Moyamoya disease is a rare blood vessel disorder in which the carotid artery in the skull becomes blocked or narrowed. The carotid artery is a major artery that brings blood to the brain. When it's blocked, blood flow to the brain is reduced. Tiny blood vessels then develop at the base of the brain in an attempt to supply the brain with blood.

The condition may cause a ministroke, known as a transient ischemic attack, or a stroke. It also can cause bleeding in the brain. Moyamoya disease can affect how well the brain functions and can cause cognitive and developmental delays or disability.

Moyamoya disease most commonly affects children. However, adults may have the condition as well. Moyamoya disease is found all over the world. But it's more common in East Asian countries, especially Korea, Japan and China. This may be due to certain genetic factors in those populations.

Moyamoya symptoms

Moyamoya disease may occur at any age. But symptoms are most common in children between ages 5 and 10 and in adults between ages 30 and 50. Spotting symptoms early is very important to prevent complications such as a stroke.

Moyamoya disease causes different symptoms in adults and children. In children, the first symptom is usually a stroke or recurrent transient ischemic attack (TIA). Adults may experience these symptoms, as well. But adults also may experience bleeding in the brain, known as a hemorrhagic stroke. The bleeding occurs because of the way blood vessels in the brain formed.

Symptoms of moyamoya disease related to reduced blood flow to the brain include:

  • Headache.
  • Seizures.
  • Weakness, numbness or paralysis in your face, arm or leg. This is typically on one side of your body.
  • Vision problems.
  • Trouble speaking or understanding others, known as aphasia.
  • Cognitive or developmental delays.
  • Involuntary movements.

These symptoms can be triggered by exercise, crying, coughing, straining or a fever.

When to see a doctor

Seek immediate medical attention if you notice any symptoms of a stroke or ministroke, even if they seem to come and go or disappear.

Think "FAST" and do the following:

  • Face. Ask the person to smile. Does one side of the face droop?
  • Arms. Ask the person to raise both arms. Does one arm drift downward? Or is one arm unable to rise up?
  • Speech. Ask the person to repeat a simple phrase. Is the person's speech slurred or strange?
  • Time. If you observe any of these signs, call 911 or emergency medical help immediately.

Call 911 or your local emergency number right away. Don't wait to see if symptoms go away. Every minute counts. The longer a stroke goes untreated, the greater the potential for brain damage and disability.

If you're with someone you suspect is having a stroke, watch the person carefully while waiting for emergency assistance.

See your health care provider if you have any of the symptoms of moyamoya disease. Early detection and treatment can help prevent a stroke and serious complications.

Moyamoya causes

The exact cause of moyamoya disease is unknown. Moyamoya disease is most commonly seen in Japan, Korea and China. But it also occurs in other parts of the world. Researchers believe the greater prevalence in these Asian countries strongly suggests a genetic factor in some populations.

Sometimes changes to the blood vessels, known as vascular changes, can occur that mimic moyamoya disease. These changes may have different causes and symptoms. This is known as moyamoya syndrome.

Moyamoya syndrome is also associated with certain conditions, such as Down syndrome, sickle cell anemia, neurofibromatosis type 1 and hyperthyroidism.

Risk factors

Though the cause of moyamoya disease is unknown, certain factors may increase your risk of having the condition. They include:

  • Asian heritage. Although moyamoya disease is found all over the world, it's more common in East Asian countries, especially Korea, Japan and China. This may be due to certain genetic factors in those populations. This same higher prevalence has been documented among Asians living in Western countries.
  • Family history of moyamoya disease. If you have a family member with moyamoya disease, your risk of having the condition is 30 to 40 times higher than that of the general population. This strongly suggests a genetic component.
  • Medical conditions. Moyamoya syndrome sometimes occurs in association with other disorders, including neurofibromatosis type 1, sickle cell disease and Down syndrome, among many others.
  • Being female. Females have a slightly higher incidence of moyamoya disease.
  • Being young. Though adults can have moyamoya disease, children younger than 15 years old are most commonly affected.


Most complications from moyamoya disease are associated with the effects of strokes. They include seizures, paralysis and vision problems. Other complications include speech problems, movement disorders and developmental delays. Moyamoya disease can cause serious and permanent damage to the brain.

Moyamoya disease care at Mayo Clinic

April 18, 2023
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