PTGS2 and major depressive disorder: 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.