Patient Guide to Spinal Muscular Atrophy

Spinal Muscular Atrophy: What You Need to Know

What it is, what it does, and how to get your child the treatment they need.

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Parents worry, especially new parents. Everything about babies—from their heads to their toes to their immune systems—is so delicate. Worry can justifiably turn to out-and-out terror upon hearing that your child was (or will be) born with spinal muscular atrophy (SMA).

SMASMA usually affects babies and young children.

But we’re here to tell you that there’s hope. Between emerging treatments and the dedication and expertise of treatment teams around the world, SMA has never been more manageable.

What Is SMA?

Spinal muscular atrophy is an inherited disease that causes weakness and wasting (break down) in muscles that control movement and breathing. The disease is progressive, meaning that symptoms worsen over time. Spinal muscular atrophy most commonly begins in babies before the age of 6 months, but can start at any age depending on which type of SMA a person has.

SMA is considered a rare disease, affecting up to 1 in 11,000 births, but it is also the leading genetic cause of infant death in the United States. Many people are genetic carriers—about 6 million Americans, or 1 in 50—meaning that they have the potential to have children with this disease.

Fortunately, new treatments have changed the natural history of SMA disease. With early diagnosis and treatment, many children and adults with SMA can limit their disease progression, extend their life expectancy, and live with a better quality of life.

“It is a privilege and extremely gratifying to be able to participate in these life-changing treatments and see a disease that was formerly deadly convert into a disease that people can live and thrive with,” says Claudia A. Chiriboga, MD, MPH, Professor of Neurology and Pediatrics at Columbia University Medical Center in New York, NY.

What Causes SMA?

The short story is that people with SMA do not make enough of a protein that keeps motor neurons (nerves responsible for movement) healthy. Without motor neurons, muscles become weak and atrophy (waste away) over time. People with SMA may lose the ability to walk, breathe, and swallow.

Motor neuronA motor neuron

The long story is that SMA is caused by defects in the SMN1 and SMN2 genes on chromosome 5 that causes these genes to produce low levels of survival motor neuron (SMN) protein. This protein helps keep motor neurons in the brain and spinal cord healthy. Without enough SMN protein, motor neurons die and muscles become weak because they cannot contract.

SMA typically occurs in people who inherit two defective copies of the SMN1 gene—one from each parent. The disease affects both genders equally, as well as people of all races and ethnicities.

What Are the Symptoms and Types of SMA?

The main symptoms of SMA are muscle weakness and wasting or breakdown (atrophy) that get worse over time. However, when symptoms start and symptom severity depends on which of the five SMA types of a person has.

“The earlier this onset of symptoms, the more severe the disease process,” Dr. Chiriboga says.

  • Spinal muscular atrophy type 0 is the most severe form and starts in babies before birth, with babies having difficulty moving, swallowing, and breathing at birth.
  • SMA type 1 is the most common form of SMA disease and starts in early infancy, usually in babies less than 6 months of age. Symptoms include low muscle tone, breathing and swallowing problems, and eventually the inability to sit up without help.
  • Spinal muscular atrophy type 2 is found in children between the ages of 6 and 18 months. These children slowly lose muscle strength and function over time, and many lose the ability to sit and stand on their own by adolescence and develop breathing problems.
  • Spinal muscular atrophy type 3 starts in early childhood (older than 18 months of age), adolescence, and early adulthood, with slowly progressive symptoms including falls and trouble walking up and down stairs.
  • Type 4 begins in people in their 20s and 30s and has mild to moderate symptoms of muscle weakness (mostly in the hips and legs), tremor, and mild breathing problems.

Without treatment, muscle weakness gets progressively worse over time in all SMA types.

How is SMA Diagnosed?

Diagnosis of SMA disease is typically made using a genetic test (blood test), which is 95% accurate. The test looks for SMN1 gene mutations to diagnose SMA disease and also is used to count the number of SMN2 copies a person has, which determines disease type.

“In general, the less of these extra SMN2 copies you have, the earlier the symptoms start and the more severe the disease,” Dr. Chiriboga says. The SMN2 gene also makes SMN protein, but at a much lower level than the SMN1 gene. The more copies of SMN2 a person has, the more SMN protein their body makes. For example, babies with SMA type 1 generally have two SMN2 copies, while people with SMA type 4 have up to six copies.

ChromosomesChromosomes in various stages of division

Newborn screening tests can be used immediately after birth to see if a baby is at risk for developing SMA. This allows for immediate confirmation testing and treatment to prevent symptoms from starting or getting worse.

Additionally, carrier screening is recommended for all women before or during pregnancy to determine the risk of having a baby with SMA. If a woman has 1 defective copy of the SMN1 gene, her partner should be tested as well. If both partners are carriers, their baby has a 25% risk of having SMA. Some carriers choose to have prenatal screening (before birth) to determine if their baby has SMA.

How is SMA Treated?

New treatments for SMA offer hope for many people with this disease. These treatments are the first that target the underlying cause of SMA disease, and may be able to prevent the disease from developing or getting worse:

  1. Nusinersen (Spinraza) is approved for of all types of SMA.1
  2. Onasemnogene abeparvovec-xioi (Zolgensma) is a gene therapy approved for children up to age 2 years.2

Another agent—risdiplam—is awaiting approval by the U.S. Food and Drug Administration.3

Additionally, much can be done for SMA patients in terms of preserving their muscle strength and function including respiratory (breathing), nutritional, and rehabilitation care. Physical and occupational therapy may help to improve posture, prevent joint immobility, and slow muscle weakness and atrophy.

Stretching and strengthening exercises may help reduce contractures, increase range of motion, and keep circulation flowing. Some individuals require additional therapy for speech and swallowing difficulties. Assistive devices such as supports or braces, orthotics, speech synthesizers, and wheelchairs may be helpful to improve functional independence.

This patient guide provides more information on the symptoms/types of SMA, diagnosis, and treatment options, with the goal of helping families understand SMA disease and ways to improve patients’ quality of life.

“Improving function at any level and offering the hope of stabilizing the disease is in itself life altering for many of our patients,” Dr. Chiriboga notes.


Updated on: 10/19/20
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Spinal Muscular Atrophy: Types and Symptoms
Khoi D. Than, MD
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Spinal Muscular Atrophy: Types and Symptoms

It’s so important to recognize the signs of spinal muscular atrophy, a serious condition that affects babies and young children. The earlier you start treatment, the more successful it can be, and it all starts with knowing what to look for.
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