PLP1 and Pelizeaus-Merzbacher spectrum disorder: This is consistent with the mild phenotype of our patient compared to PMD boys with three copies of PLP1. It has been proposed that triplications at the PLP1 locus result from a duplication-inverted triplication-duplication (DUP-TRP/INV-DUP) likely based on a replication based mechanism and that relies on the presence of segmental duplications in an inverted orientation [14].