According to data results from molecular genetic studies Faraone and Biederman [21], cautiously suggest that the susceptibility to ADHD may be due to the presence of three polymorphic genes; the D4 DA receptor gene, the DA transporter gene, and the D2 DA receptor gene However, other genes also have been associated with ADHD. The gene discussed is SLC6A3; the disease is attention deficit-hyperactivity disorder.