280th ENMC International Workshop: The ERN EURO-NMD mitochondrial diseases working group; diagnostic criteria and outcome measures in primary mitochondrial myopathies. Hoofddorp, the Netherlands, 22-24 November 2024

The 280th ENMC International Workshop, held in Hoofddorp, The Netherlands, November 22-24, 2024, focused on primary mitochondrial myopathies (PMM). The workshop aimed to update diagnostic criteria, outcome measures, and explore new digital health technologies (DHTs) in the context of clinical trial design and conduct for PMM. Key points discussed included: (i) PMM definition and phenotypes; PMM are genetically determined mitochondrial disorders with prominent skeletal muscle involvement with two major phenotypes: mitochondrial myopathy (MiMy) either with or without chronic progressive external ophthalmoplegia (PEO); (ii) diagnostic criteria, with emphasis on the importance of genetic testing and muscle biopsy for accurate diagnosis; (iii) outcome measures: consensus on clinical scales, functional tests, performance measures, and patient-reported outcome measures (PROMs) for both adults and children; (iv) digital health technologies, with exploration of wearable and non-wearable technologies for gait analysis, physical activity monitoring, and other assessments; (v) potential and limitations of biomarkers for PMM diagnosis and monitoring. The workshop concluded with a strong consensus on the updated definition of PMM, its phenotypes, and the recommended outcome measures for clinical studies. Further research is needed to validate digital health technologies and biomarkers for PMM.