Primary Mitochondrial Disease

The goal of this observational study is to develop and validate tools to measure disease course in patients with primary mitochondrial myopathy (PMM). The main aims of this study are: * Development, validation, and optimization of objective outcome measures for mitochondrial myopathy * Defining the natural history of mitochondrial myopathy Researchers will compare data from patients with primary mitochondrial myopathy to healthy controls. Data from healthy controls will also help define normative data for future studies. Participants will perform clinical exams of muscle strength and endurance and will complete surveys.

The primary objective of the FALCON study is to evaluate the efficacy of KL1333 on selected disease manifestations of primary mitochondrial disease (PMD) following 48 weeks of treatment. This objective involves evaluating the efficacy of KL1333 versus placebo on fatigue symptoms and impacts on daily living as well as on functional lower extremity strength and endurance. Additionally, the study evaluates the safety and tolerability of KL1333.

Primary Mitochondrial Disease (PMD) is a genetic neurometabolic disorder, leading to central nervous system degeneration and increased risk of early mortality. There is a strong link between the pathophysiology of mitochondrial disease and biomarkers related to the biochemistry of redox imbalance, involving the levels of glutathione. Investigators will use Magnetic Resonance Imaging and Spectroscopy to non-invasively measure glutathione and other chemicals in the brain to identify redox imbalance in patients with PMD.