This is an observational study of patients with Primary Mitochondrial Disease with either signs or symptoms suggestive of myopathy. The Investigator will identify potential patients through existing medical records and one on-site visit.

An observational study of patients with presumed Primary Mitochondrial Disease designed to better characterize and correlate symptoms and signs of myopathy and genetic test results and the use of commonly prescribed treatments. The study will help define and identify a subject population for a future trial of an investigational product to treat primary mitochondrial disease associated with signs and symptoms of myopathy.

Inclusion Criteria:

• Willing and able to provide a signed informed consent form (ICF) prior to participation in any-trial related procedures
• Patient has clinical presentation of PMD with either signs or symptoms suggestive of myopathy
• Patient is ambulatory and able to attempt 6MWT

Exclusion Criteria:

• Patient has symptoms of PMD due to secondary mitochondrial dysfunction
• Patient has had prior exposure to elamipretide
• Patient does not have the cognitive capacity to understand and complete all study assessments
• Patient has a medical history of severe renal impairment
• History of active alcoholism or drug addiction during the year before enrollment

Patients with clinical presentation of PMD with either signs or symptoms suggestive of myopathy