Childhood body size directly increases type 1 diabetes risk based on a lifecourse Mendelian randomization approach.

The rising prevalence of childhood obesity has been postulated as an explanation for the increasing rate of individuals diagnosed with type 1 diabetes (T1D). In this study, we use Mendelian randomization (MR) to provide evidence that childhood body size has an effect on T1D risk (OR = 2.05 per change in body size category, 95% CI = 1.20 to 3.50, P = 0.008), which remains after accounting for body size at birth and during adulthood using multivariable MR (OR = 2.32, 95% CI = 1.21 to 4.42, P = 0.013). We validate this direct effect of childhood body size using data from a large-scale T1D meta-analysis based on n = 15,573 cases and n = 158,408 controls (OR = 1.94, 95% CI = 1.21 to 3.12, P = 0.006). We also provide evidence that childhood body size influences risk of asthma, eczema and hypothyroidism, although multivariable MR suggested that these effects are mediated by body size in later life. Our findings support a causal role for higher childhood body size on risk of being diagnosed with T1D, whereas its influence on the other immune-associated diseases is likely explained by a long-term effect of remaining overweight for many years over the lifecourse.

Sugar-Sweetened Beverage Consumption May Modify Associations Between Genetic Variants in the CHREBP (Carbohydrate Responsive Element Binding Protein) Locus and HDL-C (High-Density Lipoprotein Cholesterol) and Triglyceride Concentrations.

BACKGROUND: ChREBP (carbohydrate responsive element binding protein) is a transcription factor that responds to sugar consumption. Sugar-sweetened beverage (SSB) consumption and genetic variants in the CHREBP locus have separately been linked to HDL-C (high-density lipoprotein cholesterol) and triglyceride concentrations. We hypothesized that SSB consumption would modify the association between genetic variants in the CHREBP locus and dyslipidemia. METHODS: Data from 11 cohorts from the Cohorts for Heart and Aging Research in Genomic Epidemiology consortium (N=63 599) and the UK Biobank (N=59 220) were used to quantify associations of SSB consumption, genetic variants, and their interaction on HDL-C and triglyceride concentrations using linear regression models. A total of 1606 single nucleotide polymorphisms within or near CHREBP were considered. SSB consumption was estimated from validated questionnaires, and participants were grouped by their estimated intake. RESULTS: In a meta-analysis, rs71556729 was significantly associated with higher HDL-C concentrations only among the highest SSB consumers (ß, 2.12 [95% CI, 1.16-3.07] mg/dL per allele; P<0.0001), but not significantly among the lowest SSB consumers (P=0.81; PDiff <0.0001). Similar results were observed for 2 additional variants (rs35709627 and rs71556736). For triglyceride, rs55673514 was positively associated with triglyceride concentrations only among the highest SSB consumers (ß, 0.06 [95% CI, 0.02-0.09] ln-mg/dL per allele, P=0.001) but not the lowest SSB consumers (P=0.84; PDiff=0.0005). CONCLUSIONS: Our results identified genetic variants in the CHREBP locus that may protect against SSB-associated reductions in HDL-C and other variants that may exacerbate SSB-associated increases in triglyceride concentrations. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT00005133, NCT00005121, NCT00005487, and NCT00000479.

Promoter (4G/5G) plasminogen activator inhibitor-1 genotype and plasminogen activator inhibitor-1 levels in blacks, Hispanics, and non-Hispanic whites: the Insulin Resistance Atherosclerosis Study.

BACKGROUND: The 4G/5G polymorphism of the plasminogen activator inhibitor-1 (PAI-1) gene has been related to cardiovascular disease. METHODS AND RESULTS: Insulin resistance was measured with a frequently sampled intravenous glucose tolerance test in the Insulin Resistance Atherosclerosis Study (IRAS), and PAI-1 4G/5G promoter genotype was established by allele-specific polymerase chain reaction amplification of genomic DNA. There were 287 subjects with the 4G/4G genotype (18.4%), 691 heterozygote subjects (44.2%), and 586 carriers of the 5G/5G genotype (37.5%). The genotype distribution was different across the 3 ethnic groups (P=0.001). PAI-1 levels were lower in blacks than in non-Hispanic whites and Hispanics and lower in non-Hispanic whites than in Hispanics (all P=0.0001). Subjects homozygous for the 4G allele had the highest plasma PAI-1, heterozygote subjects were intermediate, and 5G homozygotes had the lowest levels of PAI-1. These patterns remained unaffected by adjustments for age, gender, clinical center, glucose tolerance status, body mass index, waist, triglycerides, and insulin resistance. Multiple linear regression analyses showed that the 4G/5G genotype explained very little of the variation in PAI-1 levels (0.63% in non-Hispanic whites, 0.99% in Hispanics, and 2.37% in blacks), and interaction analyses revealed no significant differences in the relation of circulating PAI-1 levels to the 4G/5G genotype by ethnicity (P=0.4). CONCLUSIONS: We have shown ethnic differences in the PAI-1 4G/5G polymorphism along with corresponding differences in circulating PAI-1 levels. The association of the genotype with PAI-1 levels was seen consistently among all 3 ethnic groups and was unaffected by metabolic covariates, including insulin resistance.

Minimal model-based insulin sensitivity has greater heritability and a different genetic basis than homeostasis model assessment or fasting insulin.

Insulin resistance is an important risk factor for development of type 2 diabetes as well as other chronic conditions, including hypertension, cardiovascular disease, and colon cancer. To find genes for insulin resistance it is necessary to assess insulin action in large populations. We have previously measured insulin action in a large cohort of subjects (Insulin Resistance and Atherosclerosis Study [IRAS] Family Study) using the minimal model approach. In this study, we compare sensitivity from the minimal model (insulin sensitivity index [S(I)]) with the measure of insulin resistance emanating from the homeostasis model assessment (HOMA) approach. The former measure emerges from the glycemic response to endogenous and exogenous insulin; the latter is based solely on fasting measures of glucose and insulin. A total of 112 pedigrees were represented, including 1,362 individuals with full phenotypic assessment. Heritability of S(I) was significantly greater than that for HOMA (0.310 vs. 0.163) and for fasting insulin (0.171), adjusted for age, sex, ethnicity, and BMI. In addition, correlation between S(I) and either HOMA or fasting insulin was only approximately 50% accounted for by genetic factors, with the remainder accounted for by environment. Thus S(I), a direct measure of insulin sensitivity, is determined more by genetic factors rather than measures such as HOMA, which reflect fasting insulin.