Evaluating clinical mitochondrial respiratory chain enzymes from biopsy specimens presenting skewed probability distribution of activity data.

Due to the relative rarity of mitochondrial diseases, generating reference ranges is problematic in evaluation of respiratory chain activities particularly in pediatric cases. We determined the sample distribution of respiratory chain enzyme activities in skeletal muscle biopsies collected from pediatric patients suspected of neuromuscular disorders. Activities of NADH-ubiquinone reductase, NADH-cytochrome c reductase, succinate-cytochrome c reductase; ubiquinol-cytochrome c reductase and cytochrome c oxidase activities have log-normal distributions even when confirmed mitochondrial diseases were ruled out. Impact of the log-normal distribution of the respiratory chain enzyme activities on clinical diagnostics is discussed.