(A) Brain areas with statistical significance were the left orbital frontal cortex and temporal pole (OFC [TPO].L), right orbital frontal cortex (OFC.R), bilateral anterior cingulate cortex (ACC), right insula (INS.R), and right temporal pole (TPO.R). (B) Compared with T allele carriers, C allele carriers presented an increase in GMV compared with healthy controls, but a significant decrease in GMV was observed in heroin abusers. C allele carriers with heroin addiction exhibited a significant decrease in GMV in these areas compared with healthy C allele carriers. In T carriers, heroin abusers exhibited no changes in GMV, with the exception of the ACC, which exhibited a marked increase in GMV compared with healthy controls. No significant difference was found between C allele heroin abusers and T allele controls or between T allele heroin abusers and C allele controls. *p < 0.05, compared with healthy controls in each genotype; #p < 0.05, compared with the other genotype of heroin abusers and healthy controls. Error bars indicate standard errors.