Spinal muscular atrophy is a genetically inherited disorder that causes muscle weakness. Adults can get spinal muscular atrophy, but it’s rare in adults and progresses slowly. It doesn’t typically limit a person’s ability to walk or shorten their lifespan.

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Spinal muscular atrophy (SMA) is a group of disorders that causes muscle weakness and wasting. SMA affects approximately, 1 in every 6,000 to 10,000 people. Adult-onset SMA usually happens sometime after age 30 and produces mild to moderate symptoms.

Learn more about spinal muscular atrophy.

SMA is the second leading cause of neuromuscular disorders.

A neuromuscular disorder is a disease that causes you to experience issues within your nervous system. The messages between the motor and sensory nerves in the brain and spinal cord do not effectively communicate with the rest of your body, causing muscle weakness.

There are five main subtypes of SMA (type 0 to 4). The adult-onset type is considered type 4, and symptoms are less severe than types that begin in childhood. The reason why is linked to the motor milestones established for your lifespan, like walking.

For a confirmed SMA type 4 diagnosis, symptoms must begin between ages 18 and 50 years, according to the Better Health Channel. Symptoms can range from mild to moderate and may begin with weakness in the leg muscles.

Other symptoms can include:

SMA is a genetic condition, which means it’s present at birth.

SMA type 4 is passed on during reproduction through an autosomal recessive pattern. This means you must inherit an affected gene – in this case, deletion or mutation of the SMN1 gene – from both parents during conception.

The SMN1 gene makes a protein that supports motor neurons in your body. When this protein is missing, the neurons die off, leading to the symptoms of the disease.

If you notice symptoms of SMA, it’s important that you make an appointment with a doctor. At your appointment, the doctor will perform a physical exam and request important medical information, like any family history of SMA.

They may order additional tests like:

There is no cure for SMA. Treatment is focused on slowing disease progression and improving a person’s quality of life.

Physical and occupational therapy may be beneficial for working on mobility and retaining range of motion. Likewise, some people may benefit from using assistive devices like orthotics or wheelchairs.

Newer drugs that may help include:

  • Nusinersen: Nusinersen (Spinraza) is used to treat SMA in both children and adults. This medication is injected into the fluid around the spinal cord and works by supporting the function of SMN protein.
  • Risdiplam (Evrysdi): This is an oral medication used to treat SMA in people over 2 months of age, including adults. It works by increasing SMN protein in the body.

Again, SMA is genetically inherited. It’s important to note that males and females carry the same risk of developing SMA.

The biggest risk factor for SMA type 4 is having two parents who carry the gene mutation.

Here’s the risk breakdown when both parents are carriers:

  • 25% chance of developing SMA
  • 50% chance of being a carrier
  • 25% chance of not having the disease or being a carrier

According to the Better Health Channel, adults diagnosed with SMA typically have a standard life expectancy. In general, the disease progression does not affect the muscles controlling swallowing and breathing. And while mobility may be affected, only a small group of people will need wheelchair support.

Receiving a progressive disease diagnosis can be overwhelming. It’s important to know that there are steps that you can take that can support you in enjoying an active, full life while living with SMA. Here are some examples:

  • Be open with your doctor. Let your doctor know when symptoms interfere with your everyday life. They can recommend therapies that you can try that may help.
  • Stay active. In many cases, people with SMA type 4 can continue living and working independently without the use of assistive devices.
  • Learn ways to adapt. If you’re having trouble doing an everyday task, ask your doctor for recommendations on ways you might make adaptations or modifications to your approach that work well for you.
  • Consider joining a support group. Cure SMA is one organization that offers support, plans events, and advocates for the SMA community. For more information about available support groups, consider talking with your medical team.
  • Prioritize your mental health. Your doctor can refer you to a therapist to help you cope with your feelings.

How common is adult-onset SMA?

Of the people who have SMA, adult-onset is relatively rare. Just 1% of people with SMA have type 4, or adulthood-onset SMA.

What types of doctors treat SMA?

You may work with a team of doctors to support your overall health, including neurologists, physical or occupational therapists, geneticists, gastroenterologists, and others, as needed.

What if I’m looking to start a family?

Your doctor may suggest meeting with a genetic counselor. You can discuss your risks, genetic testing options, and other family planning needs.

SMA is a slow-progressing neuromuscular disorder. When it begins in adulthood – SMA type 4 – the symptoms do not usually cause total loss of function or shorten a person’s life expectancy.

You can work with your doctor and medical team to find the right mix of therapies and support to help you live your best life.