They found significant differences in the distribution of the BDNF Val66Met genotype between people addicted to methamphetamine or heroin and the control group, which suggests that a lower frequency of the 66Met carrier is associated with substance abuse, which is also confirmed by studies by Jia et al. [27], who also analysed whether the rs6265 polymorphism of the BDNF gene is associated with heroin addiction. The gene discussed is BDNF; the disease is heroin dependence.