HLA-DR and the 5' insulin gene polymorphism in insulin-dependent diabetes

Diabetes vaccines: a future to be realized

Immune-mediated (type 1) diabetes mellitus (IMD) is an autoimmune disease resulting from the chronic destruction of pancreatic islet cells by autoreactive T lymphocytes. Although there has been much advancement in diabetes management, targeting the precise etiology of the disease process has remained elusive. Recent progress in the understanding of the immunopathogenesis of IMD, however, has led to new intervention strategies, especially antigen-based therapies given as altered peptide ligands (APLs) or as vaccines. Instead of using immunosuppressive agents to suppress an already dysfunctional immune system, antigen specific vaccines or even non-antigen specific immunostimulants present a unique opportunity to boost regulatory function and thereby regain tolerance to self. We discuss here the pathogenesis of IMD as it relates to therapeutic possibilities, review various intervention strategies that have been successful in rodent models, and then present recent progress in human trials of diabetes intervention and prevention through vaccine prototypes.

DRB1*04 and DQ alleles: expression of 21-hydroxylase autoantibodies and risk of progression to Addison's disease

Of 957 patients with type 1 diabetes without known Addison's disease 1.6% (n = 15) were positive for 21-hydroxylase autoantibodies. Among DQ8/DQ2 heterozygous patients, the percentage expressing 21-hydroxylase autoantibodies was 5% (10 of 208) vs. less than 0.5% of patients with neither DQ8 nor DQ2. Three of the diabetic patients found to have 21-hydroxylase autoantibodies on screening were subsequently diagnosed with Addison's disease. Overall, the genotype DQ8/DQ2, consisting of DRB1*0404/DQ8 with DRB1*0301/DQ2, was present in 14 of 21 patients with Addison's disease (8 of 12 with diabetes and 6 of 9 without diabetes or antiislet autoantibodies) vs. 0.7% of the general population (109 of 15,547; P < 10(-6)) and 11% of patients with DM without Addison's disease (62 of 578; P < 10(-6)). Among patients with diabetes with DQ8, Addison's disease was strongly associated with the specific DRB1 subtype, DRB1*0404 (8 of 9 patients from 8 families, in contrast to only 109 of 408 DQ8 DM patients with diabetes without Addison's disease having DRB1*0404; P < 0.001). Among 21-hydroxylase autoantibody-positive DQ8 patients, 80% with DRB1*0404 (12 of 15) had Addison's disease, in contrast to 1 of 10 autoantibody-positive patients with DRB1*0401 or DRB1*0402 (P < 0.001). We conclude that patients with DRB1*0404 and 21-hydroxylase autoantibodies are at high risk for Addison's disease. Patients with DRB1*0401 and DRB1*0402 have more limited progression to Addison's disease despite the presence of 21-hydroxylase autoantibodies.

Genetics of insulin-dependent diabetes mellitus

Recent studies that have focused on the detection of non-MHC susceptibility loci in insulin-dependent diabetes mellitus are reviewed. It has been confirmed that the region on human chromosome 11p contains such a susceptibility locus and recent research has attempted to identify the causative DNA variants and their functional role in disease.

In Finland insulin gene region encoded susceptibility to IDDM exerts maximum effect when there is low HLA-DR associated risk. DiMe (Childhood Diabetes in Finland) Study Group

An association between insulin-dependent diabetes mellitus (IDDM) and polymorphisms of the insulin gene on chromosome 11p15 (INS) is a consistent finding in Europid populations. While one study suggested that the INS association is restricted to HLA-DR4-positive individuals, studies in other Europid populations have shown the disease-associated INS genotype to confer susceptibility independently of HLA-DR. We have investigated the role of INS in susceptibility to IDDM in Finland, which has the highest incidence of diabetes mellitus in the world, at two polymorphic restriction sites, 5' and 3' to the insulin gene. From the DiMe (Childhood Diabetes in Finland) Study we studied 154 diabetic children without regard to HLA-DR type; 108 DR4 positive/non-DR3 diabetic children; 39 DR3 positive/non-DR4 diabetic children; 30 DR4/DR3 positive diabetic children; 31 non-DR4/non-DR3 diabetic children; 96 matched DiMe control subjects and 86 other healthy, non-diabetic Finnish control subjects. We found an overall association between IDDM and INS in the high-risk Finnish population only with the 5' polymorphism and identified an INS haplotype negatively associated with IDDM in Finland. However, among diabetic subjects with a reduced HLA-associated susceptibility (non-DR4/non-DR3) both 3' and 5' INS loci showed an association with IDDM (p values 0.02 and 0.0002, respectively). Thus, in the Finnish population insulin gene-encoded susceptibility to IDDM exerts a maximum effect in those with reduced HLA-associated risk.

Molecular genetics of diabetes mellitus

As a result of advances in technology, genome searches have been carried out for susceptibility genes for type 1 diabetes in humans and in the NOD mouse. These have shown that, in the NOD mouse, diabetes susceptibility is under the control of at least ten separate chromosomal loci. In the human, in addition to HLA and INS, two new susceptibility genes have been localized, IDDM4 on chromosome 11q and IDDM5 on 6q, demonstrating the polygenic nature of type 1 diabetes and the role of HLA as the major locus. Candidate genes at these loci are the subject of current investigation. Genetic and immunological markers of disease may be of value in screening the general population for individuals at risk of developing type 1 diabetes. The predictive power of different screening strategies should be tested in order to work out the potential value to the general population of preventive therapies that are now undergoing clinical trials in high risk 'pre-diabetics'. Type 2 diabetes is genetically heterogeneous, and, since 1992, two distinct genetic subtypes have been identified. The first is defined by mutations in the GCK gene, which cause up to 60% of cases of MODY. The second, designated MIDD (maternally inherited diabetes and deafness), is defined by mutation in the mitochondrial gene for tRNA(Leu(UUR)). MIDD patients are less obese than is usual for typical type 2 diabetes, may present in early adult life or occasionally in childhood and may have been diagnosed as having autoimmune type 1 diabetes, type 2 diabetes or MODY. Typically, patients with MIDD require insulin earlier than do type 2 diabetics without mitochondrial mutations. Genetically complex diseases, such as diabetes, hypertension, cancer and coronary heart disease, are common in most populations. The approaches to the genetic analysis of diabetes outlined in this review are likely to be useful to the genetic analysis of many of these disorders. Progress in this area will have important implications for public health strategies in the next decade and beyond.

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.

IDDM susceptibility associated with polymorphisms in the insulin gene region. A study of blacks, Caucasians and orientals

Previous studies have suggested an association between polymorphisms in the insulin gene region and insulin-dependent diabetes mellitus (IDDM). Most of the studies so far have been performed in Caucasoid populations. We have investigated 418 random IDDM patients and 422 healthy control subjects from three different ethnic groups; Tanzanian blacks, Norwegian Caucasians and Japanese orientals. Our data suggest that polymorphisms in the insulin gene region confer susceptibility to IDDM in Caucasians, and that a similar tendency though not statistically significant is observed among Tanzanian blacks, while no significant contribution is seen among Japanese orientals. We further demonstrate that the disease-associated genotype INS +/+ confers susceptibility independently of HLA class II alleles associated with IDDM. Compared to the contribution of particular HLA-DQ alleles in IDDM susceptibility, the additional risk conferred by the insulin gene region polymorphism is, however, small. Genotyping of the insulin gene region will therefore most probably not be a useful tool in the prediction of IDDM.

Insulin gene region-encoded susceptibility to type 1 diabetes is not restricted to HLA-DR4-positive individuals

Type 1 or insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease of the insulin-producing pancreatic beta-cells which is determined by both genetic and environmental factors. The major histocompatibility complex and the insulin gene region (INS) on human chromosomes 6p and 11p, respectively, contain susceptibility genes. Using a mostly French data set, evidence for linkage of INS to IDDM was recently obtained but only in male meioses (suggesting involvement of maternal imprinting) and only in HLA-DR4-positive diabetics. In contrast, we find evidence for linkage in both male and female meioses and that the effect of the susceptibility gene(s) in the INS region is not dependent on the presence of HLA-DR4.

Lack of association of the insulin gene region with type 1 (insulin-dependent) diabetes mellitus in Japanese subjects

Although the insulin gene region is implicated in susceptibility to Type 1 (insulin-dependent) diabetes mellitus in Caucasians, significance of this region to Type 1 diabetes in Japanese remains unclear because the class 1 alleles (shorter insertion) of the variable number of tandem repeat in the 5' region of the insulin gene are predominant in both diabetic and non-diabetic subjects. The 5' insulin gene polymorphism was analysed in 75 Japanese patients and 69 control subjects with a precise method using PvuII and a polymorphism specific probe, which enabled us to divide class 1 alleles into four subclasses. Allelic frequencies were not significantly different between Type 1 diabetic patients and control subjects. The polymorphism in the 3' untranslated region of the insulin gene (1127/PstI) was also analysed and found to be tightly linked to the 5' insulin gene polymorphism, and thus was not associated with diabetes. Interaction between HLA-DR and the insulin gene region, which was reported in the French study, was not observed in Japanese. These results suggest that the insulin gene region is not a valuable genetic risk factor for Type 1 diabetes in Japanese.

Susceptibility to insulin dependent diabetes mellitus maps to a 4.1 kb segment of DNA spanning the insulin gene and associated VNTR

Recent studies have demonstrated that a locus at 11p15.5 confers susceptibility to insulin dependent diabetes mellitus (IDDM). This locus has been shown to lie within a 19 kb region. We present a detailed sequence comparison of the predominant haplotypes found in this region in a population of French Caucasian IDDM patients and controls. Identification of polymorphisms both associated and unassociated with IDDM has allowed us to define further the region of association to 4.1 kb. Ten polymorphisms within this region are in strong linkage disequilibrium with each other and extend across the insulin gene locus and the variable number tandem repeat (VNTR) situated immediately 5' to the insulin gene. These represent a set of candidate disease polymorphisms one or more of which may account for the susceptibility to IDDM.