Heteroplasmic mitochondrial DNA mutation in a patient with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes.

A 16-year-old female presented with clinical, morphologic and molecular features of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). Her early development was normal. Starting from the age of 14 years, she experienced recurrent episodes of headaches, with vomiting, seizures, transient right hemiparesis and decreased visual acuity. Computed tomographic brain scans revealed calcification in the bilateral basal ganglia. Biopsied specimens from her left biceps brachii and rectus femoris muscles revealed ragged-red fibers and strong succinate dehydrogenase-reactive blood vessels. Electron microscopy revealed paracrystalline inclusions in muscle mitochondria. Analysis of mitochondrial DNA (mtDNA) from blood, hair follicles and muscle specimens showed an A to G point mutation at nucleotide position 3,243 in the transfer RNA(Leu(UUR)). The proportion of mutant mtDNA in the patient's blood was 43%, in hair follicles 62% and in muscle 82%. The patient was followed up for 4 years and had progressive mental deterioration and died of an episode of status epilepticus. This patient and 5 other MELAS patients reported in Taiwan are compared.