Jørn Nerup

Genome-wide association study and meta-analysis find that over 40 loci affect risk of type 1 diabetes

Type 1 diabetes (T1D) is a common autoimmune disorder that arises from the action of multiple genetic and environmental risk factors. We report the findings of a genome-wide association study of T1D, combined in a meta-analysis with two previously published studies. The total sample set included 7,514 cases and 9,045 reference samples. Forty-one distinct genomic locations provided evidence for association with T1D in the meta-analysis (P < 10−6). After excluding previously reported associations, we further tested 27 regions in an independent set of 4,267 cases, 4,463 controls and 2,319 affected sib-pair (ASP) families. Of these, 18 regions were replicated (P < 0.01; overall P < 5 × 10−8) and 4 additional regions provided nominal evidence of replication (P < 0.05). The many new candidate genes suggested by these results include IL10, IL19, IL20, GLIS3, CD69 and IL27.

A Taql polymorphism in the human interleukin-1β (IL-1β) gene correlates with IL-1β secretion in vitro

Abstract. In the present study we searched for restriction fragment length polymorphisms (RFLP) in the human interleukin‐1β (IL‐lβ) gene and for correlations to monocyte (Mo) function in non‐related healthy donors and insulin‐dependent diabetic patients. We demonstrated a diallelic polymorphism with the restriction enzyme TaqI consisting of fragments of 9.4 kb and 13.4 kb. No differences in allele or genotype frequencies of this RFLP were observed between randomly selected controls and randomly selected patients with insulin‐dependent diabetes mel‐litus (IDDM). However, when analysing IDDM patients negative for HLA‐DR3 and ‐DR4, our data demonstrate that the 13.4 kb allele is more frequent in this group compared to a matched control group. The functional impact of this RFLP was studied by analysing in vitro stimulated Mo IL‐1β response. An IL‐lβ allele dosage effect on secretory capacity was observed after LPS‐stimulation: 13.4/13.4 kb homo‐zygous individuals secreted significantly more IL‐lβ than 9.4/13.4 kb heterozygous individuals, who secreted significantly more than 9.4/9.4 kb homozygous individuals. Analyses of supernatants from LPS‐sti‐mulated Mo cultures from individuals with each Taql IL‐lβ genotype revealed no differences in the mouse thymocyte co‐stimulatory assay when compared on a molar basis, indicating that the Taql polymorphism gave rise only to quantitative differences in expression levels and probably not to a mutant IL‐lβ. We conclude that the 13.4 kb allele represents an IL‐1β‘high‐secretor’ phenotype, that the observed RFLP may be a genetic susceptibility marker for IDDM in non‐DR3 and non‐DR4 individuals and that high IL‐1β secretory capacity may be a pathogenic factor for IDDM in these patients.

Susceptibility to human type 1 diabetes at IDDM2 is determined by tandem repeat variation at the insulin gene minisatellite locus

The IDDM2 locus encoding susceptibility to type 1 diabetes was mapped previously to a 4.1–kb region spanning the insulin gene and a minisatellite or variable number of tandem repeats (VNTR) locus on human chromosome 11p15.5. By ‘cross–match’ haplotype analysis and linkage disequilibrium mapping, we have mapped the mutation IDDM2 to within the VNTR itself. Other polymorphisms were systematically excluded as primary disease determinants. Transmission of IDDM2 may be influenced by parent–of–origin phenomena. Although we show that the insulin gene is expressed biallelically in the adult pancreas, we present preliminary evidence that the level of transcription in vivo is correlated with allelic variation within the VNTR. Allelic variation at VNTRs may play an important general role in human disease.

RELATION BETWEEN BREAST-FEEDING AND INCIDENCE RATES OF INSULIN-DEPENDENT DIABETES MELLITUS: A Hypothesis

The variations in incidence rates of insulin-dependent diabetes mellitus (IDDM) in childhood within and between genetically very similar Scandinavian populations and the variations in incidence rates with time are difficult to explain. Epidemiological data show that the incidence of childhood IDDM may now be declining and suggest an inverse correlation between breast-feeding frequency and IDDM in childhood. Case-control data show that diabetic children were breast-fed for shorter periods of time than their healthy siblings and the population at large and that a smaller proportion of diabetic children were ever breast-fed. It is postulated that insufficient breast-feeding of genetically susceptible newborn infants may lead to beta-cell infection and IDDM later in life.

Affinity-purified human Interleukin I is cytotoxic to isolated islets of Langerhans

SummaryAddition of highly purified human Interleukin-1 to the culture medium of isolated rat islets of Langerhans for 6 days led to 88% inhibition of glucose-induced insulin-release, reduction of islet contents of insulin and glucagon to 31% and 8% respectively, and disintegration of the islets. These effects were dose-dependent and reproducible when using three different Interleukin-1 preparations. Highly purified human Interleukin-2, Lymphotoxin, Leucocyte Migration Inhibitory Factor and Macrophage Migration Inhibitory Factor were ineffective. These findings suggest that Interleukin-1 may play an important role in the molecular mechanisms underlying autoimmune B-cell destruction leading to Type 1 (insulin-dependent) diabetes mellitus.

HLA-D and -DR antigens in genetic analysis of insulin dependent diabetes mellitus

SummaryThree groups of patients with insulin-dependent diabetes mellitus, ascertained by different procedures, were investigated for HLA-A, B, C and D antigens (n=164), and a subset (n=93) for HLA-DR. Both HLA-D/DR3 and D/DR4 were strongly positively associated and D/DR2 was negatively associated with insulin-dependent diabetes. HLA-DR4 was found to be a better marker for insulin-dependent diabetes than Dw4. The HLA-B associations (B8, B15 and B18) were clearly secondary to the increases of HLA-D/DR3 and D/DR 4. The HLA associations did not differ between familial and isolated cases indicating that these two groups may well have a common genetic background. Based on analysis of HLA-haplotype sharing in affected sibling pairs, a simple dominant model of inheritance could be ruled out, and a simple recessive model was found unlikely. The relative risks for the HLA-Dw3,4 and HLA-DR3,4 phenotype were 21.2 and 44.4 respectively and exceeded those of both the HLA-Dw3 and HLA-DR3 (5.6 and 4.3) as well as the HLA-Dw4 and DR4 (10.1 and 10.5) phenotypes. This argues against an intermediate genetic model but further studies are needed to clarify whether there is more than one susceptibility gene for insulin-dependent diabetes mellitus within the HLA-system.

Genetics of Type 1 Diabetes: What's Next?

The discovery of the association between HLA in the major histocompatibility complex (MHC) on chromosome 6p21 with type 1 diabetes, but not with type 2 diabetes, suggested that these disease entities were of different genetic background and pathogenesis. The discovery that some individuals with diabetes had autoantibodies in their blood provided additional evidence that type 1 diabetes had an autoimmune origin. Recently, increasing knowledge of the genome, coupled with rapidly improving genotyping technology and availability of increasingly large numbers of samples, has enabled statistically robust, systematic, genome-wide examinations for discovery of loci contributing to type 1 diabetes susceptibility, including within the MHC itself. Currently, there are over 50 non-HLA regions that significantly affect the risk for type 1 diabetes (http://www.t1dbase.org). Many of these regions contain interesting, but previously unrecognized, candidate genes. A few regions contain genes of unknown function or no known annotated genes, suggesting roles for long-distance gene regulatory effects, noncoding RNAs, or unknown mechanisms. Against a background of ever-improving knowledge of the genome, particularly its transcriptional regulation, and with massive advances in sequencing, specific genes, rather than regions that impinge upon type 1 diabetes risk, will be identified soon. Here we discuss follow-up strategies for genome-wide association (GWA) studies, causality of candidate genes, and genetic association in a bioinformatics approach with the anticipation that this knowledge will permit identification of the earliest events in type 1 diabetes etiology that could be targets for intervention or biomarkers for monitoring the effects and outcomes of potential therapeutic agents. The International Type 1 Diabetes Genetics Consortium (T1DGC) has established significant resources for the study of genetics of type 1 diabetes. These resources are available to the research community and provide a basis for future discovery in the transition from gene mapping to discovery of disease mechanisms. The T1DGC (http://www.t1dgc.org) is an …

Rapid changes in chromatographically determined haemoglobin A1c induced by short-term changes in glucose concentration

SummaryChromatographically determined haemoglobin A1c concentration was measured during short-term (1–24 h) changes in glucose concentration in vitro and in vivo. In vitro at 37 °C the HbA1c concentration increased with glucose concentration and time both in normal and diabetic erythrocytes. In normal erythrocytes incubated in 20–100 mmol/l glucose, the increases in the HbA1c concentration were maximal after 4–6 h and then stable for the next 18–20 h. During the first hour, increases in the HbA1c concentration were linear with time and on average 0.034% HbA1c × h−1 × mmol/l glucose−1. In erythrocytes, after a rapidly produced increase (2h), HbA1c decreased to preincubation concentrations during a further incubation of the erythrocytes in a glucose-free medium at 37 °C for 4–6 h. The mean rate of linear decrease was 0.017% × h−1 × mmol/l glucose−1. After incubation of erythrocytes in 100 mmol/l glucose for 24 h, 1.3% HbA1c remained stable for 6 h in saline. The rapid increase in HbA1c concentration, as determined by chromatography, was not due to stable HbA1c (ketoamine linked glucose) as no increase was found in the HbA1c concentrations determined by the thiobarbiturate method. In juvenile diabetics controlled by an artificial beta-cell, rapid changes of blood glucose concentration (up to 20 mmol/l) resulted in increases in HbA1c concentration of as much as 1.9% within 12 h (mean 1.1%). Rapid in vivo increases in HbA1c concentration were reversible by normalization of the blood glucose concentration. That rapid changes in HbA1c may occur in daily diabetic life was evidenced by differences in HbA1c concentration between blood samples from out-patient diabetics incubated in saline for 16 hours at 4 °C and 37 °C (range of differences 0.2–1.4% HbA1c). The differences correlated to the blood glucose concentration at the time of sampling blood for HbA1c determination. Thus, incubation of blood at a low glucose concentration prior to determination of the glycosylated haemoglobin concentration may overcome interference from rapidly produced HbA1c.

Cytokines cause functional and structural damage to isolated islets of Langerhans

Cytokines are soluble, antigen non‐specific, non‐immunoglobulin mediators produced and secreted by blood mononuclear cells interacting in the cellular immune‐response. To test the possibility that cytokines participate in the autoimmune destruction of the pancreatic beta‐cells leading to insulin‐dependent diabetes mellitus, isolated human or rat islets of Langerhans were incubated for 7 days with cytokine‐rich, cell‐free supernatants of blood mononuclear cells from healthy human donors stimulated with or without purified protein derivative of tuberculin or phytohaemagglutinin. Glucose stimulated insulin‐release, and contents of insulin and glucagon in islets incubated with cytokine‐rich supernatants were markedly reduced. This impairment of islet function was due to a cytotoxic effect of cytokine‐rich supernatants as judged by disintegration of normal light‐microscopic morphology.

Diabetes mellitus in cystic fibrosis : effect of insulin therapy on lung function and infections

The effect of insulin therapy on lung function and lung infections was studied in a retrospective case‐control design in 18 diabetic cystic fibrosis (CF) patients; 18 non‐diabetic CF patients, matched for sex, age and presence of chronic Pseudomonas aeruginosa lung infection. served as controls. Parameters of CF clinical status were collected for six years before and two years after the onset of insulin therapy in the diabetic patients. Before onset of insulin therapy, body mass index (BMI) and forced vital capacity (FVC) in (pre)diabetic patients deviated increasingly from those in control patients. Decreases in BMI and lung function during the past three months before onset of insulin therapy were reverted within three months of insulin therapy. From three months to two years after onset of insulin therapy, differences in BMI and lung function diminished between diabetic and control patients. After two years of insulin therapy, BMI was similar in diabetic and non‐diabetic patients and the percentage differences in forced expiratory volume in 1s (FEV1) and FVC between the two groups were similar to those found six years before the onset of insulin therapy. The finding that insulin therapy improves lung function in diabetic CF patients suggests strongly that the insidious decline in lung function seen during the years before the diagnosis of diabetes mellitus results from the pre‐diabetic condition. After onset of insulin therapy, the percentages of sputum examinations positive for Haemophilus infuenzae and Streptococcus pneumoniae decreased in the diabetic patients, whereas parameters of lung infections with P. aeruginosa and Staphylococcus aureus remained unchanged. In conclusion, since insulin therapy improves lung function and reduces the number of infections with H. influenzae and S. pneumoniae in diabetic CF patients, we suggest that insulin therapy should be started when diabetes mellitus is diagnosed.