The condition is believed to be hereditary and linked to q25.3, on chromosome 17. They have a higher risk of recurrent stroke and may be experiencing a distinct underlying pathophysiology compared to patients from Japan. Data suggest a potential benefit with surgery if early diagnosis is made.^[1] The pathogenesis of moyamoya disease is unknown.

Once it begins, the process of blockage (vascular occlusion) tends to continue despite any known medical management. In some people this leads to repeated strokes and severe functional impairment or even death. In others, this blockage may not cause any symptoms.

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.^[2] Brain radiation therapy in children with neurofibromatosis increases the risk of its development.

The constrictions of the arteries in moyamoya disease are unlike the constrictions in atherosclerosis. In atherosclerosis, the inner layer (lumen) of the arteries suffers an immune reaction, fills with inflammatory cells, and accumulates fatty cells and debris. In moyamoya, the inner layer of the carotid artery overgrows inward to constrict the artery, and the artery also fills with blood clots, which cause strokes.^[3]