Testing the possible negative association of type 1 diabetes and atopic disease by analysis of the interleukin 4 receptor gene

Variations in the interleukin 4 receptor A (IL4RA) gene have been reported to be associated with atopy, asthma, and allergy, which may occur less frequently in subjects with type 1 diabetes (T1D). Since atopy shows a humoral immune reactivity pattern, and T1D results from a cellular (T lymphocyte) response, we hypothesised that alleles predisposing to atopy could be protective for T1D and transmitted less often than the expected 50% from heterozygous parents to offspring with T1D. We genotyped seven exonic single nucleotide polymorphisms (SNPs) and the -3223 C>T SNP in the putative promoter region of IL4RA in up to 3475 T1D families, including 1244 Finnish T1D families. Only the -3223 C>T SNP showed evidence of negative association (P=0.014). There was some evidence for an interaction between -3233 C>T and the T1D locus IDDM2 in the insulin gene region (P=0.001 in the combined and P=0.02 in the Finnish data set). We, therefore, cannot rule out a genetic effect of IL4RA in T1D, but it is not a major one.

Increased concentrations of the oxidative DNA adduct 7, 8-dihydro-8-oxo-2-deoxyguanosine in the germ-line of men with type 1 diabetes

The effects of diabetes mellitus on male reproductive health have not been clearly defined. A previous publication from this group reported significantly higher levels of nuclear DNA fragmentation and mitochondrial DNA deletions in spermatozoa from men with type 1 diabetes. This study compared semen profiles, sperm DNA fragmentation and levels of oxidative DNA modification in spermatozoa of diabetic and non-diabetic men. Semen samples from 12 non-diabetic, fertile men and 11 type 1 diabetics were obtained and subjected to conventional light microscopic semen analysis. Nuclear DNA fragmentation was assessed using an alkaline Comet assay and concentrations of 7,8-dihydro-8-oxo-2-deoxyguanosine (8-OHdG), an oxidative adduct of the purine guanosine, were assessed by high-performance liquid chromatography. Conventional semen profiles were similar in both groups, whilst spermatozoa from type 1 diabetics showed significantly higher levels of DNA fragmentation (44% versus 27%; P < 0.05) and concentrations of 8-OHdG (3.6 versus 2.0 molecules of 8-OHdG per 105 molecules of deoxyguanosine; P < 0.05). Furthermore, a positive correlation was observed between DNA fragmentation and concentrations of 8-OHdG per 105 molecules of deoxyguanosine (rs = 0.7, P < 0.05). The genomic damage evident in spermatozoa of type 1 diabetics may have important implications for their fertility and the outcome of pregnancies fathered by these individuals.

Investigation of DNA polymorphisms in SMAD genes for genetic predisposition to diabetic nephropathy in patients with type 1 diabetes mellitus

Aims/hypothesis: SMAD proteins are involved in multiple signalling pathways and are key modulators of gene expression. We hypothesised that genetic variation in selected SMAD genes contributes to susceptibility to diabetic nephropathy. Methods: We selected 13 haplotype tag (ht) single nucleotide polymorphisms (SNPs) from 67 variants identified by resequencing the SMAD2 and SMAD3 genes. For SMAD1, SMAD4 and SMAD5 genes, genotype data were downloaded for 217 SNPs from Phase II of the International HapMap project. Of these, 85 SNPs met our inclusion criteria, resulting in the selection of 13 tag SNPs for further investigation. A case-control approach was employed, using 267 nephropathic patients and 442 controls with type 1 diabetes from Ireland. Two further populations (totalling 1,407 patients, 2,238 controls) were genotyped to validate initial findings. Genotyping was conducted using iPLEX, TaqMan and gel electrophoresis.
Results: The distribution of genotypes was in Hardy-Weinberg equilibrium. Analysis by the ? 2 test of genotype and allele frequencies in patients versus controls in the Irish population (n?=?709) revealed evidence for the association of one allele at 5% level of significance (rs10515478, p uncorrected?=?0.006; p corrected?=?0.04). This finding represents a relatively small difference in allele frequency of 6.4% in the patient group compared with 10.7% in the control group; this difference was not supported in subsequent investigations using DNA from European individuals with similar phenotypic characteristics.
Conclusions/interpretation: We selected an appropriate subset of variants for the investigation of common genetic risk factors and assessed SMAD1 to SMAD5 genes for association with diabetic nephropathy. We conclude that common polymorphisms in these genes do not strongly influence genetic susceptibility to diabetic nephropathy in white individuals with type 1 diabetes mellitus.

Molecular detection of exercise-induced free radicals following ascorbate prophylaxis in type 1 diabetes mellitus: a randomised controlled trial

Aims/hypothesis: Patients with type 1 diabetes mellitus are more susceptible than healthy individuals to exercise-induced oxidative stress and vascular endothelial dysfunction, which has important implications for the progression of disease. Thus, in the present study, we designed a randomised double-blind, placebo-controlled trial to test the original hypothesis that oral prophylaxis with vitamin C attenuates rest and exercise-induced free radical-mediated lipid peroxidation in type 1 diabetes mellitus. Methods: All data were collected from hospitalised diabetic patients. The electron paramagnetic resonance spectroscopic detection of spin-trapped a-phenyl-tert-butylnitrone (PBN) adducts was combined with the use of supporting markers of lipid peroxidation and non-enzymatic antioxidants to assess exercise-induced oxidative stress in male patients with type 1 diabetes (HbA1c 7.9±1%, n=12) and healthy controls (HbA1c 4.6±0.5%, n=14). Following participant randomisation using numbers in a sealed envelope, venous blood samples were obtained at rest, after a maximal exercise challenge and before and 2 h after oral ingestion of 1 g ascorbate or placebo. Participants and lead investigators were blinded to the administration of either placebo or ascorbate treatments. Primary outcome was the difference in changes in free radicals following ascorbate ingestion. Resuts: Six diabetic patients and seven healthy control participants were randomised to each of the placebo and ascorbate groups. Diabetic patients (n=12) exhibited an elevated concentration of PBN adducts (p<0.05 vs healthy, n=14), which were confirmed as secondary, lipid-derived oxygen-centred alkoxyl (RO•) radicals (a nitrogen=1.37 mT and aßhydrogen=0.18 mT). Lipid hydroperoxides were also selectively elevated and associated with a depression of retinol and lycopene (p<0.05 vs healthy). Vitamin C supplementation increased plasma vitamin C concentration to a similar degree in both groups (p<0.05 vs pre-supplementation) and attenuated the exercise-induced oxidative stress response (p<0.05 vs healthy). There were no selective treatment differences between groups in the primary outcome variable. Conclusions/ interpretation: These findings are the first to suggest that oral vitamin C supplementation provides an effective prophylaxis against exercise-induced free radical-mediated lipid peroxidation in human diabetic blood.

Maternal age at birth and childhood type 1 diabetes: a pooled analysis of 30 observational studies

OBJECTIVE - The aim if the study was to investigate whether children born to older mothers have an increased risk of type 1 diabetes by performing a pooled analysis of previous studies using individual patient data to adjust for recognized confounders.
RESEARCH DESIGN AND METHODS - Relevant studies published before June 2009 were identified from MEDLINE, Web of Science, and EMBASE. Authors of studies were contacted and asked to provide individual patient data or conduct prespecified analyses. Risk estimates of type 1 diabetes by maternal age were calculated for each study, before and after adjustment for potential confounders. Meta-analysis techniques were used to derive combined odds ratios and to investigate heterogeneity among studies.
RESULTS - Data were available for 5 cohort and 25 case-control studies, including 14,724 cases of type 1 diabetes. Overall, there was, on average, a 5% (95% CI 2-9) increase in childhood type 1 diabetes odds per 5-year increase in maternal age (P = 0.006), but there was heterogeneity among studies (heterogeneity I 2 = 70%). In studies with a low risk of bias, there was a more marked increase in diabetes odds of 10% per 5-year increase in maternal age. Adjustments for potential confounders little altered these estimates. CONCLUSIONS - There was evidence of a weak but significant linear increase in the risk of childhood type 1 diabetes across the range of maternal ages, but the magnitude of association varied between studies. A very small percentage of the increase in the incidence of childhood type 1 diabetes in recent years could be explained by increases in maternal age.