Myoclonus, epilepsy, progressive ataxia, muscle weakness, deafness, and dementia
Cause: Mitochondrial DNA point mutations: A8344G, T8356C
MERRF is a progressive multi-system syndrome presenting in childhood or in adulthood. The rate of progression varies widely. Onset and extent of symptoms can differ among affected siblings.
The classic features of MERRF include:
- Myoclonus (brief, sudden, muscle jerks) the most characteristic symptom
- Epileptic seizures
- Ataxia (impaired coordination)
- Ragged-red fibers (a characteristic microscopic abnormality observed in muscle biopsy of patients with MERRF and other mitochondrial disorders) Additional manifestations may include: hearing loss, short stature, exercise intolerance, dementia, multiple lipomas (fat tumors under the skin), cardiac defects, eye abnormalities, and speech impairment.
- Most cases of MERRF are maternally inherited due to mtDNA mutations. The most common MERRF mutation is A8344G, which accounted for over 80% of the cases (GeneReview article). Four other mitochondrial DNA mutations have been reported to cause MERRF.
As with all mitochondrial disorders, there is no cure for MERRF. Therapies may include coenzyme Q10, L-carnitine, and various vitamins, often in a cocktail combination. Management of seizures usually requires anticonvulsant drugs.
The prognosis for MERRF varies widely depending on age of onset, type and severity of symptoms, organs involved, and other factors.