The most frequent genetic alteration underlying PMD sporadic forms is the duplication of the entire PLP1 gene [14] Together, PMD and the X-linked form of spastic paraplegia (SPG2) are allelic diseases related to the PLP1 locus [15,16], thus increasing the phenotype of PLP1-related disorders. Here, PLP1 is linked to Pelizeaus-Merzbacher spectrum disorder.