PLP1 and Pelizeaus-Merzbacher spectrum disorder: Mutations in the PLP1 gene are associated with a broad spectrum of neurological disorders ranging from severe connatal forms of PMD through intermediate severity, classical forms and PLP1 null spectrum disorder, to the milder allelic disorder, spastic paraplegia 2 (SPG2) (Garbern and Hobson, 2002; Garbern et al., 2002; Garbern, 2007; Osório and Goldman, 2018).