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A group of metabolic disorders primarily of infancy characterized by the subacute onset of psychomotor retardation, hypotonia, ataxia, weakness, vision loss, eye movement abnormalities, seizures, dysphagia, and lactic acidosis. Pathological features include spongy degeneration of the neuropile of the basal ganglia, thalamus, brain stem, and spinal cord. Patterns of inheritance include X-linked recessive, autosomal recessive, and mitochondrial. Leigh disease has been associated with mutations in genes for the PYRUVATE DEHYDROGENASE COMPLEX; CYTOCHROME-C OXIDASE; ATP synthase subunit 6; and subunits of mitochondrial complex I. (From Menkes, Textbook of Child Neurology, 5th ed, p850).