CrCest Study in Primary Mitochondrial Disease

Inclusion Criteria (Mitochondrial Disease Patients): * Males and females, between the ages of 7 and 75, inclusive * Suspected (based on clinical presentation) or definite genetic mitochondrial disease diagnosis (i.e., genetic mutations in the constituents of the mitochondrial respiratory chain and/or genetic mutations that are likely to affect mitochondrial function) * Clinically eligible for an MRI of the lower leg. We are conducting clinical leg MRI scans of patients with definite mitochondrial disease for indications that include muscle weakness and muscle fatigue. * Able to perform sub-maximal ankle dorsiflexion leg exercise during the MRI study Inclusion Criteria (Healthy Controls): * Males and females, between the ages of 7 and 75 years, inclusive * Able to perform sub-maximal ankle dorsiflexion leg exercise during the MRI study Inclusion Criteria (Evaluable Healthy Controls and Cases for Data Analysis): * To note, we will merge coded datasets from Institutional Review Board (IRB) #15-012445, IRB #16-013364, and IRB #08-006177 with data from this study as part of our data analysis plan. * Complete and evaluable healthy control and cases from IRB #15-012445, IRB #16-013364, and IRB #08-006177 Exclusion Criteria (Mitochondrial Disease Patients and Healthy Controls): * In the investigator's opinion, inability to fully comply with research procedures * Active alcohol and/or substance abuse, including tobacco-use * A pacemaker; any metal-based medical or non-medical d…