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Purpose: Mitochondrial disease is the most common neuromuscular disease and has a profound impact upon daily life, disease and longevity. Exercise therapy has been shown to improve mitochondrial function in patients with mitochondrial disease. However, no information exists about the level of habitual physical activity of people with mitochondrial disease and its relationship with clinical phenotype., Methods: Habitual physical activity, genotype and clinical presentations were assessed in 100 patients with mitochondrial disease. Comparisons were made with a control group individually matched by age, gender and BMI., Results: Patients with mitochondrial disease had significantly lower levels of physical activity in comparison to matched people without mitochondrial disease (steps/day; 6883±3944 vs. 9924±4088, p = 0.001). 78% of the mitochondrial disease cohort did not achieve 10,000 steps per day and 48% were classified as overweight or obese. Mitochondrial disease was associated with less breaks in sedentary activity (Sedentary to Active Transitions, % per day; 13±0.03 vs. 14±0.03, p = 0.001) and an increase in sedentary bout duration (bout lengths/fraction of total sedentary time; 0.206±0.044 vs. 0.187±0.026, p = 0.001). After adjusting for covariates, higher physical activity was moderately associated with lower clinical disease burden (steps/day; r(s) = -0.49; 95% CI -0.33, -0.63, P<0.01). There were no systematic differences in physical activity between different genotypes mitochondrial disease., Conclusions: These results demonstrate for the first time that low levels of physical activity are prominent in mitochondrial disease. Combined with a high prevalence of obesity, physical activity may constitute a significant and potentially modifiable risk factor in mitochondrial disease.

Purpose: Single large-scale mitochondrial DNA deletions account for a quarter of mitochondrial disease cases and occur sporadically with unknown risk factors. Mitochondrial DNA deletions accumulate with age in many tissues. Primordial germ cells, the precursors of oocytes are made by our grandmothers, therefore we wanted to determine whether age of maternal grandmother is a risk factor for sporadic mitochondrial DNA deletions., Methods: Twenty-nine patients with sporadic single mitochondrial DNA deletions from the Newcastle UK cohort provided dates of birth for mothers and maternal grandmothers plus father and paternal grandmother (healthy controls)., Results: Mean age for grandmothers at birth of a mother of an affected patient was 28.5 years (SD +/- 6.9) for single mitochondrial DNA deletions maternal grandmothers and 28.2 years (SD +/- 6.1) for healthy control paternal grandmothers., Conclusion: Maternal grandmother age is not a risk factor for sporadic mitochondrial DNA deletions, an important observation in a population where many women are delaying reproduction.