HSPD1 and Rotary nystagmus: Allelic mutations of the HSPD1 gene cause leukodystrophy, hypomyelinating, 4 (HLD4, MIM 612233), a severe autosomal recessive, hypomyelinating leukodystrophy, characterized by infantile-onset rotary nystagmus, progressive spastic paraplegia, neurologic regression, motor impairment, profound mental retardation, with death occurring within the first two decades.