GJC2 and Pelizaeus-Merzbacher-like disease: These include: (1) a severe early onset central nervous system dysmyelinating disorder, Pelizaeus-Merzbacher-like disease (PMLD1 or HLD2) [22]; (2) a milder, later onset disorder, Hereditary Spastic Paraplegia (SPG44) [23]; and (3) a recently described subclinical leukodystrophy [24].