Amyotrophic lateral sclerosis (ALS) is a progressive neurological condition that eventually results in the loss of the ability to walk, talk, and swallow. In most cases, the cause of ALS is unknown.

However, about 10% of people with ALS have the familial form, which links to genetic changes called mutations. Some research suggests a possible link between ALS and head injuries or exposure to environmental agents like heavy metals and agricultural chemicals. However, such links have not been proven.

ALS is typically more common in older adults and males, as well as white people and non-Hispanic individuals.

This article discusses what causes ALS and examines risk factors. It also answers commonly asked questions.

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In most cases, it is unknown why people develop ALS.

The cause of one form of ALS is known. There are two forms of the condition: sporadic and familial. That said, hereditary risk plays a role in about 10% of all ALS cases. Familial cases stem from genetic mutations that a person inherits. However, sporadic cases have no clear links with risk factors or a family history.

ALS — formerly called Lou Gehrig’s disease — is a condition affecting nerve cells in the brain and spinal cord that control breathing and voluntary movements. People develop symptoms of ALS when the nerve cells in a certain region of the spinal cord and brainstem die. This, in turn, prevents these nerve cells from sending messages to muscles to contract.

Early symptoms include:

As the condition progresses, muscle weakness affects other parts of the body, resulting in difficulty with:

  • speaking
  • chewing and swallowing
  • drooling
  • breathing
  • constipation
  • unintentional emotional displays, such as laughing or crying
  • maintaining a moderate weight and getting enough nutrients

Eventually, people with ALS lose their ability to walk, talk, swallow, and breathe.

A 2018 report notes that the prevalence of ALS cases in the United States was 5.2 per 100,000 individuals in 2015, which equates to 16,583 cases.

Learn more about how ALS affects the brain and body.

The disease is more common among the following groups:

  • Age: ALS can affect individuals of any age, but it most commonly affects people ages 55–75 years old.
  • Race and ethnicity: Although the condition may affect any person, white people and non-Hispanic individuals have a higher risk.
  • Biological sex: Males have a slightly higher likelihood than females, but among older adults, both biological sexes have an equal risk.

Also, some research suggests that military veterans have a 1.5–2 times higher likelihood of having ALS, possibly due to exposure to environmental toxins. Some studies also indicate a link between head injuries and higher risk.

Other research suggests a possible link with exposure to heavy metals, such as mercury and lead. Studies also suggest a link with exposure to agricultural chemicals, trace elements, radiation, and solvents.

Learn about the age of onset for ALS.

Below are answers to commonly asked questions:

What are the main causes of ALS?

Doctors cannot identify a cause for most people with ALS. However, about 10% of individuals have the familial form, which is due to genetic mutations.

How can you avoid ALS?

This is not known. Some research suggests links between ALS and exposure to environmental toxins. However, these links lack evidence. Avoiding environmental toxins is always a good idea, but this does not guarantee someone will not get ALS.

However, a 2020 review notes that ALS shares essential molecular effects with aging, and it suggests that pro-aging strategies may help prevent ALS. One approach involves eating a balanced diet that is rich in antioxidants and anti-inflammatory foods early in life. Another approach includes engaging in low to moderate exercises regularly.

Is ALS fatal?

Yes, the average survival rate for people with ALS after symptoms start is 3–5 years. Roughly 30% of people with ALS are alive after 5 years, and 10–20% are alive after 10 years.

In ALS, the nerve cells that control voluntary muscle movement degenerate and die, which results in muscle weakness. In most cases, doctors do not know what causes ALS. Exceptions to this involve the 10% of people who have the familial form, which comes from genetic mutations.

Risk factors may include being an older adult, male, white, or non-Hispanic. Some research suggests that being a military veteran and having a head injury may increase the likelihood. Other studies show that exposure to heavy metals or agricultural chemicals may raise the risk, but further research is necessary to prove this.