Moyamoya disease is a disorder of blood vessels in the brain, specifically the internal carotid arteries and the arteries that branch from them. These vessels, which provide oxygen-rich blood to the brain, narrow over time. Narrowing of these vessels reduces blood flow in the brain. In an attempt to compensate, new networks of small, fragile blood vessels form. These networks, visualized by a particular test called an angiogram, resemble puffs of smoke, which is how the condition got its name: "moyamoya" is an expression meaning "something hazy like a puff of smoke" in Japanese.

The genetics of moyamoya disease are not well understood. Research suggests that the condition can be passed through families, and changes in one gene, RNF213, have been associated with the condition. Other genes that have not been identified may be involved in moyamoya disease. It is also likely that other factors (such as infection or inflammation) in combination with genetic factors play a role in the condition's development.

Moyamoya disease was first identified in Japan, where it is most prevalent, affecting about 5 in 100,000 individuals. The condition is also relatively common in other Asian populations. It is ten times less common in Europe. In the United States, Asian Americans are four times more commonly affected than whites. For unknown reasons, moyamoya disease occurs twice as often in females as in males.

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.

Published Date: October 01, 2017Published By: National Institutes of Health