Natural History Study of Mitochondrial Myopathy

Muscle strength will be measured longitudinally by handheld dynamometry strength assessments to confirm muscle weakness in proximal and distal muscle groups.

Balance will be measured by: (1) Standing tandem with eyes closed, (2) Standing tandem with eyes open, and (3) Single leg stand with eyes closed tests.

Dexterity will be measured by 9 Hole Peg Test (9HPT) and Functional Dexterity Test (FDT).

All subjects will complete the 'gold standard' Newcastle Scale of disease burden.

Newcastle Adult Scale (NMDAS): Each question in the NMDAS has a possible score from 0-5. Each of the first 3 section scores are calculated by simply summing the scores obtained for each question in that section. The higher the score the more severe the disease. The quality of life section has separate scoring.

All subjects and their parents will complete the 'gold standard' Newcastle Scale of disease burden.

Newcastle Pediatric Scale (NPMDS): NPMDS is scored by section and the final (total) score is the sum of all section scores. The section scores vary by age group (0-24 months, 2-11 years, and 12-18 years). Maximum possible total NPMDS scores are 95 for subjects under 24 months of age and 107 for those between two and 18 years of age. Higher scores indicate worse conditions.

All subjects and their parents will complete the Karnofsky-Lansky score to assess functional abilities at each visit.

Karnofsky Lansky Scale: 0-100. 0-40: Unable to care for self, requires equivalent of institutional or hospital care; disease may be progressing rapidly. 50-70: Unable to work; able to live at home and care for most personal needs; varying amount of assistance needed. 80-100: Able to carry on normal activity and to work; no special care needed.

The MMFS (In Person and Telemedicine Versions) will be used to quantify motor performance in NUBPL-disease in abilities to complete functional tasks such as standing, walking and gait. MMFS data will be correlated using Pearson correlation coefficient to Newcastle and Karnofsky scores, and objective measures to assess for clinical meaning.

MMFS Scale: 3: Able (fully meets criteria); 2: Moderately Able (partially meets, some compensation needed); 1: Minimally Able (significant compensation needed); 0: Unable

MMFS Totals: In-person Version: Total score: */ 66 (max score), Telemedicine Version: Total score: */54 (max score)

Patients will be marked as either "alive" or "deceased" at the time of a given visit date.

Patients will have their vitals recorded at the date of visit to obtain BMI (Kg/m^2)) measurement, Height (m) and weight (kg) are required to calculate BMI.

Patients will have other illnesses not related to their mitochondrial disease recorded along with date of diagnosis and stability.

Patients will have prior hospitalizations counted and recorded. Any hospitalizations occurring within a year from the visit date will have specific information recorded including the dates of admission and discharge, and the reasons for admission and discharge.

Patients will have their ambulatory status assessed by recording whether or not they can take 5 steps on their own. Patients' use of different kinds of wheelchairs will be recorded (manual, power assist, or power wheelchair or scooter) along with whether they are able to ambulate in the community or only in the household.

As part of a patient's cardiopulmonary exercise test (CPET), pacemaker status will be assessed, and if a patient utilizes a pacemaker, it's make, model, and settings will be recorded.

As part of a patient's respiratory history, ventilatory support status will be assessed by recording whether a patient uses the any of the following respiratory equipment: cough assist device, non-invasive ventilation including continuous positive airway pressure (CPAP) and Bi-pap, chest percussion, suctioning devices, other ventilation devices.

As part of a patient's nutritional assessment, a patient's gastrostomy status will be assessed by determining whether a patient utilizes a gastrostomy tube (or g-tube), when they had their g-tube placed and why, and whether it resulted in weight gain.

In-depth qualitative interviews to assess their perspective of meaningful change of individual domain assessments of the MM-COAST and MM-Function Scale.

Preliminary MM-IMPACT PROM, a multi-item scale which currently consists of 45 questions

Investigators will utilize a similar approach to development of the MM-COAST and MMFS and systematically collate and administer existing ataxia scales, focusing on quantitation of cerebellar ataxia, dysarthria and tremor, and introduce modifications to ensure PMD-specificity of this outcome measure. Once developed, investigators will administer the devised ataxia scale to the NUBPL subjects at every clinic visit, where the time to completion and modifications needed are assessed. Further iterations of the ataxia scale will be re-assessed in the NUBPL-subjects at every clinic visit and compared to the performance of the scale in PMD patients with other genetic etiologies. Participants will be instructed to refrain from strenuous exercise 24 hours prior to each visit. Feasibility and testing reproducibility of the PMD-ataxia scale will be evaluated at 2 different time points. The ataxia scale will be developed in months 0-6 and administered in months 6-12 of the 1-year project period.

All subjects will complete the following patient/parent-reported surveys: Newcastle Adult Scale (NMDAS) has 3 section scores that are calculated by summing the scores of each question (0-5). The Newcastle Quality of Life (Section IV) has separate scoring. Newcastle Pediatric Scale (NPMDS) is scored by section(scores vary by age group) and the final (total) score is the sum of all section scores. The maximum possible total NPMDS scores are 95 for subjects under 24 months of age and 107 for those 2-18 years of age. In both, higher scores indicate worse conditions. Karnofsky Lansky Scale is scaled 0-100. 0-40: unable to care for self, 50-70: unable to work; able to live at home, care for most personal needs, 80-100: Able to carry on normal activity and work; no special care needed.

To assess if the quantified ataxia scores will be clinically meaningful: correlation to the 'gold standard' Newcastle Scale of disease severity and MM-COAST objective assessments in Aim 1 will be assessed.

PedsQL is a 23-item questionnaire that evaluates health-related quality of life that is reported as a total score and 3 summary scores that include Physical Health, Psychosocial Health and School/Work with a higher score indicating better quality of life.

The range for the scores are 0-100.

The Pediatric Evaluation of Disability Inventory Computer Adaptive Test (PEDI-CAT) is a test that evaluates daily functional activities. A t-score of 50 represents the function of the general population (SD of 10). A t-score below 30 reflects poor performance compared to the general population.

The range for the scores are 20-80.