Complications From Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a group of diseases that impact motor neurons, a special type of cell in your spinal cord and brain. These neurons control movement in your arms, legs, chest, face, throat, and tongue.

Since SMA destroys motor neurons and weakens your muscles, people with SMA can have problems with breathing, moving, and swallowing.

How severe those are be depends on many things.

There are five different types of SMA. They’re based on when symptoms first showed up and the highest physical milestones you reached when they did.

The most severe form, known as type 0, is rare, and usually fatal, either before the child is born, or shortly after.

Type 1 is the most common and is diagnosed at birth to 6 months of age. It is also a severe form of SMA. On the other hand, type 4, diagnosed in adults, is the least common and is the least severe.

Symptoms can overlap, but in general, the earlier you get SMA, the more serious your complications can be.

It is important to remember that no two cases are alike, and all people with SMA go through different things.

Type 1

Breathing: Infants with this form of the disease can have serious breathing complications. That’s because the muscles that control breathing and sucking are severely affected by the disease.

Some complications can include:

  • Noisy breathing
  • A weak cry
  • Pneumonia and other chest infections

Some children with type 1 may have trouble breathing that comes on suddenly. That’s because the muscle separating your child’s abdomen from their diaphragm becomes paralyzed at some point between 6 weeks and 6 months of age. That may require lifelong breathing assistance with a ventilator.

Movement: Infants with type 1 SMA also have a lot of trouble moving, thanks to less muscle tone and fewer reflexes.

Fetuses have limited movement. They can be born with contractures. Those are basically stiff muscles, tendons, and ligaments that aren’t elastic.

Other complications that affect movement include:

  • Fasciculations (muscle twitching)
  • Scoliosis, also called curvature of the spine. This can also make it hard to sit and stand.


Feeding complications: Because muscles control how we chew and swallow, your child may have issues tied to eating.

Weak swallowing can lead to aspirating (inhaling) food. That can cause choking and respiratory infections.

Because eating takes a lot of effort, your child may use a lot of energy simply trying to breathe and feed themselves. This can cause them to not gain enough weight, or to lose weight.

Your child might also have trouble opening their mouth. Food may get stuck in their cheeks, too.

Type 2

This form of SMA is intermediate. Symptoms first show up between 6 and 18 months of age. But some children can show symptoms earlier. Kids with this type of SMA can sit without help, but can’t stand or walk without assistance.

They may have something called hypoventilation while they sleep. It’s breathing that’s too shallow and too slow. It leads to a buildup of carbon dioxide in the blood, which can cause fatigue.

They’re also likely to get scoliosis.

Type 3

Symptoms of this form generally don’t begin until your child is 18 months of age or older. Your medical team may call it Kugelberg-Welander disease. Your child can walk without help, but could have a tough time running, climbing stairs, or getting up from a chair. Other complications include:

  • Hand tremors
  • Scoliosis
  • Respiratory infections


Type 4

This rare category usually happens after age 21. Symptoms are generally mild to moderate. People with this can walk during adulthood, but can have muscle weakness that gets worse over time.

WebMD Medical Reference Reviewed by Hansa D. Bhargava, MD on November 04, 2020



Columbia University Motor Neuron Center: “About Motor Neurons.”

NIH, National Institute of Neurological Disorders and Stroke: “Spinal Muscular Atrophy Fact Sheet.”

Cure SMA: “About SMA for Healthcare Providers.”

Cleveland Clinic: “Spinal Muscular Atrophy.”

MDA, Muscular Dystrophy Association: “Spinal Muscular Atrophy.”

Genetics Home Reference: “Spinal muscular atrophy with respiratory distress type 1.”

UPMC Orthopedic Care: “Joint and Muscle Contractures.”

Spinal Muscular Atrophy UK: “Looking after your child who has had a recent diagnosis,” “Scoliosis in Spinal Muscular Atrophy.”

U.S. National Library of Medicine: “Hypoventilation.”

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