title: Genome-wide DNA methylation study in human placenta identifies novel loci associated with maternal smoking during pregnancy.
abstract: We conducted an epigenome-wide association study (EWAS) of DNA methylation in placenta in relation to maternal tobacco smoking during pregnancy and examined whether smoking-induced changes lead to low birthweight.
  
  
  
  DNA methylation in placenta was measured using the Illumina HumanMethylation450 BeadChip in 179 participants from the INfancia y Medio Ambiente (INMA) birth cohort. Methylation levels across 431 311 CpGs were tested for differential methylation between smokers and non-smokers in pregnancy. We took forward three top-ranking loci for further validation and replication by bisulfite pyrosequencing using data of 248 additional participants of the INMA cohort. We examined the association of methylation at smoking-associated loci with birthweight by applying a mediation analysis and a two-sample Mendelian randomization approach.
  
  
  
  Fifty CpGs were differentially methylated in placenta between smokers and non-smokers during pregnancy [false discovery rate (FDR) < 0.05]. We validated and replicated differential methylation at three top-ranking loci: cg27402634 located between LINC00086 and LEKR1, a gene previously related to birthweight in genome-wide association studies; cg20340720 (WBP1L); and cg25585967 and cg12294026 (TRIO). Dose-response relationships with maternal urine cotinine concentration during pregnancy were confirmed. Differential methylation at cg27402634 explained up to 36% of the lower birthweight in the offspring of smokers (Sobel P-value < 0.05). A two-sample Mendelian randomization analysis provided evidence that decreases in methylation levels at cg27402634 lead to decreases in birthweight.
  
  
  
  We identified novel loci differentially methylated in placenta in relation to maternal smoking during pregnancy. Adverse effects of maternal smoking on birthweight of the offspring may be mediated by alterations in the placental methylome.
authors: IMIB-Arrixaca Biomedical Research Institute, Virgen de la Arrixaca University Hospital, 30120 Murcia, Spain, embarto@hotmail.com.|CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.
authors: Eva
authors: E
authors: Morales
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Centre for Research in Environmental Epidemiology (CREAL), 08003 Barcelona, Catalonia, Spain.|Genomics and Disease Group, Bioinformatics and Genomics Program, Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology, 08003 Barcelona, Catalonia, Spain.|Universitat Pompeu Fabra (UPF), 08003 Barcelona, Catalonia, Spain.
authors: Nadia
authors: N
authors: Vilahur
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Centre for Research in Environmental Epidemiology (CREAL), 08003 Barcelona, Catalonia, Spain.|Universitat Pompeu Fabra (UPF), 08003 Barcelona, Catalonia, Spain.|Department of Epidemiology, Geisel School of Medicine at Dartmouth College, Lebanon, NH 03756, USA.
authors: Lucas A
authors: LA
authors: Salas
authors: EPIGET-Epidemiology, Epigenetics and Toxicology Lab-Department of Clinical Sciences and Community Health, Università degli Studi di Milano, 20122 Milano, Italy.
authors: Valeria
authors: V
authors: Motta
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Instituto de Investigación Biosanitaria (ibs.GRANADA), University of Granada, San Cecilio University Hospital, 18012 Granada, Spain.
authors: Mariana F
authors: MF
authors: Fernandez
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|FISABIO-Universitat de València-Universitat Jaume I Joint Research Unit of Epidemiology and Environmental Health, 46020 Valencia, Spain.
authors: Mario
authors: M
authors: Murcia
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|FISABIO-Universitat de València-Universitat Jaume I Joint Research Unit of Epidemiology and Environmental Health, 46020 Valencia, Spain.
authors: Sabrina
authors: S
authors: Llop
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Molecular Epidemiology of Cancer Unit, University Institute of Oncology, University of Oviedo, 33003 Oviedo, Spain.
authors: Adonina
authors: A
authors: Tardon
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Molecular Epidemiology of Cancer Unit, University Institute of Oncology, University of Oviedo, 33003 Oviedo, Spain.
authors: Guillermo
authors: G
authors: Fernandez-Tardon
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Subdirección de Salud Pública y Adicciones de Gipuzkoa, 20010 Donostia/San Sebastián, Spain.|Instituto de Investigación Sanitaria BIODONOSTIA, 20014 Donostia/San Sebastián, Spain and.
authors: Loreto
authors: L
authors: Santa-Marina
authors: Instituto de Investigación Sanitaria BIODONOSTIA, 20014 Donostia/San Sebastián, Spain and.|Faculty of Pharmacy, University of the Basque Country UPV/EHU, 01006 Vitoria-Gasteiz, Spain.
authors: Mara
authors: M
authors: Gallastegui
authors: EPIGET-Epidemiology, Epigenetics and Toxicology Lab-Department of Clinical Sciences and Community Health, Università degli Studi di Milano, 20122 Milano, Italy.
authors: Valentina
authors: V
authors: Bollati
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Genomics and Disease Group, Bioinformatics and Genomics Program, Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology, 08003 Barcelona, Catalonia, Spain.|Universitat Pompeu Fabra (UPF), 08003 Barcelona, Catalonia, Spain.
authors: Xavier
authors: X
authors: Estivill
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Instituto de Investigación Biosanitaria (ibs.GRANADA), University of Granada, San Cecilio University Hospital, 18012 Granada, Spain.
authors: Nicolas
authors: N
authors: Olea
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Centre for Research in Environmental Epidemiology (CREAL), 08003 Barcelona, Catalonia, Spain.|Universitat Pompeu Fabra (UPF), 08003 Barcelona, Catalonia, Spain.
authors: Jordi
authors: J
authors: Sunyer
authors: CIBER Epidemiología y Salud Pública (CIBERESP), 28029 Madrid, Spain.|Centre for Research in Environmental Epidemiology (CREAL), 08003 Barcelona, Catalonia, Spain.|Genomics and Disease Group, Bioinformatics and Genomics Program, Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology, 08003 Barcelona, Catalonia, Spain.|Universitat Pompeu Fabra (UPF), 08003 Barcelona, Catalonia, Spain.
authors: Mariona
authors: M
authors: Bustamante
mesh_terms: D000328:Adult; D001724:Birth Weight / Q000235:genetics*; D015331:Cohort Studies; D003367:Cotinine / Q000652:urine; D018899:CpG Islands / Q000235:genetics*; D019175:DNA Methylation / Q000235:genetics*; D044127:Epigenesis, Genetic; D005260:Female; D055106:Genome-Wide Association Study; D006801:Humans; D007231:Infant, Newborn; D016014:Linear Models; D008297:Male; D018811:Maternal Exposure / Q000009:adverse effects; D057182:Mendelian Randomization Analysis; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D013030:Spain; D000073869:Tobacco Smoking / Q000009:adverse effects*
chemical_list: D003367:Cotinine
keywords: DNA methylation; birthweight; epigenetics; fetal programming; placenta; tobacco smoking