What causes amyotrophic lateral sclerosis (ALS)?

The exact cause of ALS is not yet known, but researchers are constantly learning more about the disease. In the vast majority of the cases—somewhere between 90 to 95 percent—there is no known cause, and is deemed as being sporadic ALS.

In the remaining 5 to 10 percent of cases, the disease is called familial ALS because it is passed down through families. A child born to someone with familial ALS has a 50-50 chance of getting the disease, as well.

In 1993, researchers made a huge breakthrough regarding the gene responsible for familial ALS. They discovered a change, or mutation, in a gene called superoxide dismutase (SOD1), which is the gene responsible for familial ALS.

When the gene is normal, it protects the motor neurons from by damage by directing the production of an enzyme to guard against free radicals. When the gene is mutated, however, the enzyme is unable to protect the motor neurons, which then are vulnerable to the free radicals.

An estimated 20 percent of the people who have familial ALS also have the SOD1 gene mutation. Researchers continue to search for other genes that might be involved.

Researchers think some other possible causes for ALS might include:

  • An autoimmune response, in which the body attacks its motor neurons by mistake
  • An exposure to viruses or toxic substances
  • An abnormality of the immune system that leads to inflammation in the spinal cord and the brain
  • A diet lacking in certain nutrients
  • Trauma

However, there is a lack of scientific evidence to prove any of these theories.

Over the years, a host of factors have been thought to increase the risk of acquiring amyotrophic lateral sclerosis (ALS), or Lou Gehrig's disease. These have included exposure to welding, mercury, lead, aluminum and electric shock, among others.

However, to date, the only established risk factors are age and family history. There are a number of gene mutations being studied in non-familial ALS. These have provided clues to identify possible susceptible genetic influences, but they are not definitive and more research is needed.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.