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Genetic and Rare Diseases Information Center (GARD)

Myoclonic epilepsy with ragged red fibers

Other Names for this Disease
  • Merrf syndrome
  • Myoclonic epilepsy associated with ragged red fibers
  • Fukuhara syndrome
  • Myoencephalopathy ragged-red fiber disease
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Your Question

I have been diagnosed with MERRF and I am looking for information and treatment options for this condition that I can share with my local doctor.

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is Myoclonic Epilepsy with Ragged Red Fibers (MERRF)?

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]
Last updated: 3/16/2016

What are mitochondria?

The mitochondria is thought of as the power plant of every cell in our body (except red blood cells). They are rod-shaped or spherical structures located in our cells, and their job is to produce energy for the cell. The mitochondria have their own DNA, separate from the main DNA found in the nucleus of the cell.

If the mitochondria is not working well,  less and less energy is generated within the cell. Cell injury and even cell death can follow. If this process is repeated throughout the body, whole systems begin to fail, and the life of the person in whom this is happening is severely compromised. The onset of mitochondrial diseases is usually during childhood, but symptoms can develop in adulthood.. Diseases of the mitochondria appear to cause the most damage to cells of the brain, heart, liver, skeletal muscles, kidney and the endocrine and respiratory systems. Depending on which cells are affected, symptoms may include loss of motor control, muscle weakness and pain, gastro-intestinal disorders and swallowing difficulties, poor growth, cardiac disease, liver disease, diabetes, respiratory complications, seizures, visual/hearing problems, lactic acidosis, developmental delays and susceptibility to infection.[3]

Last updated: 6/17/2008

What are the symptoms of myoclonic epilepsy association with ragged red fibers (MERRF)?

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. [4]

However, the exact symptoms aren't the same for everyone, because a person with mitochondrial disease can have a unique mixture of healthy and non-working mitochondria, with a unique distribution in the body.

Despite their many potential effects, mitochondrial diseases sometimes cause little disability. Sometimes, a person has enough healthy mitochondria to compensate for the defective ones.[5]

Last updated: 6/17/2008

How is myoclonic epilepsy association with ragged red fibers treated?  What are some resources that I can share with my local doctor to help manage my medical care?

As with all mitochondrial disorders, there is no cure for MERRF.  The seizure disorder can be treated with conventional anticonvulsant therapy.  The myoclonus improved in some individuals treated with levetiracetam. Click here to view an article about levetiracetam.  Physical therapy is helpful for any impaired motor abilities.  Aerobic exercise is helpful in MERRF and other mitochondrial diseases.  Standard pharmacologic therapy is used to treat cardiac symptoms. 

Coenzyme Q10 (100 mg three times a day) and L-carnitine (1000 mg three times a day) and various vitamins, often in a “cocktail” combination  are often used in hopes of improving mitochondrial function.  You can read more information about treatment for mitochondrial diseases in general on the United Mitochondrial Diseases Foundation Web site at:

The prognosis for MERRF varies widely depending on age of onset, type and severity of symptoms, organs involved, and other factors.

The resources listed below may be helpful to your doctor as he/she manages your medical care:

  • GeneReviews has a condition summary written for health professionals at:
  • United Mitochondrial Disease Foundation  provides information to assist health care providers care for individuals with mitochondrial diseases at:
  • You can find relevant journal articles on MERRF disease through a service called PubMed, a searchable database of medical literature. Information on finding an article and its title, authors, and publishing details is listed here. To obtain the full article, contact a medical/university library (or your local library for interlibrary loan), or order it online using the following link. Using “"MERRF Syndrome"[Mesh]" as your search term should locate articles of interest. To give you an idea of the type of information you can find, click here to find a sample search.

    The National Library of Medicine (NLM) Web site has a page for locating  libraries in your area that can provide direct access to journals (print or online) or where you can get articles through interlibrary loan and Loansome Doc (an NLM document-ordering service). You can access this page at the following link:
Last updated: 1/9/2009

Is myoclonic epilepsy associated with ragged red fibers genetic? If so, how is it inherited?

MERRF is caused by mutations in the mitochondrial DNA and is transmitted by maternal inheritance. It is called maternal inheritance because a child inherits the great majority of their mitochondria from their mother through the egg.   The Centre for Genetics Education provides a detail description of maternal inheritance. 

The mother of an individual with MERRF usually has a mitochondrial mutation and may or may not have symptoms.  Or, an individual with MERRF may have a mitochondrial mutation that just occurred in them, called a de novo mutation. 

If the mother has the mitochondrial mutation, all of her children will inherit the mutation and may or may not have symptoms.  All of her daughters children will also inherit the mitochondrial mutation.  Her son's children are not at risk of inheriting the mutation.[1]
Last updated: 6/17/2008

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:
Last updated: 6/5/2014

Other Names for this Disease
  • Merrf syndrome
  • Myoclonic epilepsy associated with ragged red fibers
  • Fukuhara syndrome
  • Myoencephalopathy ragged-red fiber disease
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.