Age of onset
ALS can also be classified based on the age of onset. While the peak age of onset is 58 to 63 for sporadic ALS and 47 to 52 for familial ALS, about 10% of all cases of ALS begin before age 45 ("young-onset" ALS), and about 1% of all cases begin before age 25 (juvenile ALS). People who develop young-onset ALS are more likely to be male, less likely to have bulbar onset of symptoms, and more likely to have a slower progression of disease. Juvenile ALS is more likely to be familial than adult-onset ALS; genes known to be associated with juvenile ALS include ALS2, SETX, SPG11, FUS, and SIGMAR1. Although most people with juvenile ALS live longer than those with adult-onset ALS, some of them have specific mutations in FUS and SOD1 that are associated with a poor prognosis. Late onset (after age 65) is associated with a more rapid functional decline and shorter survival. Signs and symptoms
The disorder causes muscle weakness, atrophy, and muscle spasms throughout the body due to the degeneration of the upper motor and lower motor neurons. Individuals affected by the disorder may ultimately lose the ability to initiate and control all voluntary movement, although bladder and bowel function and the extraocular muscles (the muscles responsible for eye movement) are usually spared until the final stages of the disease.Cognitive or behavioral dysfunction is present in 30–50% of individuals with ALS.
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%.