Risk factors

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

• Asian heritage. 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. 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 — a factor that 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.