DNA methylation of GFI1 as a mediator of the association between prenatal smoking exposure and ADHD symptoms at 6 years: the Hokkaido Study on Environment and Children's Health

Abstract

Background: Prenatal smoking exposure has been associated with childhood attention-deficit/hyperactivity disorder (ADHD). However, the mechanism underlying this relationship remains unclear. We assessed whether DNA methylation differences may mediate the association between prenatal smoking exposure and ADHD symptoms at the age of 6 years.

Results: We selected 1150 mother-infant pairs from the Hokkaido Study on the Environment and Children's Health. Mothers were categorized into three groups according to plasma cotinine levels at the third trimester: non-smokers (≤ 0.21 ng/mL), passive smokers (0.21-11.48 ng/mL), and active smokers (≥ 11.49 ng/mL). The children's ADHD symptoms were determined by the ADHD-Rating Scale at the age of 6 years. Maternal active smoking during pregnancy was significantly associated with an increased risk of ADHD symptoms (odds ratio, 1.89; 95% confidence interval, 1.14-3.15) compared to non-smoking after adjusting for covariates. DNA methylation of the growth factor-independent 1 transcriptional repressor (GFI1) region, as determined by bisulfite next-generation sequencing of cord blood samples, mediated 48.4% of the total effect of the association between maternal active smoking during pregnancy and ADHD symptoms. DNA methylation patterns of other genes (aryl-hydrocarbon receptor repressor [AHRR], cytochrome P450 family 1 subfamily A member 1 [CYP1A1], estrogen receptor 1 [ESR1], and myosin IG [MYO1G]) regions did not exert a statistically significant mediation effect.

Conclusions: Our findings demonstrated that DNA methylation of GFI1 mediated the association between maternal active smoking during pregnancy and ADHD symptoms at the age of 6 years.

Keywords: ADHD; Birth cohort; DNA methylation; DOHaD; GFI1; Prenatal smoking exposure.

Fig. 1

The association between maternal smoking exposure during pregnancy and DNA methylation. a AHRR, b CYP1A1, c ESR1, d GFI1, and e MYO1G. The squares indicate the average methylation of all analyzed CpG sites (regions). The triangle indicates the CpG cluster shown in Additional file 1: Fig. S1. The circles indicate the methylation of individual CpG sites. Standardized partial regression coefficient (β) was adjusted for maternal age, family income, maternal alcohol consumption during pregnancy, parity, child sex, and pre-pregnancy BMI. The error bars display the 95% confidence intervals. *p < 0.05

Fig. 2

Association of DNA methylation with ADHD symptoms by logistic regression analysis. a AHRR, b CYP1A1, c ESR1, d GFI1, and e MYO1G. Odds ratios were adjusted for maternal age, family income, maternal cotinine levels, maternal alcohol consumption during pregnancy, parity, child sex, and pre-pregnancy BMI. The squares indicate the average methylation of all analyzed CpG sites (regions). The triangle indicates the CpG cluster shown in Fig. S1. The circles indicate the methylation of individual CpG sites. The error bars display the 95% confidence intervals. *p < 0.05

Fig. 3

Mediation of the association between active smoking during pregnancy and ADHD symptoms via DNA methylation of GFI1 regions. Mediation analysis was adjusted for maternal alcohol consumption during pregnancy, family income, pre-pregnancy BMI, parity, gestational age, and infant sex. Percent mediation was calculated as the indirect effect derived by the total (indirect + direct) effect × 100%