Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) refers to a group of inherited neuromuscular diseases that affect the nerve cells (motor neurons) and the control of voluntary muscles.

SMA, the leading genetic cause of death in infants and toddlers, causes lower motor neurons in the base of the brain and the spinal cord to disintegrate, preventing them from delivering the necessary signals for normal muscle function.

Involuntary muscles, such as those that control bladder and bowel function, are not affected in SMA. Hearing and vision are not affected, nor is someone’s learning or social skills.

Types of SMA

The three major childhood-onset forms of SMA are now usually called Type 1, Type 2, and Type 3. All three types are also known as autosomal recessive SMA, meaning both parents must pass on the defective gene in order for their children to inherit the disease.

All forms of SMA affect the skeletal muscles of the trunk and limbs. In general, those muscles closer to the center of the body are more affected than those farther away.

SMA Type 1, the most severe form, mostly affects the neurons controlling the mouth and throat muscles and therefore involves more problems with chewing and swallowing. Respiratory muscles are involved to varying degrees in all forms of the disease. In SMA Type 1, the onset of the disease has historically been noted within the first six months of the child’s life. SMA Type 1 can be fatal early in life if not treated.

SMA Type 2 is an intermediate form of the disease. Onset has historically been between seven and eighteen months. Children with SMA Type 2 are usually able to sit without support but have historically not been able to walk and therefore use a wheelchair.

SMA Type 3 is a milder form of this condition. Onset occurs after the age of eighteen months and most often between the ages of five and fifteen. Weakness of the muscles of chewing and swallowing is rare, and respiratory effects are generally not as severe as in the first two forms. Individuals with SMA are usually able to walk initially, but may lose mobility as they grow older.

Treatment

The first FDA-approved treatment drug for SMA became available in 2016; since then, two more treatment drugs have become available. As of 2023, people with SMA have three medication treatment options if they choose to pursue that: Spinraza, Zolgensma, and Evrysdi.

While Spinraza and Evrysdi are approved for people of all ages, Zolgensma is only available for children under 2 years old.

In addition, physical therapy and orthopedic devices can help preserve walking function. Respiratory therapy can provide crucial interventions for breathing abilities. Braces or surgery may also help to counteract scoliosis, or curvature of the spine.

Resources

If you are looking for more information on spinal muscular atrophy or have a specific question, our Information Specialists are available business weekdays, Monday through Friday, toll-free at 800-539-7309 from 9:00 am to 8:00 pm ET.

Additionally, the Reeve Foundation maintains a SMA fact sheet with additional resources from trusted Reeve Foundation sources.  Check out our repository of fact sheets on hundreds of topics ranging from state resources to secondary complications of paralysis.

We encourage you to reach out to spinal muscular atrophy support groups and organizations, including:

• CureSMA provides support programs for people living with SMA and their families, as well as funding and directing comprehensive research for treatments and a cure. Toll-free 1-800-886-1762.
• Spinal Muscular Atrophy Foundation hopes to accelerate the development of a treatment or cure for SMA. Toll-free 1-877-FUND-SMA.
• Muscular Dystrophy Association (MDA) provides services and supports research for a group of hereditary muscle-destroying disorders, including spinal muscular atrophies. Toll-free 1-800-572-1717; search under “Diseases.”