In total, the recently characterized R59Q variation within the human RGS12 protein provides a biologically plausible molecular link between inherited BD risk and abnormal dopaminergic tone, thereby offering a mechanistic rationale for investigating whether RGS12 dysfunction influences psychostimulant responsiveness in BD patients with comorbid ADHD [40,41]. This evidence concerns the gene RGS12 and attention deficit-hyperactivity disorder.