Moreover, gene-associated studies showed a possible relationship between the risk of schizophrenia and some variants in genes related to dopamine signaling, i.e., catechol-O-methyltransferase (COMT), monoamine oxidase (MAO), dopamine transporter (SLC6A3), and dystrobrevin-binding protein 1 (DTNBP1) [39]. Here, SLC6A3 is linked to schizophrenia.