Carriers of the m.3242A>G mutation often have clinical symptoms which can include migraines, seizures, strokes, hearing loss, balance issues, gastrointestinal issues, and many other symptoms. The investigators would like to learn more about these disorders and have designed a "Natural History Study" to monitor these conditions over time so that physicians and scientists can not only understand the problems that patients have, but work on developing treatments. The focus of the current work is to evaluate known mutation carriers of the m.3243A>G (mitochondrial DNA) and their maternal relatives (carrier status not a requirement for participation). Paternal relatives will serve as controls. This study involves no treatment.