Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is an extremely rare genetic condition that begins in childhood.

The disorder affects many areas of the body, especially the brain and nervous system (encephalo-) and muscles (myopathy). MELAS is also characterized by a buildup of lactic acid in the body (lactic acidosis) as well as stroke-like symptoms, such as temporary muscle weakness.

The condition is caused by a change in one of several genes that help create mitochondria, cell structures that convert food into energy.


Symptoms of MELAS vary depending on what area of the body is affected. Symptoms related to the brain, nervous system and muscles may include:

  • Difficulty understanding or thinking
  • Temporary muscle weakness or paralysis (hemiparesis)
  • Seizures
  • Hallucinations
  • Difficulty speaking
  • Changes in behavior

Symptoms related to the buildup of lactic acid in the body may include:

  • Vomiting
  • Abdominal pain
  • Fatigue
  • Muscle weakness
  • Difficulty breathing

The condition is also associated with stroke-like episodes. Symptoms include:

  • Loss of (or abnormal) sensation in an arm, leg or one side of the body
  • Weakness or paralysis of an arm or leg or one side of the body
  • Partial loss of vision or hearing
  • Double vision
  • Dizziness
  • Slurred speech
  • Problems thinking of or saying the right word
  • Inability to recognize parts of the body
  • Imbalance and falling
  • Confusion

Causes and Risk Factors

MELAS is caused by a change in one of several genes that help build mitochondria, cell structures that convert food into energy.

MELAS is usually diagnosed in childhood, between the ages of 2 and 15. Patients diagnosed between 15 and 40 years of age are considered to have delayed onset of the condition. Nearly 75 percent of cases are diagnosed before the age of 20.

Patients who have MELAS in their family, particularly those with a mother who has MELAS, are at an increased risk of developing the condition.

MELAS affects men and women at equal rates.


Diagnosis of MELAS usually begins with a physical exam and a review of the patient's medical history and symptoms. The only way to positively diagnose MELAS is through genetic testing. Clinical tests to help diagnose the condition may include imaging, muscle biopsies, or measuring lactic acid in the muscles.

Imaging tests, such as magnetic resonance imaging (MRI), can help the medical team better understand what is going on inside the body.

A muscle biopsy also may be performed. During a biopsy, the medical team will use a needle to remove a small amount of tissue that they will then study under a microscope. If the patient has MELAS, the biopsy tissue will show ragged red fibers.


There is no cure for MELAS. Treatment for the condition varies and focuses on managing the symptoms of the condition.

Anticonvulsant medications are often used to prevent seizures that can occur with MELAS. For patients who have experienced hearing loss, cochlear implants may be used to restore some hearing ability. Some medications, including coenzyme q10 and L-carnitine, can help increase the energy output of mitochondria and slow the progression of the disorder.

Physician-approved exercise, such as moderate activity on a treadmill, can help manage some symptoms of MELAS, including lowering the amount of lactic acid present in the body.

For patients with a hereditary condition, genetic counseling, available through the Cedars-Sinai Medical Genetics Institute, can help identify families at risk and provide referrals to specialized health care providers.

© 2000-2022 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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