Myelin protein zero (P0, MPZ) is a single membrane glycoprotein which in humans is encoded by the MPZ gene. P0 is a major structural component of the myelin sheath in the peripheral nervous system (PNS). Myelin protein zero is expressed by Schwann cells and accounts for over 50% of all proteins in the peripheral nervous system, making it the most common protein expressed in the PNS. Mutations in myelin protein zero can cause myelin deficiency and are associated with neuropathies like Charcot–Marie–Tooth disease and Dejerine–Sottas disease.