RePOWER: An International, Prospective, Non-Interventional Registry of Patients With Primary Mitochondrial Myopathy.

Primary mitochondrial myopathies (PMMs), a group of genetic mitochondrial oxidative phosphorylation disorders, primarily affect skeletal muscle function. No approved treatments for PMM exist, and patient information is limited. The international RePOWER registry (NCT03048617) assessed genotypic and phenotypic relationships in PMM and identified patients for MMPOWER-3 (elamipretide Phase 3 study). RePOWER enrolled screened and ambulatory patients aged 16-80 years. With signs and/or symptoms of PMM (N = 376; 60.4% female; mean [SD] age 42.6 [14.4] years; ~75% with an mtDNA variant and ~25% with an nDNA variant). Baseline information, current symptoms, qualityoflife, and functional assessments (6-Minute Walk Test [6MWT], Triple-Timed Up-and-Go [3TUG] Test, and 5-Times Sit-to-Stand Test [5XSST]) were captured. Accredited laboratory and genetic testing methods were available to most patients. The majority of enrolled PMM patients presented with progressive external ophthalmoplegia and fatigue. US patients were observed to use more medical interventions. Compared to non-US patients, US patients did not perform as well on the 6MWT (mean 364.6 vs. 375.2 m) and 5XSST (mean 21.6 vs. 18.6 s); US patients performed better on the 3TUG test (mean 40.2 vs. 45.0 s). The RePOWER registry provided data on patients with genetically confirmed PMM, thereby improving our understanding of PMM diagnosis and treatment and the differences in global mitochondrial clinical practice.