The human P2RX1 gene encodes P2X1, an ionotropic ATP receptor that functions as an ATP- or ADP-activated cation channel, expressed in smooth muscle, platelets, and sensory neurons. A P2RX1 mutation has been linked to a severe bleeding disorder arising from impaired ADP-induced platelet aggregation. P2X1 receptors are therapeutic targets in treatment of urinary incontinence and pain.