Uysal et al. [88], in a study on first episode schizophrenia patients who had not taken antipsychotics prior to the study, found that prior to treatment the patients had lower levels of D-serine, DAAO, and D-serine/DAAO ratio than healthy controls, but that after six months of treatment, the levels of D-serine and DAAO were higher in these patients, but at levels still lower than those in the controls. This evidence concerns the gene DAO and schizophrenia.