Tove Fall

Common Genetic Variants Highlight the Role of Insulin Resistance and Body Fat Distribution in Type 2 Diabetes, Independent of Obesity

We aimed to validate genetic variants as instruments for insulin resistance and secretion, to characterize their association with intermediate phenotypes, and to investigate their role in type 2 diabetes (T2D) risk among normal-weight, overweight, and obese individuals. We investigated the association of genetic scores with euglycemic-hyperinsulinemic clamp– and oral glucose tolerance test–based measures of insulin resistance and secretion and a range of metabolic measures in up to 18,565 individuals. We also studied their association with T2D risk among normal-weight, overweight, and obese individuals in up to 8,124 incident T2D cases. The insulin resistance score was associated with lower insulin sensitivity measured by M/I value (β in SDs per allele [95% CI], −0.03 [−0.04, −0.01]; P = 0.004). This score was associated with lower BMI (−0.01 [−0.01, −0.0]; P = 0.02) and gluteofemoral fat mass (−0.03 [−0.05, −0.02; P = 1.4 × 10−6) and with higher alanine transaminase (0.02 [0.01, 0.03]; P = 0.002) and γ-glutamyl transferase (0.02 [0.01, 0.03]; P = 0.001). While the secretion score had a stronger association with T2D in leaner individuals (Pinteraction = 0.001), we saw no difference in the association of the insulin resistance score with T2D among BMI or waist strata (Pinteraction > 0.31). While insulin resistance is often considered secondary to obesity, the association of the insulin resistance score with lower BMI and adiposity and with incident T2D even among individuals of normal weight highlights the role of insulin resistance and ectopic fat distribution in T2D, independently of body size.

Large-scale metabolomic profiling identifies novel biomarkers for incident coronary heart disease.

Analyses of circulating metabolites in large prospective epidemiological studies could lead to improved prediction and better biological understanding of coronary heart disease (CHD). We performed a mass spectrometry-based non-targeted metabolomics study for association with incident CHD events in 1,028 individuals (131 events; 10 y. median follow-up) with validation in 1,670 individuals (282 events; 3.9 y. median follow-up). Four metabolites were replicated and independent of main cardiovascular risk factors [lysophosphatidylcholine 18∶1 (hazard ratio [HR] per standard deviation [SD] incrementu200a=u200a0.77, P-value<0.001), lysophosphatidylcholine 18∶2 (HRu200a=u200a0.81, P-value<0.001), monoglyceride 18∶2 (MG 18∶2; HRu200a=u200a1.18, P-valueu200a=u200a0.011) and sphingomyelin 28∶1 (HRu200a=u200a0.85, P-valueu200a=u200a0.015)]. Together they contributed to moderate improvements in discrimination and re-classification in addition to traditional risk factors (C-statistic: 0.76 vs. 0.75; NRI: 9.2%). MG 18∶2 was associated with CHD independently of triglycerides. Lysophosphatidylcholines were negatively associated with body mass index, C-reactive protein and with less evidence of subclinical cardiovascular disease in additional 970 participants; a reverse pattern was observed for MG 18∶2. MG 18∶2 showed an enrichment (P-valueu200a=u200a0.002) of significant associations with CHD-associated SNPs (P-valueu200a=u200a1.2×10−7 for association with rs964184 in the ZNF259/APOA5 region) and a weak, but positive causal effect (odds ratiou200a=u200a1.05 per SD increment in MG 18∶2, P-valueu200a=u200a0.05) on CHD, as suggested by Mendelian randomization analysis. In conclusion, we identified four lipid-related metabolites with evidence for clinical utility, as well as a causal role in CHD development.

A Central Role for GRB10 in Regulation of Islet Function in Man

Variants in the growth factor receptor-bound protein 10 (GRB10) gene were in a GWAS meta-analysis associated with reduced glucose-stimulated insulin secretion and increased risk of type 2 diabetes (T2D) if inherited from the father, but inexplicably reduced fasting glucose when inherited from the mother. GRB10 is a negative regulator of insulin signaling and imprinted in a parent-of-origin fashion in different tissues. GRB10 knock-down in human pancreatic islets showed reduced insulin and glucagon secretion, which together with changes in insulin sensitivity may explain the paradoxical reduction of glucose despite a decrease in insulin secretion. Together, these findings suggest that tissue-specific methylation and possibly imprinting of GRB10 can influence glucose metabolism and contribute to T2D pathogenesis. The data also emphasize the need in genetic studies to consider whether risk alleles are inherited from the mother or the father.

Antibiotics in fetal and early life and subsequent childhood asthma: nationwide population based study with sibling analysis

Objective To investigate the association between exposure to antibiotics in fetal and early life and asthma in childhood, with adjustment for confounding factors. Design Nationwide prospective population based cohort study, including sibling control design. Setting Swedish population identified from national demographic and health registers. Participants 493u2009785 children born 2006-10; 180u2009894 of these were eligible for sibling analyses. Main outcome measure Asthma defined as having both an asthma diagnosis and dispensed asthma drugs. The association between antibiotic exposure and asthma was investigated in the whole cohort with Cox proportional hazard regression. A stratified proportional hazards model conditional on sibling group was used to adjust for shared factors within families. Confounding by respiratory infections was assessed by investigating whether specific groups of antibiotics were associated with asthma. Results Antibiotic exposure in fetal life was associated with an increased risk of asthma in cohort analyses (hazard ratio 1.28, 95% confidence interval 1.25 to 1.32), but not in sibling analyses (0.99, 0.92 to 1.07). In cohort analyses, antibiotics used to treat respiratory infections in childhood were associated with a more pronounced increased risk of asthma (4.12, 3.78 to 4.50) than antibiotics used for urinary tract and skin infections (1.54, 1.24 to 1.92). In sibling analyses, the excess risks after exposure to antibiotics for respiratory infections decreased (2.36, 1.78 to 3.13) and disappeared for antibiotics for urinary tract and skin (0.85, 0.47 to 1.55). Conclusions Previous positive associations between exposure to antibiotics in fetal and early life and subsequent childhood asthma could have been caused by confounding by shared familial factors, in addition to confounding by respiratory infections.

Global DNA hypermethylation is associated with high serum levels of persistent organic pollutants in an elderly population

Dioxin exposure has experimentally been associated with changes in DNA methylation, an epigenetic change that is associated with disease. The present study aims to investigate if serum levels of dioxin and other persistent environmental pollutants are related to global DNA methylation in a human sample. In the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (all aged 70), global DNA methylation was measured by the Luminometric Methylation Assay in 524 subjects. Twenty-three different POPs, including 16 PCBs, five pesticides, one dioxin (OCDD) and one brominated flame retardant (BDE47) were analysed by HRGC/HRMS. Ten single nucleotide polymorphisms (SNPs) in the Aryl hydrocarbon (Ah)-receptor were analysed by mini-sequencing. High levels of toxic equivalency (TEQ) for PCBs and dioxin were associated with DNA hypermethylation (p=0.030). This was mainly attributed to coplanar non-ortho PCBs. While no significant associations were found between DNA methylation and SNPs in the Ah-receptor, an interaction was found between the SNP rs2237297 and TEQ so that TEQ was associated with hypermethylation (p=0.009) only in subjects with one G-allele (n=103). Also high levels of the PCB126 congener, the OCDD, and the pesticide metabolite p,p-DDE were related to DNA hypermethylation (p=0.01, 0.03 and 0.003, respectively). In conclusion, in a sample of elderly subjects, high TEQ including PCBs and the dioxin OCDD and high serum levels of PCB126, OCDD, and p,p-DDE were related to global DNA hypermethylation in a cross-sectional analysis.

Early Exposure to Dogs and Farm Animals and the Risk of Childhood Asthma

IMPORTANCEnThe association between early exposure to animals and childhood asthma is not clear, and previous studies have yielded contradictory results.nnnOBJECTIVEnTo determine whether exposure to dogs and farm animals confers a risk of asthma.nnnDESIGN, SETTING AND PARTICIPANTSnIn a nationwide cohort study, the association between early exposure to dogs and farm animals and the risk of asthma was evaluated and included all children born in Sweden from January 1, 2001, to December 31, 2010 (Nu2009=u20091,011,051), using registry data on dog and farm registration, asthma medication, diagnosis, and confounders for parents and their children. The association was assessed as the odds ratio (OR) for a current diagnosis of asthma at age 6 years for school-aged children and as the hazard ratio (HR) for incident asthma at ages 1 to 5 years for preschool-aged children. Data were analyzed from January 1, 2007, to September 30, 2012.nnnEXPOSURESnLiving with a dog or farm animal.nnnMAIN OUTCOMES AND MEASURESnChildhood asthma diagnosis and medication used.nnnRESULTSnOf the 1,011,051 children born during the study period, 376,638 preschool-aged (53,460 [14.2%] exposed to dogs and 1729 [0.5%] exposed to farm animals) and 276,298 school-aged children (22,629 [8.2%] exposed to dogs and 958 [0.3%] exposed to farm animals) were included in the analyses. Of these, 18,799 children (5.0%) in the preschool-aged childrens cohort experienced an asthmatic event before baseline, and 28,511 cases of asthma and 906,071 years at risk were recorded during follow-up (incidence rate, 3.1 cases per 1000 years at risk). In the school-aged childrens cohort, 11,585 children (4.2%) experienced an asthmatic event during the seventh year of life. Dog exposure during the first year of life was associated with a decreased risk of asthma in school-aged children (OR, 0.87; 95% CI, 0.81-0.93) and in preschool-aged children 3 years or older (HR, 0.90; 95% CI, 0.83-0.99) but not in children younger than 3 years (HR, 1.03; 95% CI, 1.00-1.07). Results were comparable when analyzing only first-born children. Farm animal exposure was associated with a reduced risk of asthma in both school-aged children and preschool-aged children (OR, 0.48; 95% CI, 0.31-0.76, and HR, 0.69; 95% CI, 0.56-0.84), respectively.nnnCONCLUSIONS AND RELEVANCEnIn this study, the data support the hypothesis that exposure to dogs and farm animals during the first year of life reduces the risk of asthma in children at age 6 years. This information might be helpful in decision making for families and physicians on the appropriateness and timing of early animal exposure.

Large-Scale Genome-Wide Association Studies and Meta-Analyses of Longitudinal Change in Adult Lung Function

Background Genome-wide association studies (GWAS) have identified numerous loci influencing cross-sectional lung function, but less is known about genes influencing longitudinal change in lung function. Methods We performed GWAS of the rate of change in forced expiratory volume in the first second (FEV1) in 14 longitudinal, population-based cohort studies comprising 27,249 adults of European ancestry using linear mixed effects model and combined cohort-specific results using fixed effect meta-analysis to identify novel genetic loci associated with longitudinal change in lung function. Gene expression analyses were subsequently performed for identified genetic loci. As a secondary aim, we estimated the mean rate of decline in FEV1 by smoking pattern, irrespective of genotypes, across these 14 studies using meta-analysis. Results The overall meta-analysis produced suggestive evidence for association at the novel IL16/STARD5/TMC3 locus on chromosome 15 (P u200a=u200a 5.71 × 10-7). In addition, meta-analysis using the five cohorts with ≥3 FEV1 measurements per participant identified the novel ME3 locus on chromosome 11 (P u200a=u200a 2.18 × 10-8) at genome-wide significance. Neither locus was associated with FEV1 decline in two additional cohort studies. We confirmed gene expression of IL16, STARD5, and ME3 in multiple lung tissues. Publicly available microarray data confirmed differential expression of all three genes in lung samples from COPD patients compared with controls. Irrespective of genotypes, the combined estimate for FEV1 decline was 26.9, 29.2 and 35.7 mL/year in never, former, and persistent smokers, respectively. Conclusions In this large-scale GWAS, we identified two novel genetic loci in association with the rate of change in FEV1 that harbor candidate genes with biologically plausible functional links to lung function.

Protein Biomarkers for Insulin Resistance and Type 2 Diabetes Risk in Two Large Community Cohorts

Insulin resistance (IR) is a precursor of type 2 diabetes (T2D), and improved risk prediction and understanding of the pathogenesis are needed. We used a novel high-throughput 92-protein assay to identify circulating biomarkers for HOMA of IR in two cohorts of community residents without diabetes (n = 1,367) (mean age 73 ± 3.6 years). Adjusted linear regression identified cathepsin D and confirmed six proteins (leptin, renin, interleukin-1 receptor antagonist [IL-1ra], hepatocyte growth factor, fatty acid–binding protein 4, and tissue plasminogen activator [t-PA]) as IR biomarkers. Mendelian randomization analysis indicated a positive causal effect of IR on t-PA concentrations. Two biomarkers, IL-1ra (hazard ratio [HR] 1.28, 95% CI 1.03–1.59) and t-PA (HR 1.30, 1.02–1.65) were associated with incident T2D, and t-PA predicted 5-year transition to hyperglycemia (odds ratio 1.30, 95% CI 1.02–1.65). Additional adjustment for fasting glucose rendered both coefficients insignificant and revealed an association between renin and T2D (HR 0.79, 0.62–0.99). LASSO regression suggested a risk model including IL-1ra, t-PA, and the Framingham Offspring Study T2D score, but prediction improvement was nonsignificant (difference in C-index 0.02, 95% CI −0.08 to 0.12) over the T2D score only. In conclusion, proteomic blood profiling indicated cathepsin D as a new IR biomarker and suggested a causal effect of IR on t-PA.

Age- and Sex-Specific Causal Effects of Adiposity on Cardiovascular Risk Factors

Observational studies have reported different effects of adiposity on cardiovascular risk factors across age and sex. Since cardiovascular risk factors are enriched in obese individuals, it has not been easy to dissect the effects of adiposity from those of other risk factors. We used a Mendelian randomization approach, applying a set of 32 genetic markers to estimate the causal effect of adiposity on blood pressure, glycemic indices, circulating lipid levels, and markers of inflammation and liver disease in up to 67,553 individuals. All analyses were stratified by age (cutoff 55 years of age) and sex. The genetic score was associated with BMI in both nonstratified analysis (P = 2.8 × 10−107) and stratified analyses (all P < 3.3 × 10−30). We found evidence of a causal effect of adiposity on blood pressure, fasting levels of insulin, C-reactive protein, interleukin-6, HDL cholesterol, and triglycerides in a nonstratified analysis and in the <55-year stratum. Further, we found evidence of a smaller causal effect on total cholesterol (P for difference = 0.015) in the ≥55-year stratum than in the <55-year stratum, a finding that could be explained by biology, survival bias, or differential medication. In conclusion, this study extends previous knowledge of the effects of adiposity by providing sex- and age-specific causal estimates on cardiovascular risk factors.

FTO genetic variants and risk of obesity and type 2 diabetes: A meta-analysis of 28,394 Indians

To investigate the magnitude of association of FTO variants with obesity, type 2 diabetes (T2DM), and related traits among Asian Indians.