Statistics.

Descriptive statistics were computed for each subgroup including means and measures of variability. Values for Mt/N, ΔmtDNA⁴⁹⁷⁷, and myocardial MRI T2* were log transformed prior to analysis, since the measures had a skewed distribution. Means were compared using the 2-tailed Student’s t test or ANOVA models. Linear regression analyses and Pearson correlations were calculated to determine the association between mtDNA assay results and clinical variables. P < 0.05 was considered statistically significant. Analyses were performed using Prism 6.0a (GraphPad Software).