An initial study [182] showed no association between pre-proghrelin gene (GHRL) variations and susceptibility to the development of methamphetamine dependence in a sample of the Korean population but found a significant correlation between carrying the GHRL single nucleotide (Leu72Met) polymorphism and emotional problems, such as depression or anxiety, which are associated with drug addiction. The gene discussed is GHRL; the disease is depressive disorder.