Amyotrophic lateral sclerosis (ALS) is a rare disease that affects a person’s abilities to voluntarily control their movements. It’s also called Lou Gehrig’s disease.

The vast majority of ALS cases are sporadic, which means that they arise with no known family history of the condition.

However, a small percentage of people with ALS have an inherited form of the condition. Keep reading to find out more about what researchers know about the genetics of how ALS is inherited.

An estimated 5% to 10% of people with amyotrophic lateral sclerosis (ALS) have an inherited form of the disease. Doctors call this form familial ALS or fALS. Most of the time, ALS is sporadic, meaning that a random gene mutation triggers ALS.

For years, researchers have worked to determine how ALS is inherited. They know that only one parent has to pass the gene on for a child to have ALS. This inheritance pattern is known as a “dominant” inheritance pattern. This means that parents with ALS have a high likelihood of passing on the condition.

Identifying inherited ALS is important because researchers are attempting to create treatments called gene therapies. These therapies would “target” gene mutations in an attempt to treat or slow the progression of ALS.

Researchers are working to target the exact gene mutations that cause ALS to occur. Some of the most common mutations occur on the following genes:

  • C9ORF72: A defect in this gene causes an estimated 25% to 40% of all inherited cases of ALS. People with this genetic mutation may also have a unique dementia type called frontotemporal dementia.
  • SOD1: An estimated 12% to 20% of people with inherited ALS have this mutation. This type was the first one researchers identified in 1993. The SOD1 mutation is involved in producing an enzyme (a substance that causes a chemical reaction) called copper-zinc superoxide dismutase 1.
  • SPTLC1: Researchers more recently discovered this type, which causes a genetic form of ALS that affects children, sometimes as young as age 4.

Other genetic variants include TDP-43, FUS/TLS, OPTN, and TBK1. Researchers have discovered many others, but more research needs to be done to find further genes and to determine how the mutations affect ALS.

ALS genetic testing has expanded over the past decade. Today, laboratories can perform genetic testing to identify multiple potential genetic mutations, including SOD1 and C9orf72.

But not all laboratories will perform ALS genetic testing at their lab. One lab may collect a sample to send to these laboratories for further testing.

Currently, there are no standard guidelines or recommendations on when you should have genetic testing for ALS. The results from ALS genetic testing can vary in complexity. Some labs may test using different approaches and may test in panels that range from 19 to 49 genes or more at a time.

However, the promise of targeted therapies can make genetic testing worthwhile. Ideally, researchers will one day be able to create therapies that reduce the toxic effects of these mutations whenever possible.

Also, some people with ALS use genetic testing even if they have no known family history of the condition so that they can determine whether they’ll pass the mutation down to their children.

Genetic testing considerations

The challenge with ALS genetic testing is that the testing is still in development. This means that sometimes it’s hard to know exactly how to interpret results.

For example, a person may have a percentage of genetic mutation, but it’s unclear whether these results impact a their family or ALS prognosis.

It’s also possible a person could have ALS, but their genetic testing doesn’t reveal anything conclusive. This could be because the person has a gene mutation that researchers haven’t yet identified.

Genetic testing isn’t used to diagnose ALS or determine whether someone will develop ALS in the future. Right now, it can only help confirm a diagnosis. It’s important to understand why and what information you could learn before undergoing genetic testing for ALS.

The complexity of genetic testing and potentially confusing results illustrate why it’s so important for a doctor specializing in ALS treatment and a genetic counselor to review and discuss the results with you.

When preparing for your appointment, it may be helpful to write out a list of all the questions you have.

Genetic testing costs depend upon several factors. The testing may require a blood sample, a saliva sample, or both.

It’s helpful to undergo some genetic counseling before taking the test. Some people diagnosed with ALS or who have a genetic tendency in their family may not wish to undergo testing.

According to the ALS Association, current costs for genetic testing for ALS may range from $1,600 to $5,000 if a laboratory is testing for multiple genes. Testing for one specific gene may be a lesser cost of between $500 and $1,500.

Some people may already know the exact gene mutation their family has. When this is the case, genetic testing is usually less costly because a laboratory is looking for one specific mutation. The estimate for this cost is $400, according to the ALS Association.

Insurance policies vary on coverage but will likely always require a doctor to request that the tests be done. Contact your insurance company before you go for genetic testing so that you can get a clear sense of how much the costs may be.

Only a small portion of those with ALS have an inherited form. Researchers have identified numerous genetic variations thought to trigger ALS and are currently examining whether their knowledge of these genes could lead to targeted therapies.

If you or a family member has been diagnosed with ALS, talk with your doctor and possibly a genetic counselor about genetic testing and its potential risks and benefits. You may also consider the cost and how the information could benefit or detract from your well-being.