Regine Bergholdt

A human type 1 diabetes susceptibility locus maps to chromosome 21q22.3.

OBJECTIVE— The Type 1 Diabetes Genetics Consortium (T1DGC) has assembled and genotyped a large collection of multiplex families for the purpose of mapping genomic regions linked to type 1 diabetes. In the current study, we tested for evidence of loci associated with type 1 diabetes utilizing genome-wide linkage scan data and family-based association methods. RESEARCH DESIGN AND METHODS— A total of 2,496 multiplex families with type 1 diabetes were genotyped with a panel of 6,090 single nucleotide polymorphisms (SNPs). Evidence of association to disease was evaluated by the pedigree disequilibrium test. Significant results were followed up by genotyping and analyses in two independent sets of samples: 2,214 parent-affected child trio families and a panel of 7,721 case and 9,679 control subjects. RESULTS— Three of the SNPs most strongly associated with type 1 diabetes localized to previously identified type 1 diabetes risk loci: INS, IFIH1, and KIAA0350. A fourth strongly associated SNP, rs876498 (P = 1.0 × 10−4), occurred in the sixth intron of the UBASH3A locus at chromosome 21q22.3. Support for this disease association was obtained in two additional independent sample sets: families with type 1 diabetes (odds ratio [OR] 1.06 [95% CI 1.00–1.11]; P = 0.023) and case and control subjects (1.14 [1.09–1.19]; P = 7.5 × 10−8). CONCLUSIONS— The T1DGC 6K SNP scan and follow-up studies reported here confirm previously reported type 1 diabetes associations at INS, IFIH1, and KIAA0350 and identify an additional disease association on chromosome 21q22.3 in the UBASH3A locus (OR 1.10 [95% CI 1.07–1.13]; P = 4.4 × 10−12). This gene and its flanking regions are now validated targets for further resequencing, genotyping, and functional studies in type 1 diabetes.

Identification of Novel Type 1 Diabetes Candidate Genes by Integrating Genome-Wide Association Data, Protein-Protein Interactions, and Human Pancreatic Islet Gene Expression

Genome-wide association studies (GWAS) have heralded a new era in susceptibility locus discovery in complex diseases. For type 1 diabetes, >40 susceptibility loci have been discovered. However, GWAS do not inevitably lead to identification of the gene or genes in a given locus associated with disease, and they do not typically inform the broader context in which the disease genes operate. Here, we integrated type 1 diabetes GWAS data with protein-protein interactions to construct biological networks of relevance for disease. A total of 17 networks were identified. To prioritize and substantiate these networks, we performed expressional profiling in human pancreatic islets exposed to proinflammatory cytokines. Three networks were significantly enriched for cytokine-regulated genes and, thus, likely to play an important role for type 1 diabetes in pancreatic islets. Eight of the regulated genes (CD83, IFNGR1, IL17RD, TRAF3IP2, IL27RA, PLCG2, MYO1B, and CXCR7) in these networks also harbored single nucleotide polymorphisms nominally associated with type 1 diabetes. Finally, the expression and cytokine regulation of these new candidate genes were confirmed in insulin-secreting INS-1 β-cells. Our results provide novel insight to the mechanisms behind type 1 diabetes pathogenesis and, thus, may provide the basis for the design of novel treatment strategies.

Genetic Susceptibility Markers in Danish Patients with Type 1 (Insulin-Dependent) Diabetes-Evidence for Polygenecity in Man

Fifty-five Danish families with two offspring concordant for type 1 diabetes-identified through a nationwide population-based survey, and 57 “true sporadic” cases-matched with familial cases for age at onset, but with no IDDM-affected first-degree relatives and long disease duration, and 110 control subjects were typed for putative genetic susceptibility markers for type 1 diabetes identified from a pathogenetic model. The markers included MHC class I, II and III loci, the manganese superoxide dismutase (MnSOD) locus (chr. 6q), interleukin-1β (IL1B), the IL-1 receptor antagonist (IL1RN), and the IL-1 type 1 receptor (IL1RI) loci (each chr. 2q). No significant differences between familial and sporadic cases were found within the MHC region (including the following loci: HLA-DQ,-DR, heat shock protein (HSP) 70, tumour necrosis factor (TNF), HLA-B and-A). In both groups of patients 11% were negative for both DQA1*0301-DQB 1*0302 and DQA1*0501-DQB1*0201 genotypes, and 7% of the type 1 diabetics had genotypes ...

PTPN22 R620W Functional Variant in Type 1 Diabetes and Autoimmunity Related Traits

The PTPN22 gene, encoding the lymphoid-specific protein tyrosine phosphatase, a negative regulator in the T-cell activation and development, has been associated with the susceptibility to several autoimmune diseases, including type 1 diabetes. Based on combined case-control and family-based association studies, we replicated the finding of an association of the PTPN22 C1858T (R620W) functional variant with type 1 diabetes, which was independent from the susceptibility status at the insulin gene and at HLA-DR (DR3/4 compared with others). The risk contributed by the 1858T allele was increased in patients with a family history of other autoimmune diseases, further supporting a general role for this variant on autoimmunity. In addition, we found evidence for an association of 1858T allele with the presence of GAD autoantibodies (GADA), which was restricted to patients with long disease duration (>10 years, P < 0.001). This may help define a subgroup of patients with long-term persistence of GADA. The risk conferred by 1858T allele on GAD positivity was additive, and our meta-analysis also supported an additive rather than dominant effect of this variant on type 1 diabetes, similar to previous reports on rheumatoid arthritis and systemic lupus erythematosus.

Integrative analysis for finding genes and networks involved in diabetes and other complex diseases

We have developed an integrative analysis method combining genetic interactions, identified using type 1 diabetes genome scan data, and a high-confidence human protein interaction network. Resulting networks were ranked by the significance of the enrichment of proteins from interacting regions. We identified a number of new protein network modules and novel candidate genes/proteins for type 1 diabetes. We propose this type of integrative analysis as a general method for the elucidation of genes and networks involved in diabetes and other complex diseases.

Increased prevalence of Down’s syndrome in individuals with type 1 diabetes in Denmark: a nationwide population-based study

Aims/hypothesisIn patients with Down’s syndrome, dogma has long held that the prevalence of diabetes is increased. The aim of the present study was to determine the actual prevalence of Down’s syndrome among type 1 diabetic patients.Subjects, materials and methodsThe background population included all children born in Denmark between 1981 and 2000. Registry-validated and clinical data on type 1 diabetes and Down’s syndrome diagnoses were obtained from the National Disease Register and Danish Cytogenetic Central Register, respectively.ResultsThe prevalence of Down’s syndrome in the background population was 0.09%, whereas we identified a prevalence of Down’s syndrome in type 1 diabetes patients of 0.38% (95% CI 0.17–0.75), corresponding to a 4.2-fold increased prevalence compared with the background population (p=7.3×10−5).Conclusions/interpretationTo the best of our knowledge this is the first population-based study addressing the prevalence of Down’s syndrome among verified type 1 diabetes patients. A more than fourfold increased prevalence of Down’s syndrome among type 1 diabetes patients supports the notion that genes on chromosome 21 may confer risk for type 1 diabetes, probably also in the general population.

Further evidence that mutations in INS can be a rare cause of Maturity-Onset Diabetes of the Young (MODY)

BackgroundInsulin gene (INS) mutations have recently been described as a common cause of permanent neonatal diabetes (PNDM) and a rare cause of diabetes diagnosed in childhood or adulthood.MethodsINS was sequenced in 116 maturity-onset diabetes of the young (MODYX) patients (n = 48 Danish and n = 68 Czech), 83 patients with gestational diabetes mellitus (GDM), 34 type 1 diabetic patients screened negative for glutamic acid decarboxylase (GAD), and 96 glucose tolerant individuals. The control group was randomly selected from the population-based sampled Inter99 study.ResultsOne novel heterozygous mutation c.17G>A, R6H, was identified in the pre-proinsulin gene (INS) in a Danish MODYX family. The proband was diagnosed at 20 years of age with mild diabetes and treated with diet and oral hypoglycaemic agent. Two other family members who carried the INS R6H were diagnosed with diabetes when 51 years old and with GDM when 27 years old, respectively. A fourth mutation carrier had normal glucose tolerance when 20 years old. Two carriers of INS R6H were also examined twice with an oral glucose tolerance test (OGTT) with 5 years interval. They both had a ~30% reduction in beta-cell function measured as insulinogenic index. In a Czech MODYX family a previously described R46Q mutation was found. The proband was diagnosed at 13 years of age and had been treated with insulin since onset of diabetes. Her mother and grandmother were diagnosed at 14 and 35 years of age, respectively, and were treated with oral hypoglycaemic agents and/or insulin.ConclusionMutations in INS can be a rare cause of MODY and we conclude that screening for mutations in INS should be recommended in MODYX patients.

Huntingtin-interacting protein 14 is a type 1 diabetes candidate protein regulating insulin secretion and beta-cell apoptosis

Type 1 diabetes (T1D) is a complex disease characterized by the loss of insulin-secreting β-cells. Although the disease has a strong genetic component, and several loci are known to increase T1D susceptibility risk, only few causal genes have currently been identified. To identify disease-causing genes in T1D, we performed an in silico “phenome–interactome analysis” on a genome-wide linkage scan dataset. This method prioritizes candidates according to their physical interactions at the protein level with other proteins involved in diabetes. A total of 11 genes were predicted to be likely disease genes in T1D, including the INS gene. An unexpected top-scoring candidate gene was huntingtin-interacting protein (HIP)-14/ZDHHC17. Immunohistochemical analysis of pancreatic sections demonstrated that HIP14 is almost exclusively expressed in insulin-positive cells in islets of Langerhans. RNAi knockdown experiments established that HIP14 is an antiapoptotic protein required for β-cell survival and glucose-stimulated insulin secretion. Proinflammatory cytokines (IL-1β and IFN-γ) that mediate β-cell dysfunction in T1D down-regulated HIP14 expression in insulin-secreting INS-1 cells and in isolated rat and human islets. Overexpression of HIP14 was associated with a decrease in IL-1β–induced NF-κB activity and protection against IL-1β–mediated apoptosis. Our study demonstrates that the current network biology approach is a valid method to identify genes of importance for T1D and may therefore embody the basis for more rational and targeted therapeutic approaches.

Genetic and functional evaluation of an interleukin-12 polymorphism (IDDM18) in families with type 1 diabetes.

Type 1 (insulin dependent) diabetes mellitus (T1DM) [MIM 222100] is an autoimmune disease with both genetic and environmental components. The HLA region is the major genetic susceptibility region, but in addition several minor susceptibility loci have been suggested. Their identification is, however, difficult because of the complexity of the disease.1 Recently, a new susceptibility locus, IDDM18 [MIM 605598], was reported and mapped to chromosome 5q31.1-q33.1, close to the IL12B gene, which encodes the p40 subunit of interleukin (IL) 12.2–4 IL-12p40 production influences T cell response, and may therefore be important in T1DM pathogenesis.5 IL-12 drives the differentiation of T lymphocytes towards the Th1 subset, characterised by production of cytokines leading to cell mediated immunity.6–8 Furthermore, in the non-obese diabetic (NOD) mouse, IL-12 has been shown to play a primary role in T1DM induction.5,9,10 In addition, IL-12 is important in immune reactivity against infections, but it has been shown that in the absence of infection, IL-12 induced autoreactive T cell responses might predispose to self destructive immunity.11,12 IL-12 is a disulphide linked heterodimer composed of a heavy chain of 40 kDa, p40, and a light chain of 35 kDa, p35, encoded by two separate genes.2,13 The gene for the p35 subunit, IL12A , is located on chromosome 3p12-q13.2. The two subunits of IL-12 are in contrast to most cytokines, which possess only one polypeptide chain. Many cell types express the p35 chain, while the p40 subunit is expressed principally by activated macrophages and B cells.2 The heterodimer, p70 or p75, is the biologically active IL-12.13 IL12B is a candidate for IDDM18 , as linkage disequilibrium is confined to a 30 kb region on chromosome 5, in which IL12B is the only known gene.4 Several polymorphisms …

CBLB variants in type 1 diabetes and their genetic interaction with CTLA4

Type 1 diabetes (T1D) is a multifactorial disease with genetic and environmental components involved. Recent studies of an animal model of T1D, the Komeda diabetes‐prone rat, have demonstrated that the Casitas‐B‐lineage lymphoma b (cblb) gene is a major susceptibility gene in the development of diabetes and other autoimmune features of this rat. As a result of the inhibitory role of Cbl‐b in T cell costimulation, dysregulation of Cbl‐b may also contribute to autoimmune diseases in man. Different isoforms of Cbl‐b exist; we evaluated expression levels of two known transcript variants. Constitutive expression of both isoforms was demonstrated, as well as an increased expression, after cytokine exposure, of an isoform lacking exon 16, suggesting a possible role of this variant in the pathogenesis of autoimmunity. We screened coding regions of the human CBLB gene for mutations in a panel of individuals affected with several autoimmune diseases. Eight single nucleotide polymorphisms (SNPs) were detected. One SNP in exon 12 of the CBLB gene was significantly demonstrated to be associated to T1D in a large Danish T1D family material of 480 families. Evidence for common genetic factors underlying several autoimmune diseases has come from studies of cytotoxic T lymphocyte antigen 4 (CTLA4), which encodes another negatively regulatory molecule in the immune system. Gene‐gene interactions probably play substantial roles in T1D susceptibility. We performed stratification of CBLB exon 12 SNP data, according to an established CTLA4 marker, CT60, and evidence for a genetic interaction between the CTLA4 and CBLB genes, involved in the same biological pathway of T cell receptor signaling, was observed.