Temporal trends of HLA genotype frequencies of type 1 diabetes patients in Sweden from 1986 to 2005 suggest altered risk

Environmental factors in the etiology of type 1 diabetes, celiac disease, and narcolepsy

The etiology of human leukocyte antigen (HLA)-associated organ-specific autoimmune diseases is incomplete. In type 1 diabetes and celiac disease, the strongest associations are with the HLA-DR3-DQ2 and DR4-DQ8 haplotypes, whereas the DQB1*06:02 allele has a strong negative association. In contrast, narcolepsy, especially as recently triggered by the Pandemrix(®) H1N1 vaccine (GlaxoKlineSmith (GSK), Brentford, Middlesex, UK), did not seem to develop without at least one copy of the latter allele. The overall hypothesis is that the role of these different HLA haplotypes, especially in Finland and Sweden, is related to the immune response to infectious agents that are common in these two populations. The high incidence of both type 1 diabetes and celiac disease in Scandinavia may be the result of the HLA-DR3-DQ2 and DR4-DQ8 haplotypes, and the DQB1*06:02 allele are common because they protected people from succumbing to common infections. The timing of dissecting the autoimmune response is critical to understand the possible role of environmental factors. First, an etiological trigger may be a common virus infecting beta cells or with antigens inducing beta-cell cross reactivity. Second, an autoimmune reaction may ensue, perhaps in response to beta-cell apoptosis or autophagy, resulting in autoantigen-specific T cells and autoantibodies. It is critical in at-risk children to dissect the immune response prior to the appearance of autoantibodies in order to identify cellular reactions in response to environmental factors that are able to induce an HLA-associated immune reaction.

Recognition of ZnT8, Proinsulin, and Homologous MAP Peptides in Sardinian Children at Risk of T1D Precedes Detection of Classical Islet Antibodies

As numerous studies put in evidence the increasing incidence of type 1 diabetes (T1D) in children, an early diagnosis is of great importance to define correct treatment and diet. Currently, the identification of classical islet autoantibodies is the primary biomarker for diagnosis in subjects at risk, especially in pediatric patients. Recent studies suggest that detection of antibodies against ZnT8 protein in preclinical phase can predict the development of T1D. We previously demonstrated a significant association of Mycobacterium avium subspecies paratuberculosis (MAP) with T1D in adult Sardinian patients. To enforce this finding, we investigated the presence of antibodies against ZnT8 and proinsulin (PI) with respective homologous epitopes: MAP3865c133-141/ZnT8186-194, MAP3865c125-133/ZnT8178-186, MAP2404c70-85/PI46-61, and MAP1,4αgbp157-173/PI64-80, in 23 children at risk for T1D, formerly involved in the TRIGR study, and 22 healthy controls (HCs). Positivity to anti-MAP and homologous human peptides was detected in 48% of at-risk subjects compared to 5,85% HCs, preceding appearance of islet autoantibodies. Being MAP easily transmitted to humans with infected cow's milk and detected in retail infant formulas, MAP epitopes could be present in extensively hydrolyzed formula and act as antigens stimulating β-cell autoimmunity.

Cell-surface MHC density profiling reveals instability of autoimmunity-associated HLA

Polymorphisms within HLA gene loci are strongly associated with susceptibility to autoimmune disorders; however, it is not clear how genetic variations in these loci confer a disease risk. Here, we devised a cell-surface MHC expression assay to detect allelic differences in the intrinsic stability of HLA-DQ proteins. We found extreme variation in cell-surface MHC density among HLA-DQ alleles, indicating a dynamic allelic hierarchy in the intrinsic stability of HLA-DQ proteins. Using the case-control data for type 1 diabetes (T1D) for the Swedish and Japanese populations, we determined that T1D risk-associated HLA-DQ haplotypes, which also increase risk for autoimmune endocrinopathies and other autoimmune disorders, encode unstable proteins, whereas the T1D-protective haplotypes encode the most stable HLA-DQ proteins. Among the amino acid variants of HLA-DQ, alterations in 47α, the residue that is located on the outside of the peptide-binding groove and acts as a key stability regulator, showed strong association with T1D. Evolutionary analysis suggested that 47α variants have been the target of positive diversifying selection. Our study demonstrates a steep allelic hierarchy in the intrinsic stability of HLA-DQ that is associated with T1D risk and protection, suggesting that HLA instability mediates the development of autoimmune disorders.

Temporal trends of HLA, CTLA-4 and PTPN22 genotype frequencies among type 1 diabetes in Continental Italy

The incidence of type 1 diabetes has, progressively, increased worldwide over the last decades and also in Continental Italian population. Previous studies performed in northern European countries, showed, alongside a general increase in the disease incidence, a decreasing frequency of the highest risk HLA genotype in type 1 diabetes populations, thus emphasizing the role of environmental factors. The aim of the study was to evaluate whether a decreasing trend of high risk HLA, CTLA-4 and PTPN22 genotypes would be present in type 1 diabetes subjects of Continental Italy, a country considered at low incidence of the disease compared to northern European populations. N = 765 type 1 diabetes patients diagnosed from 1980 to 2012 in Lazio region were included. For HLA, CTLA4 and PTPN22 temporal trend evaluation, subjects were subdivided into groups of years according to age at diagnosis. All subjects were typed for HLA-DRB1 and DQB1 by a reverse line blot. The CT60 polymorphism of the CTLA4 and C1858T of the PTPN22 gene were genotyped using ABI PRISM 7900HT (n = 419 and n = 364 respectively). HLA genotypes were divided in high, moderate and low risk categories. The proportion of the HLA risk categories was not statistically different over the three decades in subjects with age of onset <15 years and ≥ 15 years. The genotype distribution of CT60 polymorphism of CTLA4 gene did not show any change in the frequencies during time. The analysis of the PTPN22 C1858T variant revealed, instead, that the frequency of CT+TT susceptibility genotypes decreased during time (23.9% vs 13.6%, p = 0.017). We can hypothesize that the pressure of the diabetogenic environment could be milder and therefore not sufficient to reduce the need of a strong genetic background (HLA) "to precipitate" diabetes; the increased pressure of the environment could have, instead, some effects on minor susceptibility genes in our population.

The multiple origins of Type 1 diabetes

It is widely accepted that Type 1 diabetes is a complex disease. Genetic predisposition and environmental factors favour the triggering of autoimmune responses against pancreatic β-cells, eventually leading to β-cell destruction. Over 40 susceptibility loci have been identified, many now mapped to known genes, largely supporting a dominant role for an immune-mediated pathogenesis. This role is also supported by the identification of several islet autoantigens and antigen-specific responses in patients with recent onset diabetes and subjects with pre-diabetes. Increasing evidence suggests certain viruses as a common environmental factor, together with diet and the gut microbiome. Inflammation and insulin resistance are emerging as additional cofactors, which might be interrelated with environmental factors. The heterogeneity of disease progression and clinical manifestations is likely a reflection of this multifactorial pathogenesis. So far, clinical trials have been mostly ineffective in delaying progression to overt diabetes in relatives at increased risk, or in reducing further loss of insulin secretion in patients with new-onset diabetes. This limited success may reflect, in part, our incomplete understanding of key pathogenic mechanisms, the lack of truly robust biomarkers of both disease activity and β-cell destruction, and the inability to assess the relative contributions of various pathogenic mechanisms at various time points during the course of the natural history of Type 1 diabetes. Emerging data and a re-evaluation of histopathological, immunological and metabolic findings suggest the hypothesis that unknown mechanisms of β-cell dysfunction may be present at diagnosis, and may contribute to the development of hyperglycaemia and clinical symptoms.

Etiopathogenesis of insulin autoimmunity

Autoimmunity against pancreatic islet beta cells is strongly associated with proinsulin, insulin, or both. The insulin autoreactivity is particularly pronounced in children with young age at onset of type 1 diabetes. Possible mechanisms for (pro)insulin autoimmunity may involve beta-cell destruction resulting in proinsulin peptide presentation on HLA-DR-DQ Class II molecules in pancreatic draining lymphnodes. Recent data on proinsulin peptide binding to type 1 diabetes-associated HLA-DQ2 and -DQ8 is reviewed and illustrated by molecular modeling. The importance of the cellular immune reaction involving cytotoxic CD8-positive T cells to kill beta cells through Class I MHC is discussed along with speculations of the possible role of B lymphocytes in presenting the proinsulin autoantigen over and over again through insulin-carrying insulin autoantibodies. In contrast to autoantibodies against other islet autoantigens such as GAD65, IA-2, and ZnT8 transporters, it has not been possible yet to standardize the insulin autoantibody test. As islet autoantibodies predict type 1 diabetes, it is imperative to clarify the mechanisms of insulin autoimmunity.

Country-specific birth weight and length in type 1 diabetes high-risk HLA genotypes in combination with prenatal characteristics

OBJECTIVE

To examine the relationship between high-risk human leukocyte antigen (HLA) genotypes for type 1 diabetes and birth size in combination with prenatal ch aracteristics in different countries.

STUDY DESIGN

Four high-risk HLA genotypes were enrolled in the Environmental determinants of Diabetes in the Young study newborn babies from the general population in Finland, Germany, Sweden and the United States. Stepwise regression analyses were used to adjust for country, parental physical characteristics and environmental factors during pregnancy.

RESULT

Regression analyses did not reveal differences in birth size between the four type 1 diabetes high-risk HLA genotypes. Compared with DQ 4/8 in each country, (1) DQ 2/2 children were heavier in the United States (P=0.028) mostly explained however, by parental weight; (2) DQ 2/8 (P=0.023) and DQ 8/8 (P=0.046) children were longer in Sweden independent of parents height and as well as (3) in the United States for DQ 2/8 (P=0.023), but again dependent on parental height.

CONCLUSION

Children born with type 1 diabetes high-risk HLA genotypes have comparable birth size. Longitudinal follow-up of these children should reveal whether birth size differences between countries contribute to the risk for islet autoimmunity and type 1 diabetes.

Enrollment experiences in a pediatric longitudinal observational study: The Environmental Determinants of Diabetes in the Young (TEDDY) study

OBJECTIVE

Our objective was to identify characteristics of infants and their families who were enrolled, refused to enroll, or were excluded from The Environmental Determinants of Diabetes in the Young (TEDDY) study.

METHOD

16,435 infants screened at birth and identified as at increased genetic risk for type 1 diabetes (T1DM) were placed into one of three categories: enrolled, excluded, or refused to enroll. Enrollment, exclusion and refusal rates were compared across countries and between infants from the general population (GP) and infants with a first degree T1DM relative (FDR). A multivariate logistic model was used to identify factors associated with TEDDY enrollment.

RESULTS

TEDDY enrollment, exclusion, and refusal rates differed by country and by GP/FDR status but reasons for refusal to enroll were similar across countries and GP/FDR populations. Sweden had the highest enrollment rate, US had the highest exclusion rate, and Finland had the highest refusal rate. FDR infants were more likely to enroll than GP infants. Inability to re-contact the family was the most common reason for exclusion. Primary reasons for refusal to enroll included protocol factors (e.g. blood draws) or family factors (e.g., too busy). Study enrollment was associated with FDR status, European country of origin, older maternal age, a singleton birth, and having another child in TEDDY.

CONCLUSIONS

Findings highlight the importance of country specific estimates for enrollment targets in longitudinal pediatric studies and suggest that enrollment estimates should be lowered when the study involves the general population, painful procedures, or makes multiple demands on families.

Low risk HLA-DQ and increased body mass index in newly diagnosed type 1 diabetes children in the Better Diabetes Diagnosis study in Sweden

Objective

Type 1 diabetes and obesity has increased in childhood. We therefore tested the hypothesis that type 1 diabetes HLA-DQ risk genotypes may be associated with an increased body mass index (BMI).

Design

The type 1 diabetes high risk HLA-DQ A1*05:01-B1*02:01/A1*03:01-B1*03:02 genotype along with lower risk DQ genotypes were determined at the time of clinical onset by PCR and hybridization with allele-specific probes. Body mass index was determined after diabetes was stabilized.

Subjects

A total of 2403 incident type 1 diabetes children below 18 years of age were ascertained in the Swedish national Better Diabetes Diagnosis (BDD) studybetween May 2005 to September 2009. All children classified with type 1 diabetes including positivity for at least one islet autoantibody were investigated.

Results

Overall, type 1 diabetes HLA-DQ risk was negatively associated with BMI (p<0.0008). The proportion of the highest risk A1*05:01-B1*02:01/A1*03:01-B1*03:02 genotype decreased with increasing BMI (p<0.0004). However, lower risk type 1 diabetes DQ genotypes were associated with an increased proportion of patients who were overweight or obese (p<0.0001). Indeed, the proportion of patients with the low risk A1*05:01-B1*02:01/A1*05:01-B1*02:01 genotype increased with increasing body mass index (p<0.003). The magnitude of association on the multiplicative scale between the A1*05:01-B1*02:01/A1*05:01-B1*02:01 genotype and increased body mass index was significant (p<0.006). The odds ratio in patients with this genotype of being obese was 1.80 (95% CI 1.21–2.61; p<0.006). The increased proportion of overweight type 1 diabetes children with the A1*05:01-B1*02:01 haplotype was most pronounced in children diagnosed between 5 and 9 years of age.

Conclusions

Susceptibility for childhood type 1 diabetes was unexpectedly found to be associated with the A1*05:01-B1*02:01/A1*05:01-B1*02:01 genotype and an increased BMI. These results support the hypothesis that overweight may contribute to the risk of type 1 diabetes in children positive for HLA-DQ A1*05:01-B1*02:01.

Type 1 diabetes patients born to immigrants to Sweden increase their native diabetes risk and differ from Swedish patients in HLA types and islet autoantibodies

AIM

To determine whether type 1 diabetes mellitus (T1DM) patients, having parents who immigrated to Sweden, have increased T1DM risk before 18 yr compared with countries of origin. We also determined whether they have different human leukocyte antigen (HLA) genetic markers and islet autoantibodies at diagnosis compared with Swedish patients.

METHODS

A total of 1988 (53% males) newly diagnosed and confirmed T1DM patients <18 yr registered within the Better Diabetes Diagnosis (BDD) study (May 2005 to September 2008) were included. Participants were classified into three groups: Swedish, non-Swedish, and Mixed-origin patients according to country of origin of two generations (parents and grandparents). These groups were compared with respect to T1DM HLA markers and islet autoantibodies [glutamic acid decarboxylase autoantibodies (GAD65Ab), insulin autoantibodies (IAA), and islet antigen-2 autoantibodies (IA-2Ab)].

RESULTS

Only 30 (1.5%) patients were born outside Sweden. Swedish patients constituted 66%, non-Swedish patients 8%, Mixed origins 17%, and 9% were of uncertain origin. Confirmed T1DM in patients within the study was 22 (95% CI: 21-23) patients/10(5)/yr rate for Swedish patients compared with 14 (95% CI: 13-15) among non-Swedish patients. The HLA-DQ8 haplotype (p < 0.0001) and DQ2/8 genotype (p < 0.02) predominated among Swedish compared with non-Swedish patients. In contrast, DQ2 was the most frequent haplotype among non-Swedish patients [OR = 1.5 (95% CI: 1.0-2.0), p < 0.04]. Multiple (≥2) autoantibodies (p < 0.04) and specifically IA-2Ab (p < 0.001) were most prevalent among the Swedish patients. Multiple autoantibodies were associated with DQ8 among the Swedish patients only (p < 0.001).

CONCLUSION

Patients born to parents who had immigrated to the high T1DM incidence environment of Sweden have, compared with Swedish patients, more frequent HLA-DQ2 genetic markers and are diagnosed more often with GAD65Ab.

Co-occurrence of allergic sensitization and type 1 diabetes

BACKGROUND

The mechanisms leading to abnormal immune regulation in type 1 diabetes and allergic diseases may be partly overlapping. If so, these diseases should co-occur more often than expected. We investigated this phenomenon in two contrasting socio-economic environments, Finland and Russian Karelia.

METHODS

We screened 413 Finnish children (of whom 147 had type 1 diabetes) and 244 Russian Karelian children (132 had type 1 diabetes) for total immunoglobulin E (IgE) levels and specific IgE against birch, cat, and egg albumen. In addition we analysed diabetes-related human leukocyte antigen (HLA) haplotypes and antibodies against hepatitis A virus (HAV) and recorded allergic diseases by a questionnaire in Russian Karelia.

RESULTS

In Russian Karelia 15% of the patients with type 1 diabetes, but only 4% of the control subjects had allergen-specific IgE (P = 0.012). A similar difference was observed in the frequency of allergic symptoms. Co-occurrence of allergic sensitization and type 1 diabetes was associated with lack of HAV antibodies and was not seen in Finland where infections are less frequent than in Karelia.

CONCLUSION

Our findings support the idea of common mechanisms in the pathogenesis of allergic diseases and type 1 diabetes, which may be particularly important in an environment with low penetrance of these diseases.

Immunology of beta-cell destruction

The pancreatic islet beta-cells are the target for an autoimmune process that eventually results in an inability to control blood glucose due to the lack of insulin. The different steps that eventually lead to the complete loss of the beta-cells are reviewed to include the very first step of a triggering event that initiates the development of beta-cell autoimmunity to the last step of appearance of islet-cell autoantibodies, which may mark that insulitis is about to form. The observations that the initial beta-cell destruction by virus or other environmental factors triggers islet autoimmunity not in the islets but in the draining pancreatic lymph nodes are reviewed along with possible basic mechanisms of loss of tolerance to islet autoantigens. Once islet autoimmunity is established the question is how beta-cells are progressively killed by autoreactive lymphocytes which eventually results in chronic insulitis. Many of these series of events have been dissected in spontaneously diabetic mice or rats, but controlled clinical trials have shown that rodent observations are not always translated into mechanisms in humans. Attempts are therefore needed to clarify the step 1 triggering mechanisms and the step to chronic autoimmune insulitis to develop evidence-based treatment approaches to prevent type 1 diabetes.

Differential effects of leptin receptor mutation on male and female BBDR Gimap5-/Gimap5- spontaneously diabetic rats

Rodents homozygous for autosomal leptin receptor gene mutations not only become obese, insulin resistant, and hyperleptinemic but also develop a dysregulated immune system. Using marker-assisted breeding to introgress the Koletsky rat leptin receptor mutant (lepr-/lepr-), we developed a novel congenic BBDR.(lepr-/lepr-) rat line to study the development of obesity and type 2 diabetes (T2D) in the BioBreeding (BB) diabetes-resistant (DR) rat. While heterozygous lepr (-/+) or homozygous (+/+) BBDR rats remained lean and metabolically normal, at 3 wk of age all BBDR.(lepr-/lepr-) rats were obese without hyperglycemia. Between 45 and 70 days of age, male but not female obese rats developed T2D. We had previously developed congenic BBDR.(Gimap5-/Gimap5-) rats, which carry an autosomal frameshift mutation in the Gimap5 gene linked to lymphopenia and spontaneous development of type 1 diabetes (T1D) without sex differences. Because the autoimmune-mediated destruction of pancreatic islet beta-cells may be affected not only by obesity but also by the absence of leptin receptor signaling, we next generated BBDR.(lepr-/lepr-,Gimap5-/Gimap5-) double congenic rats carrying the mutation for Gimap5 and T1D as well as the Lepr mutation for obesity and T2D. The hyperleptinemia rescued end-stage islets in BBDR.(lepr-/lepr-,Gimap5-/Gimap5-) congenic rats and induced an increase in islet size in both sexes, while T1D development was delayed and reduced only in females. These results demonstrate that obesity and T2D induced by introgression of the Koletsky leptin receptor mutation in the BBDR rat result in islet expansion associated with protection from T1D in female but not male BBDR.(lepr-/lepr-,Gimap5-/Gimap5-) congenic rats. BBDR.(lepr-/lepr-,Gimap5-/Gimap5-) congenic rats should prove valuable to study interactions between lack of leptin receptor signaling, obesity, and sex-specific T2D and T1D.