Long-term treatment with psychostimulant drugs such as methylphenidate (MPH), which acts by inhibiting reuptake of dopamine and norepinephrine or Atomoxetine helps to increase gray matter in the prefrontal and occipital areas of ADHD children having 10/10-repeat allele with a variable number tandem repeat of 40 bp of the SLC6A3 genotype associated with ADHD compared to TD children128. The gene discussed is SLC6A3; the disease is attention deficit-hyperactivity disorder.