Amyotrophic lateral sclerosis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Charmaine Patel, M.D. [2]Mohamadmostafa Jahansouz M.D.[3]


ALS is classified into three general groups, familial ALS, sporadic ALS and Guamanian ALS.


  • "Familial ALS" accounts for approximately 5%-10% of all ALS cases and is caused by genetic factors. Of these approximately 10% are linked to a mutation in Superoxide dismutase (SOD1), a copper/zinc dependant dismutase that is responsible for scavenging free radicals.
  • Most of the remaining 90-95% of cases are classified as "sporadic ALS" and have no known hereditary component.
  • A third type, called "Guamanian ALS", represents a small cluster of cases concentrated on the Pacific island of Guam.

Guamanian ALS

There was a high incidence of this rare form of ALS from the 1940s to the 1960's, and during this time, the rates of ALS increased to 50-100 times of its incidence prior to this time. The incidence of Guamanian ALS has dropped significantly since the 1960's, but during it's peak, it killed more than 10% of the native Chamorro people of Guam.

Parkinson's and Alzheimers Association

Unique to the Guamanian form of ALS, it is associated with the development of cognitive symptoms similar to those seen in Parkinson's disease and Alzheimer's disease. Other forms of ALS tend to only effect the nerves which control the motor function, and do not affect the brain and the mental function.

Non-filtered Drinking Water

Researchers believe that there are algae and bacteria found in large quantities in areas of Guam, that produce powerful neurotoxins during particular times of the year. Prior to the 1960's, the drinking water was not filtered, and therefore people may have consumed high amounts of these toxins and subsequently developed ALS.

Food Toxins

People in Guam consumed a lot of flour made with the cycad plant, a plant which resembles the palm tree. This plant has nuts and seeds which do contain a powerful neurotoxin. Another source could be the fact that bats in the area consume a lot of the fruit from the cycad plant, and bat meat was consumed by the native people. The incidence of gaumanian ALS dropped as the native people stopped consuming bat meat.

Genetic Susceptibility

The native persons of Guam have been found to carry mutations in their genes which make them more susceptible to Guamanian ALS. Studies done in Chamarro families show specific genes that may be effected, and lead to the development of ALS.