Anna E. Long

Rising Incidence of Type 1 Diabetes Is Associated With Altered Immunophenotype at Diagnosis

The incidence of type 1 diabetes has increased rapidly over recent decades, particularly in young children. We aimed to determine whether this rise was associated with changes in patterns of humoral islet autoimmunity at diagnosis. Autoantibodies to insulin (IAA), GAD (GADA), islet antigen-2 (IA-2A), and zinc transporter 8 (ZnT8A) were measured by radioimmunoassay in sera collected from children and young adults with newly diagnosed type 1 diabetes between 1985 and 2002. The influence of date of diagnosis on prevalence and level of autoantibodies was investigated by logistic regression with adjustment for age and HLA class II genetic risk. Prevalence of IA-2A and ZnT8A increased significantly over the period studied, and this was mirrored by raised levels of IA-2A, ZnT8A, and IA-2β autoantibodies (IA-2βA). IAA and GADA prevalence and levels did not change. Increases in IA-2A, ZnT8A, and IA-2βA at diagnosis during a period of rising incidence suggest that the process leading to type 1 diabetes is now characterized by a more intense humoral autoimmune response. Understanding how changes in environment or lifestyle alter the humoral autoimmune response to islet antigens should help explain why the incidence of type 1 diabetes is increasing and may suggest new strategies for preventing disease.

The role of autoantibodies to zinc transporter 8 in prediction of type 1 diabetes in relatives: lessons from the European Nicotinamide Diabetes Intervention Trial (ENDIT) cohort.

CONTEXT Antibodies to islet autoantigens are detectable many years before clinical onset of type 1 diabetes and can be used to identify individuals at increased risk of diabetes. Zinc transporter 8 is a recently identified islet autoantigen. OBJECTIVE Our aim was to determine whether addition of zinc transporter 8 autoantibodies (ZnT8A) improved prediction of type 1 diabetes in a well-characterized cohort of islet cell antibody (ICA)-positive first-degree relatives. We were particularly interested in the role of ZnT8A in prediction in antibody-positive relatives with intermediate and low overall risk of diabetes. PARTICIPANTS AND METHODS ZnT8A were assayed in baseline samples from 526 ICA-positive first-degree relatives randomized in the European Nicotinamide Diabetes Intervention Trial. Antibodies to insulin, glutamate decarboxylase, islet antigen-2 (IA-2A) and IA-2β (IA-2βA), and human leukocyte antigen type had been previously determined. Risk of diabetes was assessed by survival analysis. RESULTS Of 221 ZnT8A-positive individuals, 113 developed diabetes during follow-up (5-yr cumulative risk, 55%). In multivariate models based on other autoantibodies, ZnT8A improved prediction in relatives at low genetic risk of diabetes (P = 0.030) and over age 20 yr (P = 0.026), but not in those with ICA alone or with one additional autoantibody (P = 0.696), IA-2A-negative relatives (P = 0.361), those at high or intermediate genetic risk, or younger relatives. CONCLUSIONS ZnT8A are useful additional risk markers in relatives at low genetic risk of diabetes and older individuals, but they add relatively little in younger populations because of the precise prediction possible with current autoantibody combinations.

Humoral Responses to Islet Antigen-2 and Zinc Transporter 8 Are Attenuated in Patients Carrying HLA-A*24 Alleles at the Onset of Type 1 Diabetes

The HLA-A*24 allele has shown negative associations with autoantibodies to islet antigen-2 (IA-2) and zinc transporter 8 (ZnT8) in patients with established type 1 diabetes. Understanding how this HLA class I allele affects humoral islet autoimmunity gives new insights into disease pathogenesis. We therefore investigated the epitope specificity of associations between HLA-A*24 and islet autoantibodies at disease onset. HLA-A*24 genotype and autoantibody responses to insulin (IAA), glutamate decarboxylase (GADA), IA-2, IA-2β, and ZnT8 were analyzed in samples collected from patients with recent-onset type 1 diabetes. After correction for age, sex, and HLA class II genotype, HLA-A*24 was shown to be a negative determinant of IA-2A and ZnT8A. These effects were epitope specific. Antibodies targeting the protein tyrosine phosphatase domains of IA-2 and IA-2β, but not the IA-2 juxtamembrane region, were less common in patients carrying HLA-A*24 alleles. The prevalence of ZnT8A specific or cross-reactive with the ZnT8 tryptophan-325 polymorphic residue, but not those specific to arginine-325, was reduced in HLA-A*24-positive patients. No associations were found between HLA-A*24 and IAA or GADA. Association of an HLA class I susceptibility allele with altered islet autoantibody phenotype at diagnosis suggests CD8 T-cell and/or natural killer cell–mediated killing modulates humoral autoimmune responses.

Attenuated humoral responses in HLA-A*24-positive individuals at risk of type 1 diabetes

Aims/hypothesisThe rate of progression from islet autoimmunity to clinical type 1 diabetes depends on the rate of beta cell destruction. The HLA-A*24 gene is associated with early diabetes onset, but previous studies have shown attenuated humoral responses to islet antigens in individuals with both recent and long-standing type 1 diabetes carrying HLA-A*24. We aimed to establish whether HLA-A*24 is also associated with attenuated humoral responses in individuals at high risk of type 1 diabetes.MethodsWe established HLA-A*24, DQ and rs9258750 (an HLA-A*24 tagged single-nucleotide polymorphism) genotype, as well as GAD, zinc transporter 8 (ZnT8), insulin, islet antigen-2 (IA-2), and IA-2β autoantibody status in 373 islet cell antibody-positive first-degree relatives participating in the European Nicotinamide Diabetes Intervention Trial.ResultsUnivariate regression analyses showed that humoral responses to GAD, ZnT8 and insulin were less common in relatives carrying HLA-A*24. The prevalence of GAD and ZnT8 autoantibodies remained negatively associated with HLA-A*24 and rs9258750 after adjusting for age, sex, proband relationship and HLA class II genotype.Conclusions/interpretationHLA-A*24 is associated with attenuated humoral responses in individuals at high risk of type 1 diabetes, and this may reflect a distinct phenotype of rapid beta cell loss.

The first 142 amino acids of glutamate decarboxylase do not contribute to epitopes recognized by autoantibodies associated with Type 1 diabetes.

Glutamate decarboxylase (GAD) antibodies are the most widely used predictive marker for Type 1 diabetes, but many individuals currently found to be GAD antibody‐positive are unlikely to develop diabetes. We have shown previously that radioimmunoassays using N‐terminally truncated 35S‐GAD65(96–585) offer better disease specificity with similar sensitivity to full‐length 35S‐GAD65(1–585). To determine whether assay performance could be improved further, we evaluated a more radically truncated 35S‐GAD65(143–585) radiolabel.

A quarter of patients with type 1 diabetes have co-existing non-islet autoimmunity: the findings of a UK population-based family study: Multiple autoimmunity in type 1 diabetes

Individuals with type 1 diabetes (T1D) are at increased risk of coeliac disease (CD), autoimmune thyroiditis and autoimmune gastritis, but the absolute risks are unclear. The aim of this study was to investigate the prevalence of autoantibodies to tissue transglutaminase (TGA), thyroid peroxidase (TPOA) and gastric H+/K+‐ATPase (ATPA) and their genetic associations in a well‐characterized population‐based cohort of individuals with T1D from the Barts–Oxford family study for whom islet autoantibody prevalence data were already available. Autoantibodies in sera from 1072 patients (males/females 604/468; median age 11·8 years, median T1D duration 2·7 months) were measured by radioimmunoassays; HLA class II risk genotype was analysed in 973 (91%) using polymerase chain reaction with sequence specific primers (PCR‐SSP). The prevalence of TGA (and/or history of CD), TPOA and ATPA in patients was 9·0, 9·6 and 8·2%, respectively; 3·1% had two or more autoantibodies. Females were at higher risk of multiple autoimmunity; TGA/CD were associated with younger age and TPOA with older age. ATPA were uncommon in patients under 5 years, and more common in older patients. Anti‐glutamate decarboxylase autoantibodies were predictive of co‐existing TPOA/ATPA. TGA/CD were associated with human leucocyte antigen (HLA) DR3‐DQ2, with the DR3‐DQ2/DR3‐DQ2 genotype conferring the highest risk, followed by DR4‐DQ8/DR4‐DQ8. ATPA were associated with DR3‐DQ2, DRB1*0404 (in males) and the DR3‐DQ2/DR4‐DQ8 genotype. TPOA were associated with the DR3‐DQ2/DR3‐DQ2 genotype. Almost one‐quarter of patients diagnosed with T1D aged under 21 years have at least one other organ‐specific autoantibody. HLA class II genetic profiling may be useful in identifying those at risk of multiple autoimmunity.

Symposium: diabetes mellitusThe epidemiology of childhood diabetes

There are large differences between countries in the incidence of type 1 diabetes. Europe shows the greatest variation, with the highest incidence in the north-east and lowest in the south-west of the continent. Much of the variation can be explained by genetic differences, but there are notable exceptions and intriguing within-country variations which suggest environmental causes for the disease. One of the most interesting findings is a dramatic increase in diabetes (3–4% per year), predominantly in younger children. The incidence in Finland is now over five times greater than it was 50 years ago. Recently the rise has been most dramatic in countries undergoing substantial socio-economic change, such as those of Eastern Europe. The increase has been attributed to many causes, including diet, enterovirus infection, hygiene, and vitamin D. Epidemiology suggests new approaches for diabetes prevention on a population-wide scale, but further research is still needed to identify factors that can be modified to help reduce diabetes risk and incidence of the disease.