RGS12 and attention deficit-hyperactivity disorder: Our goal in this study was to determine whether functional variation in the human RGS12 gene influences behavioral responses to psychostimulants such as methylphenidate, thereby informing whether such genetic findings should affect the clinical use of this central nervous system (CNS)-stimulating agent in bipolar disorder (BD) patients with comorbid attention-deficit/hyperactivity disorder (ADHD).