Specific genes which have been previously associated with ADHD included solute carrier family 6 (neurotransmitter transporter, noradrenalin), member 2 (SLC6A2) and glutamate receptor, ionotropic, N-methyl D-aspartate 2B (GRIN2B) (Table 2). This evidence concerns the gene SLC6A2 and attention deficit-hyperactivity disorder.