A detailed clinical, pathologic, biochemical, and genetic analysis of a case of lethal infantile mitochondrial disease is reported from the Departments of Biochemistry, Pediatrics, Neurology and Nephrology, Emory University School of Medicine, Atlanta, GA. During the first three months of life the child showed increasing lethargy, hypotonia, difficulty in feeding and growth retardation. On admission at three months of age there was respiratory failure, bradycardia, hypotension, and severe lactic acidosis. Over the next 21 days the condition rapidly deteriorated with a progressive hypertrophic cardiomyopathy, hepatic dysfunction, and generalized seizure activity. The patient died with bradycardia and hypotension at four months of age. There were abnormalities in the striated muscles, smooth muscle, heart and liver but not in the central nervous system. Biochemical analysis revealed a combined complex I and IV deficiency in skeletal muscle, heart and liver but not in kidney and brain. There was no abnormality in mitochondrial DNA. The disease was thought to result from a nuclear oxidative phosphorylation gene mutation. 
COMMENT. Mitochondrial encephalomyopathies attributed to mutations in the mitochondrial DNA include MERRF and Kearns-Sayre syndrome with onset in childhood through adulthood. In the neonatal period some mitochondrial myopathies have a benign course and some are lethal and a variety of oxidative phosphorylation deficiencies have been associated with these disorders.