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Several studies have investigated the relationship between genetic variation and DNA methylation with respect to type 2 diabetes, but it is unknown if DNA methylation is a mediator in the disease pathway or if it is altered in response to disease state. This study uses genotypic information as a causal anchor to help decipher the likely role of DNA methylation measured in peripheral blood in the etiology of type 2 diabetes. Illumina HumanMethylation450 BeadChip data were generated on 1,018 young individuals from the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. In stage 1, 118 unique associations between published type 2 diabetes single nucleotide polymorphisms (SNPs) and genome-wide methylation (methylation quantitative trait loci [mQTLs]) were identified. In stage 2, a further 226 mQTLs were identified between 202 additional independent non-type 2 diabetes SNPs and CpGs identified in stage 1. Where possible, associations were replicated in independent cohorts of similar age. We discovered that around half of known type 2 diabetes SNPs are associated with variation in DNA methylation and postulated that methylation could either be on a causal pathway to future disease or could be a noncausal biomarker. For one locus ( KCNQ1 ), we were able to provide further evidence that methylation is likely to be on the causal pathway to disease in later life., (© 2017 by the American Diabetes Association.)

Multiple differentially methylated sites and regions associated with adiposity have now been identified in large-scale cross-sectional studies. We tested for replication of associations between previously identified CpG sites at HIF3A and adiposity in ∼1,000 mother-offspring pairs from the Avon Longitudinal Study of Parents and Children (ALSPAC). Availability of methylation and adiposity measures at multiple time points, as well as genetic data, allowed us to assess the temporal associations between adiposity and methylation and to make inferences regarding causality and directionality. Overall, our results were discordant with those expected if HIF3A methylation has a causal effect on BMI and provided more evidence for causality in the reverse direction (i.e., an effect of BMI on HIF3A methylation). These results are based on robust evidence from longitudinal analyses and were also partially supported by Mendelian randomization analysis, although this latter analysis was underpowered to detect a causal effect of BMI on HIF3A methylation. Our results also highlight an apparent long-lasting intergenerational influence of maternal BMI on offspring methylation at this locus, which may confound associations between own adiposity and HIF3A methylation. Further work is required to replicate and uncover the mechanisms underlying the direct and intergenerational effect of adiposity on DNA methylation., (© 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

A recent study identified a low-frequency variant at CCND2 associated with lower risk of type 2 diabetes, enhanced insulin response to a glucose challenge, higher height, and, paradoxically, higher BMI. We aimed to replicate the strength and effect size of these associations in independent samples and to assess the underlying mechanism. We genotyped the variant in 29,956 individuals and tested its association with type 2 diabetes and related traits. The low-frequency allele was associated with a lower risk of type 2 diabetes (OR 0.53; P = 2 × 10(-13); 6,647 case vs. 12,645 control subjects), higher disposition index (β = 0.07 log10; P = 2 × 10(-11); n = 13,028), and higher Matsuda index of insulin sensitivity (β = 0.02 log10; P = 5 × 10(-3); n = 13,118) but not fasting proinsulin (β = 0.01 log10; P = 0.5; n = 6,985). The low frequency allele was associated with higher adult height (β = 1.38 cm; P = 6 × 10(-9); n = 13,927), but the association of the variant with BMI (β = 0.36 kg/m(2); P = 0.02; n = 24,807), estimated in four population-based samples, was less than in the original publication where the effect estimate was biased by analyzing case subjects with type 2 diabetes and control subjects without diabetes separately. Our study establishes that a low-frequency allele in CCND2 halves the risk of type 2 diabetes primarily through enhanced insulin secretion., (© 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

Rapid postnatal growth is associated with increased risk of childhood adiposity. The aim of this study was to establish whether this pathway is mediated by altered DNA methylation and gene expression. Two distinct cohorts, one preterm (n=121) and one term born (n=6,990), were studied. Exploratory analyses were performed using microarrays to identify differentially expressed genes in whole blood from children defined as "slow" (n=10) compared with "rapid" (n=10) postnatal (term to 12 weeks corrected age) growers. Methylation within the identified TACSTD2 gene was measured in both cohorts, and rs61779296 genotype was determined by Pyrosequencing or imputation and analyzed in relation to body composition at 9-15 years of age. In cohort 1, TACSTD2 expression was inversely correlated with methylation (P=0.016), and both measures were associated with fat mass (expression, P=0.049; methylation, P=0.037). Although associated with gene expression (cohort 1, P=0.008) and methylation (cohort 1, P=2.98×10(-11); cohort 2, P=3.43×10(-15)), rs61779296 was not associated with postnatal growth or fat mass in either cohort following multiple regression analysis. Hence, the lack of association between fat mass and a methylation proxy SNP suggests that reverse causation or confounding may explain the initial association between fat mass and gene regulation. Noncausal methylation patterns may still be useful predictors of later adiposity.

Objective: Low birth weight is associated with an increased risk of type 2 diabetes. The mechanisms underlying this association are unknown and may represent intrauterine programming or two phenotypes of one genotype. The fetal insulin hypothesis proposes that common genetic variants that reduce insulin secretion or action may predispose to type 2 diabetes and also reduce birth weight, since insulin is a key fetal growth factor. We tested whether common genetic variants that predispose to type 2 diabetes also reduce birth weight., Research Design and Methods: We genotyped single-nucleotide polymorphisms (SNPs) at five recently identified type 2 diabetes loci (CDKAL1, CDKN2A/B, HHEX-IDE, IGF2BP2, and SLC30A8) in 7,986 mothers and 19,200 offspring from four studies of white Europeans. We tested the association between maternal or fetal genotype at each locus and birth weight of the offspring., Results: We found that type 2 diabetes risk alleles at the CDKAL1 and HHEX-IDE loci were associated with reduced birth weight when inherited by the fetus (21 g [95% CI 11-31], P = 2 x 10(-5), and 14 g [4-23], P = 0.004, lower birth weight per risk allele, respectively). The 4% of offspring carrying four risk alleles at these two loci were 80 g (95% CI 39-120) lighter at birth than the 8% carrying none (P(trend) = 5 x 10(-7)). There were no associations between birth weight and fetal genotypes at the three other loci or maternal genotypes at any locus., Conclusions: Our results are in keeping with the fetal insulin hypothesis and provide robust evidence that common disease-associated variants can alter size at birth directly through the fetal genotype.

In the genetic analysis of common, multifactorial diseases, such as type 1 diabetes, true positive irrefutable linkage and association results have been rare to date. Recently, it has been reported that a single nucleotide polymorphism (SNP), 1858C>T, in the gene PTPN22, encoding Arg620Trp in the lymphoid protein tyrosine phosphatase (LYP), which has been shown to be a negative regulator of T-cell activation, is associated with an increased risk of type 1 diabetes. Here, we have replicated these findings in 1,388 type 1 diabetic families and in a collection of 1,599 case and 1,718 control subjects, confirming the association of the PTPN22 locus with type 1 diabetes (family-based relative risk (RR) 1.67 [95% CI 1.46-1.91], and case-control odds ratio (OR) 1.78 [95% CI 1.54-2.06]; overall P = 6.02 x 10(-27)). We also report evidence for an association of Trp(620) with another autoimmune disorder, Graves' disease, in 1,734 case and control subjects (P = 6.24 x 10(-4); OR 1.43 [95% CI 1.17-1.76]). Taken together, these results indicate a more general association of the PTPN22 locus with autoimmune disease.

Vitamin D is known to modulate the immune system, and its administration has been associated with reduced risk of type 1 diabetes. Vitamin D acts via its receptor (VDR). Four single nucleotide polymorphisms (SNPs) of the VDR gene have been commonly studied, and evidence of association with type 1 diabetes has been reported previously. We sequenced the VDR gene region and developed its SNP map. Here we analyzed association of the 98 VDR SNPs in up to 3,763 type 1 diabetic families. First, we genotyped all 98 SNPs in a minimum of 458 U.K. families with two affected offspring. We further tested eight SNPs, including four SNPs associated with P < 0.05 in the first set and the four commonly studied SNPs, in up to 3,305 additional families from the U.K., Finland, Norway, Romania, and U.S. We only found weak evidence of association (P = 0.02-0.05) of the rs4303288, rs12721366, and rs2544043 SNPs. We then tested these three SNPs in an independent set of 1,587 patients and 1,827 control subjects from the U.K. and found no evidence of association. Overall, our results indicate that common sequence variation in the VDR gene has no major effect in type 1 diabetes in the populations tested.