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, vascular changes can occur that mimic moyamoya disease but 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.