title: DNA methylation mediates the effect of maternal smoking during pregnancy on birthweight of the offspring.
abstract: BACKGROUND
  We examined whether the effect of maternal smoking during pregnancy on birthweight of the offspring was mediated by smoking-induced changes to DNA methylation in cord blood.
  
  
  METHODS
  First, we used cord blood of 129 Dutch children exposed to maternal smoking vs 126 unexposed to maternal and paternal smoking (53% male) participating in the GECKO Drenthe birth cohort. DNA methylation was measured using the Illumina HumanMethylation450 Beadchip. We performed an epigenome-wide association study for the association between maternal smoking and methylation followed by a mediation analysis of the top signals [false-discovery rate (FDR) < 0.05]. We adjusted both analyses for maternal age, education, pre-pregnancy BMI, offspring's sex, gestational age and white blood cell composition. Secondly, in 175 exposed and 1248 unexposed newborns from two independent birth cohorts, we replicated and meta-analysed results of eight cytosine-phosphate-guanine (CpG) sites in the GFI1 gene, which showed the most robust mediation. Finally, we performed functional network and enrichment analysis.
  
  
  RESULTS
  We found 35 differentially methylated CpGs (FDR < 0.05) in newborns exposed vs unexposed to smoking, of which 23 survived Bonferroni correction (P < 1 × 10(-7)). These 23 CpGs mapped to eight genes: AHRR, GFI1, MYO1G, CYP1A1, NEUROG1, CNTNAP2, FRMD4A and LRP5. We observed partial confirmation as three of the eight CpGs in GFI1 replicated. These CpGs partly mediated the effect of maternal smoking on birthweight (Sobel P < 0.05) in meta-analysis of GECKO and the two replication cohorts. Differential methylation of these three GFI1 CpGs explained 12-19% of the 202 g lower birthweight in smoking mothers. Functional enrichment analysis pointed towards activation of cell-mediated immunity.
  
  
  CONCLUSIONS
  Maternal smoking during pregnancy was associated with cord blood methylation differences. We observed a potentially mediating role of methylation in the association between maternal smoking during pregnancy and birthweight of the offspring. Functional network analysis suggested a role in activating the immune system.
authors: Departments of Epidemiology, l.k.kupers@umcg.nl.
authors: Leanne K
authors: LK
authors: Küpers
authors: Georgia Regents University, Augusta, Georgia, USA.
authors: Xiaojing
authors: X
authors: Xu
authors: Pulmonology and Genetics, and.
authors: Soesma A
authors: SA
authors: Jankipersadsing
authors: Departments of Epidemiology.
authors: Ahmad
authors: A
authors: Vaez
authors: Departments of Epidemiology.
authors: Sacha
authors: S
authors: la Bastide-van Gemert
authors: Departments of Epidemiology, LifeLines Cohort Study, University Medical Center Groningen, Groningen, The Netherlands.
authors: Salome
authors: S
authors: Scholtens
authors: Departments of Epidemiology.
authors: Ilja M
authors: IM
authors: Nolte
authors: MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.
authors: Rebecca C
authors: RC
authors: Richmond
authors: MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.
authors: Caroline L
authors: CL
authors: Relton
authors: Departments of Epidemiology, Pediatrics, The Generation R Study Group and.
authors: Janine F
authors: JF
authors: Felix
authors: Departments of Epidemiology, Pediatrics.
authors: Liesbeth
authors: L
authors: Duijts
authors: Internal Medicine, Erasmus MC, University Medical Center Rotterdam, The Netherlands.
authors: Joyce B
authors: JB
authors: van Meurs
authors: Departments of Epidemiology.
authors: Henning
authors: H
authors: Tiemeier
authors: Departments of Epidemiology, Pediatrics, The Generation R Study Group and.
authors: Vincent W
authors: VW
authors: Jaddoe
authors: Georgia Regents University, Augusta, Georgia, USA.
authors: Xiaoling
authors: X
authors: Wang
authors: Departments of Epidemiology.
authors: Eva
authors: E
authors: Corpeleijn
authors: Departments of Epidemiology.
authors: Harold
authors: H
authors: Snieder
mesh_terms: D000328:Adult; D001724:Birth Weight / Q000235:genetics*; D015331:Cohort Studies; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000235:genetics*; D044127:Epigenesis, Genetic; D005260:Female; D005312:Fetal Blood; D055106:Genome-Wide Association Study; D006801:Humans; D007231:Infant, Newborn; D016014:Linear Models; D008297:Male; D018811:Maternal Exposure / Q000009:adverse effects*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000235:genetics*; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; C498275:GFI1 protein, human; D014157:Transcription Factors
keywords: ALSPAC; DOHaD; Epigenetic epidemiology; GECKO; Generation R; epigenome-wide association study; fetal programming