NOS2 and migraine disorder: Nitric oxide (NO) is a signaling molecule with a short half-life, which is synthesized from L-arginine by 3 isozymes of nitric oxide synthase (NOS), including neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS).[6] It exerts a variety of physiological effects such as regulating blood pressure via smooth muscle relaxation, and functioning as a neurotransmitter.[7] NO in the migraine pathogenesis has been reported in several studies.[8,9] Polymorphism of NOS could affect production of NO, which may be connected with migraine.