HTR2A and schizophrenia: For instance, previous post-mortem studies have revealed hypermethylation of three CpG sites in serotonin receptor 2A (HTR2A) as well as two CpG loci in promoter of glutamic acid decarboxylase 1 (GAD1), which is the enzyme controling synthesis of GABA and associated with schizophrenia-risk single nucleotide polymorphism (SNP) (Tao et al., 2018).