The autosomal recessive syndrome characterized by mitochondrial myopathy of cardiac and skeletal muscle, congenital cataract and lactic acidosis is described in two forms following a retrospective study of 16 patients at the University of Nijmegen, The Netherlands. Four patients with the fatal form died from hypertrophic obstructive cardiomyopathy in the neonatal period. In those with the relatively benign form, cardiomyopathy developed late, causing death in 7 patients at a median age of 23 years. The prognosis in patients without subvalvular aortic stenosis is dependent on the metabolic function of skeletal muscle. It varies between moderate exercise intolerance and wheelchair existence. In both forms, bilateral cataracts, lactacidemia and mitochondrial myopathy are present from birth. If a propositus has an affected sib, he will probably suffer from the same form, and genetic counselling is important. 
COMMENT. Cataracts present at birth are the first manifestation of the syndrome in most patients. Some present with muscular hypotonia, and others with cardiac symptoms. The metabolic cause is unknown. Skeletal muscle biopsy showed abnormal mitochondrial structure or number with matrix vesicles, and the sarcoplasm contained large quantities of lipid or glycogen. Morphometric analysis demonstrated an increased volume density of subsarcolemmal mitochondria, a possible compensatory mechanism for a deficit in energy production. The findings were similar in the fatal and benign forms. Mitochondrial function showed no abnormalities. Qualitative and quatitative defects in mitochondrial DNA in infants with fatal metabolic disorders are discussed by Moraes CT (Int Pediatr 1993; 8: 40).