Hypomyelinating leukodystrophy-6, also known as hypomyelinating leukodystrophy with atrophy of the basal ganglia and cerebellum, is a neurologic disorder characterized by onset in infancy or early childhood of delayed motor development and gait instability, followed by extrapyramidal movement disorders, such as dystonia, choreoathetosis, rigidity, opisthotonus, and oculogyric crises, progressive spastic tetraplegia, ataxia, and, more rarely, seizures. Most patients have cognitive decline and speech delay, but some can function normally. Brain MRI shows a combination of hypomyelination, cerebellar atrophy, and atrophy or disappearance of the putamen. The disorder usually shows sporadic occurrence, but sibs may be affected if a parent is somatic mosaic for the mutation. Hypomyelinating leukodystrophies (HLD) comprise a genetically heterogeneous entity in which there is a substantial permanent deficit in myelin deposition within the brain, resulting in neurologic deficits. [From OMIM]