VIPR2 and attention deficit-hyperactivity disorder: Methylation of the VIPR2 gene—a gene that codes a receptor for a small neuropeptide with neurotransmitter and neuroendocrine functions—was shown to differentiate between ADHD cases and controls in boys age 7–12 [16], in a sample of twin pairs discordant for ADHD [17], and in the most recent case-control EWAS of approximately 600 children age 7–12 [15].