Mitochondrial respiratory-chain defects presenting as nonspecific featuresin children

Patients with mitochondrial respiratory-chain defects frequently exhibit la ctic acidosis, ragged red fibers in skeletal muscle samples, and abnormal e nzyme assays for the respiratory-chain complex. However, ragged red fibers and lactic acidosis are not always seen in all patients with mitochondrial respiratory-chain defects. We have encountered six children with biochemica lly proven respiratory chain defects, but typical ragged red fibers were no t found in all six patients, and only five patients had increased serum lac tate levels. Initially, they present with nonspecific features. However, pe rsistent or progressive clinical features or multiple organ involvement eve ntually led to the diagnosis of respiratory-chain defects in these patients . Mitochondrial respiratory-chain defects should be considered in the diffe rential diagnosis when persistent, progressive features and especially mult iple organ involvement occur.