GRIK1 and attention deficit-hyperactivity disorder: We, for the first time, investigated two GRIK1 exonic variants, rs363504 [c.2705T > C (p.Leu902Ser)] and rs363538 [c.522A/C (p.Thr)], in a group of ethnically matched subjects by case–control as well as family-based methods to identify their association with ADHD, different traits, post-therapeutic changes in the trait scores of the ADHD probands and GRIK1 expression in the peripheral blood.