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If you or someone you know is exhibiting symptoms of SMA, consult your medical provider immediately.

What is Spinal Muscular Atrophy?

Spinal muscular atrophy (SMA) is categorized as a rare genetic disorder that affects the ability of the body to control voluntary muscle movement. When a person has SMA, their body experiences a loss of essential cells in the spinal cord, which are important for muscle strength development and movement. Because SMA is a spectrum disease, individuals can experience symptoms that range in severity. In this article, we will cover spinal muscular atrophy symptoms, as well as the different types.

SMA Causes

There is no clear understanding of the exact genetic cause for SMA. However, there is a specific mutation that occurs. Essentially, a mutation in the survival motor neuron 1 (SMN1) gene occurs which leads to a decreased production of survival motor neurons (SMN). The body needs this in order to create muscle strength and movement.

When the body doesn’t have proper levels of SMN, then the motor neurons get lost in the spinal cord and muscles never receive the proper messages from the brain. Research is still being done to better understand SMA causes.

Common SMA Symptoms

While there are certainly a wide variety of potential symptoms, there are general symptoms that point to this disease. Common symptoms of SMA include:

  • Progressive muscle weakness.
  • Floppiness.
  • Atrophy (muscle wasting).
  • Muscle weakness on both sides of the body.

Keep in mind, some people experience mild to severe spinal muscular atrophy symptoms, depending on their exact type of SMA.

SMA Symptoms in Infants

As mentioned, spinal muscular atrophy symptoms can vary based on the severity of the disease. However, there are certain characteristics of SMA symptoms in infants that parents should be aware of.

Infant-onset SMA, also medically referred to as type 1, Werdnig-Hoffmann disease, is categorized as children who are 0 to 6 months old. Typically, children who have SMA at this age never gain the ability to sit and have a life expectancy of fewer than 2 years.

SMA symptoms in infants aged 0 to 6 months include:

  • Inability to control head movement.
  • Muscle weakness in both sides of the body.
  • Poor muscle tone.
  • A weak cough and cry.
  • Progressive muscle weakness that impacts the ability to chew and swallow.
  • 'Frog-leg' posture when lying down.
  • Weakness of muscles that impact breathing ability.

SMA Symptoms in Infants Aged 7 to 18 Months

This type of SMA is referred to as type 2, Dubowitze Disease. Children who develop SMA between the ages of 7 to 18 months have a much better survival rate. 70% of people in this category are still alive at the age of 25. They have learned to sit properly but still struggle with a variety of symptoms.

SMA symptoms for 7 to 18 months:

  • Development of spinal issues.
  • Difficulty coughing, crying, breathing and swallowing.
  • Muscle weakness.
  • Muscle pain.
  • Joint stiffness.

The most tell-tale sign that an infant may have SMA is when they do not meet certain physical milestones. While every child meets certain milestones at different stages, there are general guidelines that pediatrics follows. If you suspect your child may be physically delayed, it is important to tell your doctor about those concerns.

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SMA Symptoms in Juveniles

Type 3, Kugelberg-Welander Disease, occurs in individuals who get SMA after the age of 18 months. Life expectancy is normal and individuals can walk independently but may later lose this function as the disease progresses.

SMA symptoms for juveniles include:

  • Scoliosis.
  • Difficulty swallowing.
  • Muscles in legs are impacted.
  • Muscle pain.

SMA Symptoms in Adults

Sometimes SMA presents itself later in life. This type of SMA is called adult-onset, type 4. If this occurs, life expectancy is normal, and usually all motor milestones have been achieved but will weaken over time.

SMA symptoms in adults include:

  • Scoliosis.
  • Difficulty swallowing.
  • Muscles in legs are impacted.
  • Muscle pain.

Over time, the condition will worsen with more tremors, muscle weakness and muscle twitching.

Keep in mind that because SMA is a spectrum disease, people may not experience all of the symptoms in their defined type of SMA. Progression may be faster or slower for some individuals, and the age of the person when they first experience the onset of SMA will also greatly influence the severity of the symptoms.

Up to 25% of people diagnosed with SMA do not have the exact symptoms of their diagnosed type of SMA. There is a range of severity with each type, but muscle weakness typically appears on both sides of the body.


SMA is a serious condition that should be monitored by a doctor who specializes in this condition. Typically, there is a need for home health care and regular check-ups to monitor the progression of the disease. People may also need to learn ways to make home modifications to make it easier to live with SMA or participate in physical therapy to maintain independence as long as possible.

If you or someone you know may have SMA, it is important to discuss your options with your medical provider. Keep in mind, the symptoms of SMA mirror other diseases, so proper diagnosis is critical. Reach out to your doctor to learn more.