An immunocytochemical approach to detection of mitochondrial disorders

Mitochondrial disorders can lead to a confusing array of symptoms, which frequently makes a diagnosis difficult. Traditional approaches to such diagnoses are based on enzyme activity assays, with further characterization provided by genetic analysis. However, these methods require relatively large sample sizes, are time-consuming, labor-intensive, and show variability between laboratories. Here, we report an immunocytochemical test that makes use of monoclonal antibodies to subunits from each of the oxidative phosphorylation complexes and pyruvate dehydrogenase to aid in the detection of mitochondrial disorders. It can be completed and data analyzed in less than 4 hr. We have used this test to study fibroblast cultures from patients with mitochondrial disorders arising from both mitochondrial DNA and nuclear DNA defects. We have also examined cases of Leigh syndrome arising from different genetic causes. We show that patients can be categorized on the basis of which complexes are affected and whether or not the defect being studied shows a mosaic distribution, an indicator of whether the causal mutation(s) is/are in the mitochondrial or nuclear genome. Immunocytochemical analysis as described here should be considered as an initial screen for mitochondrial disorders by which to direct (and limit) the subsequent enzymatic and genetic tests required to make an unambiguous diagnosis.