Around half of people with ALS die within 30 months of their symptoms beginning, and about 20% of people with ALS live between five and ten years after symptoms begin. Guitarist Jason Becker has lived since 1989 with the disorder, while cosmologist Stephen Hawking lived for 55 more years following his diagnosis, but they are considered unusual cases. Cause
Though the exact cause of ALS is unknown, genetic and environmental factors are thought to be of roughly equal importance. The genetic factors are better understood than the environmental factors; no specific environmental factor has been definitively shown to cause ALS. A liability threshold model for ALS proposes that cellular damage accumulates over time due to genetic factors present at birth and exposure to environmental risks throughout life. Genetics
ALS can be classified as familial or sporadic, depending on whether or not there is a family history of the disease. There is no consensus among neurologists on the exact definition of familial ALS. The strictest definition is that a person with ALS must have two or more first-degree relatives (children, siblings, or parents) who also have ALS. A less strict definition is that a person with ALS must have at least one first-degree or second-degree relative (grandparents, grandchildren, aunts, uncles, nephews, nieces or half-siblings) who also has ALS. Familial ALS is usually said to account for 10% of all cases of ALS, though estimates range from 5% to 20%.
Moyamoya disease is a disease in which certain arteries in the brain are constricted. Blood flow is blocked by constriction and blood clots (thrombosis). A collateral circulation develops around the blocked vessels to compensate for the blockage, but the collateral vessels are small, weak, and prone to bleeding, aneurysm and thrombosis. On conventional angiography, these collateral vessels have the appearance of a "puff of smoke" (described as "もやもや (moyamoya)" in Japanese).When moyamoya is diagnosed by itself, with no underlying correlational conditions, it is diagnosed as moyamoya disease. This is also the case when the arterial constriction and collateral circulation are bilateral. Moyamoya syndrome is unilateral arterial constriction, or occurs when one of the several specified conditions is also present. This may also be considered as moyamoya being secondary to the primary condition. Mainly, occlusion of the distal internal carotid artery occurs. On angiography, a "puff of smoke" appearance is seen, and the treatment of choice is surgical bypass. Presentation
Patients usually present with TIA, ischemic/hemorrhagic stroke, or seizure. The age distribution is bimodal being either young adolescence or mid-forties. Cause
About 10% of cases of moyamoya disease are familial, and some cases result from specific genetic mutations. Susceptibility to moyamoya disease-2 (MYMY2; 607151) is caused by variation in the RNF213 gene (613768) on the long arm of chromosome 17 (17q25).