Spinal Muscular Atrophy (SMA)

​​​​​Spinal muscular atrophy (SMA) is a genetic disease affecting the part of the nervous system that controls our ability to move our muscles voluntarily. This disease affects the muscles, causing them to be inactive and get smaller (atrophy). This diagnosis can have a wide range of presentations with different ages of onset, symptoms and rate of progression.

What Are the Types of Spinal Muscular Atrophy? 

There are 4 types of SMA that an individual may have. Children with more severe types of SMA are usually diagnosed at a younger age and have more limited muscle strength and functional abilities. 

Type 1 

This is the most common form of SMA which typically leads to symptoms at birth or during infancy. Children with Type 1 SMA are not able to independently sit on their own. It can lead to respiratory failure requiring a need for breathing and feeding support.

Type 2 

Children with Type 2 SMA typically show symptoms between 6-18 months of age. These children master sitting, but are not able to walk or stand without support.

Type 3

Symptoms typically begin after 18 months of age. In Type 3 SMA, patients are able to master walking, but may lose ambulation.

Type 4

This is an adult onset form of SMA. Symptoms don’t typically begin until after age 20 or 30.

The natural history of spinal muscular atrophy will continue to change, as more treatment options become available. The FDA has approved two treatment opportunities for patients with Spinal Muscular Atrophy. These treatments include: Nusinersen (Spinraza) and Zolgensma.

What Causes Spinal Muscular Atrophy?

SMA is an autosomal recessive genetic disorder. The patient inherits one copy of the missing gene (SMN1) from each parent in order to have the disease. SMN1 produces around 90% of protein necessary for proper muscle function. There is a backup gene called: SMN2. For patients that have spinal muscular atrophy, this is their only source of SMN protein. Typically, the more copies of SMN2 the child has, the less severe of symptoms the patient will present with.

How Is Spinal Muscular Atrophy Diagnosed? 

If SMA is suspected, your provider will order genetic testing to determine if the SMN1 protein is missing.

What Are Common Signs & Symptoms of Spinal Muscular Atrophy?

  • Hypotonia (“floppy” baby)
  • “Frog legs”
  • Feeding difficulties
  • Weak sucking
  • Tongue fluttering
  • Weak cry
  • Lack of motor development or delay in motor milestones
  • Lack of reflexes
  • Belly Breathing
  • Small muscles
  • Proximal muscle weakness

What Is the Treatment for Spinal Muscular Atrophy?

The occupational and physical therapists' roles may change slightly based on the type of SMA your child has.

Children with SMA 1 may benefit most from assistance with positioning, contracture management, opportunities for early mobility so they may experience age-appropriate activities, and adaptations of their environment to help them participate appropriately.

For the child with SMA type 2 and 3, the therapy focus is also on increasing independent mobility as well as energy conservation techniques. The therapists provide mobility options that are both efficient and safe for the child, while enabling them to participate actively in life skills and interactions between family and community.

For individuals with SMA who are in need of ongoing services as they age, there is a transition clinic which provides resources for the patient and family.

Spinal Muscular Atrophy FDA Approved Treatment Options

  • Spinraza (Nusinersen)
    • Spinraza is the first FDA approved treatment for spinal muscular atrophy. Spinraza has been approved to treat all patients diagnosed with any type of SMA. In patients with SMA, the SMN1 gene is missing, and the SMN2 gene is the only source of protein production. Spinraza works by targeting the SMN2 gene to promote a more functional protein that is critical for motor neuron cell survival. Spinraza contains an antisense oligonucleotide that increases the ability of the SMN2 gene to produce a full-length SMN protein. The goal of Spinraza is to promote motor neuron health and change the natural progression of spinal muscular atrophy.
  • Zolgensma (Gene Replacement Therapy)
    • Zolgensma was the second drug approved by the FDA for SMA. In May 2019, Zolgensma was approved for all patients with SMA under age 2. Zolgensma targets the genetic cause of spinal muscular atrophy by replacing the missing SMN1 gene. The SMN1 gene is critical to motor neuron cell survival. It is made up of a new SMN gene that is placed inside a viral vector called adeno-associated virus 9 (AAV9). This vector will travel through the body to deliver the new gene. Once the new gene has been delivered, the motor neuron cells will now be able to produce SMN protein. 

Gene Therapy Breakthrough for Spinal Muscular Atrophy Patients 

Zolgensma, a new gene therapy that was recently approved by the FDA for patients under two years old with spinal muscular atrophy, is now commercially available. This is a one-time medication that is designed to replace the survival motor neuron (SMN1) gene. Watch below for a glimpse of the first days of this promising new treatment, and meet the families who are being impacted.

Nusinersen Is Delivered to First Patient After FDA Approval

Alexandria has spinal muscular atrophy. Her family was given new hope when they received the very first dosage of nusinersen after it was FDA-approved.