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Disease Profile

Myoclonic epilepsy with ragged red fibers

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Merrf syndrome; MERRF; Myoclonic epilepsy associated with ragged red fibers;


Congenital and Genetic Diseases; Eye diseases; Heart Diseases;


Myoclonic epilepsy with ragged red fibers (MERRF) is a multisystem disorder characterized by myoclonus, which is often the first symptom, followed by generalized epilepsy, ataxia, weakness, and dementia. Symptoms usually first appear in childhood or adolescence after normal early development. The features of MERRF vary widely from individual to individual, even within families. Other common findings include hearing loss, short stature, optic atrophy, and cardiomyopathy with Wolff-Parkinson-White (WPW) syndrome.[1][2] The diagnosis is based on clinical features and a muscle biopsy finding of ragged red fibers (RRF).[1] In over 80% of cases, MERRF is caused by mutations in the mitochondrial gene called MT-TK. Several other mitochondrial genes have also been reported to cause MERRF, but many of the individuals with mutations in these other genes have additional signs and symptoms.[2] Seizures associated with MERRF are generally treated with conventional anticonvulsant therapy. Coenzyme Q10 and L-carnitine are often used with the hope of improving mitochondrial function.[1]


Because muscle cells and nerve cells have especially high energy needs, muscular and neurological problems are common features of diseases that affect the mitochondria. MERRF is a progressive multi-system syndrome with symptoms that begin during childhood, but onset may occur in adulthood. The rate of progression varies widely. Onset and extent of symptoms can differ widely from individual to individual and among affected siblings.

The classic features of MERRF include:

  • Myoclonus (brief, sudden, twitching muscle spasms) – 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 symptoms may include: hearing loss, lactic acidosis (elevated lactic acid level in the blood), short stature, exercise intolerance, dementia, cardiac defects, eye abnormalities, and speech impairment.[1][2]


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Abnormality of movement
Movement disorder
Unusual movement

[ more ]

EMG abnormality
Generalized myoclonic seizure
Muscle tissue disease
Ragged-red muscle fibers
Sensorineural hearing impairment
30%-79% of people have these symptoms
Cognitive impairment
Abnormality of cognition
Cognitive abnormality
Cognitive defects
Cognitive deficits
Intellectual impairment
Mental impairment

[ more ]

Multiple lipomas
Multiple fatty lumps
Optic atrophy
Short stature
Decreased body height
Small stature

[ more ]

Percent of people who have these symptoms is not available through HPO
Increased serum lactate
Increased serum pyruvate
Mitochondrial inheritance
Muscle weakness
Muscular weakness
Involuntary muscle stiffness, contraction, or spasm


Myoclonic epilepsy with ragged red fibers (MERRF) is caused by mutations in the mitochondrial DNA. Mitochondria are structures present in every cell in our body that produce usable energy from food. Although most of our DNA is located within the nucleus of our cells, mitochondria have a small amount of their own DNA known as mitochondrial or mtDNA. MtDNA contains 37 genes.[3]

Mutations in the MT-TK gene are the most common cause of MERRF. Other genes that might be involved include but are not limited to: MT-TL1, MT-TH, and MT-TS1. Mutations within these genes reduce the ability of the mitochondria to maintain its normal function including building proteins, using oxygen, and producing energy. Organs and tissues with high energy requirements, such as the brain and muscles, are most impacted by these mutations.[2]


Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.


    While there is no cure for MERRF, there are various medications and therapies that can be helpful in managing symptoms. This includes: Antiseizure medications, levetiracetam for myoclonus, physical therapy, and aerobic exercise. Standard medication is used to treat cardiac symptoms.

    Daily use of Coenzyme Q10 and L-carnitine have been of some benefit to individuals. Other supplements that might be utilized include creatinine and lipoic acid.[1]


    Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

    Organizations Supporting this Disease

      Organizations Providing General Support

        Learn more

        These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

        Where to Start

          In-Depth Information

          • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
          • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
          • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
          • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
          • PubMed is a searchable database of medical literature and lists journal articles that discuss Myoclonic epilepsy with ragged red fibers. Click on the link to view a sample search on this topic.


            1. DiMauro, S. and Hirano, M. MERRF. GeneReviews. January 29, 2015; https://www.ncbi.nlm.nih.gov/books/NBK1520/.
            2. Myoclonic epilepsy with ragged-red fibers. Genetics Home Reference (GHR). May 2014; https://ghr.nlm.nih.gov/condition/myoclonic-epilepsy-with-ragged-red-fibers.
            3. mitochondrial DNA. Genetics Home Reference. 2/2016; https://ghr.nlm.nih.gov/mitochondrial-dna.

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