Genetic determinants of type 1 diabetes across populations

A Review of Stage 0 Biomarkers in Type 1 Diabetes: The Holy Grail of Early Detection and Prevention?

Type 1 diabetes mellitus (T1D) is an incurable autoimmune disease characterized by the destruction of pancreatic islet cells, resulting in lifelong dependency on insulin treatment. There is an abundance of review articles addressing the prediction of T1D; however, most focus on the presymptomatic phases, specifically stages 1 and 2. These stages occur after seroconversion, where therapeutic interventions primarily aim to delay the onset of T1D rather than prevent it. This raises a critical question: what happens before stage 1 in individuals who will eventually develop T1D? Is there a "stage 0" of the disease, and if so, how can we detect it to increase our chances of truly preventing T1D? In pursuit of answers to these questions, this narrative review aimed to highlight recent research in the field of early detection and prediction of T1D, specifically focusing on biomarkers that can predict T1D before the onset of islet autoimmunity. Here, we have compiled influential research from the fields of epigenetics, omics, and microbiota. These studies have identified candidate biomarkers capable of predicting seroconversion from very early stages to several months prior, suggesting that the prophylactic window begins at birth. As the therapeutic landscape evolves from treatment to delay, and ideally from delay to prevention, it is crucial to both identify and validate such "stage 0" biomarkers predictive of islet autoimmunity. In the era of precision medicine, this knowledge will enable early intervention with the potential for delaying, modifying, or completely preventing autoimmunity and T1D in at-risk children.

HLA-DQA1 and HLA-DQB1 Gene Polymorphism in Indonesian Children with Type I Diabetes Mellitus

BACKGROUND

More than 40 genes influence the progression of type 1 diabetes mellitus (T1DM), including human leukocyte antigen (HLA) alleles. Different HLA genotype patterns result in diverse rates of T1DM development. HLA class II DR, DQ, and DP vary among different populations and ethnicities. Data on HLA polymorphism in T1DM in Indonesia are lacking. Therefore, this study was designed to evaluate the gene polymorphism of HLA-DQA1 and HLA-DQB1 in Indonesian children with T1DM.

PATIENTS AND METHODS

In this study, 31 patients with T1DM and 31 controls were enrolled from April 2020 to April 2021. This study was conducted at Dr. Soetomo Hospital, Indonesia. We evaluated the gene polymorphism of HLA-DQA1 and HLA-DQB1 using polymerase chain reaction-restriction fragment length polymorphism. The primers used were as follows: for HLA-DQA1, DQAS34: 5'-GGTGTAAACTTGTACCAG-3' (forward) and DQAA261: 5'-ATTGGTAGCAGCGGTAGA-3' (reverse); for HLA-DQB1, DQBS43: 5'-TGCTACT- TCACCAA(C/T)GGG-3' (forward) and DQBA249: 5'-GTAGTTGTGTCTGCA (C/T)AC-3' (reverse).

RESULTS

The most common HLA-DQA1 subtype in the T1DM group was 0101/0102 accounting for 67.6%, and 01/03 and 02/03 were found in the T1DM group only. Meanwhile, the most common HLA-DQB1 subtype in the T1DM group was 0301, accounting for 54.8%. Most subjects in this study were Javanese.

CONCLUSION

HLA-DQA1 0101/0102 and HLA-DQB1 0301 were commonly found in Indonesian children with T1DM.

DNA Methylation Patterning and the Regulation of Beta Cell Homeostasis

Pancreatic beta cells play a central role in regulating glucose homeostasis by secreting the hormone insulin. Failure of beta cells due to reduced function and mass and the resulting insulin insufficiency can drive the dysregulation of glycemic control, causing diabetes. Epigenetic regulation by DNA methylation is central to shaping the gene expression patterns that define the fully functional beta cell phenotype and regulate beta cell growth. Establishment of stage-specific DNA methylation guides beta cell differentiation during fetal development, while faithful restoration of these signatures during DNA replication ensures the maintenance of beta cell identity and function in postnatal life. Lineage-specific transcription factor networks interact with methylated DNA at specific genomic regions to enhance the regulatory specificity and ensure the stability of gene expression patterns. Recent genome-wide DNA methylation profiling studies comparing islets from diabetic and non-diabetic human subjects demonstrate the perturbation of beta cell DNA methylation patterns, corresponding to the dysregulation of gene expression associated with mature beta cell state in diabetes. This article will discuss the molecular underpinnings of shaping the islet DNA methylation landscape, its mechanistic role in the specification and maintenance of the functional beta cell phenotype, and its dysregulation in diabetes. We will also review recent advances in utilizing beta cell specific DNA methylation patterns for the development of biomarkers for diabetes, and targeting DNA methylation to develop translational approaches for supplementing the functional beta cell mass deficit in diabetes.

Retro-inverso D-peptides as a novel targeted immunotherapy for Type 1 diabetes

Over the past four decades, the number of people with Type 1 Diabetes (T1D) has increased by 4% per year, making it an important public health challenge. Currently, no curative therapy exists for T1D and the only available treatment is insulin replacement. HLA-DQ8 has been shown to present antigenic islet peptides driving the activation of CD4⁺ T-cells in T1D patients. Specifically, the insulin peptide InsB:9-23 activates self-reactive CD4⁺ T-cells, causing pancreatic beta cell destruction. The aim of the current study was to identify retro-inverso-d-amino acid based peptides (RI-D-peptides) that can suppress T-cell activation by blocking the presentation of InsB:9-23 peptide within HLA-DQ8 pocket. We identified a RI-D-peptide (RI-EXT) that inhibited InsB:9-23 binding to recombinant HLA-DQ8 molecule, as well as its binding to DQ8 expressed on human B-cells. RI-EXT prevented T-cell activation in a cellular antigen presentation assay containing human DQ8 cells loaded with InsB:9-23 peptide and murine T-cells expressing a human T-cell receptor specific for the InsB:9-23-DQ8 complex. Moreover, RI-EXT blocked T-cell activation by InsB:9-23 in a humanized DQ8 mice both ex vivo and in vivo, as shown by decreased production of IL-2 and IFN-γ and reduced lymphocyte proliferation. Interestingly, RI-EXT also blocked lymphocyte activation and proliferation by InsB:9-23 in PBMCs isolated from recent onset DQ8-T1D patients. In summary, we discovered a RI-D-peptide that blocks InsB:9-23 binding to HLA-DQ8 and its presentation to T-cells in T1D. These findings set the stage for using our approach as a novel therapy for patients with T1D and potentially other autoimmune diseases.

Human Leukocyte Antigen (HLA) and Islet Autoantibodies Are Tools to Characterize Type 1 Diabetes in Arab Countries: Emphasis on Kuwait

The incidence rate of type 1 diabetes in Kuwait had been increasing exponentially and has doubled in children ≤ 14 years old within almost two decades. Therefore, there is a dire need for a careful systematic familial cohort study. Several immunogenetic factors affect the pathogenesis of the disease. The human leukocyte antigen (HLA) accounts for the major genetic susceptibility to the disease. The triggering agents initiate disease onset by type 1 destruction of pancreatic β-cells. Both HLA and anti-islet antibodies can be used to characterize, predict susceptibility to the disease, innovate, or delay the β-cell destruction. Evidence from prospective longitudinal studies suggested that the underlying disease process represents a continuum that begins before the symptoms are clinically evident. Autoimmunity of the functional pancreatic β-cells results in symptomatic type 1 diabetes and lifelong insulin dependence. The autoantibodies against glutamic acid decarboxylase (GADA), insulinoma antigen-2 (IA-2A), insulin (IAA), and zinc transporter-8 (ZnT-8A) comprise the most reliable biomarkers for type 1 diabetes in both children and adults. Although Kuwait is the second among the top 10 countries with a high incidence rate of type 1 diabetes, there have been no proper diagnostic and prediction tools as per the World Health Organization. The Kuwaiti Type 1 Diabetes Study (KADS) was initiated to understand the disease pathogenesis as well as the HLA and anti-islet autoantibody profile of type 1 diabetes in Kuwait. Understanding the disease sequela in a homogenous gene pool and highly consanguineous population of Kuwaitis could help solve the challenges and pathogenesis, as well as hasten the prevention, of type 1 diabetes.

Genetic aspects of type 1 diabetes

Type 1 diabetes mellitus (T1DM) is characterized by autoimmune destruction of pancreatic beta-cells in genetically predisposed individuals, eventually resulting in severe insulin deficiency. It is the most common form of diabetes in children and adolescents. Genetic susceptibility plays a crucial role in development of T1DM. The human leukocyte antigen complex plays a key role in the pathogenesis of T1DM. Furthermore, genome-wide association studies and linkage analysis have recently made a significant contribution to current knowledge relative to the impact of genetics on T1DM development and progression. This review focuses on current knowledge of genetics as a pathogenesis for T1DM. It also discusses mechanisms by which genes influence the risk of developing T1DM as well as the clinical and research applications of genetic risk scores in T1DM.

Comprehensive human leukocyte antigen genotyping of patients with type 1 diabetes mellitus in Taiwan

BACKGROUND

Type 1 diabetes (T1D) mellitus is an autoimmune disorder involving both complex genetic and environmental factors. The incidence rates are low in Asian countries, and the specific, explanatory genetic factors underlying this have been investigated. The aim of this study was to elucidate the association of human leukocyte antigen (HLA) alleles/haplotypes with T1D in Taiwan.

METHODS

We performed direct comprehensive genotyping of 6 classical HLA loci (HLA-A, -B, -C, -DPB1, -DQB1, and -DRB1) to 4-digit resolution in 104 unrelated T1D patients and 504 controls. Twenty-four of the 104 patients also exhibited thyroid autoimmunity.

RESULTS

Three major susceptibility haplotypes were identified: DRB1*03:01-DQB1*02:01 (odds ratio [OR] = 5.39 under the dominant model, P = 2.3 × 10^-13 ), DRB1*04:05-DQB1*04:01 (OR = 2.44, P = 5.0 × 10^-4 ), and DRB1*09:01-DQB1*03:03 (OR = 2.02, P = 1.4 × 10^-3 ); one protective haplotype was identified: DRB1*08:03-DQB1*06:01 (OR = 0.10, P = 1.6 × 10^-3 ). DRB1*03:01-DQB1*02:01, the major T1D susceptibility haplotype, was found at a lower frequency in T1D patients with thyroid autoimmunity. The T1D protective allele DRB1*12:02 was shown to be protective against Graves' disease in our previous report.

CONCLUSION

In addition to clarifying the roles of several known T1D HLA alleles and haplotypes, we discovered that the DRB1*08:03-DQB1*06:01 haplotype is protective against T1D. The DRB1*12:02 allele protected against both T1D and Graves' disease.

Infancy-Onset T1DM, Short Stature, and Severe Immunodysregulation in Two Siblings With a Homozygous LRBA Mutation

CONTEXT

Type 1 diabetes mellitus (T1DM) is caused by autoimmunity against pancreatic β-cells. Although a significant number of T1DM patients have or will develop further autoimmune disorders during their lifetime, coexisting severe immunodysregulation is rare.

OBJECTIVE

Presuming autosomal-recessive inheritance in a complex immunodysregulation disorder including T1DM and short stature in two siblings, we performed whole-exome sequencing.

CASE PRESENTATION

Two Libyan siblings born to consanguineous parents were presented to our diabetology department at ages 12 and 5 years, respectively. Apart from T1DM diagnosed at age 2 years, patient 1 suffered from chronic restrictive lung disease, mild enteropathy, hypogammaglobulinemia, and GH deficiency. Fluorescence-activated cell sorting analysis revealed B-cell deficiency. In addition, CD4(+)/CD25(+) and CD25(high)/FoxP3(+) cells were diminished, whereas an unusual CD25(-)/FoxP3(+) population was detectable. The younger brother, patient 2, also developed T1DM during infancy. Although his enteropathy was more severe and electrolyte derangements repeatedly led to hospitalization, he did not have significant pulmonary problems. IgG levels and B-lymphocytes were within normal ranges.

RESULTS

By whole-exome sequencing we identified a homozygous truncating mutation (c.2445_2447del(C)3ins(C)2, p.P816Lfs*4) in the lipopolysaccharide-responsive beige-like anchor (LRBA) gene in both siblings. The diagnosis of LRBA deficiency was confirmed by a fluorescence-activated cell sorting-based immunoassay showing the absence of LRBA protein in phytohemagglutinin-stimulated peripheral blood mononuclear cells.

CONCLUSION

We identified a novel truncating LRBA mutation in two siblings with T1DM, short stature, and severe immunodysregulation. LRBA mutations have previously been reported to cause multiorgan autoimmunity and immunodysfunction. In light of the variable phenotypes reported so far in LRBA-mutant individuals, LRBA deficiency should be considered in all patients presenting with T1DM and signs of severe immunodysregulation.

Association study of IL2RA and CTLA4 Gene Variants with Type I Diabetes Mellitus in children in the northwest of Iran

Introduction: A variety of genetic predisposing factors and environmental factors are known to influence the pathogenesis of type-1 diabetes (T1D). This study intended to investigate the association of cytotoxic T-lymphocyte associated protein 4 (CTLA4) and interleukin 2 receptor subunit alpha (IL2RA) gene polymorphisms with type 1 diabetes in children of northwest of Iran. Methods: Genomic DNA was extracted by salting-out method. PCR amplification and direct sequencing methods were used for genotyping of CTLA4 (exon 1) and IL2RA (intron 1) genes in all patients and controls. SNPStats was used to calculate odds ratios (ORs), 95% confidence intervals (CIs), and p values. Results: In this study, the frequency of G allele and GG genotype of CTLA-4 (+49A/G) polymorphism in T1D patients were significantly different from those in the controls (26% vs. 11%, p = 0.006). Moreover, a significant difference was observed between patients and control group in the allele frequencies of the new SNP (chr2:203868145) that was identified in exon one of CTLA4 (14% vs. 3%, p = 0.006). The results showed that the GG homozygous genotype of +49 A>G was associated with increased glycemic level in T1D patients in the study population (95% CI = 10.47, p = 0.0067). However, no significant association was found between IL2RA (ss52580101C>A) polymorphism and T1D patients (2% vs. 4%, p = 0.41). Conclusion: The results further support the association of T1D with +49A>G SNP in the CTLA4 gene in the population of northwest of Iran. However, no significant relationship was observed between ss52580101C>A polymorphism of IL2RA gene and T1D in this study.

Reestablishing T Cell Tolerance by Antibody-Based Therapy in Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disease in which the insulin-producing β cells are selectively destroyed. β cell-specific T cells are considered to be the major mediators of pathology. Accordingly, most immunotherapies tested in the clinic to date have focused on reestablishing self-tolerance within the T cell compartment. Monoclonal antibodies (Ab) targeting a variety of lymphocyte surface proteins have demonstrated benefits in preclinical and clinical settings. Indeed, the use of Ab to target T cells directly or indirectly has proven to be an effective strategy to rapidly suppress β cell autoimmunity and establish tissue-specific, long-term tolerance in rodent T1D models. In this review, we describe a number of these Ab-based immunotherapies, discuss associated immune regulatory mechanisms, and highlight results obtained in T1D clinical trials.

Study of factors influencing susceptibility and age at onset of type 1 diabetes: A review of data from Continental Italy and Sardinia

AIM: To investigate the role of protein tyrosin phosphatase 22 (PTPN22), maternal age at conception and sex on susceptibility and age at onset of type 1 diabetes (T1D) in Continental Italy and Sardinian populations.

METHODS: Three hundred seventy six subjects admitted consecutively to the hospital for T1D and 1032 healthy subjects as controls were studied in Continental Italy and 284 subjects admitted consecutively to the hospital for T1D and 5460 healthy newborns were studied in Sardinia. PTPN22 genotype was determined by DNA analysis. Maternal age at conception and age at onset of disease were obtained from clinical records. χ² test of independence, student t test for differences between means and odds ratio analysis were carried out by SPSS programs. Three way contingency table analysis was carried out according to Sokal and Rohlf.

RESULTS: The pattern of association between PTPN22 and T1D is similar in Continental Italy and Sardinia: the proportion of *T allele carriers is 13.6% in T1D vs 6.7% in controls in Continental Italy while in Sardinia is 7.3% in T1D vs 4.4% in controls. The association between T1D and maternal age at conception is much stronger in Sardinia than in Italy: the proportion of newborn from mother aging more than 32 years is 89.3% in T1D vs 32.7% in consecutive newborn in Sardinia (P < 10^-6) while in Continental Italy is 32.2% in T1D vs 19.1% in consecutive newborns (P = 0.005). This points to an important role of ethnicity. A slight prevalence of T1D males on T1D females is observed both in Continental Italy and Sardinia. PTPN22 genotype does not exert significant effect on the age at onset neither in Continental Italy nor and Sardinia. Maternal age does not influence significantly age at onset in Italy (8.2 years in T1D infants from mothers aging 32 years or less vs 7.89 years in T1D infants from mothers aging more than 32 years: P = 0.824) while in Sardinia a border line effect is observed (5.75 years in T1D infants from mothers aging 32 years or less vs 7.54 years in T1D infants from mothers aging more than 32 years: P = 0.062). No effect of sex on age at onset is observed in Continental Italy while in Sardinia female show a lower age at onset of T1D as compared to males (8.07 years in males vs 6.3 years in females: P = 0.002).

CONCLUSION: The present data confirm the importance of ethnicity on susceptibility and on the age at onset of T1D.

DNA methylation profiles in type 1 diabetes twins point to strong epigenetic effects on etiology

Type 1 diabetes (T1D) shows ∼40% concordance rate in monozygotic twins (MZ) suggesting a role for environmental factors and/or epigenetic modifications in the etiology of the disease. The aim of our study was to dissect the contribution of epigenetic factors, particularly, DNA methylation (DNAm), to the incomplete penetrance of T1D. We performed DNAm profiling in lymphocyte cell lines from 3 monozygotic (MZ) twin pairs discordant for T1D and 6 MZ twin pairs concordant for the disease using HumanMethylation27 BeadChip. This assay assesses the methylation state of 27,578 CpG sites, mostly located within proximal promoter regions. We identified 88 CpG sites displaying significant methylation changes in all T1D-discordant MZ twin pairs. Functional annotation of the genes with distinct CpG methylation profiles in T1D samples showed differential DNAm of immune response and defense response pathways between affected and unaffected twins. Integration of DNAm data with GWAS data mapped several known T1D associated genes, HLA, INS, IL-2RB, CD226, which showed significant differences in DNAm between affected and unaffected of twins. Our findings suggest that abnormalities of DNA methylation patterns, known to regulate gene transcription, may be involved in the pathogenesis of T1D.

Immunomodulation of antigen presenting cells promotes natural regulatory T cells that prevent autoimmune diabetes in NOD mice

Progression towards type 1 diabetes (T1D) in susceptible patients is linked to a progressive decline in the capacity of regulatory T cells (Treg) to maintain tolerance. As such, therapies aimed at redressing the failing Treg compartment have been the subject of intense investigation. Treg dysfunction in T1D has recently been linked to a reduced capacity of antigen presenting cells (APCs) to maintain Treg function rather than Treg intrinsic defects. This suggests that therapies aimed simply at addressing the failing Treg compartment are unlikely to provide long-term protection. Here, we demonstrate that modulation of the inflammatory status of CD11b+CD11c− APCs favors the upregulation of protective Tregs in a mouse model of T1D. We further demonstrate that reduced expression of the costimulatory molecule CD40 plays a role in this increased immunoregulatory capacity. Strikingly, Treg upregulation resulted exclusively from an increase in natural Tregs rather than the peripheral conversion of conventional T cells. This suggests that modulation of CD11b+ CD11c− APCs inflammatory properties favors the establishment of natural Treg responses that, unlike adaptive Treg responses, are likely to maintain tolerance to a broad range of antigens. As such, modulation of this APC subset represents a potential therapeutic avenue to reestablish peripheral tolerance and protect from autoimmune diseases such as T1D.

The CTLA4 -819 C/T and +49 A/G dimorphisms are associated with Type 1 diabetes in Egyptian children

BACKGROUND:

Type 1 diabetes (T1D) is an organ-specific autoimmune disease characterized by T cell-mediated destruction of pancreatic islets. T cell proliferation is negatively regulated by cytotoxic lymphocyte antigen-4 (CTLA-4). CTLA-4 polymorphisms are associated with T1D in some but not all populations.

AIMS:

The study was conducted to investigate the association of the C-819T and A+49G single nucleotide polymorphisms (SNP) of CTLA-4 gene in T1D patients in the Egyptian population.

METHODS:

The association of the C-819T SNP in intron 1 and A+49G SNP in exon 1 of the CTLA-4 gene with T1D were investigated in 396 Egyptian patients ≤14 years old and 396 control subjects >24 years old, with the same ratio of males to females in both groups. The diagnosis of T1D was made on the basis of ketoacidosis or ketosis with severe symptoms of acute onset at presentation and continuous dependence on insulin. Controls were negative for anti-GAD antibodies and were greater than 24 years of age. Genotyping was performed using single strand conformation polymorphism (SSCP), temperature gradient gel electrophoresis (TGGE), and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS:

The results demonstrated an association of the C-819T and A+49G SNPs in the CTLA-4 gene with T1D patients (P=0.0047) and (P=0.000575), respectively. Moreover, this association was stratified by gender and age to female patients with age at onset 0-5 years old (P=0.0186) and (P=0.00115) more than male patient with the age at onset 0-5 years old (P= 0.3120) and (P=0.345161), respectively.

CONCLUSION:

The results support an association of the C-819T and A+49G SNPs in the CTLA-4 gene with Egyptian children, specifically, females of onset age 0-5 years old.

Human type 1 diabetes is associated with T cell autoimmunity to zinc transporter 8

Recently we demonstrated that zinc transporter 8 (ZnT8) is a major target of autoantibodies in human type 1 diabetes (T1D). Because the molecules recognized by T1D autoantibodies are typically also targets of autoreactive T cells, we reasoned that this would likely be the case for ZnT8. To test this hypothesis, IFN-γ-producing T cells specific for ZnT8 in the peripheral blood of 35 patients with T1D (<6 mo after onset at blood draw) and 41 age-matched controls were assayed by ELISPOT using a library of 23 overlapping dipeptide pools covering the entire 369 aa primary sequence. Consistent with our hypothesis, patients showed significantly higher T cell reactivity than the matched controls, manifest in terms of the breadth of the overall response and the magnitude of responses to individual pools. Therefore, the median number of pools giving positive responses (stimulation index ≥ 3) in the control group was 1.0 (range, 0-7) compared with 6.0 (range, 1-20; p < 0.0001) for the patients. Similarly, the median stimulation index of positive responses in controls was 3.1 versus 5.0 in the patients (p < 0.0001). Individually, 7 of 23 pools showed significant disease association (p < 0.001), with several of the component peptides binding the disease associated HLA-DR3 (0301) and -DR4 (0401) molecules in vitro. We conclude that ZnT8 is also a major target of disease-associated autoreactive T cells in human T1D, and we suggest that reagents that target ZnT8-specific T cells could have therapeutic potential in preventing or arresting the progression of this disease.

Genetic Predisposition for Type 1 Diabetes Mellitus - The Role of Endoplasmic Reticulum Stress in Human Disease Etiopathogenesis

The increasing incidence of diabetes mellitus worldwide has prompted a rapid growth in the pace of scientific discovery of the mechanisms involved in the etiopathogenesis of this multifactorial disease. Accumulating evidence suggests that endoplasmic reticulum stress plays a role in the pathogenesis of diabetes, contributing to pancreatic beta cell loss and insulin resistance. Wolfram syndrome is an autosomal recessive neurodegenerative disorder accompanied by insulin-dependent diabetes mellitus and progressive optic atrophy. The pathogenesis of this rare neurodegenerative genetic disease is unknown. A Wolfram gene (WFS1 locus) has recently been mapped to chromosome 4p16.1, but there is evidence for locus heterogeneity, including the mitochondrial genome deletion. Recent positional cloning led to identification of the second WFS locus, a mutation in the CISD2 gene, which encodes an endoplasmic reticulum intermembrane small protein. Our results were obtained by the analysis of a families belonging to specific population, affected by Wolfram syndrome. We have identified the newly diagnosed genetic alteration of WFS1 locus, a double non-synonymous and frameshift mutation, providing further evidence for the genetic heterogeneity of this syndrome. Newly identified mutations may contribute to the further elucidation of the pathogenesis of Wolfram syndrome, as well as of the complex mechanisms involved in diabetes mellitus development.

The Osteopontin Gene +1239A/C Single Nucleotide Polymorphism is Associated with Type 1 Diabetes Mellitus in the Italian Population

Secreted phosphoprotein 1, also known as Osteopontin (Opn), is a proinflammatory cytokine involved in the TH1 response and is highly expressed in the islets and pancreatic lymph nodes of non-obese diabetic mice before the onset of diabetes. In humans, typing of the +1239A/C single nucleotide polymorphism (SNP) in the 3'UTR of the Opn gene (SPP1) showed that +1239C carriers displayed higher Opn serum levels than +1239A homozygotes and a higher risk of developing autoimmune/lymphoproliferative syndrome, multiple sclerosis, and systemic lupus erythematosus. The aim of this work is to evaluate whether +1239A/C is also associated with type 1 diabetes mellitus (T1DM). We typed +1239A/C in an initial cohort of 184 T1DM patients and 361 controls, and confirmed our data in a second cohort of 513 patients and 857 controls. In both cohorts, +1239C carriers displayed a significantly higher risk of T1DM than +1239A homozygotes (combined cohorts: OR=1.63, 95%CI: 1.34–1.97). Clinical analysis did not detect any differences between patients carrying or not +1239C in terms of gender distribution and age at T1DM diagnosis. These data suggest that SPP1 variants marked by +1239C are associated with T1DM development in the Italian population. The predisposing effect may depend on its effect on Opn levels.

Brd2 disruption in mice causes severe obesity without Type 2 diabetes

Certain human subpopulations are metabolically healthy but obese, or metabolically obese but normal weight; such mutations uncouple obesity from glucose intolerance, revealing pathways implicated in Type 2 diabetes. Current searches for relevant genes consume significant effort. We have reported previously a novel double bromodomain protein called Brd2, which is a transcriptional co-activator/co-repressor with SWI/SNF (switch mating type/sucrose non-fermenting)-like functions that regulates chromatin. In the present study, we show that wholebody disruption of Brd2, an unusual MHC gene, causes lifelong severe obesity in mice with pancreatic islet expansion, hyperinsulinaemia, hepatosteatosis and elevated pro-inflammatory cytokines, but, surprisingly, enhanced glucose tolerance, elevated adiponectin, increased weight of brown adipose tissue, heat production and expression of mitochondrial uncoupling proteins in brown adipose tissue, reduced macrophage infiltration in white adipose tissue, and lowered blood glucose, leading to an improved metabolic profile and avoiding eventual Type 2 diabetes. Brd2 is highly expressed in pancreatic beta-cells, where it normally inhibits beta-cell mitosis and insulin transcription. In 3T3-L1 pre-adipocytes, Brd2 normally co-represses PPAR-gamma (peroxisome-proliferator-activated receptor-gamma) and inhibits adipogenesis. Brd2 knockdown protects 3T3-L1 adipocytes from TNF-alpha (tumour necrosis factor-alpha)-induced insulin resistance, thereby decoupling inflammation from insulin resistance. Thus hypomorphic Brd2 shifts energy balance toward storage without causing glucose intolerance and may provide a novel model for obese metabolically healthy humans.

Genetic-induced variations in the GAD65 T-cell repertoire governs efficacy of anti-CD3/GAD65 combination therapy in new-onset type 1 diabetes

To enhance efficacy of forthcoming type 1 diabetes (T1D) clinical trials, combination therapies (CTs) are envisaged. In this study, we showed that efficacy of a CT, using anti-CD3 antibody and glutamic acid decarboxylase of 65 kd (GAD65)-expressing plasmid, to reverse new-onset T1D was dependent upon the genetic background. Synergism between both treatments was only observed in the RIP-LCMV-GP but not in the nonobese diabetic (NOD) or RIP-LCMV-NOD models. Efficacy was associated with an expansion of bystander suppressor regulatory T cells (Tregs) recognizing the C-terminal region of GAD65 and secreting interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta), and interferon-gamma (IFN-gamma). In addition, we found that frequency and epitope specificity of GAD65-reactive CD4(+) T cells during antigen priming at diabetes onset and Tregs detected after CT correlated. Consequently, NOD mice harbored significantly lower levels of GAD65-reactive CD4(+) T cells than RIP-LCMV-GP before and after treatment. Our results demonstrate that antigen-specific T cells available at treatment may differ between various major histocompatibility complex (MHC) and genetic backgrounds. These cells play a major role in shaping T-cell responses following antigen-specific immune intervention and determine whether a beneficial Tregs response is generated. Our findings hold important implications to understand and predict the success of antigen-based clinical trials, where responsiveness to immunotherapy might vary from patient to patient.

Interplay between PTPN22 C1858T polymorphism and cow's milk formula exposure in type 1 diabetes

Genetic heterogeneity may affect the analysis of risk factors associated with type 1 diabetes (T1D). We studied the effect of the INS -23A/T, PTPN22 1858C/T, and CTLA-4 +49A/G polymorphisms on the emergence of T1D-associated autoimmunity in children exposed to cow's milk (CM) based formula during early or late infancy. The study comprised of 156 children from the Finnish DIPP cohort who had developed >or= 2 types of autoantibodies (ICA, IAA, GADA or IA-2A) or clinical T1D and 563 control children. The PTPN22 1858T allele was associated with the appearance of the autoantibodies and clinical T1D among children exposed to CM formula before the age of 6 months (PTPN22: for all P <or= 0.001, Log Rank test), but not among children exposed later on. Cox regression analysis showed an interaction between early CM exposure and 1858T allele and enhanced appearance of ICA, IAA and IA-2A (for all P <or= 0.04). Our results imply that the PTPN22 polymorphism affects the development of T1D-associated autoimmunity only if children are exposed to CM formula during early infancy suggesting an interplay between genetic and environmental factors. This may provide an explanation for the contradictory findings on the significance of CM formula exposure in T1D.

Analysis of maternal-offspring HLA compatibility, parent-of-origin and non-inherited maternal effects for the classical HLA loci in type 1 diabetes

AIM

Type 1 diabetes (T1D) is a complex trait for which variation in the classical human leucocyte antigen (HLA) loci within the Major Histocompatibility Complex (MHC) significantly influences disease risk. To date, HLA class II DR-DQ genes confer the strongest known genetic effect in T1D. HLA loci may also influence T1D through additional inherited or non-inherited effects. Evidence for the role of increased maternal-offspring HLA compatibility, and both parent-of-origin (POO) and non-inherited maternal HLA (NIMA) effects in autoimmune disease has been previously established. The current study tested hypotheses that classical HLA loci influence T1D through these mechanisms, in addition to genetic transmission of particular risk alleles.

METHODS

The Type 1 Diabetes Genetics Consortium (T1DGC) cohort was of European descent and consisted of 2271 affected sib-pair families (total n = 11 023 individuals). Class I genes HLA-A, Cw and B, and class II genes HLA-DRB1, DQA1, DQB1, DPA1 and DPB1 were studied. The pedigree disequilibrium test was used to examine transmission of HLA alleles to individuals with T1D. Conditional logistic regression was used to model compatibility relationships between mother-offspring and father-offspring for all HLA loci. POO and NIMA effects were investigated by comparing frequencies of maternal and paternal transmitted and non-transmitted HLA alleles for each locus. Analyses were also stratified by gender of T1D-affected offspring.

RESULTS

Strong associations were observed for all classical HLA loci except for DPA1, as expected. Compatibility differences between mother-offspring and father-offspring were not observed for any HLA loci. Furthermore, POO and NIMA HLA effects influencing T1D were not present.

CONCLUSIONS

Maternal-offspring HLA compatibility, POO and NIMA effects for eight classical HLA loci were investigated. Results suggest that these HLA-related effects are unlikely to play a major role in the development of T1D.

Epidemiology of type 1 diabetes and what animal models teach us about the role of viruses in disease mechanisms

There is a consensus among epidemiologists that the worldwide incidence rate of type 1 diabetes has been rising in recent decades. The cause of this rise is unknown, but epidemiological studies suggest the involvement of environmental factors, and viral infections in particular. Data demonstrating a cause-and-effect relationship between microbial infections and type 1 diabetes and how viruses may cause disease in humans are currently lacking. However, new evidence from animal models supports the hypothesis that viruses induce disease via mechanisms linked with innate immune upregulation. In the BioBreeding Diabetes Resistant rat, infection with a parvovirus induces islet destruction via upregulation of the toll-like receptor 9 (TLR9) signaling pathway. Data from mouse models of diabetes implicate TLR2, TLR3, and TLR7 in the disease process. Understanding the link between environmental agents and innate immune pathways involved in early stages of diabetes may advance the design of immune interventions to prevent disease in genetically susceptible individuals.

Joint genetic susceptibility to type 1 diabetes and autoimmune thyroiditis: from epidemiology to mechanisms

Type 1 diabetes (T1D) and autoimmune thyroid diseases (AITD) frequently occur together within families and in the same individual. The co-occurrence of T1D and AITD in the same patient is one of the variants of the autoimmune polyglandular syndrome type 3 [APS3 variant (APS3v)]. Epidemiological data point to a strong genetic influence on the shared susceptibility to T1D and AITD. Recently, significant progress has been made in our understanding of the genetic association between T1D and AITD. At least three genes have been confirmed as major joint susceptibility genes for T1D and AITD: human leukocyte antigen class II, cytotoxic T-lymphocyte antigen 4 (CTLA-4), and protein tyrosine phosphatase non-receptor type 22. Moreover, the first whole genome linkage study has been recently completed, and additional genes will soon be identified. Not unexpectedly, all the joint genes for T1D and AITD identified so far are involved in immune regulation, specifically in the presentation of antigenic peptides to T cells. One of the lessons learned from the analysis of the joint susceptibility genes for T1D and AITD is that subset analysis is a key to dissecting the etiology of complex diseases. One of the best demonstrations of the power of subset analysis is the CTLA-4 gene in T1D. Although CTLA-4 showed very weak association with T1D, when analyzed in the subset of patients with both T1D and AITD, the genetic effect of CTLA-4 was significantly stronger. Gene-gene and genetic-epigenetic interactions most likely play a role in the shared genetic susceptibility to T1D and AITD. Dissecting these mechanisms will lead to a better understanding of the etiology of T1D and AITD, as well as autoimmunity in general.

Advances in type I diabetes associated tolerance mechanisms

Type 1 diabetes (T1D) is an autoimmune disease resulting from the destruction of insulin-producing pancreatic beta cells by autoreactive T cells. The polygenic trait for T1D risk implicates many genes that have an impact on fundamental immunological processes such as central and peripheral tolerance. Several pieces of evidence have suggested that many of the genetic loci that are directly linked to type 1 diabetes susceptibility modulate the generation and/or the activation of autoreactive T-lymphocytes. We and others have proposed a critical role for medullary thymic epithelial cells (mTEC) forming the Hassall's corpuscles in T-cell tolerance. Indeed, mTEC have been found to express promiscuous self-antigens, used directly or through thymic dendritic cells to drive either negative selection of insulin-reacting precursors or their differentiation into naturally occurring regulatory Foxp3+ CD4+ CD25+ T cells. In the periphery, naturally occurring Foxp3+ CD4+ CD25+regulatory T (Treg) cells represent the master cells in dominant peripheral T-cell tolerance. The development and function of Treg cells are ultimately linked to IL-2 and Foxp3 expression. This review addresses recent literature and emerging concepts of central and peripheral T-cell tolerance with regards to T1D.

Relation of circulating concentrations of chemokine receptor CCR5 ligands to C-peptide, proinsulin and HbA1c and disease progression in type 1 diabetes

Th1 related chemokines CCL3 and CCL5 and Th2 related CCL4 as ligands of the receptor CCR5 contribute to disease development in animal models of type 1 diabetes. In humans, no data are available addressing the role of these chemokines regarding disease progression and remission. We investigated longitudinally circulating concentrations of CCR5 ligands of 256 newly diagnosed patients with type 1 diabetes. CCR5 ligands were differentially associated with beta-cell function and clinical remission. CCL5 was decreased in remitters and positively associated with HbA1c suggestive of a Th1 associated progression of the disease. Likewise, CCL3 was negatively related to C-peptide and positively associated with the beta-cell stress marker proinsulin but increased in remitters. CCL4 associated with decreased beta-cell stress shown by negative association with proinsulin. Blockage of chemokines or antagonism of CCR5 by therapeutic agents such as maraviroc may provide a new therapeutic target to ameliorate disease progression in type 1 diabetes.

Variations of the perforin gene in patients with type 1 diabetes

OBJECTIVE

Perforin plays a key role in cell-mediated cytotoxicity. Mutations of its gene, PRF1, cause familial hemophagocytic lymphohistiocytosis but have also been associated with lymphomas and the autoimmune/lymphoproliferative syndrome. The aim of this work was to investigate the role of PRF1 variations in type 1 diabetes.

RESEARCH DESIGN AND METHODS

We typed for the N252S and A91V variations in an initial population of 352 type 1 diabetic patients and 816 control subjects and a second population of 365 patients and 964 control subjects. Moreover, we sequenced the coding sequence and intron-exons boundaries in 200 patients and 300 control subjects.

RESULTS

In both cohorts, allelic frequency of N252S was significantly higher in patients than in control subjects (combined cohorts: 1.5 vs. 0.4%; odds ratio 6.68 [95% CI 1.83-7.48]). Sequencing of the entire coding region detected one novel mutation in one patient, causing a P477A amino acid change not detected in 199 patients and 300 control subjects. Typing for HLA-DQA1 and DQB1 alleles showed that type 1 diabetes-predisposing DQ alpha/DQ beta heterodimers were less frequent in patients carrying N252S or P477A than in those carrying wild-type PRF1. We previously found that natural killer (NK) activity is not decreased in most N252S heterozygotes, but we detected one whose NK activity was normal at the age of 12 but strikingly low in early childhood. Here, we discovered that NK function was low in three heterozygotes in early childhood, one homozygous adult, and in the subject carrying P477A.

CONCLUSIONS

These data suggest that N252S and possibly other PRF1 variations are susceptibility factors for type 1 diabetes development.