The genes, for which our data showed associations of CpGs sites with functional aspects and ADHD behaviour fulfilling our statistical criteria (COMT, ANKK1, BDNF, NGFR, DPP10, TPH2), have not been considered in the candidate-gene methylation studies in ADHD e.g., refs 19–22 and have not been reported to be differentially methylated in the methylome-wide studies23, 24. Here, TPH2 is linked to attention deficit-hyperactivity disorder.