**2. Disease incidence and prevalence**

It is more prevalent in East Asian countries [15–17], namely Japan (10.3/100,000 people in 2006) [5], Korea (9.1/100,000 in 2008) [18] and China (3.92/100,000 in 2010) [19] than in the USA [20] and Europe [21].

Moyamoya incidence and prevalence have been increasing steadily over the years. In Japan the reported incidence rose from 0.35/100,00 in 1995 [16] to 0.54/100,000 in 2003 [5] and 0.94/100,000 in 2006 and the prevalence from 3.16/100,000 in 1995 [16], to 6.03/100,000 in 2003 [5] and 10.4/100,000 in 2006 [5], with a 1.8:1 female to male ratio [22] and a 10%-15% [5, 22, 23] familial cases. Another important aspect is that while the affected parents presented moyamoya related clinical symptoms at 22-36 years of age, their siblings showed the first symptoms when they were 5-11 years old [24]. In the USA [25] and Europe [21], the incidence in 10 times smaller, and the female to male ratio 2.2:1 [21]. In 2005 in the USA, the incidence was 0.086 cases/100,000 inhabitants [20].

Moyamoya disease has two peaks in incidence. The first in children before 18 years of age (maximum at 5-9 years old) and the second in adults in the fourth and fifth decades of life (highest rate from 35 to 45 years of age) [5, 17, 22, 26, 27]. In 47.8% of the patients, symptoms start before ten years of age [14]. In Japan, the paediatric prevalence is the highest worldwide, with 3 cases per 100,000 children [5, 22, 28].
