Most patients with moyamoya disease are sporadic cases, but in Japan, 10-15% of patients with moyamoya disease have affected first-degree relatives [1-3]. In the United States, 6% of patients have a family history of the disease [4, 5]. The presence of familial cases in many countries suggests that genetic factors participate in the etiology of moyamoya disease. There may be some minor differences of clinical presentations between familial and sporadic cases. The ratio of women to men is 5.0 in familial cases and 1.6 in sporadic cases. Age of onset (mean ± SD) was 11.8 ± 11.7 in familial cases while in sporadic cases it was 30.0 ± 20.9 .
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