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Spinal muscular atrophy is a rare genetic disease affecting nerve cells in the brain stem and spinal cord. It causes low muscle tone, muscle weakness, and muscle wasting. These problems lead to a progressive loss of muscle strength, mobility, and function. All movement skills can be affected by the disease, such as walking, swallowing, eating, and breathing. SMA is the most common genetic cause of death in infants worldwide. About one in 40 to one in 60 people carry the SMA gene. However, it affects between one in 6,000 to one in 10,000 babies. People of any race or gender can be born with SMA.

Physical therapists help children and adults with SMA develop muscle strength. They help them achieve the ability to move and function at the highest level possible. Physical therapists are movement experts. They improve quality of life through hands-on care, patient education, and prescribed movement. You can contact a physical therapist directly for an evaluation. To find a physical therapist in your area, visit Find a PT.

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What is Spinal Muscular Atrophy?

SMA is a genetic disease that affects the nerves in your muscles. It impairs the chemicals in nerves that help muscles work. A gene called the survival motor neuron 1, or SMN1, is missing or altered in people with SMA. In healthy people, the SMN1 gene produces the SMN protein. This protein is vital to the function of nerves that control muscles. Without the protein, nerve cells cannot work properly and die, which leads to severe muscle weakness.

The SMN2 gene is a backup gene that can also produce some SMN protein. But the SMN2 gene cannot fully make up for the loss of the SMN1 gene. The number of SMN2 genes varies from person to person. People with more SMN2 genes usually have a less severe form of the disease. The severity of SMA ranges from mild muscle weakness to total paralysis and the need for support to breathe.

Signs and Symptoms

Muscle weakness is a hallmark feature of SMA. This muscle weakness relates to other problems, such as:

  • Muscle wasting (atrophy).
  • Low muscle tone (hypotonia). A child's body may feel loose or floppy.
  • Absent or noticeably decreased deep tendon reflexes (such as knee-jerk reflex).
  • Involuntary (done without thinking) tongue movements or tongue quivering.
  • Hand tremors.
  • Tight joints that do not bend or stretch all the way or possibly don't move at all.
  • Poor balance.
  • Spinal deformity (scoliosis).
  • Respiratory infections and lung disease.

SMA differs with each person. Symptoms and how the disease progresses range from mild to severe based on the types of SMA. The onset of SMA can occur any time from birth to adulthood. Generally, as a person ages, muscle strength decreases, and symptoms get worse. However, people with SMA can experience plateaus (periods when the disease stays stable) at different times.

Loss of function varies based on the level of impairment. Loss of function may limit a person's ability to take part in activities. While children with severe SMA may die in infancy or childhood, some people with less severe SMA live a typical life span.

Early research on the use of recently introduced disease-modifying therapies has shown people with SMA type 1 live longer than those for whom these treatments were not available.

How Is It Diagnosed?

Diagnosing SMA begins by observing any signs and symptoms of the disease. If suspected, a blood test can find the specific gene mutation that causes SMA in about 95% of cases. Further testing is needed to detect a rarer form of SMA in the other 5% of cases. In these rarer cases, doctors may perform a muscle biopsy to test for nerve problems. Electromyography (a test that measures nerve signals and muscle activity) may be used to assess how well the nerves control the muscles and how the muscles are activated.

The three most common types of SMA are:

SMA Type 1 (Werdnig–Hoffmann disease). This is the most often diagnosed and most severe form of SMA. The disease appears at birth or in the first six months of life, and the child never learns to roll or sit on their own. A child with SMA type 1 will have severe muscle weakness and low muscle tone. Infants typically have:

  • Muscle wasting.
  • Weakness in the head and neck, arms, legs, and trunk.
  • Decreased movement.

The child may move their tongue without thinking about it and may have hand tremors. Children may get frequent respiratory infections and need breathing support. Before advanced medicines to treat SMA were available, most children with SMA died before age two. Children with SMA type 1 historically did not learn to sit without treatment. With the development of medicines and therapy interventions focused on motor skills, many children with SMA type 1 learn to sit independently and may even learn to walk.

SMA Type 2 (intermediate form). This type develops between six and 18 months of age. It causes less severe weakness than SMA type 1. Children with SMA type 2 can learn to sit without support, but need braces and assistance to stand and walk. Tongue movements and hand trembling may be seen, but are less apparent than in SMA type 1. Tightening of joints and scoliosis are common. Respiratory infections and other problems often occur, and it is typical for people with SMA type 2 to need help breathing as the disease progresses. Children may gradually lose the ability to sit without support. Life expectancy is lower, but most people with SMA type 2 live into their teens or young adulthood.

SMA Type 3 (Kugelberg–Welander disease). Children with SMA type 3 show signs and symptoms later and have a better prognosis than children with type 1 or type 2. SMA type 3 is usually diagnosed between 18 months and 3 years of age. Weakness is frequently not noticed until later in childhood or early adulthood, which may delay diagnosis until as late as age 17 in mild cases. Children with SMA type 3 typically reach developmental milestones and walk on their own. Some may continue to walk into their teens or adulthood, but they likely will have:

  • Poor balance.
  • Slight backward knee bending (hyper-extended knees).
  • Waddling walking pattern.

Children with SMA type 3 also develop muscle tightness, joint stiffness, and deformities. They also may have scoliosis and fall often. Muscle weakness mainly occurs around the trunk (torso) and hips. SMA type 3 is less severe than in SMA types 1 and 2.

SMA type 4. The signs and symptoms develop after age 21. Weakness is typically less severe when compared with other types of SMA.

Rare SMAs. Other forms of SMA are rare. Genes other than the SMN1 gene cause them. Your doctor or physical therapist can inform you about the more rare forms of the disease.

The terms non-sitter, sitter, and walker have been used to label function level for children with SMA. These terms aid parents and health care providers when making decisions about how to manage the condition. The terms can help when describing patient progress, as treatments evolve and people with SMA gain abilities they would not have otherwise reached.

Early treatment with medicines and physical therapy at or shortly after diagnosis may greatly change the course of the disease and improve outcomes.

How Can a Physical Therapist Help?

Evaluation by a physical therapist is vital for guiding the treatment of a child with SMA. Your physical therapist will conduct a full evaluation. It will include taking a health history and a hands-on physical exam. Evaluation of the following is of great importance:

  • Posture and body alignment.
  • Muscle strength and the ability to move against gravity.
  • Assessing movement (motor) and functional abilities, such as floor mobility, rolling, sitting, walking, climbing, and transferring from a chair, car, or bed.
  • Balance.
  • Joint motion.
  • Breathing function.
  • Ability to take part in activities with family and friends.
  • Quality of life.

Physical therapy treatment helps people with SMA reach the highest level of independence and mobility possible. It also can help to prevent or delay related problems. Physical therapists work closely with children and adults with SMA and their families to develop treatment programs for their specific needs. They work with you to set goals based on ability, function, and interests. Evidence supports the value of structured exercise programs for people with SMA to reduce disability and maintain mobility.

Physical therapy treatment for people with SMA may include activities to:

Maintain and improve overall movement and function. This includes improving developmental skills in infants and children such as:

  • Head and trunk control.
  • Rolling.
  • Crawling.
  • Sitting.
  • Changing positions.

Your child's physical therapist will work on skills like getting in and out of bed or pulling to stand. They also may work with your child on balance and coordination for more advanced skills like going up and down stairs and walking.

Prevent or slow the progression of muscle shortening (tightness), stiffness, and joint deformities. Physical therapists help you learn specific flexibility and range-of-motion exercises and positioning. They also may recommend splints, braces, standing devices, or serial casting (to reshape deformed limbs or joints).

Manage scoliosis and bone problems. Physical therapists work with people to help keep the spine and body supported and aligned during daily activities. They design treatment programs and may use braces or supportive seating to help people with SMA maintain good posture and protect their bones and joints. If scoliosis or other joint problems caused by SMA require surgery, physical therapy may be provided before and after surgery.

Manage breathing complications. Respiratory exercise training is essential for people with SMA to prevent breathing problems. It also is vital before and after surgery. Physical therapists teach parents and caregivers methods for chest drainage. They also help you and your child learn how to clear the chest and teach coughing and breathing practices to keep the lungs free of fluids so they can breathe well. Chest physical therapy also includes core and breathing exercises and postural support through good positioning. They also recommend custom and molded wheelchair seating systems and custom sleeping systems.

Select assistive devices. Many people with SMA need adaptive or assistive devices to help them function, especially after surgery. Physical therapists work with other specialists to select and modify suitable devices to meet each person's specific needs. Physical therapists teach patients and caregivers how to safely use assistive devices to help people with SMA eat, play, move, communicate, or work. Assistive devices to support positioning and movement may include strollers, wheelchairs, customized seating systems, walkers, and standers. These devices help people with SMA be as independent and mobile as possible.

Strengthen muscles and maintain aerobic fitness. Exercise may help to improve aerobic fitness in people with SMA. Physical therapists select the right type and intensity of exercises to help people with SMA move and stay as active as possible.

Promote standing. Physical therapists help people who cannot stand on their own get any equipment needed to start a daily standing program for home or school. This allows children to be face-to-face with their friends, improves muscle function, and helps prevent joint tightness.

Improve function during mealtime. Physical therapists work closely with speech and occupational therapists to promote healthy feeding. They teach you how to align and support your child's head and body for safe eating and meal enjoyment. They also may teach you ways to help chewing and swallowing. Due to problems swallowing, many children with SMA are on special diets under the guidance of a registered dietician. To ensure that they get enough calories and balanced nutrition, some people with SMA receive their feedings through tubes (either through the nose or a surgically placed feeding tube). Others need tube feedings to add to their food intake. Therefore, therapists and families must receive clearance from the child's doctor before working on feeding.

Your child's physical therapist will choose exercises, games, and fun tasks that will be taught during therapy. They also teach families positioning and activities to help improve everyday habits at home. Physical therapists carefully monitor exercise and activity levels to avoid fatigue. They help patients and families understand how to reduce the risk of overworking muscles.

Another treatment option is aquatic therapy or hydrotherapy (therapy provided in a pool). Some physical therapists have expertise in aquatic therapy. They use the physical properties of water (such as buoyancy and pressure) to reduce the risk of fatigue or overworked muscles. The buoyancy and decreased gravity in water allow people with SMA to move, stand, and walk more easily than they can on land. The water's support can enable strengthening, balance training, and aerobic training. Some non-sitters can participate safely in aquatic therapy with proper head and neck support and supervision.

How Can a Physical Therapist Help Before and After Surgery?

People with SMA may need surgery for scoliosis, hip alignment, or to release joint tightness. A physical therapist will evaluate you or your child before any scheduled surgery. They will plan for equipment needs and design a treatment program after surgery. Early movement after surgery is often recommended, so developing a plan of action before surgery is important.

Physical therapists also will evaluate you or your child again shortly after surgery. Resuming physical therapy as soon as possible helps maintain comfort, muscle strength, and provides education for after-surgery care. Physical therapists also provide modified movement plans for the early treatment phase after surgery. Longer-term physical therapy allows for continued improvements in function and mobility after surgery.

Can This Injury or Condition Be Prevented?

SMA is a genetic disorder passed from parent to child. Most people have two copies of the SMN1 gene. People who have one faulty copy and one functioning copy of the gene are carriers. While carriers do not have SMA, they may pass the defective gene to their children. Both parents must pass on the gene for their child to have SMA. A simple blood test can tell whether a person carries the SMA gene. Most people do not know they carry the gene until they have a child with SMA.

Excellent prenatal care is important for all pregnant women and their babies. A test during pregnancy can find out if the baby has SMA. If doctors discover SMA during pregnancy, physical therapists and other health care providers can lessen problems that can occur after birth such as:

  • Developmental delay.
  • Difficulty with feeding.
  • Abnormal posture and scoliosis.
  • Loss of joint range of motion.
  • Limited ability to move.
  • Breathing problems.

Your physical therapist is ready to help ensure that you or your child can live to the fullest extent possible. Recently, several medicines have advanced treatment and improved the lives of people with SMA. Newborn screening for SMA occurs in many states. Improved outcomes and potential also have led to changes in physical therapy recommendations (see Standard of Care Documents of 2018).

What Kind of Physical Therapist Do I Need?

All physical therapists are prepared through education and experience to treat patients with SMA. However, you may want to consider:

  • A physical therapist with experience in pediatrics, neuromuscular disorders, and/or developmental disorders. Some physical therapists have a pediatric practice and will work with you and your child or teen in the clinic, home, school, or community. Adults also may receive treatment from physical therapists at home, school, or in a clinic.
  • A physical therapist who is a board-certified clinical specialist or who has completed a residency, fellowship, or training in pediatric or neurologic physical therapy. This physical therapist has advanced knowledge, experience, and skills that may apply to developmental conditions, such as SMA.
  • An experienced pediatric or neurologic physical therapist who works on a team with the other health care providers to achieve the best outcomes for people with SMA.
  • A physical therapist who focuses on treating infants, children, or adults with neuromuscular disorders and has some experience with or willingness to learn more about the SMA Standards of Care.

You can find physical therapists in your area with these credentials and clinical expertise on Find a PT, a tool built by the American Physical Therapy Association.

General tips when you're looking for a physical therapist (or any other health care provider):

  • Get recommendations from family, friends, or other health care providers.
  • When you contact a physical therapy clinic or home health agency for an appointment, ask about the physical therapists' experience in helping people with neuromuscular disorders, SMA, or other developmental disorders.
  • Be prepared to describe your symptoms in as much detail as possible during your first visit. Make a note of what makes your symptoms better or worse.

Find a PT Near You!

The APTA Academy of Pediatric Physical Therapy contributed to this consumer resource. It is for information purposes only and is not intended to represent the position of APTA Pediatrics.

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The American Physical Therapy Association believes that consumers should have access to information to help them make informed decisions and prepare them for their visit with a health care provider.

The following resources offer some of the best scientific evidence related to physical therapy treatment for SMA. They report recent research and provide information on the standards of practice both in the United States and internationally. They link to a PubMed* abstract (which may also offer free access to the full text) or other resources. You can read them or print out a copy to bring with you to your health care provider.

Trenkle J, Brugman J, Peterson A, Roback K, Krosschell KJ. Filling the gaps in knowledge translation: physical therapy recommendations for individuals with spinal muscular atrophy compared to standard of care guidelines. Neuromuscul Disord. 2021;31(5):397–408. Article Summary on PubMed.

Rathore FA, Afridi A. Does physical exercise training improve functional performance in type 3 spinal muscular atrophy? A Cochrane Review summary with commentary. Dev Med Child Neurol. 2020;62(9):1014–1016. Article Summary on PubMed.

National Institute of Neurological Disorders and Stroke. NINDS spinal muscular atrophy fact sheet. Published May 2019. Accessed April 21, 2021.

Dangouloff T, Servais L. Clinical evidence supporting early treatment of patients with spinal muscular atrophy: current perspectives. Ther Clin Risk Manag. 2019;15:1153–1161. Article Summary on PubMed.

Magri F, Vanoli F, Corti S. miRNA in spinal muscular atrophy pathogenesis and therapy. J Cell Mol Med. 2018;22(2):755–767. Article Summary on PubMed.

Finkel RS, Mercuri E, Meyer OH, et al. Diagnosis and management of spinal muscular atrophy: part 2—pulmonary and acute care; medications, supplements, and immunizations; other organ systems; and ethics. Neuromuscul Disord. 2018;28(3):197–207. Article Summary on PubMed.

Mercuri E, Finkel RS, Muntoni F, et al. Diagnosis and management of spinal muscular atrophy: part 1—recommendations for diagnosis, rehabilitation, orthopedic, and nutritional care. Neuromuscul Disord. 2018;28(2):103–115. Article Summary in PubMed.

Cure SMA. Updated 2018 SMA Standards of Care Statements. Accessed April 21, 2021.

Verhaart IE, Robertson A, Wilson IJ, et al. Prevalence, incidence, and carrier frequency of 5q-linked spinal muscular atrophy: a literature review. Orphanet J Rare Dis. 2017;12(1):124. Article Summary on PubMed.

Bowerman M, Becker CG, Yáñez-Muñoz RJ, et al. Therapeutic strategies for spinal muscular atrophy: SMN and beyond. Dis Model Mech. 2017;10(8):943–954. Article Summary on PubMed.

Madsen KL, Hansen RS, Preisler N, Thøgersen F, Berthelsen MP, Vissing J. Training improves oxidative capacity, but not function, in spinal muscular atrophy type III. Muscle Nerve. 2015;52(2):240–244. Article Summary in PubMed.

Cure SMA. Cure SMA website. Accessed April 21, 2021.

US National Library of Medicine, Medline Plus. Spinal muscular atrophy. Accessed April 21, 2021.

D'Amico A, Mercuri E, Tiziano FD, Bertini E. Spinal muscular atrophy. Orphanet J Rare Dis. 2011;6:71. Article Summary on PubMed.

Wang CH, Finkel RS, Bertini ES, et al. Consensus statement for standard of care in spinal muscular atrophy. J Child Neurol. 2007;22(8):1027–1049. Article Summary on PubMed.

*PubMed is a free online resource developed by the National Center for Biotechnology Information. PubMed contains millions of citations to biomedical literature, including citations in the National Library of Medicine's MEDLINE database.