Heather H. Burris

Cohort Profile: Project Viva

We established Project Viva to examine prenatal diet and other factors in relation to maternal and child health. We recruited pregnant women at their initial prenatal visit in eastern Massachusetts between 1999 and 2002. Exclusion criteria included multiple gestation, inability to answer questions in English, gestational age ≥22 weeks at recruitment and plans to move away before delivery. We completed in-person visits with mothers during pregnancy in the late first (median 9.9 weeks of gestation) and second (median 27.9 weeks) trimesters. We saw mothers and children in the hospital during the delivery admission and during infancy (median age 6.3 months), early childhood (median 3.2 years) and mid-childhood (median 7.7 years). We collected information from mothers via interviews and questionnaires, performed anthropometric and neurodevelopmental assessments and collected biosamples. We have collected additional information from medical records and from mailed questionnaires sent annually to mothers between in-person visits and to children beginning at age 9 years. From 2341 eligible women, there were 2128 live births; 1279 mother-child pairs provided data at the mid-childhood visit. Primary study outcomes include pregnancy outcomes, maternal mental and cardiometabolic health and child neurodevelopment, asthma/atopy and obesity/cardiometabolic health. Investigators interested in learning more about how to obtain Project Viva data can contact Project_Viva@hphc.org.

Vitamin D deficiency in pregnancy and gestational diabetes mellitus

OBJECTIVE We examined the association of second-trimester maternal plasma 25-hydroxyvitamin D (25[OH]D) during pregnancy with gestational diabetes mellitus (GDM). STUDY DESIGN Among 1314 pregnant women who participated in Project Viva, a birth cohort study, we measured 25(OH)D levels at 26-28 weeks gestation during GDM screening using a 1-hour 50-g glucose challenge test. RESULTS We found 25(OH)D levels of <25 nmol/L in 44 of 1087 women (4.0%) with normal glucose tolerance, 9 of 159 women (5.7%) with impaired glucose tolerance, and 9 of 68 women (13.2%) with GDM. Analyses that were adjusted for sociodemographics, season, maternal body mass index, gestational weight gain, and dietary factors suggested that women with 25(OH)D levels of <25 vs ≥25 nmol/L may have higher odds of experiencing GDM (odds ratio, 2.2; 95% confidence interval, 0.8-5.5). Glucose levels after the glucose challenge test were associated inversely with 25(OH)D levels (P < .01). CONCLUSION Second-trimester 25(OH)D levels were associated inversely with glucose levels after 1-hour 50-g glucose challenge test; low 25(OH)D levels may be associated with increased risk of GDM.

Gestational intake of methyl donors and global LINE-1 DNA methylation in maternal and cord blood: prospective results from a folate-replete population.

Maternal diet affects offspring DNA methylation in animal models, but evidence from humans is limited. We investigated the extent to which gestational intake of methyl donor nutrients affects global DNA methylation in maternal and umbilical cord blood. Among mother-infant pairs in Project Viva, a folate-replete US population, we estimated maternal intakes of vitamin B12, betaine, choline, folate, cadmium, zinc and iron periconceptionally and during the second trimester. We examined associations of these nutrients with DNA methylation, measured as %5-methyl cytosines (%5mC) in Long Interspersed Nuclear Element-1 (LINE-1), in first trimester (n = 830) and second trimester (n = 671) maternal blood and in cord blood at delivery (n = 516). Cord blood methylation was higher for male than female infants {mean [standard deviation (SD)] 84.8 [0.6] vs. 84.4 [0.7]%}. In the multivariable-adjusted model, maternal intake of methyl donor nutrients periconceptionally and during the second trimester of pregnancy was not positively associated with first trimester, second trimester or cord blood LINE-1 methylation. Periconceptional betaine intake was inversely associated with cord blood methylation [regression coefficient = -0.08% (95% confidence interval (CI): -0.14,-0.01)] but this association was attenuated after adjustment for dietary cadmium, which itself was directly associated with first trimester methylation and inversely associated with cord blood methylation. We also found an inverse association between periconceptional choline [-0.10%, 95% CI: -0.17,-0.03 for each SD (~63 mg/d)] and cord blood methylation in males only. In this folate-replete population, we did not find positive associations between intake of methyl donor nutrients during pregnancy and DNA methylation overall, but among males, higher early pregnancy intakes of choline were associated with lower cord blood methylation.

Plasma 25-hydroxyvitamin D during pregnancy and small-for-gestational age in black and white infants.

PURPOSE In a prospective prenatal cohort study, we examined associations of second trimester and cord plasma 25-hydroxyvitamin D (25[OH]D) with small-for-gestational age (SGA) and the extent to which vitamin D might explain black/white differences in SGA. METHODS We studied 1067 white and 236 black mother-infant pairs recruited from eight obstetrical offices early in pregnancy in Massachusetts. We analyzed 25(OH)D levels using an immunoassay and performed multivariable logistic models to estimate the odds of SGA by category of 25(OH)D level. RESULTS Mean (SD) second trimester 25(OH)D level was 60 nmol/L (SD, 21) and was lower for black (46 nmol/L [SD, 22]) than white (62 nmol/L [SD, 20]) women. Fifty-nine infants were SGA (4.5%), and more black than white infants were SGA (8.5% vs. 3.7%). The odds of SGA were higher with maternal 25(OH)D levels less than 25 versus 25 nmol/L or greater (adjusted odds ratio, 3.17; 95% confidence interval, 1.16-8.63). The increased odds of SGA among black versus white participants decreased from an odds ratio of 2.04(1.04, 4.04) to 1.68(0.82, 3.46) after adjusting for 25(OH)D. CONCLUSIONS Second trimester 25(OH)D levels less than 25 nmol/L were associated with higher odds of SGA. Our data raise the possibility that vitamin D status may contribute to racial disparities in SGA.

Associations of LINE-1 DNA Methylation with Preterm Birth in a Prospective Cohort Study

Preterm birth affects over 12% of all infants born in the US yet the biology of early delivery remains unclear, including whether epigenetic mechanisms are involved. We examined associations of maternal and umbilical cord blood long interspersed nuclear element-1 (LINE-1) DNA methylation with length of gestation and odds of preterm birth in singleton pregnancies in Project Viva. In white blood cells from maternal blood during 1(st) trimester (n=914) and 2(nd) trimester (n=922), and from venous cord blood at delivery (n=557), we measured LINE-1 by pyrosequencing (expressed as %5 methyl cytosines within the LINE-1 region analyzed [%5mC]). We ran linear regression models to analyze differences in gestation length, and logistic models for odds of preterm birth (<37 v. ≥37 weeks gestation), across quartiles of LINE-1. Mean(SD) LINE-1 levels were 84.3(0.6), 84.5(0.4), and 84.6(0.7) %5mC for 1(st) trimester, 2(nd) trimester and cord blood, respectively. Mean(SD) gestational age was 39.5(1.8) weeks, and 6.5% of infants were born preterm. After adjustment for maternal age, race/ethnicity, BMI, education, smoking status, and fetal sex, women with the highest vs. lowest quartile of 1(st) trimester LINE-1 had longer gestations (0.45 weeks [95% CI 0.12, 0.78]) and lower odds of preterm birth (OR 0.40 [0.17, 0.94]), whereas associations with cord blood LINE-1 were in the opposite direction (-0.45 weeks, -0.83, -0.08) and (OR 4.55 [1.18, 17.5]). In conclusion, higher early pregnancy LINE-1 predicts lower risk of preterm birth. In contrast, preterm birth is associated with lower LINE-1 in cord blood.

Vitamin D status among preterm and full-term infants at birth

Background:Risk factors for maternal vitamin D deficiency and preterm birth overlap, but the distribution of 25-hydroxyvitamin D (25(OH)D) levels among preterm infants is not known. We aimed to determine the associations between 25(OH)D levels and gestational age.Methods:We measured umbilical cord plasma levels of 25(OH)D from 471 infants born at Brigham and Women’s Hospital in Boston. We used generalized estimating equations to determine whether preterm (<37 wks’ gestation) or very preterm (<32 wks’ gestation) infants had greater odds of having 25(OH)D levels below 20 ng/ml than more mature infants. We adjusted for potential confounding by season of birth, maternal age, race, marital status, and singleton or multiple gestation.Results:Mean cord plasma 25(OH)D level was 34.0 ng/ml (range: 4.1–95.3 and SD: 14.1). Infants born before 32 wks’ gestation had increased odds of having 25(OH)D levels below 20 ng/ml in unadjusted (odds ratio (OR): 2.2; 95% confidence interval (CI): 1.1–4.3) and adjusted models (OR: 2.4; 95% CI: 1.2–5.3) as compared with more mature infants.Conclusion:Infants born in <32 wks’ gestation are at higher risk than more mature infants for low 25(OH)D levels. Further investigation of the relationships between low 25(OH)D levels and preterm birth and its sequelae is thus warranted.

Environmental Epigenetics: From Novelty to Scientific Discipline

Epigenetic phenomena have sparked much interest resulting in an exponential increase in scientific investigation in the last two decades. While growing, the field of environmental epigenetics remains small when compared to other areas of epigenetic inquiry such as cancer research. In this paper, our objective is to describe the status of the field of environmental epigenetics and lay out our vision for its future. While environmental epigenetic studies represent fewer than 5% of all epigenetic publications, the National Institute of Environmental Health Sciences ranks second in proportion of dollars spent on epigenetics of all NIH Institutes. Such investment highlights the hypothesis that epigenetic marks are modified by environmental exposures and the hope that interventions targeted at epigenetic mechanisms may ultimately lead to improved health outcomes. The road to achieve this vision will require: (1) attention to tissue specificity; (2) focused interventional studies; (3) collaboration among cohorts; (4) inclusion of environmental exposures in new large‐scale epigenomic studies; and (5) understanding of multiple mechanisms beyond DNA methylation and histone modifications. The investment in environmental epigenetic inquiry will lead to great rewards if we can understand the biology of how phenotype results from environmental stimuli and genetic code. Understanding the epigenetic implications of our actions and exposures may benefit generations to come. Copyright

Association between birth weight and DNA methylation of IGF2, glucocorticoid receptor and repetitive elements LINE-1 and Alu

AIM We examined the association between birth weight and methylation in the imprinted IGF/H19 loci, the nonimprinted gene NR3C1 and repetitive element DNA (LINE-1 and Alu). MATERIALS & METHODS We collected umbilical cord venous blood from 219 infants born in Mexico City (Mexico) as part of a prospective birth cohort study and analyzed DNA methylation using pyrosequencing. RESULTS Birth weight was not associated with DNA methylation of the regions studied. One of the CpG dinucleotides in the IGF2 imprinting control region (ICR)1 includes a potential C-T SNP. Among individuals with an absence of methylation at this site, probably due to a paternally inherited T allele, birth weight was associated with mean methylation status of both IGF2 ICR1 and ICR2. However, this association would not have survived adjustment for multiple testing. CONCLUSION While we did not detect an association between DNA methylation and birth weight, our study suggests a potential gene-epigene interaction between a T allele in the IGF2 ICR1 and methylation of ICRs of IGF2, and fetal growth.

Offspring DNA methylation of the aryl-hydrocarbon receptor repressor gene is associated with maternal BMI, gestational age, and birth weight

Prenatal smoke exposure, maternal obesity, aberrant fetal growth, and preterm birth are all risk factors for offspring metabolic syndrome. Cord blood aryl-hydrocarbon receptor repressor (AHRR) DNA methylation is responsive to maternal smoking during pregnancy. AHRR serves not only to inhibit aryl-hydrocarbon receptor (AHR) transcription, which is involved in mediating xenobiotic metabolism, but it is also involved in cell growth and differentiation. Other than maternal smoking, other predictors of offspring AHRR DNA methylation status remain unknown; we sought to identify them among newborns. We enrolled pregnant women in the PROGRESS birth cohort in Mexico City. Using pyrosequencing, we analyzed DNA methylation of 3 CpG sites within the AHRR gene promoter from the umbilical cord blood of 531 infants. We used generalized estimating equations to account for the correlation of DNA methylation between CpG sites. Multivariable models were used to adjust for maternal age, BMI, education, parity, smoke-exposure, infant sex, gestational age, and birth weight-for-gestational age. AHRR DNA methylation was positively associated with maternal BMI (P = 0.0009) and negatively associated with the length of gestation (P < 0.0001) and birth weight-for-gestational age (P < 0.0001). AHRR DNA methylation was 2.1% higher in offspring of obese vs. normal weight mothers and 3.1% higher in preterm vs. term infants, representing a third and a half standard deviation differences in methylation, respectively. In conclusion, offspring AHRR DNA methylation was associated with maternal obesity during pregnancy as well as infant gestational age and birth weight-for-gestational age. Further work to discover the health impacts of altered AHRR DNA methylation is warranted.

Association between length of gestation and cervical DNA methylation of PTGER2 and LINE 1-HS

Worldwide, more than 1 in 10 infants is born prior to 37 weeks gestation. Preterm birth can lead to increased mortality risk and poor life-long health and neurodevelopmental outcomes. Whether environmental risk factors affect preterm birth through epigenetic phenomena is largely unstudied. We sought to determine whether preterm risk factors, such as smoke exposure and education, were associated with cervical DNA methylation in the prostaglandin E receptor 2 gene (PTGER2) and a repetitive element, long interspersed nuclear element-1 Homo sapiens-specific (LINE 1-HS). Second, we aimed to determine whether mid-pregnancy DNA methylation of these regions in cervical samples could predict the length of gestation. We obtained a cervical swab between 16–19 weeks gestation from 80 women participating in a Mexico City birth cohort, used pyrosequencing to analyze DNA methylation of PTGER2 and LINE 1-HS, and examined associations with maternal covariates. We used accelerated failure time models to analyze associations of DNA methylation with the length of gestation. DNA methylation of both sequences was associated with Pap smear inflammation. LINE 1-HS methylation was associated with smoke exposure, BMI and parity. In adjusted models, gestations were 3.3 days longer (95%CI 0.6, 6.0) for each interquartile range of PTGER2 DNA methylation. Higher LINE 1-HS methylation was associated with shorter gestations (-3.3 days, 95%CI -6.5, -0.2). In conclusion, cervical DNA methylation was associated with risk factors for preterm birth and the length of gestation.