Mutations in glypican family members have been implicated in multiple neurological disorders that have underlying synaptic dysfunction, including autism spectrum disorder (ASD), attention-deficit hyperactivity disorder (ADHD), and schizophrenia (Doan et al., 2016, Lesch et al., 2008, Potkin et al., 2010). Here, GPC1 is linked to attention deficit-hyperactivity disorder.