Because P0 is the most aboundant myelin protein and because P0 mutations are responsible for hypomyelinating, dysmyelinating, and demyelinating CMT1B neuropathies, we first studied the ultrastructure of myelin sheaths in sciatic nerves from MpzT124M mice (Fig 2A–2D). The gene discussed is MPZ; the disease is Charcot-Marie-Tooth disease type 1B.