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Spinal muscular atrophy

(Spinal • muscular • AT-ruh-fee)

General Condition Information

Other Names

  • SMA
  • Spinal Muscular Atrophy due to homozygous deletion of exon 7 in SMN1
  • Werdnig-Hoffman Disease

Condition Type

Birth Prevalence

  • It is estimated that hundreds of babies are born with this condition each year in the United States.
  • Visit GeneReviews to learn more about how often this condition occurs.

Screening Finding

Absence of exon 7 in the SMN1 gene

What is Spinal muscular atrophy

Spinal muscular atrophy (SMA) is an inherited (genetic) condition that affects the nerve cells that carry messages from the brain to the muscles of the body.

The brain uses nerves called motor neurons to control muscle movement. Motor neurons need the survival motor neuron (SMN) protein to work correctly.

In SMA, your baby’s body cannot make enough SMN protein. When a baby cannot make enough SMN protein, motor neurons die, damaging the connection between the brain and the muscles. The brain will then have trouble telling the muscles to move, which causes the muscles to break down.

This results in muscle weakness and decreased muscle size (atrophy), which can cause breathing and swallowing difficulties. Loss of motor neurons also leads to other signs and symptoms of the condition.

There are several forms of SMA, and the severity of the condition depends on how much normal SMN protein your baby makes.

Newborn Screening and Follow-Up

Condition Details

Treatment and Management

Two new treatments can change how the genes work in some cases of SMA. A medicine called nusinersen can help the SMN2 gene make more SMN protein. Gene therapy can replace the nonworking SMN1 gene with a working copy. It is important to talk to your health care provider about which treatment(s) are best for your baby. The goal of these treatments is to prevent muscle weakness and resulting health problems. 

Some children with SMA will require other types of support that can include:

  • Physical therapy
  • Feeding support for babies who cannot swallow
  • Breathing support

The outcomes of these treatments vary depending on the form and severity of the condition.

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