To the best of our knowledge, only one study has reported that the efficacy of transcranial direct current stimulation (tCDS) as a supplement to antipsychotic treatment of AVHs is weaker in schizophrenia patients with the COMT-met genotype than in those with the COMT-val genotype (Chhabra et al., 2018). Here, COMT is linked to schizophrenia.