Inclusion Criteria:  Have an active account on the Champ Foundation Registry (CFR) or be willing to create an account on the CFR. Must have a genetic diagnosis of a single large-scale mitochondrial DNA deletion and must upload their genetic report to the CFR. Have a clinical diagnosis or history of Pearson syndrome OR have symptom onset prior to five years of age and a genetic diagnosis of a single large-scale mitochondrial DNA deletion OR in the opinion of the principal investigator the participant is suitable for participating in this study based on clinical presentation.  Participants may be of any age or gender, and originate from any country.