Characterization of hair cortisol concentration pre-conception and during pregnancy.

BACKGROUND: The hypothalamic pituitary adrenal (HPA) axis is a system involved in stress and pregnancy regulation, and hair cortisol concentration (HCC) is a promising biomarker of its activity. Assessing factors that influence HCC in the prenatal period is critical to understand whether and how HPA axis (dys-)regulation influences maternal health and child development, particularly in high-risk populations from low- and middle-income countries (LMICs). AIMS: This study aimed at characterizing preconception and pregnancy HCC with respect to multiple sociodemographic, pregnancy-related, and hair-related factors. METHODS: In a sample of N = 2581 pregnant women in Perú, participants from two cohort studies provided a 6 cm scalp hair sample at three prenatal timepoints. Each hair sample was cut into two segments of 3 cm that represent cortisol secretion at four times: preconception, first-, second- and third trimester of pregnancy. Hair cortisol was extracted using liquid chromatography tandem mass spectrometry (LC-MS/MS). Spearman correlations, paired t-tests, and ANOVA were used to assess differences in log-transformed values of HCC (logHCC) across maternal sociodemographic, pregnancy-related, and hair-related factors. Multivariable linear regressions were used to examine independent associations of HCCs with selected correlates. RESULTS: Mean logHCC values showed an increase across the four prenatal periods. Preconception BMI was consistently associated with HCC in all three trimesters, while difficulty accessing basic foods, education, hair dyeing, and infant sex showed time-specific associations with HCCs. In sensitivity analyses, we detected no substantial segment effects in the associations of HCCs with maternal characteristics. CONCLUSION: This study is the largest to characterize HCC in pregnant women from a LMIC. Our findings provide a foundation for the use of HCC as a biomarker of prenatal HPA axis activity for future studies. This foundation may contribute to finding valid biomarkers of stress-response systems to promote maternal and child health.

Genetic association study of Preterm birth and Gestational age in a population-based case-control study in Peru: Genetics of PTB and GA in pregnant women in Peru.

Preterm birth (PTB) is an adverse pregnancy outcome affecting ~15 million pregnancies worldwide. Genetic studies have identified several candidate loci for PTB, but results remain inconclusive and limited to European populations. Thus, we conducted a genome-wide association study (GWAS) of PTB and gestational age at delivery (GA) among 2,212 Peruvian women. PTB cases delivered ≥ 20 weeks' but < 37 weeks' gestation, while controls delivered at term (≥ 37 weeks but < 42 weeks). After imputation (TOPMED) and quality control, we assessed the association of ~6 million SNPs with PTB and GA using multivariable regression models adjusted for maternal age and the first two genetic principal components. In silico functional analysis (FUMA-GWAS) was conducted among top signals detected with an arbitrary P < 1.0×10-5 in each GWAS. We sought to replicate genetic associations with PTB and GA identified in Europeans, and we developed a genetic risk score for GA based on European markers. Mean GA was 30 ± 4 weeks in PTB cases (N=933) and 39 ± 1 in the controls (N=1,279). PTB cases were slightly older and had higher C-sections and vaginal bleeding than controls. No association was identified at genome-wide level. Top suggestive (P < 1.0×10-5) signals were seen at rs13151645 (LINC01182) for PTB, and at rs72824565 (CTNNA2) for GA. Top PTB variants were enriched for biological pathways associated with polyketide, progesterone, steroid hormones, and glycosyl metabolism. Top GA variants were enriched in intronic regions and cancer pathways, and these genes were upregulated in the brain and subcutaneous adipose tissue. In combination with non-genetic risk factors, top SNPs explained 14% and 15% of the phenotypic variance of PTB and GA in our sample, but these results need to be interpreted with caution. Variants in WNT4 associated with GA in Europeans were replicated in our study. The genetic risk score based in European markers, was associated with a 2-day longer GA (R2=0.003, P=0.002) per standard deviation increase in the score in our sample. This genetic association study identified various signals suggestively associated with PTB and GA in a non-European population; they were linked to relevant biological pathways related to the metabolism of progesterone, prostanoid, and steroid hormones, and genes associated with GA were significantly upregulated in relevant tissues for the pathophysiology of PTB based on the in-silico functional analysis. None of these top variants overlapped with signals previously identified for PTB or GA in Europeans.

Correlates of preconception and pregnancy hair cortisol concentrations.

Assessing factors that influence chronic stress biomarkers like hair cortisol concentrations (HCCs) in pregnancy is critical to prevent adverse pregnancy outcomes. Thus, we aimed to identify correlates of HCC preconception and during pregnancy. 2,581 pregnant women participated in the study. HCC was available at four time periods: pre-pregnancy (0-3 months preconception, n = 1,023), and in the first (1-12 weeks, n = 1,734), second (13-24 weeks, n = 1,534), and third (25-36 weeks, n = 835) trimesters. HCC was assessed using liquid chromatography tandem mass spectrometry (LC-MS/MS). Sociodemographic, pregnancy- and hair-related characteristics, and measures of psychosocial stress, were interrogated as potential correlates of HCC. Spearman correlations, paired t-tests, and ANOVA were used to assess differences in log-transformed values of HCC (logHCC) across maternal characteristics. Multivariable linear regressions were used to identify the correlates of HCCs after adjusting for confounders. Mean logHCC values increased across the four prenatal periods (P < 0.001). In multivariable analyses, pre-pregnancy BMI was consistently associated with all HCCs, while gestational age, economic hardship, hair dyeing, and depression, showed time-specific associations with HCC. In conclusion, this study showed evidence of factors influencing HCC levels before and during pregnancy. The most consistent association was seen with pre-pregnancy BMI. Depression was also associated with HCC concentrations.

Maternal glycemia in pregnancy is longitudinally associated with blood DNAm variation at the FSD1L gene from birth to 5 years of age.

BACKGROUND: In utero exposure to maternal hyperglycemia has been associated with an increased risk for the development of chronic diseases in later life. These predispositions may be programmed by fetal DNA methylation (DNAm) changes that persist postnatally. However, although some studies have associated fetal exposure to gestational hyperglycemia with DNAm variations at birth, and metabolic phenotypes in childhood, no study has yet examined how maternal hyperglycemia during pregnancy may be associated with offspring DNAm from birth to five years of age. HYPOTHESIS: Maternal hyperglycemia is associated with variation in offspring DNAm from birth to 5 years of age. METHODS: We estimated maternal hyperglycemia using the area under the curve for glucose (AUCglu) following an oral glucose tolerance test conducted at 24-30 weeks of pregnancy. We quantified DNAm levels in cord blood (n = 440) and peripheral blood at five years of age (n = 293) using the Infinium MethylationEPIC BeadChip (Illumina). Our total sample included 539 unique dyads (mother-child) with 194 dyads having DNAm at both time-points. We first regressed DNAm M-values against the cell types and child age for each time-point separately to account for the difference by time of measurement for these variables. We then used a random intercept model from the linear mixed model (LMM) framework to assess the longitudinal association between maternal AUCglu and the repeated measures of residuals of DNAm. We adjusted for the following covariates as fixed effects in the random intercept model: maternal age, gravidity, smoking status, child sex, maternal body mass index (BMI) (measured at first trimester of pregnancy), and a binary variable for time-point. RESULTS: In utero exposure to higher maternal AUCglu was associated with lower offspring blood DNAm levels at cg00967989 located in FSD1L gene (ß = - 0.0267, P = 2.13 × 10-8) in adjusted linear regression mixed models. Our study also reports other CpG sites for which DNAm levels were suggestively associated (P < 1.0 × 10-5) with in utero exposure to gestational hyperglycemia. Two of these (cg12140144 and cg07946633) were found in the promotor region of PRDM16 gene (ß: - 0.0251, P = 4.37 × 10-07 and ß: - 0.0206, P = 2.24 × 10-06, respectively). CONCLUSION: Maternal hyperglycemia is associated with offspring DNAm longitudinally assessed from birth to 5 years of age.

Investigating causality in the association between DNA methylation and type 2 diabetes using bidirectional two-sample Mendelian randomisation.

AIMS/HYPOTHESIS: Several studies have identified associations between type 2 diabetes and DNA methylation (DNAm). However, the causal role of these associations remains unclear. This study aimed to provide evidence for a causal relationship between DNAm and type 2 diabetes. METHODS: We used bidirectional two-sample Mendelian randomisation (2SMR) to evaluate causality at 58 CpG sites previously detected in a meta-analysis of epigenome-wide association studies (meta-EWAS) of prevalent type 2 diabetes in European populations. We retrieved genetic proxies for type 2 diabetes and DNAm from the largest genome-wide association study (GWAS) available. We also used data from the Avon Longitudinal Study of Parents and Children (ALSPAC, UK) when associations of interest were not available in the larger datasets. We identified 62 independent SNPs as proxies for type 2 diabetes, and 39 methylation quantitative trait loci as proxies for 30 of the 58 type 2 diabetes-related CpGs. We applied the Bonferroni correction for multiple testing and inferred causality based on p<0.001 for the type 2 diabetes to DNAm direction and p<0.002 for the opposing DNAm to type 2 diabetes direction in the 2SMR analysis. RESULTS: We found strong evidence of a causal effect of DNAm at cg25536676 (DHCR24) on type 2 diabetes. An increase in transformed residuals of DNAm at this site was associated with a 43% (OR 1.43, 95% CI 1.15, 1.78, p=0.001) higher risk of type 2 diabetes. We inferred a likely causal direction for the remaining CpG sites assessed. In silico analyses showed that the CpGs analysed were enriched for expression quantitative trait methylation sites (eQTMs) and for specific traits, dependent on the direction of causality predicted by the 2SMR analysis. CONCLUSIONS/INTERPRETATION: We identified one CpG mapping to a gene related to the metabolism of lipids (DHCR24) as a novel causal biomarker for risk of type 2 diabetes. CpGs within the same gene region have previously been associated with type 2 diabetes-related traits in observational studies (BMI, waist circumference, HDL-cholesterol, insulin) and in Mendelian randomisation analyses (LDL-cholesterol). Thus, we hypothesise that our candidate CpG in DHCR24 may be a causal mediator of the association between known modifiable risk factors and type 2 diabetes. Formal causal mediation analysis should be implemented to further validate this assumption.

Association between trauma exposure and glucocorticosteroid concentration in hair during pregnancy.

BACKGROUND: Traumatic events, including child abuse and intimate partner violence, are highly prevalent among women of child-bearing age. These traumatic experiences may impact maternal and offspring physical and mental health. A proposed mechanism for these effects is maternal hypothalamic-pituitary-adrenal (HPA) axis dysregulation which can be measured using hair corticosteroid levels. AIMS: This study aims to examine the association of child abuse and intimate partner violence exposure with HPA axis functioning, as measured by hair corticosteroid levels in a cohort of pregnant women. METHODS: We included data from 1822 pregnant women (mean gestational age 17 weeks) attending a prenatal clinic in Lima, Peru. We extracted cortisol and cortisone concentrations from hair samples using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Each participant provided 6-cm hair samples: 3 cm hair segment closest to the scalp reflecting HCC in early pregnancy (first three months), and 3-6 cm from the scalp reflecting HCC in pre-pregnancy (three months prior to conception). Multivariable linear regression procedures were used to assess the association between maternal trauma exposure and hair corticosteroid levels. RESULTS: Overall, women who experienced child abuse on average had higher levels of cortisol (p < 0.01) and cortisone (p < 0.0001) after adjustment for age, race, adult access to basic foods and hair treatments. For the hair segment reflecting early pregnancy, presence of child abuse was associated with a 0.120 log unit increase in cortisol and a 0.260 log unit increase in cortisone (p < 0.001). For the hair segment reflecting pre-pregnancy, a history of child abuse was associated with a 0.100 log unit increase in cortisol and a 0.180 log unit increase in cortisone (p < 0.01). Results also suggested an impact of intimate partner violence on HPA regulation; however, associations were not statistically significant after controlling for child abuse. CONCLUSIONS: These results underscore the long-lasting impacts of exposure to adversity and trauma during early life. Our study findings will have implications for research investigating HPA axis function and long-term effects of violence on corticosteroid regulation.

Maternal hair cortisol concentrations and its association with increased insulin resistance in midpregnancy.

PURPOSE: Stress and elevated maternal glycemia have negative effects on pregnancy. We evaluated the association of hair cortisol concentrations (HCC), a marker of chronic stress, with insulin resistance and gestational diabetes (GDM). METHODS: In total, 527 women from Lima, Peru, provided a hair sample in the second trimester of their pregnancy to measure HCC using liquid chromatography-tandem mass spectrometry. Each 6 cm of hair captured HCC in early (T1=1-12 weeks) and midpregnancy (T2 = 13-24 weeks). GDM diagnosis was conducted in midpregnancy. Multivariable regression models adjusted for putative risk factorsincluding maternal sociodemographic factors, diabetes history, and hair characteristics, were used to estimate the association of HCC with GDM and various glycemic traits. RESULTS: GDM was diagnosed in 122 (23%) women. Mean HCC across pregnancy was T1 = 3.7 (±3.4) pg/mg and T2 = 4.8 (±3.4) pg/mg. HCC was associated with increased log-transformed units of fasting insulin (T1 = 0.15 [0.03, 0.27], T2 = 0.17 [0.04, 0.30]), homeostasis model assessment for insulin resistance (T1 = 0.14 [0.01, 0.26], T2 = 0.17 [0.03, 0.30]), and homeostasis model assessment for ß-cell function (T1 = 0.20 [0.05, 0.34], T2 = 0.20 [0.04, 0.36]), but not with GDM (T1 = 0.95 [0.63, 1.40], T2 = 1.11 [0.74, 1.67]). CONCLUSIONS: Elevated maternal HCC was associated with abnormal insulin homeostasis in pregnancy. Dysregulation of the hypothalamic-pituitary-adrenal axis, as reflected by high HCC, may also contribute to insulin resistance syndrome in pregnancy.

Personal and Work-Related Burnout Is Associated with Elevated Diastolic Blood Pressure and Diastolic Hypertension among Working Adults in Chile.

We aimed at investigating the association of personal and work-related burnout with blood pressure and hypertension among working adults in Chile. We conducted a cross-sectional study among 1872 working adults attending the Hospital del Trabajador in Santiago, Chile, between September 2015 and February 2018. The Copenhagen Burnout Inventory was used to assess personal and work-related burnout. Blood pressure was measured by medical practitioners. Multivariable linear and logistic regressions were used to estimate the association of burnout status with systolic blood pressure (SBP), diastolic blood pressure (DBP), and hypertension. After adjusting for confounders, participants with both types of burnout had a 1.66 (95% confidence interval [CI]: 0.02-3.30) mmHg higher mean DBP than those without burnout. The odds of isolated diastolic hypertension among the participants with only personal burnout and both types of burnout were 2.00-fold (odds ratio [OR] = 2.00; 95% CI: 1.21-3.31) and 2.08-fold (OR = 2.08; 95% CI: 1.15-3.78) higher than those without burnout. The odds of combined systolic/diastolic hypertension among the participants with only work-related burnout increased by 59% (OR = 1.59; 95% CI: 1.01-2.50) compared with those without burnout. Both work-related and personal burnouts were associated with increased DBP and odds of diastolic hypertension among working adults in Chile.

Pain, mood, and suicidal behavior among injured working adults in Chile.

BACKGROUND: Chronic pain is comorbid with psychiatric disorders, but information on the association of chronic pain with depressive symptoms, generalized anxiety, and suicidal behavior among occupational cohorts is inadequate. We investigated these associations among employed Chilean adults. METHODS: A total of 1946 working adults were interviewed during their outpatient visit. Pain was assessed using the Short Form McGill Pain questionnaire (SF-MPG) while depression and generalized anxiety were examined using the Patient Health Questionnaire-9 (PHQ-9) and Generalized Anxiety Disorder-7 (GAD-7), respectively. The Columbia-Suicide Severity Rating Scale was used to assess suicidal behavior and suicidal ideation. Multivariable logistic regression models were used to estimate adjusted odds ratios (aORs) and 95% confidence intervals (95%CI) for the association of chronic pain with mood disorders, as well as suicidal behavior. RESULTS: High chronic pain (SF-MPG > 11) was reported by 46% of participants. Approximately two-fifths of the study participants (38.2%) had depression, 23.8% generalized anxiety, 13.4% suicidal ideation, and 2.4% suicidal behavior. Compared to those with low pain (SF-MPG ≤11), participants with high chronic pain (SF-MPG > 11) had increased odds of experiencing depression only (aOR = 2.87; 95% CI: 2.21-3.73), generalized anxiety only (aOR = 2.38; 95% CI: 1.42-3.99), and comorbid depression and generalized anxiety (aOR = 6.91; 95% CI: 5.20-9.19). The corresponding aOR (95%CI) for suicidal ideation and suicidal behavior were (aOR = 2.20; 95% CI: 1.58-3.07) and (aOR = 2.18 = 95% CI: 0.99-4.79), respectively. CONCLUSIONS: Chronic pain is associated with increased odds of depression, generalized anxiety, and suicidal behavior. Mental health support and appropriate management of patients experiencing chronic pain are critical.

Evaluating the performance of the Pain Interference Index and the Short Form McGill Pain Questionnaire among Chilean injured working adults.

BACKGROUND: Chronic pain can lead to economic instability, decreased job productivity, and poor mental health. Therefore, reliable identification and quantification of chronic pain is important for clinical diagnosis and treatment. OBJECTIVE: To determine the psychometric properties of the Spanish language versions of the Pain Interference Index (PII) and the Short Form McGill Pain Questionnaire (SF-MPG) among a population of working adults who experienced injury in Santiago, Chile. METHODS: A total of 1,975 participants with work-related injuries were interviewed to collect sociodemographic, occupational, and chronic pain characteristics. Construct validity and factorial structure of the PII and SF-MPG were assessed through exploratory factor analyses (EFA). Cronbach's alpha was used to evaluate internal consistency. RESULTS: The PII mean score was 3.84 ± 1.43 among all participants. The SF-MPG median score was 11 [IQR: 6-16] in this study population. Cronbach's alpha for the PII was 0.90 and 0.87 for the SF-MP. EFA resulted in a one factor solution for the PII. A two-factor solution was found for the SF-MPG. The two-factors for SF-MPG were sensory and affective subscales with Cronbach's alpha of 0.82 and 0.714, respectively. When the two scales were combined, an EFA analysis confirmed the PII and SF-MPG measure different aspects of chronic pain. CONCLUSIONS: The PII and SF-MPG had good construct validity and reliability for assessing different aspects of chronic pain among working Chilean adults.

Maternal Glycemic Dysregulation During Pregnancy and Neonatal Blood DNA Methylation: Meta-analyses of Epigenome-Wide Association Studies.

OBJECTIVE: Maternal glycemic dysregulation during pregnancy increases the risk of adverse health outcomes in her offspring, a risk thought to be linearly related to maternal hyperglycemia. It is hypothesized that changes in offspring DNA methylation (DNAm) underline these associations. RESEARCH DESIGN AND METHODS: To address this hypothesis, we conducted fixed-effects meta-analyses of epigenome-wide association study (EWAS) results from eight birth cohorts investigating relationships between cord blood DNAm and fetal exposure to maternal glucose (Nmaximum = 3,503), insulin (Nmaximum = 2,062), and area under the curve of glucose (AUCgluc) following oral glucose tolerance tests (Nmaximum = 1,505). We performed lookup analyses for identified cytosine-guanine dinucleotides (CpGs) in independent observational cohorts to examine associations between DNAm and cardiometabolic traits as well as tissue-specific gene expression. RESULTS: Greater maternal AUCgluc was associated with lower cord blood DNAm at neighboring CpGs cg26974062 (ß [SE] -0.013 [2.1 × 10-3], P value corrected for false discovery rate [PFDR] = 5.1 × 10-3) and cg02988288 (ß [SE]-0.013 [2.3 × 10-3], PFDR = 0.031) in TXNIP. These associations were attenuated in women with GDM. Lower blood DNAm at these two CpGs near TXNIP was associated with multiple metabolic traits later in life, including type 2 diabetes. TXNIP DNAm in liver biopsies was associated with hepatic expression of TXNIP. We observed little evidence of associations between either maternal glucose or insulin and cord blood DNAm. CONCLUSIONS: Maternal hyperglycemia, as reflected by AUCgluc, was associated with lower cord blood DNAm at TXNIP. Associations between DNAm at these CpGs and metabolic traits in subsequent lookup analyses suggest that these may be candidate loci to investigate in future causal and mediation analyses.

Associations between an integrated component of maternal glycemic regulation in pregnancy and cord blood DNA methylation.

Background: Previous studies suggest that fetal programming to hyperglycemia in pregnancy is due to modulation of DNA methylation (DNAm), but they have been limited in their maternal glycemic characterization. Methods: In the Gen3G study, we used a principal component analysis to integrate multiple glucose and insulin values measured during the second trimester oral glucose tolerance test. We investigated associations between principal components and cord blood DNAm levels in an epigenome-wide analysis among 430 mother-child pairs. Results: The first principal component was robustly associated with lower DNAm at cg26974062 (TXNIP; p = 9.9 × 10-9) in cord blood. TXNIP is a well-known DNAm marker for type 2 diabetes in adults. Conclusion: We hypothesize that abnormal glucose metabolism in pregnancy may program dysregulation of TXNIP across the life course.

Lay abstract Elevated maternal levels of glucose affect the in utero environment and play a crucial role in the adequate development of the fetus and the long-term health of the child. Increasing evidence shows that a regulatory process called DNA methylation (DNAm), which affects gene expression, may be an epigenetic mechanism responsible for linking in utero exposures and long-term health. In this study, we derived a marker reflecting elevated maternal glucose and insulin levels during pregnancy. Next, we used this marker to assess its association with DNAm measured in the child's cord blood collected at delivery. We found that overall higher circulating levels of both maternal glucose and insulin in pregnancy were related to cord blood DNAm at a gene called TXNIP. This gene has been previously recognized as a type 2 diabetes epigenetic signature in blood cells of adults from different populations. Thus, we may have identified a cord blood DNAm marker that signals long-term risk of diabetes over the life course.

DNA methylation of blood cells is associated with prevalent type 2 diabetes in a meta-analysis of four European cohorts.

BACKGROUND: Type 2 diabetes (T2D) is a heterogeneous disease with well-known genetic and environmental risk factors contributing to its prevalence. Epigenetic mechanisms related to changes in DNA methylation (DNAm), may also contribute to T2D risk, but larger studies are required to discover novel markers, and to confirm existing ones. RESULTS: We performed a large meta-analysis of individual epigenome-wide association studies (EWAS) of prevalent T2D conducted in four European studies using peripheral blood DNAm. Analysis of differentially methylated regions (DMR) was also undertaken, based on the meta-analysis results. We found three novel CpGs associated with prevalent T2D in Europeans at cg00144180 (HDAC4), cg16765088 (near SYNM) and cg24704287 (near MIR23A) and confirmed three CpGs previously identified (mapping to TXNIP, ABCG1 and CPT1A). We also identified 77 T2D associated DMRs, most of them hypomethylated in T2D cases versus controls. In adjusted regressions among diabetic-free participants in ALSPAC, we found that all six CpGs identified in the meta-EWAS were associated with white cell-types. We estimated that these six CpGs captured 11% of the variation in T2D, which was similar to the variation explained by the model including only the common risk factors of BMI, sex, age and smoking (R2 = 10.6%). CONCLUSIONS: This study identifies novel loci associated with T2D in Europeans. We also demonstrate associations of the same loci with other traits. Future studies should investigate if our findings are generalizable in non-European populations, and potential roles of these epigenetic markers in T2D etiology or in determining long term consequences of T2D.

Epigenome-wide association study of maternal hemoglobin A1c in pregnancy and cord blood DNA methylation.

Background: Gestational hyperglycemia is associated with adverse perinatal outcomes and long-term offspring metabolic programming, likely through dysregulation of DNA methylation (DNAm). Materials & methods: We tested associations between maternal HbA1c and cord blood DNAm among 412 mother-child pairs in the genetics of glucose regulation in gestation and growth (Gen3G) and implemented Mendelian randomization to infer causality. We sought replication in an independent sample from Healthy Start. Results: Higher second trimester HbA1c levels were associated with lower DNAm at cg21645848 (p = 3.9 × 10-11) near URGCP. Mendelian randomization and replication analyses showed same direction of effect between HbA1c and DNAm at cg21645848, but did not reach statistical significance. Conclusion: We found that higher maternal glycemia reflected by HbA1c is associated with cord blood DNAm at URGCP, a gene related with inflammatory pathways.

Epigenetic Link Between Statin Therapy and Type 2 Diabetes.

OBJECTIVE: To investigate the role of epigenetics in statins' diabetogenic effect comparing DNA methylation (DNAm) between statin users and nonusers in an epigenome-wide association study in blood. RESEARCH DESIGN AND METHODS: Five cohort studies' participants (n = 8,270) were classified as statin users when they were on statin therapy at the time of DNAm assessment with Illumina 450K or EPIC array or noncurrent users otherwise. Associations of DNAm with various outcomes like incident type 2 diabetes, plasma glucose, insulin, and insulin resistance (HOMA of insulin resistance [HOMA-IR]) as well as with gene expression were investigated. RESULTS: Discovery (n = 6,820) and replication (n = 1,450) phases associated five DNAm sites with statin use: cg17901584 (1.12 × 10-25 [DHCR24]), cg10177197 (3.94 × 10-08 [DHCR24]), cg06500161 (2.67 × 10-23 [ABCG1]), cg27243685 (6.01 × 10-09 [ABCG1]), and cg05119988 (7.26 × 10-12 [SC4MOL]). Two sites were associated with at least one glycemic trait or type 2 diabetes. Higher cg06500161 methylation was associated with higher fasting glucose, insulin, HOMA-IR, and type 2 diabetes (odds ratio 1.34 [95% CI 1.22, 1.47]). Mediation analyses suggested that ABCG1 methylation partially mediates the effect of statins on high insulin and HOMA-IR. Gene expression analyses showed that statin exposure and ABCG1 methylation were associated with ABCG1 downregulation, suggesting epigenetic regulation of ABCG1 expression. Further, outcomes insulin and HOMA-IR were significantly associated with ABCG1 expression. CONCLUSIONS: This study sheds light on potential mechanisms linking statins with type 2 diabetes risk, providing evidence on DNAm partially mediating statins' effects on insulin traits. Further efforts shall disentangle the molecular mechanisms through which statins may induce DNAm changes, potentially leading to ABCG1 epigenetic regulation.

DNA Methylation and Type 2 Diabetes: the Use of Mendelian Randomization to Assess Causality.

PURPOSE OF REVIEW: This review summarises recent advances in the field of epigenetics in order to understand the aetiology of type 2 diabetes (T2D). RECENT FINDINGS: DNA methylation at a number of loci has been shown to be robustly associated with T2D, including TXNIP, ABCG1, CPT1A, and SREBF1. However, due to the cross-sectional nature of many epidemiological studies and predominant analysis in samples derived from blood rather than disease relevant tissues, inferring causality is difficult. We therefore outline the use of Mendelian randomisation (MR) as one method able to assess causality in epigenetic studies of T2D. SUMMARY: Epidemiological studies have been fruitful in identifying epigenetic markers of T2D. Triangulation of evidence including utilisation of MR is essential to delineate causal from non-causal biomarkers of disease. Understanding the causality of epigenetic markers in T2D more fully will aid prioritisation of CpG sites as early biomarkers to detect disease or in drug development to target epigenetic mechanisms in order to treat patients.