Spinal Muscular Atrophy (SMA)

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What is spinal muscular atrophy?

Spinal muscular atrophy (SMA) is a group of  conditions related to the nerve cells that control muscles used to sit, stand, move, breathe, cough and swallow. These nerve cells are called motor neurons.

In SMA, there’s a problem with a  that helps your child’s body keep motor neurons healthy. This causes weak muscles. Over time, the muscles get smaller (atrophy) from not being used.

Early diagnosis is essential so treatment can start early. In the United States, newborn screening now includes a test for SMA. In some babies, their floppy muscles at birth make it clear they have SMA. Untreated, most children with severe SMA die before age 2. Some people with mild SMA have no symptoms until adulthood and live a normal lifespan.

  • Genetic causes of SMA

    In most types of SMA, a gene called survival motor neuron 1 (SMN1) is missing or abnormal.

    • Healthy SMN1 makes survival motor neuron (SMN) protein.
    • Abnormal SMN1 makes much less SMN protein or none at all.
    • Without enough SMN protein, motor neurons shrink and eventually die.

    A “backup” gene, SMN2, makes some SMN protein. It can partly make up for faulty SMN1. Some people have more copies of the SMN2 gene than other people do. Typically, the more SMN2 copies your child has, the later their symptoms will start and the milder their symptoms will be.

    If a child inherits 2 abnormal genes — 1 from each parent — the child will have SMN-related SMA. Changes to other genes besides SMN1 can cause other types of SMA. Less common types of SMA can happen when only 1 parent passes an abnormal gene to their child.

Spinal Muscular Atrophy Care at Seattle Children's

Our Neuromuscular Program’s team of experts evaluates and treats babies, children and teens with problems related to their muscles and nerves. We focus on understanding your child’s unique needs and improving their function, overall health and quality of life.

What are the symptoms of spinal muscular atrophy?

Children with SMA may show signs and symptoms right after birth or months or years later. Symptoms can range from mild to severe. The most serious type of SMA (type 1) usually causes worse symptoms that start in the first 6 months of life. But even children with the same type of SMA may have different symptoms, starting at different times.

Without treatment, weak muscles may affect your child’s ability to:

  • Hold up their head
  • Sit up or stand without help
  • Roll over, crawl, walk or run
  • Breathe or cough easily on their own
  • Swallow food and liquid safely

With type 1 SMA, your child may breathe from their stomach rather than their chest. As your child’s muscles get weaker, they may not breathe well on their own and may need equipment to help.

Children with milder types of SMA may have full muscle strength as babies or children. But without treatment they get weaker over time. As teens or adults, some may lose their ability to walk or may need a device to help them breathe while sleeping.

Over time, other health problems linked with muscle weakness may start. These include curved spine (scoliosis or kyphosis), abnormal hip joints and brittle bones that break easily.

SMA does not affect your child’s thinking or emotions.

How is spinal muscular atrophy diagnosed?

Most babies born in the United States today are screened at birth for SMA. The blood test checks for changes in SMN1, the gene that causes most SMA. Of babies with SMA caused by a different genetic change, the test identifies about 95 out of 100 cases (it misses 5%).  

If a child’s SMA was not detected by newborn screening, they may be diagnosed later as symptoms appear.  

If genetic testing or your child’s symptoms indicate they have SMA, your child’s doctor will:

  • Ask about your child’s symptoms, development and medical history
  • Ask if anyone else in your family has had the same kind of symptoms
  • Examine your child
  • Check for muscle weakness and delays in reaching for their age

If your child has symptoms of SMA but genetic tests show their SMN1 gene is normal, they may have 1 or more of these tests:

  • Blood test to check the level of an enzyme (serum creatine kinase) that is higher when muscles are damaged
  • Muscle to see if your child’s muscle cells are abnormal
  • Studies to diagnose nerve and muscle problems ( or EMG/NCV)

Seattle Children’s offers genetic counseling and testing for parents and other family members of children with SMA.

Types of SMA

Doctors group SMN-related SMA into 4 types based on your child’s highest level of abilities and number of SMN2 copies. With SMA screening at birth, the idea of SMA types is changing. If started early enough, treatment may prevent or minimize the muscle weakness SMA can cause.

Type 1 SMA:

  • Your baby cannot control their head movement well and cannot sit or stand on their own.
  • Usually diagnosed by the age of 6 months.
  • Also called Werdnig-Hoffman disease or infantile-onset SMA.

Type 2 SMA:

  • Your child can sit on their own but may need help getting into a seated position. They may be able to stand with help but cannot walk.
  • Usually diagnosed by age 2.
  • Also called intermediate SMA.

Type 3 SMA:

  • Your child can stand and walk on their own, but they may have trouble walking, running or climbing stairs as they get older.
  • Usually diagnosed by age 3 but sometimes as late as the teen years.
  • Also called Kugelberg-Welander disease or juvenile SMA.

Type 4 SMA:

  • Your young adult may have mild motor problems, like muscle weakness, and twitching.
  • Usually diagnosed after age 35 but sometimes as early as 18.
  • Also called adult-onset SMA.

Other, less common types of SMA include:

  • Spinal muscular atrophy respiratory distress (SMARD), which affects babies and causes serious breathing problems
  • Distal SMA, which mainly affects the hands and feet

How is spinal muscular atrophy treated?

Your child will receive complete care from our Neuromuscular Program team and other specialists across Seattle Children’s. These experts will work as a team, with you and your child, to support their movement, strength, comfort and health. We customize treatment to your child’s changing needs to help them be as healthy, active and independent as they can.

Treatments have greatly improved over the past decade. Since 2016, the FDA has approved 3 treatments that affect the genes involved in SMA. Zolgensma®, Spinraza® and Evrysdi® help your child’s body make enough of the survival motor neuron protein (SMN) to keep motor neurons healthy and functional.

Starting therapy soon after diagnosis is key to the best outcomes for your child. Medicines for SMA help slow down or even stop the progression of SMA. In addition, your child’s care team watches for problems related to SMA and helps prevent or manage them. As needed, your child may have , , bracing devices, surgery and breathing support. Your child may be able to take part in research studies of new ways to treat SMA.

  • Zolgensma gene replacement therapy

    Zolgensma® is gene replacement therapy. A single transfers a working copy of the SMN1 gene to your child’s motor neurons. The new gene boosts production of SMN protein to improve how your child’s motor neurons work. The FDA has approved it for children under age 2.

  • Spinraza

    Spinraza® helps your child’s body produce more, better-quality SMN protein. This keeps motor neurons healthy, slows muscle weakness and improves strength. Doctors put a needle in your child’s lower back to inject the medicine into the (CSF). Your child will need 4 treatments in the first 2 months of treatment and 1 dose every 4 months after that. The FDA approved the drug for children and adults in 2016.

  • Evrysdi

    Evrysdi® is the first oral (by mouth) drug treatment for SMA. It increases the efficiency of the SMN2 gene so your child’s body makes enough SMN protein to keep motor neurons healthy. The FDA has approved it for treatment of children at any age.

  • Physical therapy and assistive devices

    To support your child’s ability to move and do the things they want to, your child may have:

    • Physical therapy (PT) for range of motion and flexibility. We also assess if equipment may help your child move around.
    • Occupational therapy (OT) to help your child with activities like dressing and using a computer.
    • Leg braces to help your child stand and move on their own.
    • Braces to support their wrists or hands.
    • Back brace to keep a spinal curve from getting worse.
    • Devices that help your child sit up, stand, walk or get around. Options include a seating system, walker, standing frame, wheelchair, power wheelchair and motorized scooter.
  • Orthopedic surgery

    Over time, muscle weakness may cause problems like:

    • Curved spine (scoliosis or kyphosis)
    • Hip joints that don’t develop normally or that become dislocated
    • Brittle bones that break easily

    Orthopedic surgery to treat severe scoliosis or kyphosis can help your child sit up, sleep more comfortably or breathe more easily. Surgeons can implant “growing rods” in children as young as 5 (before their spine has finished growing) to help them keep an upright posture.

  • Lung care and breathing support
    • Deformities of the spine, chest wall and hips can lead to less space for the lungs and make it harder to breathe. Weak muscles can affect how well your child’s lungs work.
    • Infections can become serious if weak breathing muscles make it hard for your child to cough effectively. Our goal is to prevent respiratory infections and treat them early.
    • A device called a cough-assist machine can help your child get a deeper breath and then clear their airways. A will set up the machine and teach you how to use it.
    • Some children with SMA may need a machine to help with breathing (bilevel positive airway pressure or Bi-PAP). Some children start by using Bi-PAP only at night and increase its use over time.
  • Diet and nutrition

    Problems with swallowing may make it hard for your child to get the nutrition they need. They may suck food or liquid into their airways (aspirating). If your child has trouble feeding or swallowing, our experts in Speech and Language Services will help them.

    A and others on your child’s team will work with you and your child to:

    • Make sure your child gets the nutrition they need for the best growth and development.
    • Get the right amount of calories so they do not become overweight if they are less active.
    • Adjust your child’s diet, if needed, when they have a condition that affects the nutrition they need.
    • Learn how to use a feeding tube if your child cannot chew and swallow safely. Options include a  or .
  • Support and social work

    A helps your child and family with coping, social relationships, behavior and emotions. Along with your child’s doctors, nurses and therapists, the social worker will connect you with helpful resources at Seattle Children’s and in the community.

Why choose Seattle Children’s for spinal muscular atrophy care?

Seattle Children’s Neuromuscular Program offers the most comprehensive care in the Pacific Northwest for children with SMA. We have been named an MDA Care Center by the Muscular Dystrophy Association, a leading advocacy group for people with SMA and other neuromuscular disorders. We are 1 of 2 referral sites for newborn screening in Washington state.

Our team has the expertise and experience to diagnose your child and give them the best care for their unique needs. Our SMA team includes doctors, nurses, physical and , , and . Seattle Children’s pediatric specialists in Rehabilitation Medicine, Neurology, Orthopedics and Pulmonary and Sleep Medicine will care for your child.

Our full range of treatments includes and other medicines, and equipment, respiratory support and surgery. We work with your family to give your child the best possible function and quality of life — now and as they grow.

At regular clinics in Seattle and an annual clinic in the Tri-Cities, we bring together experts from different specialties, so your child gets the care they need on the same day. Our patients have access to the latest treatments and promising new therapies offered only in research studies.

Seattle Children’s was the first hospital in Washington state to offer a gene replacement therapy called onasemnogene abeparvovec-xioi (Zolgensma®) for SMA. We were among the first hospitals in the country to offer nusinersen (Spinraza®), the first drug approved by the Food and Drug Administration (FDA) for SMA. We took part in that led to FDA approval for Spinraza. Our treatment options also include risdiplam (Evrysdi®), the first drug for SMA taken by mouth.

A baby in a bouncer

“Gene therapy sounded like something from a science fiction movie, and I’m not sure we’ll ever completely understand how it works. But the future is now, so we decided to trust the process and let the doctors do what they do best to let Arabella have the best life possible.”

— Vitaliy Smygov, father of Arabella, whose life changed after gene therapy for SMA type 1

  • Research to improve outcomes
    • Our active clinical trials program means your child may have the chance to receive promising new therapies in a research study that matches their specific situation.
    • To learn more about neuromuscular research at Seattle Children’s, email us at: muscleresearch@seattlechildrens.org.

Contact Us

Contact the Neuromuscular Program at 206-987-6678 for a referral, a second opinion or more information.

Paying for Care

Learn about paying for care at Seattle Children’s, including insurance coverage, billing and financial assistance.