Open-Label Extension Trial to Characterize the Long-term Safety and Tolerability of Elamipretide in Subjects With Genetically Confirmed Primary Mitochondrial Myopathy (PMM)

Distance Walked on Six Minute Walk Test

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

Change From Baseline in Distance Walked (meters) on the Six-Minute Walk Test by Visit

EuroQol 5 Dimensions 5 Levels (EQ-5D-5L)

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

EuroQol 5 dimensions 5 levels (EQ-5D-5L) by visit. Count of participants per arm, or severity level of dimension. Measures 5 dimensions: mobility, self-care, usual activities, pain/discomfort, anxiety/depression. Each dimension has 5 levels: no problems, slight problems, moderate problems, severe problems and extreme problems. Score ranges from 5-25 with lower score=better outcome, and higher score means a worse outcome.

Euroquol Visual Analog Scale

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

Euroquol Visual Analog Scale (EQ VAS): A patient-reported measure. The visual scale is numbered from 0 to 100, participants are directed as follows: "100 means the best health you can imagine, 0 means the worst health you can imagine. Mark an X on the scale to indicate how your health is TODAY." Higher scores mean better outcome, lower scores mean worse outcome.

NeuroQOL Fatigue Questionnaire

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

Change from baseline in NeuroQOL Fatigue Questionnaire by visit. Questionnaire is comprised of 8 questions measuring participants incidence of fatigue affecting activities of daily living. Participants respond by choosing one of the following: 1=never, 2=rarely, 3=sometimes, 4=often, 5=always, with a lower score meaning a better outcome with fatigue affecting participant less, and high score meaning a worse outcome, with fatigue affecting the participant more. Total raw scores range from 8-40. Scores were converted to percentages: range0-100%. Change from baseline score: negative number means improved from baseline, positive number means worsened compared to baseline.

Patient Global Assessment : Categorical

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

Patient Global Assessment \[PGA\] Score by Visit, count of participants. Patient-reported current health status by visit. PGA Scale is as follows: 1=Excellent, 2=Very good, 3=Good, 4=Fair, and 5=Poor. Total score ranges from 1-5. Higher score means worse health status, means worse outcome.

Patient Global Assessment: Continuous Variable

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

Patient Global Assessment \[PGA\] Score by Visit, Patient-reported current health status by visit. PGA Scale is as follows: 1=Excellent, 2=Very good, 3=Good, 4=Fair, and 5=Poor. Total score ranges from 1-5. Higher score means worse health status, lower score means worse outcome.

Work Limitations Questionnaire

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

Work Limitations Questionnaire by visit. Comprised of 25 items, in 4 categories, or demands: Mental/Interpersonal, Output Tasks, Physical Tasks, and Time Management, measuring the degree to which employed individuals are experiencing limitations on-the-job due to their health problems, and health-related productivity loss. 1= All of the time (100%), 2= most of the time, 3=some of the time (about 50%), 4=slight bit of time, 5=none of the time (0%), 6=does not apply to my job. (Presenteeism). The WLQ items ask respondents to rate their level of difficulty or ability to perform specific job demands. Scale score range from 0 (limited none of the time=better outcome) to 100 (limited all of the time= worse outcome) and represent the reported amount of time in the prior two weeks respondents were limited on-the-job.

Physician Global Assessment Score (PhGA) by Visit

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

Physician Global Assessment- Mean Score by visit. PGA Scale asks physician to rate participant's current health status as follows: 1=Excellent, 2=Very good, 3=Good, 4=Fair, and 5=Poor. Total score ranges from 1-5. Higher score means lower health status, worse outcome; lower score means better health status, better outcome.

Physician Global Assessment (PhGA): Categorical

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

Physician Global Assessment \[PhGA\] Score by Visit, Physician-reported current health status by visit. PhGA Scale is as follows: 1=Excellent, 2=Very good, 3=Good, 4=Fair, and 5=Poor. Total score ranges from 1-5. Higher score means worse health status, means worse outcome.

PMMSA Individual Items

Time frame · Baseline, Week 13, 26, 52, 104, 156, End of Study (Week 160)

The PMMSA is a patient-reported outcome measure, assessing a participant's "worst feeling" of 10 symptoms during the last 24 hours: tiredness at rest, tiredness during activities, muscle weakness at rest, muscle weakness during activities, balance, vision, abdominal discomfort, muscle pain, numbness, and headache using a 4-point scale: 1=Not at all, 2=Mild, 3=Moderate, and 4=Severe. Max Score =40= worse outcome, Min score= 10= better outcome on scale. PMMSA Individual Items shows number or participants with mild, moderate, severe or no symptoms at all.

Total Fatigue Score_Primary Mitochondrial Myopathy Symptom Assessment (PMMSA)

Time frame · Baseline, Month 3, Month 6 and Every 26 weeks for up to 160 weeks

Change from baseline in the Total Fatigue score Primary Mitochondrial Myopathy Symptom Assessment (PMMSA) where participants report their "worst feeling" of 4 symptoms: Tiredness at rest, Tiredness during activities, Muscle weakness at rest, Muscle weakness during activities, at the end of each treatment period. Total fatigue score is sum of Q1 to Q4 only of PMMSA) and is scored as follows: 1=Not at all, 2=Mild, 3=Moderate, and 4=Severe. Total score range is 4-16; lower score means less fatigue and better outcome, higher score means more fatigue and worse outcome. Raw scores were transformed into percentages: 0-100%. Change from baseline: the lower the score, the better the outcome,=less fatigue; the higher the score, means worse outcome= more fatigue.