Other possible causes
The other 90 to 95 percent of amyotrophic lateral sclerosis disease cases are sporadic. This means they aren’t inherited.
Researchers can’t say definitively what causes sporadic cases, but they have a few theories:
Beta-methylamino-l-alanine (BMAA). This toxin with the hard-to-pronounce name is produced by cyanobacteria — bacteria found in foods eaten by the Chamorro people of Guam, who have an unusually high rate of ALS symptoms. BMAA is known to damage motor neurons. Researchers are investigating what role it might have in triggering ALS.
Chemicals. Exposures to toxins ranging from heavy metals (lead, mercury) to organic solvents and pesticides have been investigated as possible amyotrophic lateral sclerosis causes. One study found an increased risk of ALS among people who were exposed to formaldehyde — a chemical used in building materials, laboratories, and mortuaries. Yet no one substance has been proven to trigger the disease.
Smoking. Some of the strongest evidence on amyotrophic lateral sclerosis causes centers on its link with smoking. The earlier people start smoking, the greater their risk of developing this disease. Researchers say chemicals in smoke might damage neurons.
Military service. Veterans, regardless of where or when they served, are almost twice as likely as non-veterans to develop ALS. The reason for this link is still unclear, but it might have to do with exposures to chemicals or viruses, or to extreme exertion while serving. Both the U.S. Department of Veterans Affairs and the National ALS Registry have established registries of ALS cases in veterans to help researchers identify the potential factors involved.
Intense exercise. Since Yankees great Lou Gehrig died from ALS in 1941 and the disease assumed his name, experts have wondered about the potential link between athletics and ALS. More recently, they’ve discovered a higher-than-usual incidence of the disease among Italian soccer players. Many of these athletes developed the disease in their 30s, two decades earlier than is typical. Though intense exercise might be a factor in ALS development, no one knows exactly what types of exercises are to blame, or how rigorous the activity must be to trigger the disease. Studies have shown that typical levels of physical activity don’t increase the risk for ALS, and that exercise might actually be protective.
Viruses. As with many other chronic conditions, including Lyme disease and multiple sclerosis, scientists are investigating the potential role of viruses in ALS development. The poliovirus, for example, can directly affect motor neurons — the same nerve cells ALS damages. And the HIV virus causes a reversible form of the disease.
March 16, 2020
Christopher Nystuen, MD, MBA