Genetics of autoimmune diabetes mellitus

Epigenetic Regulation in Etiology of Type 1 Diabetes Mellitus

Type 1 diabetes mellitus (T1DM) is caused by an autoimmune destruction of the pancreatic β-cells, a process in which autoreactive T cells play a pivotal role, and it is characterized by islet autoantibodies. Consequent hyperglycemia is requiring lifelong insulin replacement therapy. T1DM is caused by the interaction of multiple environmental and genetic factors. The integrations of environments and genes occur via epigenetic regulations of the genome, which allow adaptation of organism to changing life conditions by alternation of gene expression. T1DM has increased several-fold over the past half century. Such a short time indicates involvement of environment factors and excludes genetic changes. This review summarizes the most current knowledge of epigenetic changes in that process leading to autoimmune diabetes mellitus.

Classical HLA alleles tag SNP in families from Antioquia with type 1 diabetes mellitus

Introduction: The HLA region strongly associates with autoimmune diseases, such as type 1 diabetes. An alternative way to test classical HLA alleles is by using tag SNP. A set of tag SNP for several classical HLA alleles has been reported as associated with susceptibility or resistance to this disease in Europeans. Objective: We aimed at validating the methodology based on tag SNP focused on the inference of classical HLA alleles, and at evaluating their association with type 1 diabetes mellitus in a sample of 200 families from Antioquia. Materials and methods: We studied a sample of 200 families from Antioquia. Each family had one or two children with T1D. We genotyped 13 SNPs using tetra-primer ARMS-PCR or PCRRFLP. In addition, we tested the validity of the tag SNP reported for Europeans in 60 individuals from a population of Colombians living in Medellín (CLM) from the 1000 Genomes Project database. Statistical analyses included the Hardy-Weinberg equilibrium, the transmission disequilibrium and the linkage disequilibrium tests. Results: The linkage disequilibrium was low in reported tag SNP and classical HLA alleles in this CLM population. Association analyses revealed both risk and protection factors to develop type 1 diabetes mellitus. Appropriate tag SNPs for the CLM population were determined by using the genotype information available in the 1000 Genome Project database. Conclusions: Although linkage disequilibrium patterns in this CLM population were different from those reported in Europeans, we did find strong evidence of the role of HLA in the development of type 1 diabetes mellitus in the study population.

Expression of HLA-DQA1 and HLA-DQB1 genes in B lymphocytes, monocytes and whole blood

Differential expression of HLA-DQA1 and HLA-DQB1 gene alleles was analysed in three different cell populations isolated from peripheral blood-B lymphocytes, monocytes and whole-blood cells. Interallelic differences in mRNA levels were observed: DQA1*03 alleles were among the most expressed in all cell types, whereas DQA1*05 alleles were least expressed in whole blood and monocytes and among the most expressed in B cells. For DQB1 gene, DQB1*06 group of alleles were the most expressed, and DQB1*02 group the least expressed within all cell populations examined. In comparison with the rest alleles, DQB1*06 and DQB1*05:02 alleles have higher expression in monocytes than in B cells, professional antigen-presenting cells. Cell type-specific regulation of expression was observed as well, with higher and more balanced expression of alleles in B lymphocytes compared to monocytes.

Maternal obesity as a risk factor for early childhood type 1 diabetes: a nationwide, prospective, population-based case-control study

AIMS/HYPOTHESIS

Genetic and environmental factors are believed to cause type 1 diabetes. The aim of this study was to investigate the influence of maternal BMI and gestational weight gain on the subsequent risk of childhood type 1 diabetes.

METHODS

Children in the Swedish National Quality Register for Diabetes in Children were matched with control children from the Swedish Medical Birth Register. Children were included whose mothers had data available on BMI in early pregnancy and gestational weight gain, giving a total of 16,179 individuals: 3231 children with type 1 diabetes and 12,948 control children.

RESULTS

Mothers of children with type 1 diabetes were more likely to be obese (9% [n = 292/3231] vs 7.7% [n = 991/12,948]; p = 0.02) and/or have diabetes themselves (2.8% [n = 90/3231] vs 0.8% [n = 108/12,948]; p < 0.001) compared with mothers of control children. Gestational weight gain did not differ significantly between the two groups of mothers. In mothers without diabetes, maternal obesity was a significant risk factor for type 1 diabetes in the offspring (p = 0.04). A child had an increased risk of developing type 1 diabetes if the mother had been obese in early pregnancy (crude OR 1.20; 95% CI 1.05, 1.38; adjusted OR 1.18; 95% CI 1.02, 1.36). Among children with type 1 diabetes (n = 3231) there was a difference (p < 0.001) in age at onset in relation to the mother's BMI. Among children in the oldest age group (15-19 years), there were more mothers who had been underweight during pregnancy, while in the youngest age group (0-4 years) the pattern was reversed.

CONCLUSIONS/INTERPRETATION

Maternal obesity, in the absence of maternal diabetes, is a risk factor for type 1 diabetes in the offspring, and influences the age of onset of type 1 diabetes. This emphasises the importance of a normal maternal BMI to potentially decrease the incidence of type 1 diabetes.

DNA methylation and mRNA expression of HLA-DQA1 alleles in type 1 diabetes mellitus

Type 1 diabetes (T1D) belongs among polygenic multifactorial autoimmune diseases. The highest risk is associated with human leucocyte antigen (HLA) class II genes, including HLA-DQA1 gene. Our aim was to investigate DNA methylation of HLA-DQA1 promoter alleles (QAP) and correlate methylation status with individual HLA-DQA1 allele expression of patients with T1D and healthy controls. DNA methylation is one of the epigenetic modifications that regulate gene expression and is known to be shaped by the environment.Sixty one patients with T1D and 39 healthy controls were involved in this study. Isolated DNA was treated with sodium bisulphite and HLA-DQA1 promoter sequence was amplified using nested PCR. After sequencing, DNA methylation of HLA-DQA1 promoter alleles was analysed. Individual mRNA HLA-DQA1 relative allele expression was assessed using two different endogenous controls (PPIA, DRA). We have found statistically significant differences in HLA-DQA1 allele 02:01 expression (PPIA normalization, Pcorr = 0·041; DRA normalization, Pcorr = 0·052) between healthy controls and patients with T1D. The complete methylation profile of the HLA-DQA1 promoter was gained with the most methylated allele DQA1*02:01 and the least methylated DQA1*05:01 in both studied groups. Methylation profile observed in patients with T1D and healthy controls was similar, and no correlation between HLA-DQA1 allele expression and DNA methylation was found. Although we have not proved significant methylation differences between the two groups, detailed DNA methylation status and its correlation with expression of each HLA-DQA1 allele in patients with T1D have been described for the first time.

Interaction of dendritic cells and T lymphocytes for the therapeutic effect of Dangguiliuhuang decoction to autoimmune diabetes

In traditional Chinese medicine (TCM), Dangguiliuhuang decoction (DGLHD) is an effective treatment of autoimmune diabetes. Here, we studied potential anti-diabetic mechanisms of DGLHD in a non-obese diabetic (NOD) mouse model. In vitro, DGLHD and individual active ingredients enhanced glucose uptake in HepG2 cells, inhibited T lymphocyte proliferation, and suppressed dendritic cells (DCs) function. In vivo, DGLHD significantly inhibited insulitis, delayed the onset and development of diabetes, promoted insulin secretion and sensitivity, and balanced partially normalized Th1 and Th2 cytokines in NOD mice. In addition, DGLHD increased α₁-antitrypsin (AAT-1), Bcl-2, and CyclinD1, and decreased Bax levels in pancreas, spleen, thymus, DCs, and a NIT-1 cell line, all consistent with protecting and repairing islet β cell. More detailed studies indicated that DGLHD regulated the maturation and function of DCs, decreased the percentage of merocytic dendritic cells (mcDCs) subset, and increased programmed death ligand-1 (PD-L1) expression in DCs. DGLHD also impeded T lymphocyte proliferation and promoted regulatory T cells (T_regs) differentiation in vivo. A JAK2-STAT3-dependent pathway was involved in the suppression by DGLHD of interactions between DCs and T lymphocyte. The experiments implicated five active ingredients in specific anti-diabetic actions of DGLHD. The results demonstrated the reasonable composition of the formula.

Association analysis of PTPN22, CTLA4 and IFIH1 genes with type 1 diabetes in Colombian families

BACKGROUND

Protein tyrosine phosphatase, non-receptor type 22 (lymphoid) (PTPN22), cytotoxic T-lymphocyte-associated protein 4 (CTLA4), and interferon induced with helicase C domain 1 (IFIH1) are among the confirmed type 1 diabetes (T1D) susceptibility genes in several populations. The aim of this study was to evaluate the role of PTPN22, CTLA4, and IFIH1 gene variants in the development of T1D in a Colombian population.

METHODS

Associations of PTPN22, CTLA4, and IFIH1 variants with T1D were investigated in a sample of 197 nuclear families, including 205 affected children, in the Colombian population. Three to four single nucleotide polymorphisms (SNPs) were analyzed per gene: rs2476600, rs2476601, rs1217418, and rs2488457 for PTPN22; rs1990760, rs3747517, and rs10930046 for IFIH1; and rs231775, rs3087243, and rs231779 for CTLA4. A transmission disequilibrium test was performed for the global sample, in addition to stratified analysis considering autoimmunity, age at onset, and parent of origin. Haplotypes per gene were also analyzed.

RESULTS

There was no significant transmission distortion for CTLA4. Conversely, SNPs rs10930046 (IFIH1) and rs2476601 (PTPN222) exhibited significant transmission distortion of the C and T alleles, respectively, from parents to affected children (odds ratio [OR] 0.57 and 1.83, respectively). In addition, decreased transmission of the C allele for rs10930046 occurred preferentially from mothers. Stratification analysis revealed that this association was maintained in individuals who were positive for autoantibodies and in those with an age of diagnosis <5 years.

CONCLUSION

The results show that IFIH1 and PTPN22 are associated with T1D in Colombian families.

C-peptide response and HLA genotypes in subjects with recent-onset type 1 diabetes after immunotherapy with DiaPep277: an exploratory study

OBJECTIVE

To investigate whether lower risk HLA class II genotypes would influence the efficacy of DiaPep277 therapy in protecting β-cell function evaluated by C-peptide secretion in recent-onset type 1 diabetic subjects.

RESEARCH DESIGN AND METHODS

Data were collected from type 1 diabetic subjects enrolled in multicenter phase II studies with a randomized, double-blind, and placebo-controlled design in whom fasting and stimulated C-peptide levels were measured. HLA genotypes were classified in high, moderate, and low risk categories.

RESULTS

A total of 146 subjects (aged 4.3 to 58.5 years) were enrolled, including 76 children (<18 years old) and 70 adults. At baseline, there was a significant increase in fasting, maximal, and area under the curve (AUC) C-peptide from high to moderate and low risk HLA genotypes in adults (P for trend <0.04) but not in children. Children showed a decrease of the three parameters over time regardless of therapy and HLA genotype. DiaPep277-treated adults with low risk genotype had significantly higher maximal and AUC C-peptide versus placebo at 12 months (0.04 ± 0.07 vs. -0.28 ± 0.09 nmol/L, P < 0.01, and 0.53 ± 1.3 vs. -4.59 ± 1.5 nmol/L, P < 0.05, respectively). In the moderate risk genotype group, Δmaximal and AUC C-peptide values were significantly higher in DiaPep277-treated versus placebo-treated patients (P < 0.01 and P < 0.05, respectively).

CONCLUSIONS

This exploratory study demonstrates that type 1 diabetic adults with low and moderate risk HLA genotypes benefit the most from intervention with DiaPep277; the only subgroup with an increase of C-peptide at 12 months after diagnosis was the low risk DiaPep277-treated subgroup.

Prevention of type 1 diabetes: today and tomorrow

The aim of therapeutic interventions for type 1 diabetes is to suppress pathogenic autoreactivity and to preserve/restore beta-cell mass and function to physiologically sufficient levels to maintain good metabolic control. During the natural history of type 1 diabetes, several strategies have been applied at various stages in the form of primary, secondary or tertiary prevention approaches. Clinical trials using antigen-specific (e.g. DiaPep277, human glutamic acid decarboxylase 65 (GAD65)) or non-specific immune therapies (e.g. anti-CD3 monoclonal antibodies) have shown some benefit in the modulation of the autoimmune process and prevention of the insulin secretion loss in the short term after diagnosis of diabetes. A single long-term effective therapy has not been identified yet, and it is likely that in most cases a rationally designed combinatorial approach using immunotherapeutic methods coupled with islet regeneration or replacement will prove to be most effective.

Genetic dissection reveals diabetes loci proximal to the gimap5 lymphopenia gene

Congenic DRF.(f/f) rats are protected from type 1 diabetes (T1D) by 34 Mb of F344 DNA introgressed proximal to the gimap5 lymphopenia gene. To dissect the genetic factor(s) that confer protection from T1D in the DRF.(f/f) rat line, DRF.(f/f) rats were crossed to inbred BBDR or DR.(lyp/lyp) rats to generate congenic sublines that were genotyped and monitored for T1D, and positional candidate genes were sequenced. All (100%) DR.(lyp/lyp) rats developed T1D by 83 days of age. Reduction of the DRF.(f/f) F344 DNA fragment by 26 Mb (42.52-68.51 Mb) retained complete T1D protection. Further dissection revealed that a 2 Mb interval of F344 DNA (67.41-70.17 Mb) (region 1) resulted in 47% protection and significantly delayed onset (P < 0.001 compared with DR.(lyp/lyp)). Retaining <1 Mb of F344 DNA at the distal end (76.49-76.83 Mb) (region 2) resulted in 28% protection and also delayed onset (P < 0.001 compared with DR.(lyp/lyp)). Comparative analysis of diabetes frequency in the DRF.(f/f) congenic sublines further refined the RNO4 region 1 interval to approximately 670 kb and region 2 to the 340 kb proximal to gimap5. All congenic DRF.(f/f) sublines were prone to low-grade pancreatic mononuclear cell infiltration around ducts and vessels, but <20% of islets in nondiabetic rats showed islet infiltration. Coding sequence analysis revealed TCR Vbeta 8E, 12, and 13 as candidate genes in region 1 and znf467 and atp6v0e2 as candidate genes in region 2. Our results show that spontaneous T1D is controlled by at least two genetic loci 7 Mb apart on rat chromosome 4.

Brain imaging in pediatric obsessive-compulsive disorder

OBJECTIVE

To review progress in understanding pediatric obsessive-compulsive disorder (OCD). The focus is on the frontal-striatal-thalamic model of OCD, neurobiological and genetic studies of the disorder, and their influence on recent advances in treatment.

METHOD

Computerized literature searches were conducted with the key words "obsessive-compulsive disorder" in conjunction with "pediatric," "genetics," and "imaging."

RESULTS

Neuroimaging studies find evidence to support the frontal-striatal-thalamic model. Genetic and neurochemical studies also implicate glutamate in the pathological finding of OCD. This has led to the application of glutamate-modulating agents to treat OCD.

CONCLUSIONS

Studies of pediatric OCD have led to a refined frontal-striatal-thalamic model of pathogenesis and are having an evidence-based impact on treatment. Despite this progress, fully explanatory models are still needed that would allow for accurate prognosis and the development of targeted and efficacious treatments.