Large epigenome-wide association study of childhood ADHD identifies peripheral DNA methylation associated with disease and polygenic risk burden

Abstract

Epigenetic variation in peripheral tissues is being widely studied as a molecular biomarker of complex disease and disease-related exposures. To date, few studies have examined differences in DNA methylation associated with attention-deficit hyperactivity disorder (ADHD). In this study, we profiled genetic and methylomic variation across the genome in saliva samples from children (age 7-12 years) with clinically established ADHD (N = 391) and nonpsychiatric controls (N = 213). We tested for differentially methylated positions (DMPs) associated with both ADHD diagnosis and ADHD polygenic risk score, by using linear regression models including smoking, medication effects, and other potential confounders in our statistical models. Our results support previously reported associations between ADHD and DNA methylation levels at sites annotated to VIPR2, and identify several novel disease-associated DMPs (p < 1e-5), although none of them were genome-wide significant. The two top-ranked, ADHD-associated DMPs (cg17478313 annotated to SLC7A8 and cg21609804 annotated to MARK2) are also significantly associated with nearby SNPs (p = 1.2e-46 and p = 2.07e-59), providing evidence that disease-associated DMPs are under genetic control. We also report a genome-wide significant association between ADHD polygenic risk and variable DNA methylation at a site annotated to the promoter of GART and SON (p = 6.71E-8). Finally, we show that ADHD-associated SNPs colocalize with SNPs associated with methylation levels in saliva. This is the first large-scale study of DNA methylation in children with ADHD. Our results represent novel epigenetic biomarkers for ADHD that may be useful for patient stratification, reinforce the importance of genetic effects on DNA methylation, and provide plausible molecular mechanisms for ADHD risk variants.

Epigenome-wide association study of attention-deficit/hyperactivity disorder in adults

“…The second one found hypermethylated regions in genes involved in fatty acid metabolism and fatty acid oxidation pathways associated with ADHD persistence when compared to remittance 21 . In the childhood period, Wilmot et al analyzed a population cohort of school-age boys and found lower methylation levels at the VIPR2 gene in ADHD subjects compared to their age-and sex-matched controls 10 , results that were recently replicated in the largest EWAS on ADHD in children conducted so far 22 . In a similar aged population cohort, Walton et al investigated ADHD symptom trajectories from birth to adolescence and pointed to epigenetic marks in genes related to neural tube development and peroxisomal mechanisms as candidates to be involved in the different ADHD symptom trajectories across time 6 .…”

“…Studies of DNA methylation profiles in ADHD have been conducted using peripheral blood, cord blood, buccal samples or saliva 6,[9][10][11][20][21][22][23][24][25][26][27][28] . Candidate gene studies have revealed differential methylation patterns in genes involved in the dopaminergic, serotoninergic and neurotrophic systems, including SLC6A4, DRD4, COMT, ANKK1, BDNF, or NGFR, associated with ADHD symptomatology and severity [23][24][25][26][27][28] .…”

“…Candidate gene studies have revealed differential methylation patterns in genes involved in the dopaminergic, serotoninergic and neurotrophic systems, including SLC6A4, DRD4, COMT, ANKK1, BDNF, or NGFR, associated with ADHD symptomatology and severity [23][24][25][26][27][28] . Seven epigenome-wide association studies (EWASs) on ADHD have been run to date, with sample sizes ranging from 54 subjects for clinical samples 21 to 4,689 individuals in a meta-analysis considering ADHD symptomatology in general population 9 , yielding nonoverlapping findings across them 6,[9][10][11][20][21][22] . There is limited research on adults using this approach, given that most of the EWASs have focused on pediatric samples 6,10,11,20,22 .…”

“…Seven epigenome-wide association studies (EWASs) on ADHD have been run to date, with sample sizes ranging from 54 subjects for clinical samples 21 to 4,689 individuals in a meta-analysis considering ADHD symptomatology in general population 9 , yielding nonoverlapping findings across them 6,[9][10][11][20][21][22] . There is limited research on adults using this approach, given that most of the EWASs have focused on pediatric samples 6,10,11,20,22 . To the best of our knowledge, only two studies evaluated methylome-wide patterns on adults 9,21 .…”

Altered hypothalamic DNA methylation and stress-induced hyperactivity in a novel model of early life stress

“…DNA methylation is highly dynamic during human brain development [84] and perturbations in DNA methylation are associated with several neurodevelopmental disorders, including ASD [85,86], schizophrenia [87] and ADHD [88], and have also been documented following PTB [22].…”