PLP1 and Pelizeaus-Merzbacher spectrum disorder: There is a phenotype‐genotype correlation: in PMD, overexpressed or misfolded PLP is retained in the endoplasmic reticulum where it interferes with oligodendrocytes survival or myelin production, whereas loss of PLP results in type 2 spastic paraplegia, which undergoes with length‐dependent axonal degeneration secondary to the abnormal myelin compaction.