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.

The purpose of this study is to investigate the neurological and biochemical consequences of the m.3243 A>G mutation. Mitochondria are the powerhouses of the cell and are controlled by nuclear genetic material (DNA) and mitochondrial (mt) DNA. Mitochondrial DNA mutations impair mitochondrial function, and cause cellular energy failure. These mutations, when present in high abundance, cause neurological signs and symptoms that are clinically obvious. The investigators hypothesize that these mutations, when present in lesser abundance, will cause measurable alterations in the patient's neuropsychological profile and cerebral energy profile. This study does not involve any experimental or approved therapy. The investigators will evaluate the patient's condition with blood/urine tests, neurological exam, MRI/MRS, questionnaires, motor skills functioning, serum and urine biomarkers, and genetic testing.

Inclusion Criteria:

Known carrier of a the m.3243 A>G mitochondrial mutation, ,or Maternally related to someone who carries the m.3243A>G mitochondrial mutation.

A family member who is not maternally related to someone who carries the m.3243A>G mitochondrial mutation

Exclusion Criteria:

• Younger than 4 years of age
• No confirmed m.3243 A>G mitochondrial DNA mutation in the family.

Carriers of the m.3243A>G mitochondrial DNA point mutation, and their maternal relatives (carrier status documentation not required.). All patients suspected of having an mtDNA point mutation regardless of age, health status, gender, race, or ethnicity will be evaluated. The minimal age of entry into the study will be 4 years or older. We will also evaluate controls (often these are married in relatives).

When applicable, manuscript(s) regarding data will be submitted for publication