Most people with ALS don’t have a family history of it. Still, some cases of ALS are linked to inheriting specific gene mutations. Even nonfamilial cases can be linked to sporadic gene mutations that are not inherited.

Amyotrophic lateral sclerosis (ALS) is a progressive neurological disorder that causes your muscles to weaken over time. Most people who develop ALS do not have a family history of the condition.

Still, ALS can be hereditary. Familial ALS is a less common form of the condition that’s passed on genetically from parent to child.

There’s still a lot we don’t know about genetic risk factors for ALS. This article provides an overview of current research into ALS genes and inheritance.

Around 5% to 10% of people with ALS have a family history of the condition. Familial ALS is often linked to known inherited genetic mutations, but there are cases where there isn’t a recognized genetic mutation.

The remainder of ALS cases are sporadic, meaning they occur at random. But even though sporadic ALS isn’t hereditary, it still has a genetic component.

Genes are inherited from parent to child, but sometimes a genetic mutation can develop due to unknown factors. Experts believe this to be the case with nonfamilial forms of ALS.

Around 10% of people with sporadic ALS show mutations in the same genes as people with familial ALS, even if they don’t have a family history of the condition. In these cases, the family history may not be fully known, or the genetic mutation is occurring for the first time.

With sporadic ALS, environmental factors likely also play a role in triggering certain genetic changes. For example, exposure to agricultural chemicals, heavy metals, or radiation might interact with genes and lead to the development of ALS.

ALS is a motor neuron disease. Motor neurons are a type of cell found in the spinal cord. They are responsible for controlling muscles and movement.

In people with ALS, motor neurons slowly die, causing the muscles to weaken and waste away. The loss of motor neurons can sometimes be linked to a genetic mutation.

Researchers have identified dozens of gene mutations that can lead to the development of familial ALS. Some of the most common include:

  • SOD1: In the early 1990s, cytosolic copper-zinc superoxide dismutase (SOD1) was the first gene researchers linked to ALS. Many SOD1 variants can lead to ALS, together accounting for around 20% to 25% of all familial ALS cases.
  • C9ORF72: About 40% to 50% of familial ALS cases are due to problems with the C9ORF72 gene. People with this mutation are also at an increased risk of frontotemporal dementia.
  • TDP-43: Transactive response DNA-binding protein (TDP-43) variants contribute to 4% to 5% of familial ALS cases and a small number of sporadic ALS cases. People with this mutation are also at risk of developing frontotemporal dementia.
  • FUS: Variations in the fused in sarcoma (FUS) gene account for 4% to 5% of familial ALS cases. This mutation is linked to a very young age of onset and fast disease progression.

Familial ALS is most often inherited in an autosomal dominant pattern.

Autosomal” refers to genes on one of the regular 22 pairs of chromosomes found in human cells. (The 23rd pair consists of sex chromosomes.) When a condition is autosomal dominant, it means you only need one copy of the gene to develop that condition.

In other words, if one of your parents has familial ALS, you have a 50% chance of also developing the condition.

Autosomal recessive forms of ALS are less common. In these cases, you would have to inherit an ALS-associated gene from both parents to have the condition. Your parents would not have the disease if they each only had one recessive gene for ALS.

There’s also at least one known X-linked form. These cases involve a mutated gene on the X chromosome, one of the two sex chromosomes.

X-linked inheritance usually affects males, as they only have one X chromosome and do not have another copy of the gene to override or compensate for the mutated gene.

Other risk factors for ALS

It’s not clear why some people develop ALS while others don’t. Only a handful of well-established risk factors are known. They encompass very broad categories, including:

  • Age: ALS is more common among people ages 55 to 75 years.
  • Sex: ALS is slightly more common in males.
  • Ethnicity: White people and non-Hispanic people have an increased risk of developing ALS.
  • Military service: The authors of a 2020 review of 19 previous studies suggest that people who serve in the military may be at an increased risk of developing ALS. However, research is still limited.
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If both you and a close family member have ALS, the condition is likely inherited. A doctor might suggest genetic testing to see whether you have a mutation associated with ALS.

Genetic testing is an optional procedure that can provide more information about genes involved in ALS. However, not everyone who has received a diagnosis of familial ALS tests positive for a genetic mutation.

If genetic tests do reveal a mutation associated with ALS, your family members might decide to get tested, too. But some people decide they would prefer not to know whether they have the ALS mutation.

A genetic counselor can help you learn more about the risks and benefits of genetic testing.

Is ALS inherited from your grandparents?

It’s possible to inherit familial ALS if your grandparents had it. But if you don’t have a parent with ALS, you aren’t likely to develop it.

That’s because familial ALS typically has an autosomal dominant inheritance pattern. Such patterns don’t usually skip a generation. However, rarer autosomal recessive and X-linked forms can skip a generation.

If you have the ALS gene, will you get ALS?

If you have a first-degree relative (like a parent, sibling, or child) with ALS and testing reveals you also have the gene, you have a significant chance of developing the condition. However, not everyone with a known mutation will develop ALS.

Will I get ALS if my parent has it?

Most people who have a first-degree relative with sporadic ALS do not go on to develop the condition. If you have a parent or sibling with sporadic ALS, you have a 1% chance of also developing ALS.

At what age does ALS usually start?

ALS typically develops in middle age, with the age of onset ranging from 55 to 75 years. Familial ALS generally tends to appear earlier than sporadic ALS.

Early symptoms of ALS

The first symptoms of ALS can be subtle. As a result, the condition sometimes goes undetected in the early stages. Some of the early symptoms of ALS include:

  • difficulty chewing
  • difficulty swallowing
  • muscle cramps
  • slurred speech
  • stiffness
  • tripping
  • twitching
  • weakness
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Most people with ALS don’t inherit the condition. These cases are known as sporadic ALS. But in some cases, ALS can be familial, meaning it’s passed through genetic mutations from parent to child.

Scientists have identified several specific genes involved in familial ALS. These genes typically pass on in an autosomal dominant inheritance pattern. That means if one of your parents has the gene mutation, you have a 50% chance of also having the mutation.

Genetic testing is one way to pinpoint whether ALS is due to a genetic mutation known to be associated with the condition. If you have ALS, consult with a healthcare professional to learn more about the advantages and disadvantages of genetic testing.