*2.1. Human Myoblasts*

Muscle primary cells from five patients harboring the genetically confirmed m.3243A>G mutation and 5 controls were provided by the Muscle Tissue Culture Collection (MTCC) at the Friedrich-Baur-Institute (Department of Neurology, Ludwig Maximilian University, Munich, Germany; part of the German network on muscular dystrophies, MD-NET, partner of EuroBioBank) [14].

Cells were collected and processed by MTCC in compliance with all applicable laws, rules, regulations, and other requirements of any applicable governmental authority. The cells were grown in skeletal muscle cell growth medium (PromoCell, Heidelberg, Germany) supplemented with 10% fetal bovine serum (FBS). Further details are given in Table 1 and as described earlier [12]. As controls served 5 patients (2 males, 3 females), who had muscle biopsy for diagnosis of a suspected neuromuscular disorder. They were deemed 'normal controls' if they were ultimately found to have no muscle disease by combined clinical and histological criteria. Age of controls ranged from 35 to 53 years.


**Table 1.** Sex and age of five patients with genetically confirmed m.3243A>G mutation and five healthy controls as previously described [12], F: female, M: male.
