HDC and Tourette syndrome: Loss-of-function mutations in the Hdc locus is a genetic cause of Tourette syndrome, a neurological disorder characterized by repetitive and unwanted movements, and functional impairment of histaminergic neurons is associated with multiple neurodegenerative diseases (Baldan et al, 2014; Ercan-Sencicek et al, 2010; Panula and Nuutinen, 2013).