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Myoclonic epilepsy with ragged-red fibers

What is MERRF?
Myoclonic epilepsy with ragged-red fibers (MERRF) is a disorder that affects many parts of the body, particularly muscles and the nervous system. In most cases, the signs and symptoms of this disorder appear during childhood or adolescence. The features of MERRF vary widely among affected individuals, even among members of the same family.

MERRF is characterized by muscle twitches (myoclonus), weakness (myopathy), and progressive stiffness (spasticity). When the muscle cells of affected individuals are stained and viewed under a microscope, these cells usually appear abnormal. These abnormal muscle cells are called ragged-red fibers. Other features of MERRF include recurrent seizures (epilepsy), difficulty coordinating movements (ataxia), a loss of sensation in the extremities (peripheral neuropathy), and slow deterioration of intellectual function (dementia). People with this condition may also develop hearing loss or optic atrophy, which is the degeneration (atrophy) of the nerve cells that carry visual information from the eyes to the brain. Affected individuals sometimes have short stature and heart abnormalities (cardiomyopathy). Less commonly, people with MERRF develop fatty tumors just under the surface of the skin called lipomas.

How common is MERRF?
MERRF is a rare disorder; its prevalence is unknown.

What are the genetic changes related to MERRF?
Mutations in the MT-TK, MT-TL1, MT-TH, and MT-TS1 genes cause MERRF. These genes are contained in mitochondrial DNA (mtDNA). Mitochondria are structures within cells that use oxygen to convert the energy from food into a form cells can use. Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA. The genes associated with MERRF provide instructions for making molecules called transfer RNAs, which are chemical cousins of DNA. These molecules help assemble protein building blocks called amino acids into full-length, functioning proteins within mitochondria.

Mutations in the MT-TK gene are the most common cause of MERRF, occurring in more than 80 percent of all cases. Less frequently, mutations in the MT-TL1, MT-TH, and MT-TS1 genes have been reported to cause the signs and symptoms of MERRF. Individuals with mutations in these genes often have features of other mitochondrial disorders as well.

Mutations that cause MERRF impair the ability of mitochondria to make proteins, use oxygen, and produce energy. These mutations particularly affect organs and tissues with high energy requirements, such as the brain and muscles. Researchers have not determined how changes in mtDNA lead to the specific signs and symptoms of MERRF. They continue to investigate the effects of mitochondrial gene mutations in various tissues.

How do people inherit MERRF?
MERRF is inherited in a mitochondrial pattern, which is also known as maternal inheritance. This pattern of inheritance applies to genes contained in mtDNA. Because egg cells, but not sperm cells, contribute mitochondria to the developing embryo, only females pass mitochondrial conditions to their children. Mitochondrial disorders can appear in every generation of a family and can affect both males and females, but fathers do not pass mitochondrial traits to their children.

In most cases, people with MERRF inherit an altered mitochondrial gene from their mother, who may or may not show symptoms of the disorder. Less commonly, the disorder results from a new mutation in a mitochondrial gene and occurs in people with no family history of MERRF.

What other names do people use for septo-optic dysplasia?
Fukuhara disease
MERRF syndrome
Myoclonic epilepsy associated with ragged-red fibers
Myoencephalopathy ragged-red fiber disease

Where can I find information about septo-optic dysplasia?
Children's Mitochondiral Disease Network
30 Heber Walk
Chester Way
England, United Kingdom
Mito Help & Information Line: +44(0) 01606 43946

The National Information Centre for Metabolic Diseases
Climb Building
176 Nantwish Road
Crewe CW2 6BG
United Kingdom
0800 652 3181

The Epilepsy Foundation
8301 Professional Place
Landover, MD 20785-7223

United Mitochondrial Disease Foundation
8085 Saltsburg Road, Suite 201
Pittsburgh, PA 15239

14 Pembroke Street
Medford, MA 02155-4827
888-MITOACTION (648-6228)

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional.

This information was developed by the Genetics Home Reference.

Genetics Home Reference. Myoclonic epilepsy with ragged-red fibers. Available at: Accessed April 24, 2023, 2014.

The information in this document is for general educational purposes only. It is not intended to substitute for personalized professional advice. Although the information was obtained from sources believed to be reliable, MedLink LLC, its representatives, and the providers of the information do not guarantee its accuracy and disclaim responsibility for adverse consequences resulting from its use. For further information, consult a physician and the organization referred to herein.

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