Moyamoya disease may occur at any age, though symptoms most commonly occur between 5 and 10 years of age in children and between 30 and 50 years of age in adults.

The first symptom of moyamoya disease is usually stroke or recurrent transient ischemic attacks (TIAs), especially in children. Adults may also experience these symptoms but more often experience bleeding in the brain (hemorrhagic stroke) from abnormal brain vessels.

Accompanying signs and 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, typically on one side of your body
• Visual disturbances
• Difficulties with speaking or understanding others (aphasia)
• Developmental delays
• Involuntary movements
• Cognitive decline

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

The exact cause of moyamoya disease is unknown. Moyamoya disease is more common in Japan, Korea and China, but it also occurs in other parts of the world.

Researchers believe the higher concentration of moyamoya disease in these Asian countries strongly suggests the disease may have genetic causes.

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

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

• Being of Asian descent. Moyamoya disease is found all over the world, but it's more common in East Asian countries, especially Korea, Japan and China. This may possibly be due to certain genetic factors in those populations. Higher rates of moyamoya disease have been documented among Asians living in western countries.
• Having a 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 the general population — a factor that strongly suggests a genetic component to the disease and may justify screening of family members.
• Having a certain medical condition. Moyamoya disease sometimes occurs in association with another disorder, including neurofibromatosis type 1, sickle cell anemia and Down syndrome, among 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 stroke, such as:

• Vision problems. As a result of stroke, some people with moyamoya disease experience visual disturbances.
• Weakness (hemiparesis).
• Language disturbance (aphasia).
• Movement disorders. Though rare, some people with moyamoya disease experience involuntary movement of certain muscles.
• Learning or developmental issues. Following a stroke, a child may have problems with mental processing, which can affect schoolwork as well as cause emotional difficulties and low self-esteem. Adults may experience memory decline as well as challenges with other areas of cognitive function.
• Seizures.