A Trial to Evaluate the Safety and Efficacy of Elamipretide in Subjects With Primary Mitochondrial Myopathy Followed by an Open-Label Extension

PART 1:

Inclusion Criteria:

- Willing and able to provide a signed informed consent form prior to participation in
any trial-related procedures

- Agrees to adhere to the trial requirements for the length of the trial, including the
use of the elamipretide delivery system

- Subject is ≥ 16 and ≤ 80 years of age

- Diagnosed with PMM in the opinion of the investigator and confirmed by an Adjudication
Committee

- Woman of childbearing potential must agree to use a highly effective method of birth
control

Exclusion Criteria:

- Subject has myopathic signs and or/symptoms due to a neuropathic process or gait
problem that would interfere with the 6MWT, in the opinion of the Investigator

- Female who are pregnant, planning to become pregnant, or breastfeeding/lactating

- At Screening, the estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73 m^2

- Subject has undergone an in-patient hospitalization within the 30 days prior to the
Baseline Visit or has a planned hospitalization or a surgical procedure during the
trial.

- Subject has clinically significant cardiac disease or prior interventional procedure
and/or respiratory disease (medical history or current clinical findings) within 3
months of the Baseline Visit, in the opinion of the Investigator.

- Subject has QTc elongation (using the correction factor utilized at the clinical site)
defined as a QTc >450 msec in male subjects and >480 msec in female subjects.

- ECG evidence of acute ischemia, atrial fibrillation, or active conduction system
abnormalities with the exception of any of the following:

1. First degree AV-block

2. Second degree AV-block Type 1 (Mobitz Type 1 / Wenckebach type)

3. Right bundle branch block

- Subject has severe vision impairment that, in the opinion of the Investigator, may
interfere with their ability to complete all trial requirements

- Subject has a seizure disorder that, in the opinion of the Investigator, may interfere
with their ability to complete all trial requirements.

- Active malignancy or any other cancer from which the subject has been disease-free for
< 2 years.

- Subject has a solid organ transplant and/or is currently receiving treatment with
therapy for immunosuppression, in the opinion of the Investigator.

- Subject has been previously diagnosed with human immunodeficiency virus (HIV),
hepatitis B, or hepatitis C infection.

- Subject has a history of a systemic eosinophilic illness and/or an eosinophil count
>1,000 cells x10^6/L at the Screening Visit.

- Subject is currently participating or has participated in an interventional clinical
trial (i.e.,investigational product or device, stem cell therapy, gene therapy) within
30 days of the Baseline Visit; or is currently enrolled in a non-interventional
clinical trial (except for SPIMM-300) at the Baseline Visit which, in the opinion of
the Investigator, may be potentially confounding with results of the current trial
(e.g., exercise therapy trial).

- Subject has previously received elamipretide (MTP-131), for any reason.

- Subject has a history of active substance abuse during the year before the Baseline
Visit, in the opinion of the Investigator.

- Subject has any prior or current medical condition that, in the judgment of the
Investigator, would prevent the subject from safely participating in and/or completing
all trial requirements.

PART 2:

Continuation Criteria:

- Subjects must continue to be able and willing to adhere to the trial requirements.

- Subject is appropriate to continue in Part 2 (i.e. subject was compliant in Part 1),
in the opinion of the Investigator.

- Subject has not had a serious adverse event (SAE)/serious adverse device effect (SADE)
attributed to the elamipretide delivery system.

- Subject has not permanently discontinued the elamipretide delivery system.