COMT, 5-HT1B, MAOA, CHRNA4, SYP and DDC exhibited associations primarily with ADHD-I, whereas HTR2C, 5-HT1D, ADRA2C, DRD3 and NET1 were associated mainly with ADHD-C [24,35-38]. Here, DRD3 is linked to attention deficit-hyperactivity disorder.