To designate the genes of the “DDAH1 cluster” and “DDAH2 cluster” that are co-expressed with DDAH1 or DDAH2, respectively, in the control group, bipolar disorder patients and schizophrenia patients, we compared these clusters with the gene sets derived from our co-expression analysis (cut-off r > 0.3, p < 0.05). Here, DDAH2 is linked to schizophrenia.