The purpose of this new clinical trial is to investigate study drug REN001 in adult patients with Primary Mitochondrial Myopathy. REN001 is currently not approved by the U.S. Food and Drug Administration nor any other regulatory agencies for this disease; it is considered an experimental drug. The study period will last for approximately 9 months and will include at least 4 outpatient visits at CHOP, where participants will be provided the study drug or placebo and monitored for safety. The study also involves blood and urine tests, cardiac tests, physical exercise tests, and other study procedures. For more information: https://www.clinicaltrials.gov/ct2/show/NCT04535609 Participants will be able to receive travel support and reimbursement for related expenses.