Saw this one in a website and thought this can answer the question: Up to 15 percent of Japanese people with moyamoya disease have one or more family members with the condition, indicating that the condition can be passed through generations in families; however, the inheritance pattern is unknown. Research suggests that the condition follows an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. However, some people who have a copy of the altered gene never develop the condition, which is a situation known as reduced penetrance.

---

---