Gałecki et al (2012) examined the expression of four genes (PTGS2, MPO, NOS2A, PLA2GA) coding for COX-2, MPO, iNOS, and secretory phospholipase A2 type IIA, and found them all to be increased in patients with recurrent depressive disorder, underlining the role of oxidative and nitrosative stress in this condition. The gene discussed is MPO; the disease is major depressive disorder.