What Is Spinal Muscular Atrophy (SMA)?

Medically Reviewed on 9/28/2021
Spinal Muscular Atrophy (SMA)
Spinal muscular atrophy (SMA) is a hereditary disorder characterized by progressive muscle weakening and atrophy that destroys motor neurons.

Spinal muscular atrophy (SMA) is a hereditary disorder characterized by progressive muscle weakening and atrophy (when muscles get smaller). SMA can make it difficult for a child to crawl, walk, sit up or regulate their head motions. It can also harm the muscles that control breathing and swallowing.

The nerves that control muscle strength and mobility deteriorate in spinal muscular atrophy. The spinal cord and the lower part of the brain contain these nerves. They are unable to convey impulses from the brain to the muscles, which would allow them to move. Because the muscles are not used, they shrink (or atrophy).

SMA is divided into four types. While some appear earlier and with greater severity than others, all kinds of SMA require continuous medical care from a medical team. Since the condition has no cure, treatment aims to help afflicted children live better lives. Furthermore, patients with SMA can seek genetic testing to determine how likely they are to have a child with the condition.

Children with SMA benefit from a multidisciplinary approach to their care. The team includes parents, doctors, nurses, therapists, counselors, and a dietitian, among others. This strategy, combined with recent medical advancements, has improved the prospects for patients.

What are the causes of spinal muscular atrophy?

Most cases of spinal muscular atrophy (SMA) are caused by a mutation in the SMN1 gene. The gene does not produce enough of a protein required for appropriate motor neuron function. Motor neurons die and are unable to convey impulses to the muscles.

Each parent gives one copy of the SMN1 gene to a child with SMA. A child who inherits the SMN1 gene from only one parent is unlikely to develop the condition although they may pass the gene on to their children.

What are the symptoms and signs of spinal muscular atrophy?

Spinal muscular atrophy (SMA) manifests itself in various ways. Some SMA newborns are "floppy," which means they do not learn to roll or sit at the appropriate age. An older youngster may fall more frequently than younger children or have difficulty lifting objects.

Scoliosis (a curved spine) can develop in children with SMA if the back muscles are weak. A kid with severe SMA could be unable to stand or walk and may require assistance to eat and breathe.

What are the different types of spinal muscular atrophy?

Spinal muscular atrophy (SMA) is divided into four groups based on the severity of the disease and the age at which symptoms first appear.

  1. Type I: Also called Werdnig–Hoffmann disease or infantile-onset SMA. Infants aged zero to six months old get affected, with most babies showing symptoms by the age of three months. SMA in this kind is the most severe.
  2. Type II: Children aged between the ages of 7 and 18 months old are affected. Children can sit on their own but cannot walk. This kind might range from mild to severe.
  3. Type III: Commonly called Kugelberg–Welander syndrome or juvenile SMA. Children aged from 18 months to adolescence are affected. Children can walk independently, but their arms and legs are weak, and they are prone to falling. In children, this is the mildest form of SMA.
  4. Type IV: The adult type of SMA commonly presents symptoms after a person turns 35 years old, and the condition gradually worsens over time. Because type IV SMA develops slowly, many people do not realize they have it until years after symptoms appear.

How is spinal muscular atrophy diagnosed?

Spinal muscular atrophy (SMA) is diagnosed in a variety of ways, including the following tests:

  • Genetic testing is the most prevalent method of detecting SMA with the SMN1 gene tested for a deletion or variant.
  • A biopsy of the muscle is where doctors take a small sample of muscle to examine under a microscope.

What is the treatment for spinal muscular atrophy?

Although there is no cure for spinal muscular atrophy (SMA), the following treatments can help children with the disease:

  • Nusinersen (also called SpinrazaTM): A novel SMA treatment that was authorized in 2016 which increases the quantity of protein produced by the SMN1 gene that is lacking in the body. It works by making the SMN2 gene, which acts as a backup, look more like the SMN1 gene and creates the required protein.
    • A spinal tap is used to administer this with four doses given over two months, followed by four doses every four months after that.
    • Studies show that breathing, motor function, and survival have improved significantly.
  • Trials of gene therapy: Trials are ongoing and have proved to improve overall function in people with SMA.
  • Supportive treatments:
    • A mask or mouthpiece or a breathing machine can help patients breathe. A tube may be inserted into the windpipe if a breathing machine is required (called a tracheostomy).
    • Treatments to help children cough and clear mucus, which can help prevent illnesses and ensure adequate nutrition. A feeding tube or a tube is sometimes inserted into the stomach through the nose (called a gastrostomy tube or G-tube). Feedings can be delivered directly to the stomach in this manner.
    • Scoliosis can be treated with drugs, a splint, a brace, or even surgery.
    • Physical and occupational therapy are two types of therapy.
    • Support groups and counseling are an option.
Medically Reviewed on 9/28/2021
Rosenfeld J. Spinal Muscular Atrophy. Medscape. https://emedicine.medscape.com/article/1181436-overview

Muscular Dystrophy Association. Spinal Muscular Atrophy (SMA). https://www.mda.org/disease/spinal-muscular-atrophy