PLP1 and Pelizeaus-Merzbacher spectrum disorder: Unlike other leukodystrophies in which there is a period of normal cortical myelination an then comes a disruption resulting in the lost of myelin sheaths (demyelination), PMD has, from the beginning, an abnormal or low production of this very important protein (hypomyelination), due to a damage on the PLP1 gene coding for the Protelipidic Protein type 1 that interferes with the oligodendrocyte synthesis of fully functional myelin sheaths and probably also affects the peripheral function of myelinated axons 3,.8