BDNF and attention deficit-hyperactivity disorder: Dysregulation of BDNF expression and signaling, inducing changes in neuronal maturation and plasticity, is a hallmark of several neurodevelopmental diseases, such as attention-deficit hyperactivity disorder (ADHD), Rett syndrome (RTT), and ASD, suggesting that neuronal malfunction present in these disorders is suspected to be related to excessive or reduced BDNF levels [37].