NOS3 and migraine disorder: Previous reviews have summarized how a reduced expression of the endothelial nitric oxide synthase (eNOS) enzyme and subsequent decreased production of NO result in an increased susceptibility/risk to develop essential hypertension [1,2], preeclampsia [3], diabetic nephropathy [4], retinopathy [5], migraine [6], and erectile dysfunction [7]; the role of the eNOS enzyme, including its modulation, regulation, and relevance within the cardiovascular system (CVS) in both normal physiological state and in several important cardiovascular diseases is elaborated.