This group includes Pelizaeus–Merzbacher disease (PMD), caused by PLP1 gene mutations, and numerous other disorders assigned to defects in GJC2, AIMP1, HSPD1, FAM126A, POLR3A, POLR3B, RARS, PYCR2, POLR1C, and VPS11 [36]. This evidence concerns the gene PLP1 and Pelizeaus-Merzbacher spectrum disorder.