HSPA12A and attention deficit-hyperactivity disorder: The SNP associated with opioid overdose, rs12777585, is in an intron of the heat shock protein family A member 12A (HSPA12A), wherein SNPs in this region have been previously associated with externalizing behaviours (namely attention deficit hyperactivity disorder, substance use, and antisocial behaviours), educational attainment and smoking initiation59,61–63.