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Sporadic ALS is the most common form of ALS, especially in North America. It is found within 90 to 95 percent of all people diagnosed with ALS.
During research conducted between 1995-1996 at Johns Hopkins University, it was discovered that 42 percent of sporadic ALS cases have an EAAT2 protein defect, which is responsible for regulating glutamate levels. The remaining ALS cases are familial and Guamanian ALS.
Familial ALS is inherited in a genetically dominant pattern. This form of ALS is seen in only five to 10 percent of ALS cases. A mutation for the gene for Superoxide dismutase (SOD1) on chromosome 21 was found to be the cause of familial ALS in 20 percent of these patients, however the cause in the remaining 80 percent is unknown.
Since genetic mutation is inherited in an autosomal dominant pattern, the offspring of someone with familial ALS will have a 50 percent chance of being diagnosed with this disease.
Guamanian ALS is named after the United States territory of Guam where a high percentage of ALS cases were diagnosed between the 1950s to 1960s. The number of cases found among the Chamorro people of Guam had an incidence at least 50 times higher than anywhere else. What made these cases in Guam so unique was its association with the Parkinson-Dementia Complex. People presented with symptoms similar to Parkinson's and Alzheimer's disease.
However, Guamanian ALS has also been discovered in New Guinea, Japan, and the Mariana Islands. It is believed that a diet consisting of cycad nut flour is responsible, while others have proposed a mutation in a neuronal protein is the cause.
There are no ways to tell the difference between sporadic and familial ALS in terms of symptoms. Two patients with either sporadic or familial ALS will both go to their doctor with complaints of weakness and fatigue in a certain area of the body.
However, the same cannot be said of Guamanian ALS. There is a noticeable difference in the clinical symptoms of this form of ALS compared to the others. Patients diagnosed with Guamanian ALS will have symptoms of the Parkinson-Dementia Complex with the tremors characteristic of Parkinson's patients, and the memory loss that is commonly seen in Alzheimer's patients. Since the 1960s, the incidence of Guamanian ALS has dropped to worldwide levels.
|Jennifer Mathes, Ph.D.|