Plasma and aqueous humor levels of endothelin-1 (ET-1), a vasoconstrictor that binds to receptors on smooth muscle cells and pericytes to constrict blood vessels, are increased in patients with normotensive glaucoma [19,20,21], confirming abnormal vascular function as an important factor in the pathophysiology of glaucoma [15]. The gene discussed is EDN1; the disease is glaucoma.