PTPRD and attention deficit-hyperactivity disorder: PTPδ has been implicated in various brain disorders, including ADHD, restless leg syndrome, addiction, bipolar disorder, obsessive–compulsive disorder, and intellectual disability (Anney et al, 2008; Schormair et al, 2008; Elia et al, 2010; Distel et al, 2011; Malhotra et al, 2011; Yang et al, 2011; Kim et al, 2013; Jarick et al, 2014; Moore et al, 2014; Choucair et al, 2015; Drgonova et al, 2015; Mattheisen et al, 2015; Uhl et al, 2018; Uhl & Martinez, 2019).