Mitochondrial diseases are a group of highly heterogeneous disorders caused by mutations in over 300 known genes, most of which directly or indirectly impair mitochondrial energy generation. Around 50% of patients with suspected mitochondrial disease remain undiagnosed after massively parallel genome sequencing approaches, often due to the identification of variants of uncertain significance (VUS) in multiple genes and a lack of appropriate functional tests to demonstrate their pathogenicity in a timely manner. The gold-standard and National Association of Testing Authorities (NATA) accredited functional test measures the enzyme activities of mitochondrial respiratory chain complexes I-IV, however this test is not specific as defects in hundreds of genes can lead to an abnormal result. Diagnosis of most patients requires the development of bespoke tests in non-clinical labs, which means patients undergo a diagnostic odyssey of months to years. We believe quantitative proteomics can fill this gap by linking a functional phenotype in the proteome to a VUS, prioritising the variant for sequencing follow-up and providing strong evidence for pathogenicity. Here, I will present a number of recently published1, 2, 3 and unpublished case studies demonstrating our proteomics-based approaches to VUS prioritisation and functionalization with and without suggestive genome sequencing leads. As we consider moving our approaches from the research bench to the clinic, I will also discuss the utility of our approach for diagnosis of other rare diseases4, our investigations into the use of less invasive sample types and faster modes of acquisition with a view toward acute paediatric care, and the next steps toward accreditation of our technique for routine clinical use.
1 Lake, N. J. et al. Am J Hum Genet 101, 239-254 (2017).
2 Frazier, A. E. et al. Med 1, 1-25 (2020).
3 Helman, G. et al. Hum Mutat in press (2020).
4 Van Bergen, N. J. et al. J Exp Med 217, e20192040 (2020).