Objectives: In mitochondrial encephalomyopathies the diagnosis is not always straight forward and necessitates several biochemical investigations in different tissues. We have started since a few years collaboration between different centers in Belgium in order to get to the final diagnosis in certain suspected patients.
Methods: Full clinical and familial descriptions as detailed as possible, associated with the biological data in plasma and CSF are needed in order to make a differential diagnosis with other diseases. Light en electronmicroscopy of muscle allows the detection of red ragged fibers. The next step is to get biochemical data of OXPHOS complexes in muscle or other tissue. In addition Blue-Native PAGE electrophoresis and immunoblotting of the complexes with specific antibodies can be done, or search for mosaicism in fibroblasts, an indication for defects in mitochondrial DNA.
Results: Molecular analysis should be undertaken after biochemical analysis. Mutations in tRNAs, large scale deletions and mtDNA depletions are associated with defects in OXPHOS complexes, especially complex I and IV. Mitochondrial DNA analysis in protein coding genes can be indicated. Real-time PCR for mtDNA depletion and DHPLC ideal for identifying heteroplasmic mtDNA mutations are developed to study the patients further. If a nuclear gene is suspected, the study will include genes involved in structural components of or assembly genes, but also genes involved in maintaining mtDNA.
Conclusion: This multi-disciplinary approach has been successful and led to a final diagnosis in several patients.
