Infantile spinal muscular atrophy (SMA) is a neuromuscular disorder that affects the nerve cells in the spinal cord. It causes muscles to weaken and limits muscle movement.

SMA is a rare condition. According to the National Human Genome Research Institute, it affects 1 in every 6,000–10,000 people worldwide.

The SMA Foundation states that 10,000–25,000 children and adults in the United States have this disorder.

It is more likely to cause complications when doctors diagnose it in infants and children, and it can increase the risk of infant death. People who develop SMA symptoms later on have a greater chance of a positive outlook.

This article will explain what infantile SMA is, as well as the symptoms, treatment, and outlook for the condition. It will also explore options for support for those with SMA.

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According to the United Kingdom’s National Health Service (NHS), the most common symptoms of SMA are:

  • weakness in the arms and legs
  • tremors
  • curved spine
  • difficulty walking
  • difficulty sitting up

The National Library of Medicine states that SMA-related muscle weakness can lead to swallowing difficulties. These can make people more prone to tiredness, constipation, and delayed gastric emptying.

What are the first signs of SMA?

SMA can cause different symptoms depending on the type of the condition a child has:

  • Type 1: Doctors call this Werdnig-Hoffmann disease or infantile-onset SMA. It can cause breathing difficulties and can be life threatening if the infant does not receive treatment within the first year. Medical professionals may diagnose SMA type 1 before an individual gives birth if tests indicate low levels of fetal movement.
  • Type 2: SMA type 2 symptoms appear when the child is 6–18 months old. The condition may make it difficult for them to stand or walk, and they may have breathing difficulties.
  • Type 3: Infants with SMA type 3, or Kugelberg-Welander disease, develop symptoms after age 18 months. They can walk on their own, but they may have difficulty climbing stairs or getting up from a chair. They may also develop scoliosis and muscle shortening.

Learn more about SMA here.

SMA is a genetic disorder that develops when parents pass on the genes responsible for SMA to their children.

Genes come in pairs, and a person inherits a copy of each gene from each parent. SMA occurs when the SMN1 genes undergo changes, or mutations, that cause the motor neurons in the brain and spinal cord to stop working.

According to a 2021 review, 1 in 40–50 people are carriers of the mutated SMN1 gene. However, this does not mean that they have SMA.

The NHS explains that if both parents are carriers, there is a 25% chance that their child will have SMA. There is also a 25% chance that the child will not have SMA and will not inherit the mutated genes.

Learn more about SMA gene therapy here.

People may have an increased chance of having a child with SMA if they already have another child with the condition or if they have a family history of it.

Individuals can consult a genetic counselor to discuss future pregnancy risks. A genetic counselor may also suggest any tests they can perform to detect possible fetal SMA-related symptoms.

The authors of a 2017 research article note that SMA can affect immune function and reduce the quality of life. People with this condition should avoid contact with those who do not feel well, as infections can lead to complications.

A small 2015 study with nine participants suggests that people who have SMA and do not exercise may have a greater risk of developing bedsores and respiratory infections. The researchers suggest that a supervised home-based resistance-training exercise program can benefit children with SMA by helping to improve muscle strength and motor function.

According to the Centers for Disease Control and Prevention (CDC), newborn screening programs can help diagnose SMA in infants within the first 48 hours after birth.

Doctors can take a blood sample to check for any changes in the SMN1 gene.

The NHS affirms that pregnant people who have a family history of SMA or already have a child with the condition should consider seeing a genetic counselor. A counselor may perform a genetic test to find out whether the individual has the genetic change that may lead to SMA.

These tests can also take place during pregnancy:

  • Chorionic villus sampling: This test involves taking cells from the placenta during the 11th to 14th week of pregnancy.
  • Amniocentesis: Medical professionals test a sample of the amniotic fluid during the 15th to 20th week of pregnancy.

There is no cure for SMA, but medications can help improve a person’s quality of life.

Oral medications

The Food and Drug Administration (FDA) has approved Evrysdi for children who have SMA and are aged 2 months or older. It is an oral medication that contains risdiplam, and its side effects include fever, diarrhea, and skin rash.

People with SMA do not have the survival motor neuron (SMN) protein, which helps the motor neurons in the brain and spinal cord control movement. The drug increases the production of this protein and the survival rate of motor neurons.


There are also two FDA-approved injectable drugs for newborns with SMA:

  • Nusinersen: This medication slows the progression of the condition and reduces muscle weakness. It is available under the brand name Spinraza.
  • Oonasemnogene abeparvovec-xioi: This is a gene therapy drug and is available as a fusion in a single dose. The brand name is Zolgensma.

Learn more about SMA treatment here.

The outlook for SMA depends on the severity of the condition. Symptoms usually worsen if a person does not receive treatment.

SMA usually causes infant death within the first few months. However, some new drugs, such as onasemnogene abeparvovec, have been effective in those with SMA type 1 and improved their life expectancy.

If a parent or caregiver has a child with SMA, they can:

  • take them to see a physical therapist, who can suggest stretching exercises for them to do
  • help them engage in breathing exercises to strengthen their muscles
  • take them to see an occupational therapist if they have difficulty walking

Organizations and charity groups that can offer more information and resources about infantile SMA include:

SMA is a rare genetic disorder that causes walking difficulties, respiratory infections, and tremors. During pregnancy, doctors can perform some tests to determine whether a child will have this condition.

SMA is not curable, but medications can help manage symptoms and improve a person’s quality of life.