20.: A new diagnostic paradigm for mitochondrial disease

Mitochondrial disease is usually diagnosed with a combined approach of clinical investigation and histological or enzymatic analysis of muscle biopsy or genetic testing. With the discovery of new serological biomarkers and the development of accurate next-generation sequencing (NGS) methods, the opportunity to change the diagnostic paradigm for this group of disorders presents. In this study, we aim to test the accuracy of a new method to diagnose mitochondrial disease, using a combined approach of serum fibroblast growth factor-21 (FGF-21) level testing and NGS methods. We measured serum FGF-21 levels in 70 patients with mitochondrial disease using an enzyme-linked immunosorbent assay based assay. We also performed long-range polymerase chain reaction (PCR) on urinary epithelial cells from the same patients. PCR products were subjected to massively parallel sequencing (NGS) to provide at least thousand-fold coverage of the mtDNA. Serum FGF-21 levels were elevated in patients with mitochondrial disease. This was a more sensitive biomarker of mitochondrial disease than serum lactate, pyruvate creatine kinase or serum lactate/pyruvate ratios. Long-range PCR was able to detect single and multiple deletions. NGS sequencing was able to determine the breakpoints for single deletions, as well as identify point mutations in the mtDNA. Our findings demonstrate that the diagnosis of mitochondrial disease can be performed by using a combined approach of clinical evaluation, serum FGF-21 levels and next generation sequencing. Adoption of this approach would avoid the need for muscle biopsy in most patients and thus represent a shift in the diagnostic paradigm for mitochondrial disease.