Moyamoya Syndrome Risk Factors & Causes
Moyamoya syndrome is a rare progressive vascular disorder that involves the blocking or narrowing of the skull's carotid artery, which reduces blood flow to the brain. At the base of your brain, tiny blood vessels erupt to try to supply blood to the brain. The blood vessels aren't capable of providing necessary oxygen and blood to the brain, so the patient will suffer a brain injury, the severity of which will vary widely. There is no known root cause of Moyamoya syndrome, but certain characteristics increase the likelihood of developing the disease.
Associated Conditions
Some studies have linked Moyamoya disease with other conditions, including hyperthyroidism, neurofibromatosis type 1, sickle cell anemia, and Down syndrome. Individuals with these conditions may have a higher chance of developing comorbid Moyamoya syndrome.
Unfortunately, there has not been a great deal of research establishing why the comorbidity rates exist, and scientists have different theories. It's possible these disorders are all affected by the same gene or group of genes. It's also possible certain aspects of the associated disorders can increase the chances of narrowing blood vessels in the brain. Until more conclusive research is done regarding comorbidity rates, we don't have an explanation for why these diseases often occur concurrently. We just know they do.
Genetic Link
Research into the genetics of Moyamoya disease has been limited, but based on information about who the disease affects and how it does so, there is strong evidence indicating a genetic link. If a person's family member developed Moyamoya disease, they have a risk factor between thirty and forty times higher than the general population. This risk factor was calculated based on statistics regarding the individuals with Moyamoya syndrome. Thirty to forty times more patients had a relative with this condition than those who had no family history of the disease.
Some research indicates changes to the RNF213 gene might be related to Moyamoya syndrome. Other unidentified genes may also play a part in the development of this condition. The purpose of the RNF213 gene is to provide instructions for the construction of a protein with an unknown use. Studies suggest RNF213's protein is a component of blood vessel development. When this gene creates an incorrect protein, it's possible this causes the gradual blocking of blood vessels in the brain.
Gender
In documented cases of Moyamoya syndrome, the female population has slightly higher incidence rates. The reasoning for this, like many other risk factors, has not been the target of conclusive research. Scientists do have theories, as they usually do, including a connection back to the potential genetic link. Women have two X chromosomes, while men have a Y chromosome. It's possible the Y chromosome houses genes that help to reduce the potential for developing Moyamoya syndrome.
It's also possible the increased chances of this condition has nothing to do with chromosomes. Instead, it might be related to the physical and structural makeup of men versus women. Women experience different hormones, different body mass ratios, and different metabolisms. Any number of factors might be the reason females develop Moyamoya disease more often than males.
Age
Moyamoya syndrome might develop at any age, but the symptoms overwhelmingly present in children rather than adults. When adults do develop Moyamoya disease, they tend to be between thirty and fifty, and children are usually between five and ten. It's very uncommon for adolescents, young adults, and the elderly to develop Moyamoya disease.
The first symptom that manifests is usually a stroke, though it might manifest as recurrent transient ischemic attacks, something particularly common in children. Adults with the disease might experience these types of symptoms, but they're more likely to suffer brain bleeding due to abnormal vessels in the brain.
Asian Descent
Another strong suggestion of the genetic component is the fact Moyamoya syndrome occurs mostly in individuals of Asian descent. This condition is found in populations throughout the entire world, but it most commonly occurs in East Asian countries, and outside of these countries, development of the disease is exceedingly rare. China, Japan, and Korea are the East Asian countries with the highest rates of Moyamoya disease, possibly because of unknown genetic factors within those populations. When this condition does occur in Western countries, it's far more likely to affect individuals of Asian descent rather than those of European, Native American, or African descent.