oa Mitochondrial Diseases: Diagnosis and Novel Approach for Treatment

Mitochondrial diseases are clinically and genetically heterogeneous and tissue specific presentations are common. It is not known to date why different mitochondrial DNA (mtDNA) or mutations in nuclear genes encoding mitochondrial proteins result in very heterogeneous clinical presentations. The most common causes of mitochondrial diseases in adults are mutations in the mtDNA. A defect of mitochondrial protein synthesis results in respiratory chain deficiency in patients with common mttRNA mutations (such as m.3243A>G). Mutations in nuclear genes involved in mitochondrial translation affect ubiquitously expressed genes, but the result is highly tissue specific symptoms suggesting that there are additional factors, which contribute to the tissue specificity in mitochondrial translation deficiencies. Most of these gene defects result in early-onset, severe, and often fatal diseases. The diagnosis of mitochondrial diseases has changed significantly, as next generation sequencing technologies become widely available. Although diagnosing mitochondrial disorders require special clinical assessment, and sometimes biochemical analyses, there is now a strong rationale to perform first-line whole genome sequencing in mitochondrial diseases. This can accelerate the speed of diagnosis and prevent expensive and invasive investigations.