What is the definition of Myoclonic Epilepsy Associated With Ragged Red Fibers?
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. The diagnosis is based on clinical features and a muscle biopsy finding of ragged red fibers (RRF). 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. 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.
What are the alternative names for Myoclonic Epilepsy Associated With Ragged Red Fibers?
- Merrf syndrome
- Myoclonic epilepsy associated with ragged red fibers
- Fukuhara syndrome
- Myoencephalopathy ragged-red fiber disease
What are the causes for Myoclonic Epilepsy Associated With Ragged Red Fibers?
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.
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.
What are the symptoms for Myoclonic Epilepsy Associated With Ragged Red Fibers?
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.
What are the current treatments for Myoclonic Epilepsy Associated With Ragged Red Fibers?
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.
Is Myoclonic Epilepsy Associated With Ragged Red Fibers an inherited disorder?
Myoclonic epilepsy with ragged red fibers (MERRF) has mitochondrial or maternal inheritance. It is called maternal inheritance because mitochondrial DNA are inherited from maternally inherited egg cells, but not from paternally inherited sperm cells. If a mother has a mutation in her mitochondrial DNA, all of her children will inherit the mutation and may or may not have symptoms. All of her daughter's children will also inherit the mitochondrial mutation. Her son's children are not at risk of inheriting the mutation.
The mother of an individual with MERRF usually has a mitochondrial mutation and may or may not have apparent symptoms. Rarely, an individual with MERRF may have a mitochondrial mutation that just occurred in them, called a de novo mitochondrial DNA mutation.