An infant with a mitochondrial A3243G mutation demonstrating the MELAS phenotype.

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a syndrome associated with mitochondrial DNA mutations such as A3243G, the most common mutation. Ragged-red fibers and strongly succinate dehydrogenase-reactive blood vessels in the muscle are diagnostic pathologic features of MELAS. In general, the first typical attack of MELAS occurs in children at school age; it is rare for stroke-like episodes to occur in early infancy. This report describes a 4-month-old male harboring A3243G, whose phenotype at onset was consistent with that of MELAS in infancy. The patient was admitted because of disturbances of consciousness and ventilatory insufficiency. Remarkable lactic acidosis was observed. MRI revealed several bilateral lesions. Periodic lateralized epileptic discharges on the EEG suggested regional lesions. Biopsied muscle displayed scattered ragged-red fibers and succinate dehydrogenase-reactive blood vessels; over 90% of muscle mitochondrial DNA had A3243G. This case suggests that MELAS can develop in early infancy with its typical clinical presentation. The high percentage of A3243G may contribute to the early onset of the MELAS phenotype in this patient.