Natural History Study of Mitochondrial Myopathy

Muscle Strength of MM-COAST

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

Balance of the MM-COAST

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 of the MM-COAST

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

Mitochondrial Disease Burden for Adults

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.

Cerebellar Ataxia Outcome Measure for Primary Mitochondrial Disease (PMD)

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.

Clinical Meaningfulness of Ataxia Quantification.

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.

Evaluation of Health-Related Quality of Life by PedsQL

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.

Evaluation of daily functional activities by PEDI-CAT

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.