Learn about ALS

Causes

For patients without a family history of the disease, which includes ~95% of cases, there is no known cause for ALS.

There is a known hereditary factor in familial ALS (FALS), where the condition is known to run in families, although this only accounts for around 5% of all cases. An inherited genetic defect on chromosome 21 (coding for superoxide dismutase) is associated with approximately 20% of familial cases of ALS. This mutation is believed to be autosomal dominant. The most common ALS causing SOD1 mutation in North America is A4V, characterized by an exceptionally rapid progression from onset to death. The children of those diagnosed with familial ALS have a higher risk factor for developing the disease; however, those who have close family members who have been diagnosed with sporadic ALS have no greater a risk factor than the general population, suggesting again an environmental or other non-genetic cause.

Some environmental causative factors have been suggested for the increased incidence in the western Pacific. Prolonged exposure to a dietary neurotoxin called BMAA is one suspected risk factor in Guam; this neurotoxin produced by cyanobacteria is one of several possible neurotoxic compounds found in the seed of the cycad Cycas circinalis, a tropical plant found in Guam, which was used in the human food supply during the 1950s and early 1960s.

The very high incidence of the disease among Italian soccer players (more than five times higher than normally expected) has raised the concern of a possible link between the disease and the use of pesticides on the soccer fields (several of which have been linked to neuronal toxicity). A 2004 Italian study trying to link a high incidence of ALS in soccer players to Performance Enhancing Drugs failed when the group was compared to cyclists that also used PEDs and had zero ALS. A possible conclusion was that soccer players experience frequent head trauma (heading the ball, falls and collisions sustained during games) compared to cyclists who wear head protection and rarely have falls.

According to the ALS Association, veterans of the United States military are at an increased risk of contracting ALS (again, possibly implying a link to neurotoxic chemical exposure). In its report ALS in the Military, the group pointed to an almost 60% greater chance of the disease in military veterans than the general population. For Gulf War veterans, the chance is seen as twice that of veterans not deployed to the Persian Gulf in a joint study by the Veterans Affairs Administration and the DOD, another epidemiologic association suggesting a link to toxic exposure.