In addition, an increased Dnmt1 expression has been found in psychosis (Veldic et al., 2005) and DNA methylation changes have been reported in many neuropsychiatric disorders including schizophrenia (Grayson and Guidotti, 2013) and ADHD (Heinrich et al., 2017; Chen et al., 2018), further providing a possible link between Dnmt1 dysregulation and the hyperactivity-related phenotype observed in our double-hit stress group. This evidence concerns the gene DNMT1 and attention deficit-hyperactivity disorder.