Abstract
Mitochondrial disease (MD) occurs when alteration of mitochondrial respiratory chain complex function caused by genetic mutation produces a detectable disease state. These mutations may be found in either the nuclear or mitochondrial genomes, and may only be present in a subset of cells or body tissues. Thus, the phenotype of MD is extremely variable and the definitive diagnosis of MD is complex. This article provides a brief description of a strategy used in the diagnosis of MD, by integrating data from clinical, imaging, pathologic, molecular, and enzymatic assessments. Additional information on characteristic findings seen in classic MD syndromes is also provided.