The dopamine receptor gene family, which comprises DRD1 (MIM *126449), DRD2 (MIM *126450), DRD3 (MIM *126451), DRD4 (MIM * 126452) and DRD5 (MIM *126453) is a prime candidate gene family for influencing substance abuse because this gene family is thought to play one of the most important roles in the neurobehavioral signaling pathways implicated in substance addiction [15,18]. The gene discussed is DRD3; the disease is substance abuse.