GRM6 and attention deficit-hyperactivity disorder: Relative analysis on mRNA expression revealed down regulations of GRM5 (33.33), GRM6 (3.13), GRM7 (3.85), GRIA1 (4.76), GRIN2A (4.76), GRIN2B (7.14) in the ADHD probands as compared to the controls (Fig. 4B).