The condition is believed to be hereditary and linked to q25.3, on chromosome 17. Moyamoya can be either congenital or acquired. Patients with Down syndrome, neurofibromatosis, or sickle cell disease can develop moyamoya malformations. It is more common in women than in men, although about a third of those affected are male.^[1] Brain radiation therapy in children with neurofibromatosis increases the risk of its development.