ALS: the hereditary risk

After a diagnosis of ALS, it is natural to consider whether
your family could be affected—both now and in the future.

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Sporadic ALS may have a genetic component

woman at computer
woman at computer

As many as 1 in 10 people diagnosed with ALS have a family history of the disease, a likely indication that there is a genetic component involved. This is known as familial ALS (fALS). People who do not have a known family history of the disease are diagnosed with sporadic ALS (sALS), and while it may once have been assumed that people with sALS did not have a genetic component to their disease, we now know that they sometimes do.

Genetic testing can help determine the likelihood that a family member could be affected by ALS and how likely it is that the disease will be passed down to one’s children.

What are the chances that my family members may also have the disease?

The chance that one or more family members could develop ALS is largely dependent on genetics. Approximately 5% to 10% of all ALS cases occur in people with fALS. However, we now know that about 10% of sALS cases are also associated with a genetic mutation.

1 in 70 people graphic
1 in 70 people graphic

For those diagnosed with sALS—who therefore have no known family history—the total lifetime risk of first-degree relatives developing ALS is 1.4%, which means that, out of every 70 sALS patients who have no family history, one of them will have a sibling, parent, or child who is affected. 

1 in 140 people graphic
1 in 140 people graphic

Genetic testing can provide more information about the risk of inheritance. For example, for those who undergo genetic testing and are not found to have a known genetic component, the risk of first-degree relatives developing ALS is halved to 0.7%, or about 1 in 140.

For those who are found to have a genetic mutation associated with ALS, the risk may increase depending on which mutation is found. Recent scientific discoveries have found more than 25 genes that have been linked to ALS in both fALS and sALS patients. For example, a mutation in a gene called C9orf72 is an important determinant of lifetime risk and is found in 33% of fALS patients and 5% of sALS patients.

What are the chances that I will pass ALS on to my children?

For a number of ALS patients, their disease may have a genetic component, meaning specific ALS-associated mutations can be passed down from parents to their children. Due to an increase in knowledge about the disease and in genetic testing, more information about risk in both fALS and sALS patients is available.

family tree
family tree

For the majority of people who have a family history of ALS, the chance of passing the genetic mutation on to their children is 1 in 2 (or 50%).

This is because most causative genes are known as "dominant," meaning each parent has an equal chance of passing their gene on to the child. However, some forms of ALS are associated with "recessive" genes, which carry less risk of being passed on.

We now know that 1 in 10 people with sALS will also have a genetic component. This means that genetic testing may also provide helpful information on hereditary risk in people with sALS. For people with sALS who are found to have a genetic mutation associated with ALS, the risk of passing ALS to their children may increase depending on which mutation is found. In a recent study, the C9orf72 gene was found to be an important determinant of whether ALS will be passed on to their children.

Inheriting a gene associated with ALS does not guarantee that a person will develop the disease. Also, it is important to note that if your child does not inherit a genetic mutation from you, they cannot pass it on to their children.

Genetic testing in ALS

Genetic testing can provide important information about your ALS. Talk to your doctor about testing today.

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