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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes

(often shortened to MELAS)
Reviewed December 2013

What is MELAS?

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a condition that affects many of the body's systems, particularly the brain and nervous system (encephalo-) and muscles (myopathy). The signs and symptoms of this disorder most often appear in childhood following a period of normal development, although they can begin at any age. Early symptoms may include muscle weakness and pain, recurrent headaches, loss of appetite, vomiting, and seizures. Most affected individuals experience stroke-like episodes beginning before age 40. These episodes often involve temporary muscle weakness on one side of the body (hemiparesis), altered consciousness, vision abnormalities, seizures, and severe headaches resembling migraines. Repeated stroke-like episodes can progressively damage the brain, leading to vision loss, problems with movement, and a loss of intellectual function (dementia).

Most people with MELAS have a buildup of lactic acid in their bodies, a condition called lactic acidosis. Increased acidity in the blood can lead to vomiting, abdominal pain, extreme tiredness (fatigue), muscle weakness, and difficulty breathing. Less commonly, people with MELAS may experience involuntary muscle spasms (myoclonus), impaired muscle coordination (ataxia), hearing loss, heart and kidney problems, diabetes, and hormonal imbalances.

How common is MELAS?

The exact incidence of MELAS is unknown. It is one of the more common conditions in a group known as mitochondrial diseases. Together, mitochondrial diseases occur in about 1 in 4,000 people.

What are the genetic changes related to MELAS?

MELAS can result from mutations in one of several genes, including MT-ND1, MT-ND5, MT-TH, MT-TL1, and MT-TV. These genes are found in the DNA of cellular structures called mitochondria, which convert the energy from food into a form that cells can use. Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA, known as mitochondrial DNA or mtDNA.

Some of the genes related to MELAS provide instructions for making proteins involved in normal mitochondrial function. These proteins are part of a large enzyme complex in mitochondria that helps convert oxygen, fats, and simple sugars to energy. Other genes associated with this disorder provide instructions for making molecules called transfer RNAs (tRNAs), 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 a particular transfer RNA gene, MT-TL1, cause more than 80 percent of all cases of MELAS. These mutations impair the ability of mitochondria to make proteins, use oxygen, and produce energy. Researchers have not determined how changes in mtDNA lead to the specific signs and symptoms of MELAS. They continue to investigate the effects of mitochondrial gene mutations in different tissues, particularly in the brain.

Related Gene(s)

Changes in these genes are associated with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes.

  • MT-ND1
  • MT-ND5
  • MT-TH
  • MT-TL1
  • MT-TV

How do people inherit MELAS?

This condition 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, children can only inherit disorders resulting from mtDNA mutations from their mother. These disorders can appear in every generation of a family and can affect both males and females, but fathers do not pass traits associated with changes in mtDNA to their children.

In most cases, people with MELAS inherit an altered mitochondrial gene from their mother. Less commonly, the disorder results from a new mutation in a mitochondrial gene and occurs in people with no family history of MELAS.

Where can I find information about diagnosis or management of MELAS?

These resources address the diagnosis or management of MELAS and may include treatment providers.

  • Gene Review: MELAS (
  • Gene Review: Mitochondrial Disorders Overview (
  • Genetic Testing Registry: Juvenile myopathy, encephalopathy, lactic acidosis AND stroke (
  • MedlinePlus Encyclopedia: Lactic acidosis (
  • MedlinePlus Encyclopedia: Stroke (

You might also find information on the diagnosis or management of MELAS in Educational resources and Patient support.

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about MELAS?

You may find the following resources about MELAS helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for MELAS?

  • MELAS syndrome
  • mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes
  • mitochondrial myopathy, lactic acidosis, stroke-like episode
  • myopathy, mitochondrial-encephalopathy-lactic acidosis-stroke

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about MELAS?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding MELAS?

acidity ; acidosis ; acids ; ataxia ; dementia ; diabetes ; DNA ; egg ; embryo ; encephalopathy ; enzyme ; family history ; gene ; hemiparesis ; incidence ; inherit ; inheritance ; inherited ; involuntary ; kidney ; lactic acid ; lactic acidosis ; maternal ; maternal inheritance ; mitochondria ; mutation ; myoclonus ; nervous system ; new mutation ; nucleus ; oxygen ; pattern of inheritance ; protein ; RNA ; sperm ; syndrome ; transfer RNA

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Betts J, Jaros E, Perry RH, Schaefer AM, Taylor RW, Abdel-All Z, Lightowlers RN, Turnbull DM. Molecular neuropathology of MELAS: level of heteroplasmy in individual neurones and evidence of extensive vascular involvement. Neuropathol Appl Neurobiol. 2006 Aug;32(4):359-73. (
  • Gene Review: MELAS (
  • Goodfellow JA, Dani K, Stewart W, Santosh C, McLean J, Mulhern S, Razvi S. Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes: an important cause of stroke in young people. Postgrad Med J. 2012 Jun;88(1040):326-34. doi: 10.1136/postgradmedj-2011-130326. Epub 2012 Feb 10. Review. (
  • Matsumoto J, Saver JL, Brennan KC, Ringman JM. Mitochondrial encephalomyopathy with lactic acidosis and stroke (MELAS). Rev Neurol Dis. 2005 Winter;2(1):30-4. Review. (
  • Sproule DM, Kaufmann P. Mitochondrial encephalopathy, lactic acidosis, and strokelike episodes: basic concepts, clinical phenotype, and therapeutic management of MELAS syndrome. Ann N Y Acad Sci. 2008 Oct;1142:133-58. doi: 10.1196/annals.1444.011. Review. Erratum in: Ann N Y Acad Sci. 2009 Apr;1161:601. (
  • Thambisetty M, Newman NJ. Diagnosis and management of MELAS. Expert Rev Mol Diagn. 2004 Sep;4(5):631-44. Review. (


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. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: December 2013
Published: February 8, 2016