MPO and major depressive disorder: First, based on studies that on one hand suggested that gene conversion may be an effective treatment for cerebral ischemia (Driga et al., 2021), and on the other hand investigated PON1, PON2, PON3, and MPO gene expression in patients with depression (Blizniewska-Kowalska et al., 2022), we considered that elderly patients with depression can also undergo genetic testing, which may provide information for the prediction of depression.