SLC18A2 and attention deficit-hyperactivity disorder: Methylphenidate (MPH) is a psychostimulant commonly prescribed as a first-line therapy for pediatric ADHD.20,21 ADHD symptoms are believed to partly emerge from catecholamine neurotransmission dysfunction predominantly in the prefrontal cortex.22 MPH produces its therapeutic effects by elevating the levels of extracellular synaptic dopamine (DA) and norepinephrine (NE) via reuptake transporter inhibition and vesicular monoamine transporter 2 (VMAT-2) redistribution in the central nervous system.