An X-linked leukodystrophy characterized by developmental delay, nystagmus, hypotonia, spasticity, and variable intellectual deficit. It is classified into three sub-forms based on the age of onset and severity: connatal, transitional, and classic PMD. The disease is Pelizeaus-Merzbacher spectrum disorder (MONDO_0010714). Also known as: HLD1, PMD, Pelizaeus Merzbacher brain sclerosis, Pelizaeus-Merzbacher brain sclerosis, Pelizaeus-Merzbacher disease, Pelizaeus-Merzbacher disease, X-linked recessive, Sudanophilic leukodystrophy, Paelizeus-Merzbacher type, diffuse familial brain sclerosis.