Persistent DNA methylation changes associated with prenatal NO2 exposure in a Canadian prospective birth study

Background: Accumulating evidence suggests prenatal air pollution exposure alters DNA methylation (DNAm), which could go on to affect long-term health. However, it remains unclear whether prenatal DNAm alterations persist through early life. Identifying DNAm changes that persist from birth into childhood would provide greater insight into the molecular mechanisms that most likely contribute to the association of prenatal air pollution exposure with health outcomes such as atopic disease. Objectives: This study investigated the persistence of DNAm changes associated with prenatal NO2 exposure (a surrogate measure of traffic-related air pollution) at age one to begin characterizing which DNAm changes most likely to contribute to atopic disease. Methods: We used an atopy-enriched subset of CHILD study participants (N=145) to identify individual and regional cord blood DNAm differences associated with prenatal NO2, followed by an investigation of persistence in age one peripheral blood. As we had repeated DNAm measures, we also isolated postnatal-specific DNAm changes and examined their association with NO2 exposure in the first year of life. MANOVA tests were used to examine the association between DNAm changes associated with NO2 and child wheeze and atopy. Results: We identified 24 regions of altered cord blood DNAm, with several annotated to HOX genes. Two regions annotated to MPDU1 and C5orf63 were significantly associated with age one wheeze. Further, we found the effect of prenatal NO2 exposure across CpGs within all altered regions remained similar at age one. A single region of postnatal-specific DNAm annotated to HOXB6 was associated with year one NO2 and age one atopy. Discussion: Regional cord blood DNAm changes associated with prenatal NO2 exposure persist through at least the first year of life, and some of these changes are associated with age one wheeze. The early-postnatal period remains a sensitive window to DNAm perturbations that may also influence child health. ### Competing Interest Statement The authors have declared no competing interest.