FAQs About SMA

Vaidyanathan Subramaniam avatar

by Vaidyanathan Subramaniam |

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Spinal muscular atrophy (SMA) is a rare genetic disease with several subtypes. Patients and their caregivers may have a difficult time finding reliable information about SMA, so here are some frequently asked questions and answers about the disease:

What is SMA?

SMA is a neurodegenerative disease characterized by the loss of motor neurons (or nerve cells that control muscle movement) in the spinal cord and parts of the brain connected to the spinal cord. This defect leads to a loss of voluntary movements and the atrophying of muscles.

What are the different types of SMA?

Among the several types of SMA, the primary ones are numbered from type 0 to 4 based on the severity of symptoms.

Other rarer forms of the disease include Finkel type SMA, SMA with respiratory distress syndrome (SMARD1), X-linked infantile SMA (XL-SMA), Kennedy’s disease, and spinal muscular atrophy lower extremity dominant (SMA-LED).

For more information, refer to our page on “SMA Types.”

What causes SMA?

SMA types 0 to 4 are caused by mutations in the SMN1 gene. The other types are caused by mutations in other genes.

How prevalent is SMA?

About one in 8,000 to 10,000 people are estimated have SMA. Type 1 is the most common, followed by type 2 and type 3. Types 0 and 4 are rarer.

How is SMA inherited?

SMA types 0 to 4 and SMARD1 are inherited in an autosomal recessive manner. Other forms of SMA, such as LED and Finkel type, follow an autosomal dominant pattern of inheritance, while Kennedy’s disease and XL-SMA follow an X-linked inheritance pattern.

Refer to our “SMA and Genetics” page for more information.

What are the symptoms?

Symptoms vary among the different SMA types. Common symptoms include muscle weakness and poor muscle tone, impaired mobility, breathing issues, swallowing problems, and scoliosis (curved spine).

For more information, refer to our page about “SMA Symptoms.”

How is SMA diagnosed?

The diagnosis of SMA includes a physical exam and review of the patient’s family history. Delays in developmental milestones, elevated creatine kinase levels in the blood, and genetic testing can help confirm an SMA diagnosis. Other diagnostic techniques include assessing the health of muscles using electromyography or a muscle biopsy.

What is carrier testing?

Since most SMA types are inherited in an autosomal recessive manner, those who suspect that they could be carriers of the disease due to known family history can undergo carrier testing to find mutations in the SMN1 gene. Based on the results, their partners may also undergo the test to determine the risk of having children with SMA.

What is the average life expectancy?

SMA is a progressive disease with varying life expectancy for each type. The estimated life expectancy for each primary SMA type is as follows:

  • SMA type 0 – less than six months after birth.
  • SMA type 1 – less than four years after birth.
  • SMA type 2  – into adulthood with proper care.
  • SMA type 3 – same as the general population.
  • SMA type 4 – life expectancy unaffected.

For other forms of SMA, life expectancy is as follows:

  • Finkel type SMA – life expectancy unaffected.
  • SMARD1 – life expectancy affected but difficult to predict.
  • XL-SMA – less than two years after birth.
  • Kennedy’s disease – life expectancy unaffected.
  • SMA-LED – life expectancy unaffected.

What treatment options are available?

Spinraza (nusinersen) is an approved treatment for SMA that slows down disease progression by increasing the activity of another gene called SMN2 to produce more SMN protein.

Zolgensma (AVXS-101) is a gene therapy approved to treat patients up to age 2 with SMA types 0 to 4. Clinical trials are ongoing for the use of the treatment in other patients. The therapy delivers a healthy copy of the SMN1 gene directly into the patient using a genetically engineered virus.

Muscle relaxants, physiotherapy, and occupational therapy can also help to reduce the severity of symptoms in patients with SMA.

Several experimental therapies that are aimed at increasing SMN protein levels are also in the pipeline.

Can muscle function be restored?

Studies are underway in animal models of SMA and in clinical trials to evaluate the possibility of restoring lost muscle function. Some of these approaches include long-term exercise and physiotherapy, myostatin inhibition, fast skeletal troponin complex activation, and cholinesterase inhibition.

For more information about each of these therapies, refer to our page on “Restoring loss of muscle function in SMA.”

Where can I find more information?

Our website offers a wealth of information about SMA, including symptoms, diagnosis, ongoing research, current therapies, and clinical trials. We also have columns and podcasts by SMA patients along with content specially tailored for healthcare professionals.

For more information, access to support groups, and networking opportunities, check out the following organizations:


Last updated: Sept. 30, 2019


SMA News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.