We investigated this issue using a canine model (shaking pup - shp) that presents a genetic myelin disorder associated with a mutation in the proteolipid protein (PLP1) gene, allelic to Pelizaeus-Merzbacher disease (PMD), and that develops a chronic axon loss in the optic nerve, similar to the loss of demyelinated axons seen in MS patients.16 This model is particularly well suited to address this question because it is a disorder of dysmyelination without inflammation, and axons in the optic nerve predominantly lack a myelin sheath. The gene discussed is PLP1; the disease is Pelizeaus-Merzbacher spectrum disorder.