Abstract
OBJECTIVE: We investigated whether prepregnancy BMI (prePregBMI) in women with obesity was associated with differential DNA methylation (DNAm) in cord blood (CB) and whether DNAm may mediate the association of prePregBMI and early childhood BMI z score (BMIz). METHODS: From the Treatment of Obese Pregnant Women (TOP) study, 232 mother-child pairs were included. We conducted an epigenome-wide association study on prePregBMI and CB DNAm (450k array), followed by causal mediation analyses to test whether DNAm may mediate effects of prePregBMI on BMIz at age 36 months (BMIz36). RESULTS: DNAm at 5345 CpG sites annotated to 2842 genes, which were overrepresented in biological processes linked to carbohydrate metabolism and plasma lipoprotein particle clearance, was associated with prePregBMI (false discovery rate < 10%). Causal mediation analyses of 168 methylation sites associated with BMIz36 (p < 0.05) and overlapping with the 5345 prePregBMI-associated sites identified two sites on SYT7 and DEAF1, partially mediating the effect of prePregBMI on BMIz36 (p ≤ 0.01). After cross-validation, a methylation risk score including these two sites could predict the highest quartile of BMIz36 and fat mass (in grams) with area under the curve = 0.72 (95% CI: 0.58-0.85) and area under the curve = 0.71 (95% CI: 0.58-0.85), respectively. CONCLUSIONS: CB DNAm at birth may partially mediate effects of prePregBMI on early childhood BMIz36, supporting its plausible role in influencing individual future obesity risk.