PLP1 and Pelizeaus-Merzbacher spectrum disorder: Furthermore, the hereditary spastic paraplegia 2 (SPG2), the prototype of early-onset hypomyelinating leukodystrophy Pelizaeus–Merzbacher Disease (PMD) (MIM 312080), and the hereditary spastic paraplegia 35 (SPG35), have been associated with mutations in the PLP1 (SPG2 and PMD) and FA2H (SPG35) genes, both genes coding for important components of myelin sheath [15,16].