A rare autosomal recessive degenerative disorder which usually presents in late childhood or adolescence. Clinical manifestations include progressive muscle spasticity; hyperreflexia; muscle rigidity; dystonia; dysarthria; and intellectual deterioration which progresses to severe dementia over several years. (From Adams et al., Principles of neurology, 6th ed, p972; Davis & Robertson, Textbook of Neuropathology, 2nd ed, pp972-929)