What Is Spinal Muscular Atrophy?

Spinal muscular atrophy (SMA) is an inherited condition that causes severe muscle weakness. People with SMA have trouble with all muscle movements, which affects their ability to walk and talk as well as breath and swallow. People with more severe forms of SMA start showing symptoms as babies. In the past, the only thing healthcare teams could do was support people with SMA syndrome in coping with their symptoms. But now there are new gene therapies for SMA. While these therapies can’t cure SMA, they are a huge step forward. 

What causes spinal muscular atrophy?

People with SMA don’t have a working SMN1 gene. Not having this gene affects people in different ways. Some people have copies of the SMN2 gene, a backup gene that performs a similar function in the body as SMN1. People with more copies of this backup gene have milder cases of SMA.

How common is spinal muscular atrophy?

Spinal muscular atrophy is a rare condition. It affects about 0.01% of newborns. Because SMA syndrome is a genetic condition, it’s more common in certain groups of people. 

In order to have SMA, a person needs to inherit two copies of a nonworking SMN1 gene. People who have only one working copy of the gene don’t have any symptoms, but they’re “carriers,” which means they face a higher risk of having a child with SMA.  

When is spinal muscular atrophy diagnosed?

SMA is usually diagnosed when children are very young. The more severe types are diagnosed sooner because children start showing symptoms earlier. People with more severe types of SMA have fewer copies of the backup gene — SMN2. There are four types of SMA:

1. Type 1: This is the most severe form. Children start showing symptoms before 6 months of age. These children have between one and three copies of the backup gene. 

2. Type 2: This form is diagnosed when children are between 6 and 18 months old. These children have three copies of the backup gene. 

3. Type 3: This form is diagnosed after a child is 18 months old. These children have three to four copies of the backup gene. 

4. Type 4: This form is diagnosed in adults. While adults with type 4 have muscle weakness, they’re still able to walk and talk. They have four to eight copies of the backup gene.  

What are the symptoms of spinal muscular atrophy?

SMA symptoms are all related to muscle weakness. The severity of the weakness depends on what type of SMA a person has. People with more severe types of SMA can have very serious symptoms that include:

• Inability to sit and walk independently

• Inability to use their hands

• Trouble coordinating swallowing, which means they might not be able to eat on their own

• Difficulty breathing due to weakness of their respiratory muscles

People with SMA type 1 and 2 often do not live as long as their peers. People with SMA type 3 and 4 have much milder symptoms, and with treatment their life expectancy isn’t affected.

People with all types of SMA have normal cognitive function — that means they have average or above average intelligence. With treatment, children with SMA — even severe forms — lead productive lives, including going to school, engaging in activities, and spending quality time with friends and family. 

Is there a cure for spinal muscular atrophy?

There’s no cure for SMA, but medical technology allows people to live decades longer than would be possible without treatment. 

Medical technology and devices

People with severe SMA syndrome need assistance with movement, breathing, and eating. Medical devices — like wheelchairs, mobility assist devices, and speech devices — can help people with independence of movement and speaking. 

Devices like cough assists, vests, ventilators, and tracheostomies help with breathing and lung health. For people with difficulty swallowing, feeding tubes can help with nutrition. 

People with more mild forms of SMA may benefit from physical therapy, occupational therapy, and support from mobility assistance devices. 

SMA specific therapies 

Thanks to advancements in gene therapy, there are now medical therapies that are specific for the treatment of SMA. These medications can slow the progression of muscle weakness or even stop it from starting. These medications work best when they’re started as early as possible — ideally before there’s any weakness. These medications include:

• Nusinersen

• Zolgensma 

• Risdiplam 

Only certain treatment centers offer these medications. You can find a center using the Cure SMA Treatment Site Locator tool or by calling the Muscular Dystrophy Association Resource Center at 1-833-275-6321.

These medications are very expensive, but some insurance plans cover them. CureSMA.org keeps a database of insurance carriers that cover each of these medications.

Who should be tested for spinal muscular atrophy?

A simple blood test can check for SMA.

Right now, 43 states include SMA testing in their newborn screening program. That means that babies who are born in these states are automatically tested for SMA. Early screening helps to identify children who are at risk as soon as possible — so they can start treatment even before they develop any symptoms. 

People with family members who have SMA should have testing to see if they’re carriers for SMA. If you are a carrier for SMA and you have a child with someone who is also a carrier for SMA, your child has a 25% chance of being born with SMA. 

Children with symptoms of SMA, or young adults who develop weakness, often need SMA testing as part of their evaluation. 

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Written by:

Ronald W. Dworkin, MD, PhD

Ronald W. Dworkin, MD, is a board-certified anesthesiologist who has been practicing anesthesiology in a community hospital for 30 years. He has taught in the honors program at George Washington University for over 10 years and works as a senior fellow at the Hudson Institute.

Edited by:

Patricia Pinto-Garcia, MD, MPH

Patricia Pinto-Garcia, MD, MPH, is a medical editor at GoodRx. She is a licensed, board-certified pediatrician with more than a decade of experience in academic medicine.

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