci that modulate T1D risk, and what lessons have these studies provided that might be helpful in finding and characterizing additional susceptibility loci both for T1D and other autoimmune disorders? In the following review, we briefly address these issues.

Developments in the prediction of type 1 diabetes mellitus, with special reference to insulin autoantibodies

The prodromal phase of type 1 diabetes is characterised by the appearance of multiple islet-cell related autoantibodies (Aab). The major target antigens are islet-cell antigen, glutamic acid decarboxylase (GAD), protein-tyrosine phosphatase-2 (IA-2) and insulin. Insulin autoantibodies (IAA), in contrast to the other autoimmune markers, are the only beta-cell specific antibodies. There is general consensus that the presence of multiple Aab (> or = 3) is associated with a high risk of developing diabetes, where the presence of a single islet-cell-related Aab has usually a low predictive value. The most commonly used assay format for the detection of Aab to GAD, IA-2 and insulin is the fluid-phase radiobinding assay. The RBA does not identify or measure Aab, but merely detects its presence. However, on the basis of molecular studies, disease-specific constructs of GAD and IA-2 have been employed leading to somewhat improved sensitivity and specificity of the RBA. Serological studies have shown epitope restriction of IAA that can differentiate diabetes-related from unrelated IAA, but current assays do not distinguish between disease-predictive and non-predictive IAA or between IAA and insulin antibodies (IA). More recently, phage display technology has been successful in identifying disease-specific anti-idiotopes of insulin. In addition, phage display has facilitated the in vitro production of antibodies with high affinity. Identification of disease-specific anti-idiotopes of insulin should enable the production of a high affinity reagent against the same anti-idiotope. Such a development would form the basis of a disease-specific radioimmunoassay able to identify and measure particular idiotypes, rather than merely detect and titrate IAA.

Prediabetes in children: natural history, diagnosis, and preventive strategies

The clinical manifestation of type 1 diabetes mellitus is preceded by an asymptomatic prodromal period called prediabetes or preclinical diabetes. It may last from a few months to several years, during which the autoimmune destruction of the insulin-producing beta-cells in the pancreas progresses. The genes on the human leukocyte antigen (HLA) and insulin gene region are major genetic determinants for genetic disease susceptibility, while dietary compounds and viral infections are the most likely environmental factors contributing to the etiopathogenesis. T cells are thought to be the effector cells for the beta-cell destruction, and glutamic acid decarboxylase, insulinoma-associated protein 2 and insulin represent the three major autoantigens. Autoantibodies are early detectable markers of an ongoing disease process and are used to diagnose prediabetes. Among first-degree relatives of patients with type 1 diabetes, the risk for clinical disease can be graded from <5% in those with one or no antibodies to >90% in individuals who carry the HLA-DQB1*02/0302 risk genotype and are positive for multiple autoantibodies. beta-Cell function may also be tested in autoantibody-positive individuals and low first-phase insulin response is highly predictive for rapid progression to the clinical disease. However, dynamic course and individual variation of the disease process complicates the disease prediction, and it is not known whether all individuals with signs of prediabetes will inevitably progress to clinical type 1 diabetes. Until clinically applicable prevention for the condition exists, the screening for the risk markers of type 1 diabetes should actively be undertaken only in the context of research projects. Several major national and international multicenter studies are ongoing to test the potential of various agents (e.g. insulin and nicotinamide) or early elimination of dietary compounds (e.g. cow's milk proteins) to delay or prevent the onset of clinical type 1 diabetes.

Mapping genes for autoimmunity in humans: type 1 diabetes as a model

Type 1 diabetes (T1D) arises from autoimmune destruction of the beta cells of the pancreas leading to a complete dependence on exogenous insulin for survival. Like many autoimmune disorders, the etiology of T1D is complex, resulting from the action of multiple genes and environmental factors. Identification of genes that contribute to T1D susceptibility should improve disease prediction and contribute to the understanding of the underlying pathology of the disorder. Two regions of the human genome, the human leukocyte antigen (HLA) region and the insulin gene region are generally thought to contain susceptibility loci for T1D. Although additional putative T1D loci have been reported, the supporting evidence has often been of modest significance and findings have displayed poor reproducibility across multiple studies. This review summarizes the current state of genetic linkage and association studies in T1D and suggests future directions. We argue that much of the difficulty in mapping T1D susceptibility loci has resulted from inadequate sample sizes and we illustrate the substantial gains in power that can be achieved by pooling data across studies. These findings suggest that substantial progress toward the identification of susceptibility genes in T1D and other genetically complex disorders may be achieved through increased collaboration and consortium mapping efforts.

The combination of several polymorphic amino acid residues in the DQalpha and DQbeta chains forms a domain structure pattern and is associated with insulin-dependent diabetes mellitus

IDDM is positively associated with HLA-DQA1*0301-DQB1*0302 (DQ8) and DQA1*0501-DQB1*0201 (DQ2) and negatively associated with DQA1*0102-DQB1*0602 (DQ6). The aim of the present study was to analyze the importance of several polymorphic residues and domains of DQalpha and DQbeta, in addition to residue 52 DQalpha and residue 57 DQbeta, with regard to susceptibility or resistance in new-onset 0- to 15-year-old Swedish children with IDDM (n = 425) and matched controls (n = 367). HLA genotyping identified several polymorphic residues of the DQalpha and DQbeta to be either positively or negatively associated with IDDM, including Arg 52 DQalpha and Asp 57 DQbeta. Leu 69 DQalpha was positively (OR 7.02, P < 0.0001), Ala 69 DQalpha was negatively (OR 0.22, P < 0.0001), Gln 47 DQalpha was positively (OR 5.8, P < 0.0001), Cys 47 DQalpha was positively (OR 2.2, P < 0.0001), Lys 47 DQalpha was negatively (OR 0.47, P < 0.005), and Arg 47 DQalpha was negatively (OR 0.22, P < 0.005) associated with IDDM. Similarly, residues at 11, 18, 45, 48, 50, 53, 55, 61, 64, 66, 76, and 80 were either positively or negatively associated with IDDM. Likewise, for DQbeta, Leu 53 DQbeta was positively (OR 11.01, P < 0.0001), Gln 53 DQbeta was negatively (OR 0.22, P < 0.0005), Arg 70 DQbeta was positively (OR 11.01, P < 0.0001), and Gly 70 DQbeta was negatively (OR 0.19, P < 0.0001) associated like other residues at 71, 74, 84, 85, 86, 89, and 90 DQbeta with IDDM. Certain domains in the DQalpha, RFTIL (at DQalpha positions 52, 61, 64, 66, and 69), were present in 95% of patients compared to 69% of controls (OR 9.01, P(c) < 0.0001), and DQbeta domain GR (at DQbeta positions 45 and 70) was present in 95% of patients and 68% of controls (OR 8.68, P < 0.0001), which correlated better than the individual amino acid residues with IDDM. A combination of the DQalpha and DQbeta chain domains was present in 94% of patients compared to 60% of controls (OR 10.6, P < 0.001). In conclusion, domains in the DQalpha, DQbeta, or both in the DQ molecule explain susceptibility or resistance to IDDM better than individual amino acid residues of DQA1 and DQB1.

Geographical differences within Finland in the frequency of HLA-DQ genotypes associated with type 1 diabetes susceptibility. The Childhood Diabetes in Finland Study Group

Geographical variations in the HLA-DQ genotypes associated with risk for type 1 diabetes were evaluated in Finland. Samples of 280 diabetic children diagnosed in Turku (south-west of the country) and 405 in Oulu (north of the country) were studied as well as a series of 14 096 and 10 016 newborns collected from the same hospitals. There were no major differences in the risk or protection conferred by various HLA-DQB1 genotypes between south-western and northern parts of the country when genotypes of children with type 1 diabetes from these two centres were compared with those of newborns, representing the background populations. However, the distribution of various genotypes was different, both in diabetic children and in newborns, when compared between the two regions (P < 0.0001, chi2 test). These differences reflected the allele frequencies in newborn cohorts in which HLA-DQB1*02 and DQB1*0301 were found more often in Turku and DQB1*0302 more often in Oulu (P < 0.0001 for all differences). Similar types of differences were detected when children who were diagnosed as having diabetes during the national 'Childhood Diabetes in Finland' (DiMe) study between the years 1986-1989 were compared according to their residence. The observed differences in genotype and allele frequencies demonstrate the heterogeneity for HLA alleles even in a population that is generally regarded as highly homogeneous. These differences also affect the sensitivity and efficiency of the screening programme used for identifying infants with genetic susceptibility to IDDM in the ongoing Finnish Diabetes Prediction and Prevention Study.

HLA-DRB1, -DQA1, and -DQB1 genotypes in patients with nasal polyposis

OBJECTIVES/HYPOTHESIS

Genetic etiology is suspected in the development of nasal polyposis on the basis of familial aggregation. This study investigated whether there is an association between HLA-DRB1, -DQA1, and -DQB1 alleles and developing nasal polyposis.

STUDY DESIGN

Data from 50 polypectomized patients were compared with data from 50 healthy randomly selected controls. Polyp score, possible asthma, aspirin sensitivity, and ASA triad were also recorded.

METHODS

Genotyping of HLA-DRB1 alleles was carried out with the Dynal RELI SSO HLA-DRB, a direct DNA probe test that utilizes a polymerase chain reaction (PCR) and nucleic acid hybridization for the differentiation of 70 HLA-DRB alleles and 9 supertypes. For DQA1* genotyping PCR-RFLP (restriction fragment length polymorphism) was used, differentiating eight alleles. The DQB1* typing was carried out using a INNO-LiPA DQB PCR-reverse hybridization kit, allowing the discrimination of 30 alleles.

RESULTS

People carrying the HLA-DR7-DQA1*0201, and -DQB1*0202 haplotype were found to have a two to three times higher odds ratios (ORs) for developing the disease, compared with controls. Patients with ASA triad carried the above-mentioned DR7 allele with the linked alleles significantly more often (P < .001). Subjects carrying HLA-DR5 allele and the linked alleles had lower odds ratio values.

CONCLUSION

These results underline that allergy is not conditional for the formation of nasal polyps as thought before. Nasal polyposis associated with asthma and aspirin sensitivity is probably a unique form of nasal polyps. The authors plan further investigations in this field.

Prevalence of human leukocyte antigen DQA1 and DQB1 alleles in Kuwaiti Arab children with type 1 diabetes mellitus

The prevalence of human leukocyte antigen (HLA) DQB1 and DQA1 alleles has been determined in 78 Kuwaiti Arab children with insulin-dependent diabetes mellitus (IDDM) and in 57 normal healthy controls with similar ethnic background. The typing of HLA-DQ alleles was carried out using an allele-specific DNA-based polymerase chain reaction (PCR) SSP method. DR typing was also performed in 212 control subjects using PCR-SSP (sequence specific primer) method. A significantly higher frequency of DQB1*0201 allele was found in IDDM cases compared to the controls (p<0.001). There was no significant difference in the prevalence of DQB1 alleles *0302, *0501, and *0602 between IDDM cases and the controls. In contrast, DQB1 alleles *0301, *0402, *0502, *0602, and *0603 were represented at a somewhat higher frequency in controls compared to the IDDM cohort. The frequency of DQA1 allele *0301, which encode for an Arg at codon 52, was significantly higher in the IDDM patients compared to the controls (p<0.001). The frequency of DQA1 allele *0302 was also higher in IDDM cases than controls (p = 0.034) but the difference was less pronounced than DQA1*0301. Amongst the Arg52 alleles, no significant difference was detected in the frequency of *0401 between IDDM cases and the controls and the allele *0501 was detected only in controls. For non-Arg52 alleles *0103, *0104, and *0201, the differences in the two groups were not significant, with the exception of allele *0104 (p = 0.024). DR3 was the most common type in the Kuwaiti general population (28%) and DRB1*0301 was detected in 41% of the individuals with DR3 specificity. Analysis of HLA-DQBI/DQA1 haplotypes from IDDM cases and controls revealed a significantly high frequency of haplotype DQA1*0301/DQB1*0201 between Kuwaiti IDDM cases (49/78, 63%) and the controls (8/57, 14%).

A comparison of three statistical models for IDDM associations with HLA

The association between HLA-DQ haplotypes and insulin-dependent diabetes mellitus (IDDM) was studied in 48 children from 44 families ascertained from the high incidence area around Umeå, Sweden. Numerous hypotheses have been proposed to explain associations between HLA and IDDM, but comparisons of statistical models based on these hypotheses have not been attempted. The aim of the present study was to compare the goodness-of-fit and predictive abilities among different statistical models. A likelihood-based analysis rather than a conventional analysis based on contingency tables was therefore adopted. We first used parental haplotype information in a conditional likelihood analysis (1) and then compared this analysis with that of an unaffected control group which used information on geographically matched controls. Under the analysis conditional on parental haplotype, a statistical model motivated by the hypothesis that the entire DQ heterodimer is involved in IDDM pathogenesis fit the data significantly better and had greater predictive ability than either a model motivated by the explanation that an IDDM gene is linked to DQB1 or that the DQB1 chain itself is involved in IDDM pathogenesis, or a model arising from the hypothesis that single amino acids at codon 57 of DQB1 and codon 52 of DQA1, respectively, confer susceptibility. Under the case-control analysis, the identity of the best-fitting or more predictive statistical model was not as clear, although both approaches to analyzing risk suggested that the single-amino-acids model had significantly poorer fit compared to the remaining two models.

Effect of genetic risk load defined by HLA-DQB1 polymorphism on clinical characteristics of IDDM in children

Clinical and autoimmune characteristics of 150 diabetic children of mean age 7.8 years (SD 4.1 years) were recorded at clinical manifestation and during the first 2 years of IDDM in order to investigate whether subjects with high risk HLA-DQB1 genotypes differ from those without these risk markers. When comparing subjects with the DQB1*0302/0201, DQB1*0302/x, DQB1*0201/x, or other DQB1 genotypes (x = no protective allele), no differences were found in the age of the subjects at diagnosis, the duration of hyperglycaemic symptoms, or the length of clinical remission. The frequency of islet cell antibodies (ICA) and quantitative serum levels of these antibodies were of the same magnitude in all four groups. During the initial 2 years of IDDM serum C-peptide concentrations were observed to be inversely related to the degree of genetic risk (P < 0.001 in two-way analysis of variance for repeated measures), the lowest C-peptide levels being observed in the group of DQB1*0302/0201 heterozygotes (P < 0.001 vs. DQB1*0201/x; P < 0.01 vs. DQB1*0302/x; P = 0.05 vs. others). On the other hand, the subjects with the DQB1*0201 genotype had the highest serum C-peptide concentrations, the levels being even higher than those of the patients carrying neutral or protective DQB1 genotypes (P < 0.01). These subjects also had lower daily insulin doses and blood glycated haemoglobin A1 (HbA1) levels over the initial 2 years of the disease when compared with the DQB1*0302/0201 heterozygotes (P < 0.05 and P < 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Self and non-self antigen in diabetic autoimmunity: molecules and mechanisms

In this article, we have summarized current facts, models and views of the autoimmunity that leads to destruction of insulin-producing beta-cells and consequent Type 1 (insulin-dependent) diabetes mellitus. The presence of strong susceptibility and resistance gene loci distinguishes this condition from other autoimmune disorders, but environmental disease factors must conspire to produce disease. The mapping of most of the genetic risk (or disease resistance) to specific alleles in the major histocompatibility locus (MHC class II) has direct functional implications for our understanding of autoimmunity in diabetes and directly implies that presentation of a likely narrow set of peptides is critical to the development of diabetic autoimmunity. While many core scientific questions remain to be answered, current insight into the disease process is beginning to have direct clinical impact with concerted efforts towards disease prevention or intervention by immunological means. In this process, identification of the critical antigenic epitopes recognized by diabetes-associated T cells has achieved highest priority.

Inheritance of MHC class II genes in IDDM studied in population-based affected and control families

The transmission of HLA-DR and DQ was compared between 46 families with at least one child affected by insulin dependent diabetes mellitis (IDDM) and 43 healthy control families. In the patient families, there was an increased transmission of DR4 (p < 0.025) and DQB1*0302 (p < 0.01) from both parents to the index patient. There was an increased transmission of DQB1*0302 (p < 0.03) from the mothers only. The non-inherited maternal haplotypes showed a significantly decreased frequency (p < 0.01) of positively associated haplotypes (DR4-DQA1* 0301-DQB1*0302, DR3-DQA1*0501-DQB1*0201) compared to all parental haplotypes in the control families. In the control families neither transmission rates nor frequencies of non-inherited haplotypes differed from those expected in the control families. In conclusion, the observed reduction of IDDM-positively associated haplotypes in patient non-inherited maternal haplotypes, but not in non-inherited paternal haplotypes, suggests that tolerance during fetal life to maternal non-inherited HLA molecules may be important to diabetes development.

Molecular biology of IDDM

The clinical onset of insulin-dependent diabetes is associated with several autoimmune phenomena including islet cell antibodies, glutamic acid decarboxylase (the GAD65 isoform) autoantibodies (GAD65Ab) as well as insulin autoantibodies. The molecular cloning of these autoantigens has permitted the development of precise and reproducible antibody immunoassays to identify marker-positive patients and control subjects. Among patients with new-onset diabetes about 70% were GAD65Ab positive compared to 1.5% among control subjects while 46% of patients had IAA compared to 1% among control subjects. The autoreactive sites or epitopes of GAD65 and insulin remain to be determined. The disease association with HLA on chromosome 6 may help to define the epitope specificity of the autoimmune reaction. Recent data suggest that 95% of new-onset IDDM children (0-15 years of age) are positive for either DQ2, DQ8 or both compared to about 50% of healthy control subjects. HLA-DQ6 is negatively associated with the disease. Both HLA-DQ2 and DQ8 therefore seem to be necessary, but not sufficient for diabetes. Molecular modelling suggests comparable physicochemical properties of DQ2 and DQ8 but are widely different from DQ6. In 1984, the conclusion was that molecular cloning of the genes for the autoantigens, antibodies, T-cell receptors, as well as HLA class I and II molecules associated with diabetes are essential for analysing the components which control the development of pancreatic beta-cell autoimmunity. In 1994, autoantigens and HLA molecules have been cloned and recombinant reagents developed to be used in experiments aimed at testing whether it will be possible to predict IDDM.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of MHC class II antigens in Japanese IDDM by a novel HLA-typing method, hybridization protection assay

We examined HLA Class II antigens in 116 Japanese IDDM patients [84 typical IDDM (T-IDD); 32 slowly progressive IDDM (S-IDD)] by the hybridization protection assay (HPA) which is a novel HLA typing method based on hybridization of acridinium-ester-labeled DNA probes to amplified DNA. We detected HLA-DRB1, -DQA1 and -DQB1 genes by this method which is capable of analyzing over 50 samples within 4 h with high sensitivity. Positive associations were found in DRB1*0405, DRB1*0802, DRB1*0901, DQA1*0301, DQB1*0303 and DQB1*0401, negative correlations in DRB1*0403, DR2, DR12, DRB1*0801 or 03, DQA1*0101 or 02, DQA1*0501, DQB1*0301 and DQB1*0602 alleles. The absence of aspartic acid (Asp) at position 57 of the DRB1 chain and the presence of arginine (Arg) at position 52 of the DQA1 chain correlated positively with both types of IDDM. There were no significant differences in HLA between T-IDD and S-IDD. These results suggest that the absence of Asp at position 57 of the DRB1 chain and the presence of Arg at position 52 of the DQA1 chain are significant Japanese IDDM patients and that DRB1*0802, in which the amino acid at position 57 is aspartic acid, may play a role in the pathogenesis of IDDM. Also, T-IDD and S-IDD have common bases in the HLA gene.

Multi-locus analysis of HLA class II genes in DR2-positive IDDM haplotypes in Finland. The "Childhood Diabetes in Finland" (DiMe) Study Group

In this study we characterized the haplotypes found in IDDM patients that normally confer resistance to the disease in order to localize the polymorphisms relevant for the protection. We studied 15 DR2-positive subjects with IDDM for their DRB1, DRB5 and DQB1 genes using RFLP, polymerase chain reaction (PCR), oligonucleotide typing, and in some specific cases direct sequencing after allele-specific PCR. In addition we analyzed 39 DR2-positive, IDDM non-associated haplotypes representing those haplotypes that are not inherited to probands and hence are present only in healthy family members. The frequency of the DRB1*1501-DRB5*0101-DQB1*0602 haplotype was slightly decreased among diabetic patients (80% vs. 92%). In addition, two unconventional haplotypes DRB1*1501-DRB5*0101-DQB1*05031 and DRB1*1501-DRB5*0101-DQB1*0502 were found in patients with IDDM while all the control ones were conventional. The sequencing of the DQB1*0602 allele present in IDDM haplotypes showed no differences when compared to the controls. These results support the primary but not absolute role of DQ in the protection against IDDM. An additional role of factors centromeric to DQB1 gene was suggested by findings based on the bi-allelic TaqI RFLP polymorphism of the DQA2 gene. All DR2-DQB1*0602 IDDM haplotypes were associated with the 2.1-kb fragment while in the control group the 2.1-kb and 1.9-kb fragments were evenly distributed.

Defective HLA class II expression in monocytes of type 1 diabetic patients. The Childhood Diabetes in Finland Study Group

Activation of T-helper cells is modulated by the intensity of HLA class II expression on antigen-presenting cells. We evaluated whether any abnormalities could be found in the expression of HLA-DR and -DQ molecules on monocytes in type 1 diabetic subjects. DR and DQ molecules were induced by human recombinant interferon-gamma on cultured peripheral blood monocytes obtained from children with type 1 diabetes (N = 28), their siblings (N = 18) and unrelated healthy controls (N = 21). The response in DQ induction varied considerably between different individuals, but the average responsiveness was significantly lower in patients compared to siblings and unrelated controls. In addition to the diabetic subjects deficient DQ induction was also observed in three siblings. One of them had high levels of islet cell antibodies and presented with diabetes 6 months later, and another had active rheumatoid arthritis. The response in DR induction was also slightly lower in patients than in siblings, but did not differ from that in unrelated controls. The results suggest abnormalities in the regulation of HLA class II expression in type 1 diabetic subjects possibly reflecting the ongoing autoimmune process.

Tumour Necrosis Factor-beta Gene RFLP Alleles in Finnish IDDM Hapiotypes

The genes located between class II and class I HLA genes including polymorphic tumour necrosis factor (TNF) genes may contribute to the disease susceptibility in IDDM. Restriction fragment polymorphisms of the TNF-beta gene have been found to be fixed in the major IDDM susceptibility haplotypes, the B62,DR4 haplotype being associated with the 10.5-kb fragment and the B8,DR3 haplotype with a 5.5-kb fragment. We studied this TNF polymorphism in a sample of diabetic families. In all IDDM-associated haplotypes (n = 129) the 5.5-kb allele was more frequent than in haplotypes found only in healthy family members (n = 112) (58.1% versus 40.2%, P < 0.01). Among IDDM haplotypes the B62,DR4 haplotype was characterized by the 10.5-kb TNF fragment, whereas two other common Finnish IDDM-associated DR4 haplotypes--A24,B39,DR4 and A2,B56,DR4--had the 5.5-kb TNF fragment. Both IDDM-associated and non-associated DR3 positive haplotypes were linked to the 5.5-kb fragment. The distribution of various combinations of TNF alleles in IDDM probands (n = 63) did not differ from that expected according to the Hardy-Weinberg distribution. Our results indicate that the 10.5-kb allele of TNF-beta gene as such is not a risk factor contributing to DR4/DQ8-associated susceptibility. Alternatively, there may be heterogeneity in pathogenetic effector mechanisms.

Genetic dissection of autoimmune type I diabetes in the BB rat

The BB rat is among the best models of insulin-dependent diabetes mellitus--with onset and pathogenesis closely resembling the human disease. One unusual feature is a severe T-cell lymphopenia, which appears to be inherited as a recessive trait controlled by a single gene, Lyp. Based on genetic analysis of several crosses, we show that development of diabetes involves at least three genes: Lyp, which is tightly linked to the neuropeptide Y (Npy) gene on chromosome 4, a gene linked to the major histocompatibility complex (MHC) on chromosome 20, and a third unmapped gene for which the Fischer rat strain carries an allele conferring resistance.

Normal C3b receptor (CR1) genomic polymorphism in patients with insulin-dependent diabetes mellitus (IDDM): is the low erythrocyte CR1 expression an acquired phenomenon?

Expression of the erythrocyte complement receptor (C3bR = CR1 = CD35) and its genomic polymorphism (HindIII RFLP) was studied in a group of 80 patients with IDDM, 31 healthy siblings and 101 healthy blood donors. Defective CR1 expression was found in 26% of the patients with IDDM compared with 9% of the controls (P less than 0.05) and 0% of the siblings. The CR1 gene polymorphism of the IDDM patients did not significantly differ from that of the controls. The presence of a 6.9 kb (L) CR1 gene fragment was associated with a low CR1 expression in the patients (P less than 0.05) and especially in the controls (P less than 0.001). No significant association was found between the presence or absence of the HLA risk antigens for IDDM and CR1 expression. The results confirm that erythrocyte CR1 expression is genetically determined, but the CR1 deficiency associated with IDDM seems to be an acquired rather than a genetic phenomenon.

Prevention of spontaneous and cyclophosphamide-induced diabetes in non-obese diabetic (NOD) mice with oral 2-acetyl-4-tetrahydroxybutylimidazole (THI), a component of caramel colouring III

The effect of oral administration of THI, a compound present in ammonia caramel food colouring, was studied in spontaneous and induced murine diabetes mellitus. Continuous administration of THI at 400 ppm in drinking water reduced the prevalence of spontaneous diabetes in female NOD/Lt mice from 63% in untreated controls to 8% in treated animals. Since cyclophosphamide (CP) accelerates and intensifies diabetes in NOD mice, we also studied the effect of THI in this model. Diabetes incidence was reduced from 100% in mice given only CP to 13-14% in mice given THI either concurrently or from 14 days previously. Histologically, THI greatly reduced the severity of insulitis. As measured by flow cytometry, all THI-treated mice had a 60-80% reduction in splenic CD4+ and CD8+ T cells. THI-treated mice showed no untoward effects and specifically no weight loss, or pathological changes in their livers, kidneys or lungs. However, there was moderate atrophy of the thymus cortex. THI is a small imidazole-containing compound with structural similarity to histamine and urocanic acid, both known to have immunosuppressive properties. It is a widely used food additive with no known long-term toxic effects at low dosage. Thus, THI could be a useful immunosuppressive agent.

Risk for developing type 1 (insulin-dependent) diabetes mellitus and the presence of islet 64K antibodies

First-degree relatives of Type 1 (insulin-dependent) diabetic patients are at increased risk for developing clinical diabetes. The presence of islet cell or insulin autoantibodies further identifies relatives at greater risk, but not all immunologic-marker-positive relatives progress to disease. Beta-cell dysfunction, however, seems to be more prevalent than clinical Type 1 diabetes, since stable subclinical pancreatic Beta-cell dysfunction may occur. Antibodies against a Mr 64,000 (64K) islet Beta-cell protein, identified as glutamic acid decarboxylase, have been reported both at and several years prior to the clinical onset of Type 1 diabetes. We measured 64K antibodies in first-degree relatives with varying degrees of Beta-cell dysfunction and risk for subsequent Type 1 diabetes to determine whether 64K antibodies improve the predictive power of islet cell antibodies and/or insulin autoantibodies. In the Seattle Family Study first-degree relatives of Type 1 diabetic patients are followed prospectively using detailed Beta-cell function tests, insulin sensitivity, quantitative evaluation of islet cell antibodies and fluid phase assay insulin autoantibodies. 64K antibodies were measured using dog islets. Relatives were selected, based on Beta-cell function to represent individuals at high (n = 6) and low (n = 30) risk for subsequent Type 1 diabetes. The 30 low-risk individuals followed-up for 78 months, had stable Beta-cell function, and six (20%) were negative for all autoantibodies, ten (33%) were positive for insulin autoantibodies, 16 (53%) were islet cell antibody positive while six (20%) were positive for 64K antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Cross-ethnic group comparisons of HLA class II alleles and insulin dependent diabetes mellitus

HLA class II associations with IDDM in populations of non-Caucasoid origin can provide important insights into the nature of the HLA and disease association. Firstly, HLA class II alleles that are rare in Caucasoids but common in other populations can be assessed for their contributory role in IDDM. Secondly, the different HLA class II gene linkage arrangements in different populations can help map the IDDM susceptibility determinants. This chapter reviews studies of HLA class II associations with IDDM in Asian Indians, Chinese, Japanese, Africans and black Americans. Most of these studies have been based on HLA-DR serology. However, DNA analyses, based on restriction fragment length polymorphism, sequence specific oligonucleotide hybridizations of polymerase chain reaction products and DNA sequencing, have made clear the identity of genes contributing to susceptibility or resistance to IDDM in populations of non-Caucasoid origin. DNA sequence analysis of the variable regions of the HLA-DQA, DQB and DRB genes has revealed at least eight alleles at HLA-DQA, 13 at HLA-DQB and 34 at HLA-DRB1. This chapter correlates HLA-DR and DQ allelic diversity with inherited predisposition to IDDM on a global basis. IDDM is strongly associated with the serological specificities of HLA-DQ, rather than with particular amino acid substitutions in class II alleles. DQw8 has a high risk for IDDM, DQw4, DQw5 and DQw9 have a lesser risk, while DQw6 and DQw7 are protective in IDDM. DQw2 is permissive for IDDM, depending on the presence of other HLA class II alleles. Increased heterozygosity at HLA is observed in Oriental patients, as it is in Caucasoid IDDM patients. The nature of this synergism is examined in terms of possible interactive effects between DQA and DQB alleles or DRB and DQB alleles; both effects could be operating. The conclusion from this genetic analysis is that molecular mimicry at HLA-DQ, with either foreign or autoantigens, may be an important mechanism in IDDM. Additionally, the anomalous role of DQw2 in IDDM suggests that a further mechanism, such as T cell activation, may control the ability to mount an immune response against autoantigens. Further studies, possibly with transfectant cell lines, are necessary to clarify the functional role of HLA class II genes in IDDM.

HLA-DQA2 (DX alpha) polymorphism and insulin dependent diabetes

A certain HLA-DQA2 locus TaqI fragment, DX alpha"U", has been reported to be associated with insulin-dependent diabetes mellitus (IDDM). Reports of various studies in this vein have ranged from stating that the association of DQA2"U" with IDDM exists even among subjects positive for HLA-DR3 and -DR4 to stating that the association of DQA2"U" with diabetes can be attributed to linkage disequilibrium between the DQA2"U" and some component(s) on the affected haplotypes. Using a synthetic 97-base probe corresponding to a portion of an intron of DQA2, in a Southern blot analysis of IDDM and control subjects from Wisconsin, we were able to confirm the association of DQA2"U" with diabetes. However, among DR3 subjects there was no significant association between DQA2"U" and diabetes (p = 0.26). Although there was a (nonsignificant) association of IDDM with DQA2"U" among DR4-positive subjects (p = 0.14), this can be completely attributed to linkage disequilibrium between DQA2"U" and DQw8. We also sequenced most of the second exon (corresponding to the alpha 1 domain of the DQA2 glycoprotein) from five individuals that were homozygous for either DQA2"U" or DQA2"L." The only polymorphisms observed were a "silent" mutation at position 36 and one example of a difference that would result in a change of amino acid at position 41.