Spinal Muscular Atrophy (SMA)

  • "SMA was listed by the National Institutes of Health as the neurologic disease closest to finding a cure. This is not a coincidence...because the scientific community, SMA research organizations, and families are continuously pushing, dreaming and working toward a cure."

    Basil Darras, MD, Director, Neuromusuclar Program, Associate Neurologist-in-chief, Clinical Services, Boston Children's Hospital

    About SMA

    Learning that your child may have spinal muscular atrophy (SMA) can be a challenging experience. We understand that your child is important to you, and that you want your child to have the best quality of life possible. Our multidisciplinary team evaluates the complications and benefits of different supportive care options and empowers you with comprehensive and honest information to help you decide what is best for your child. SMA is a genetic condition in which muscles throughout the body are weakened because cells in the spinal cord and motor nerves do not work properly.

    Here’s what you need to know about spinal muscular atrophy (SMA):

    • SMA is the number one genetic cause of infant mortality.
    • About 10 to 16 out of every 100,000 children are born with SMA.
    • There are three types of SMA that vary greatly by age at onset and severity. SMA type is determined by the highest motor function the child achieves.
      • Type I is a severe form of SMA (Werdnig-Hoffmann Disease): Children have limited movement and cannot sit without support, have labored breathing, and have trouble feeding and swallowing. Symptoms emerge within months after birth.
      • Type II is an intermediate form of SMA. Individuals with Type II may sit unsupported at some point but cannot walk independently. Symptoms typically emerge between 6-18 months of age.
      • Type III is a milder form of SMA (Kugelberg-Welander Disease). Individuals with Type III achieve the milestone of walking but may walk with difficulty because weakness is prevalent, and some individuals may eventually need to use a wheelchair. Symptoms typically appear later than 18 months of age and may occur in early childhood.
    • The life expectancy for children with SMA depends on the type of SMA they have. Children with Type I have a life expectancy of less than 2 years if not supported with mechanical ventilation, children with Type II have an intermediate life expectancy, and individuals with Type III may have a normal life expectancy.
    • Individuals with symptoms of SMA can be diagnosed by genetic (DNA) testing at any age.

    How Children’s Hospital Boston approaches Spinal Muscular Atrophy

    Here at Children’s, we bring together experts across medical disciplines to evaluate your child’s specific needs and circumstances. Individuals with SMA and their families benefit greatly from a multidisciplinary approach to care. We recognize that your child is an individual, and we will involve you in your child’s care at every step of the way.

    At our Spinal Muscular Atrophy Clinic in the Department of Neurology, a multidisciplinary team gathers to focus on all the needs of the children we meet with SMA. Our program also gives you a chance to speak with other families experiencing similar challenges you're going through.

    The first in childhood neurology

    The Spinal Muscular Atrophy Program is one of the many programs of the storied Neurology Department at Children’s. In 1920, Bronson Crothers, MD, was one of the pioneers of Child Neurology and was appointed to lead the nation’s first pediatric Neurology Service. Today, Children’s holds the #1 ranking in the U.S. News & World Report in Child Neurology and Neurosurgery.

    Spinal Muscular Atrophy: Reviewed by Basil Darras, MD

    © Children’s Hospital Boston; posted in 2011

    Children's Hospital Boston
    300 Longwood Avenue
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    Boston MA 02115
     fax: 617-730-0279

  • Here at Children’s Hospital Boston, we specialize in innovative, family-centered care. From your first visit, you’ll work with a team of professionals who are committed to supporting all of your family’s physical and emotional needs. We understand that you probably want to learn more about your child’s diagnosis of SMA in order to be as informed as possible, and to keep your child safe and healthy.

    What is SMA?

    Spinal muscular atrophy (SMA) is a genetic condition that results in poor motor skills as a result of weakened muscles. Muscles are weakened due to dysfunctional spinal cord cells and motor nerves. SMA impacts voluntary and involuntary muscles (muscles that are not consciously controlled), such as chest muscles, which can affect breathing.

    What is the life expectancy of children with SMA?

    The life expectancy for SMA depends on the severity of the disease. Children with Type I, also known as Werdnig-Hoffmann Disease, usually develop respiratory failure by 2 years of age without breathing support. Children with Type II may live into their mid- to late-twenties or much older, and for individuals with Type III, also known as Kugelberg-Welander disease, life span of most individuals is not significantly different compared with the normal population.

    Is it curable?

    Currently there is no known cure for SMA. Treatment consists of managing the symptoms and preventing disease complications. The Spinal Muscular Atrophy Program at Children’s Hospital Boston brings together a comprehensive team of specialists who are experienced in caring for children with SMA. However, there is reason for optimism. The National Institute of Health has selected SMA as the disease closest to treatment from over 600 neurologic disorders. Researchers now understand the genetic cause of SMA, and are working towards developing treatments and cures.

    Who’s at risk?

    Because SMA is usually a genetically inherited disease, if someone in your family actually has SMA, your chance of being an SMA carrier significantly increases. In most instances, both parents must be carriers for the child to be at risk for having SMA.

    How common is SMA?

    SMA affects about 10 to 16 out of every 100,000 children born. SMA Type I is diagnosed in children 6 months old and younger, SMA Type II is diagnosed in children 6 to 18 months old, and SMA Type III is diagnosed in children as early as 18 months of age, but can surface as late as adolescence. SMA Types I and II are most prevalent.

    If my child has SMA, what are the odds that I will have another child with SMA?

    When both parents are carriers of the gene mutation that causes SMA, there is a 25% chance, with each pregnancy, that the child will be affected with SMA; a 50% chance of having a child who would be a SMA carrier (has the gene mutation but never develops the disease); and a 25% chance of having a child who would not have SMA and would not be a SMA carrier.


    Symptoms of SMA vary greatly depending on SMA Type. More severe forms of SMA affect more essential functions that are very apparent during the first 6 months of life, and less severe forms of SMA have less severe symptoms that are not noticed until later in life.

    • Muscle weakness and decreased muscle tone are the main symptoms of SMA.
    • Weakness tends to be equal between the right and left sides of the body.
    • Legs are affected more than arms, and proximal muscles (those closest to the body like hips and shoulders) are affected more than distal muscles (those farthest from the body like fingers and toes).
    • Individuals may have very limited mobility since their muscles are weak.
    • Due to a lack of weight bearing, bones may be fragile and at higher risk of fractures. Care should be taken when moving and positioning children to not exert excessive force on any bone.
    • In many children, muscles used for breathing are also affected, leading to breathing problems which can be life threatening, especially in younger children.  
    • Weak tongue and muscles used for swallowing can lead to eating and swallowing difficulties.
    • Scoliosis (curvature of the spine) occurs at some point in many children with SMA Type I and II and some with Type III.

    How severe are the different types of SMA?

    There are three types of SMA: type I, II, and III, and the severity of the diagnosis varies greatly between types and from one person to another. The older and more physically developed your child is at the time of diagnosis, the better his or her prognosis will be. If your child is diagnosed later in life, it is because the symptoms are not as obvious and are less severe, meaning your child has a greater chance for better motor function.  Non-life threatening symptoms (such as mild weakness in shoulders and muscles around the hips) may not be diagnosed as symptoms of SMA until a later age.  SMA that is diagnosed early in life is diagnosed within months after birth because essential functions such as crying, head control and muscle strength are affected. Since a baby diagnosed with type I early in life would have problems with essential functions, such as breathing and swallowing, their life expectancy would be shorter, without respiratory interventions.

    SMA type I, also known as Werdnig-Hoffmann Disease:

    • is the most severe form of SMA
    • is the most common form of SMA
    • is characterized by an inability to sit independently (without support).
    • can usually be detected in children younger than 6 months because of their severe low    muscle tone, delayed gross motor skills, breathing difficulties, lack of reflexes, and spontaneous tongue movements (referred to as tongue fasciculations). Babies also have weak cries, and difficulty feeding and swallowing.
    • often leads to a shortened life span (around 2  years) due to respiratory complications.

    SMA type II:

    • is an intermediate form of SMA.
    • is the second most common form of SMA.
    • is characterized by an ability to sit unassisted (but not walk or stand without support).
    • affects the legs more than the arms.
    • can lead to a higher body fat percentage.
    • can usually be detected in children younger than 18 months because of low muscle tone and       delayed gross motor skills.
    • can also cause the same tongue movements (fasiculations) that children with type I have, and/or a minor tremor in both hands.
    • can cause varying degrees of breathing difficulties.
    • can lead to a shortened lifespan.
    • Survival rate is at 98.5 percent among 5 year olds
    • Survival rate is 68.5 percent among 25 year olds

    SMA type III, also known as Kugelberg-Welander disease:

    • is the least severe form of SMA.
    • is characterized by the ability to stand and walk unassisted, but with progressive weakness over a number of years.
    • may lead to need for a wheelchair over time.
    • may cause hand tremors.
    • is not characterized by a shortened life span.
    • sometimes results in minor breathing problems.
    • resembles muscular dystrophy (MD).

    What causes spinal muscular atrophy?

    SMA is an autosomal recessive disease. This means that, most of the time, both parents must carry the nonworking gene, and that two copies of the gene (one inherited from each parent) are necessary for a child to have the condition.

    Individuals have two copies of a gene called “survival of motor neuron” (SMN1 and 2), and in 95 percent of cases, the SMN1 gene is missing (genetic deletion).

    People of all ages who show symptoms can be tested through genetic studies, which are typically done from a blood sample, to detect the absence of the SMN1 gene and to confirm the diagnosis of SMA.  

    When both parents are carriers, there is a one in four (25 percent) chance, with each pregnancy, that they will have a child with SMA. A test to see if parents carry the gene mutation is available in most countries .

    Questions to ask your care team

    After your child is diagnosed with SMA, you may feel overwhelmed with information. It can be easy to lose track of the questions that occur to you.

    Lots of parents find it helpful to jot down questions as they arise- that way, when you talk to your child’s team members you can be sure that all of your questions are answered. If your child is old enough, you may want to suggest that he or she writes down questions to ask your health care provider, too.

    Here are some questions to help get you started:

    • How did the doctor arrive at this diagnosis?
    • How could the recommended SMA treatment impact my child’s life, including academic performance?
    • What resources are available to help our family cope with stress of living with SMA?
    • How should I talk to my child about the SMA diagnosis?
    • How can you coordinate with my child’s school nurse to continue care at school?
      Communication and care

      Sarah Teasdale, MD, is a pediatrician at Children’s who understands that communication is a critical part of care. Medical jargon can be intimidating for parents, and Dr. Teasdale encourages parents to speak up if they need clarification. She encourages other doctors to explain medical jargon, without “dumbing down” the information. Learn more, and join the conversation on Children’s Thriving blog.

  • The first step in treating your child is forming an accurate and complete diagnosis. To diagnose your child's SMA, your specialist at Boston Children's Hospital uses a combination of medical history, physical examination and laboratory tests.

    How is spinal muscular atrophy diagnosed?

    Spinal muscular atrophy is sometimes difficult to diagnose, as symptoms can resemble other conditions or medical problems. Doctors usually diagnose it after a child has suddenly or gradually shown muscle weakness and decreased muscle tone.


    The work-up for a child with muscle weakness, when SMA is suspected, includes:

    • a detailed physical exam
    • gathering of past medical history
    • gathering of family history information
    • diagnostic testing
      • genetic blood tests
      • an electromyography (EMG) test that measures the electrical activity of a muscle or a group of muscles
      • in exceptionally rare cases, a child may need a muscle biopsy
      • creatine kinase (CPK) test (to distinguish from other types of muscle diseases, if necessary)
      • Type III SMA can often be misdiagnosed as muscular dystrophy.
      • SMA will result in normal or slightly elevated CPK enzyme levels while muscular dystrophy (MD) results in much higher CPK levels.
    • EMG lab

      Experience counts when it comes to conducting an electromyography (EMG) test correctly and compassionately. For more than 30 years, the EMG lab has been reading EMG tests and making children feel safe and comfortable during this procedure. This test is used sometimes when SMA is suspected.

      Future of child neurology

      Children’s Hospital Boston not only provides the best child neurology care, but also trains the best doctors to continue exceptional care for your children and your children’s children. Learn more about the child neurology residency program.

  • At Children's, we know how difficult a diagnosis of SMA can be, both for your child and for your whole family. That's why our providers are focused on family-centered care: from your first visit, you'll work with a team of professionals who are committed to supporting all of your family's physical and psychosocial needs. We'll work with you to create a care plan that is best for you and your child.

    What is the treatment for spinal muscular atrophy?

    The aim of treatment is to prevent respiratory problems, maintain function and strength, and provide adequate nutritional care to your child. Medication is currently not a form of SMA treatment. Current treatment may involve a breathing machine in severe cases, usually for type I.  Breathing machines may also be necessary for type II and III depending on the severity of the disease. A pulmonologist and respiratory therapist experienced with SMA will guide you in using the different machines your child may need. Additionally, physical therapy and braces may help to maintain muscle strength and function. However, specific treatment varies based on your child's age, overall health, medical history, extent of the condition, type of SMA and your goals for your child.

    It takes a multidisciplinary approach to address the effects that SMA can have on a person's respiratory system, gastrointestinal system, weight and bone structure. Our Spinal Muscular Atrophy Program brings together specialists from a variety of fields including:

    • Neurology
    • Orthopedics
    • Physical Therapy
    • Respiratory/Pulmonary
    • Nutrition
    • Gastroenterology
    • Anesthesia
    • Surgery (non-orthopedic)
    • Social Work

    At Children's Hospital, we believe it is important to preserve the highest quality of life as possible. The Neurology Department at Boston Children's Hospital offers an SMA Clinic once a month. The clinic allows you to meet with all of your child's SMA-related providers during a single visit. We provide our SMA patients with the most comprehensive team of doctors and specialists. By coordinating all SMA related care, we have the opportunity to evaluate our patients' health as a whole and make the best decisions moving forward as a united front. In addition, the clinic will provide families the chance to meet others living with SMA and to learn about our many research opportunities available. We hope that families will take this time to network and establish supportive relationships with other families, utilize our many specialists who will be on hand at the clinic, and investigate the important SMA research we conduct.

    Coping & support

    It might be helpful to remember that while SMA can feel isolating, many children and their families have faced similar challenging conditions. You are not alone. There's a lot of support available here at Children's Hospital for you and your family, and here are some of the ways we can help. Our team in the Spinal Muscular Atrophy Program at Boston Children's Hospital will talk with you about your child's condition, discuss any questions you have and try to help you find the support you need. Our list of resources may also be helpful to you.

    Visit our For Patients and Families page for all you need to know about:

    • getting to Children's
    • accommodations
    • navigating the hospital experience
    • resources that are available for your family
  • Children’s Hospital Boston has the world’s largest research program at a pediatric institution, and we are known for pioneering new treatments. A large part of our success comes from our commitment to research and to advancing the frontiers of what’s possible through our innovative ideas. 

    Part of our innovative method is a collaborative approach in which we partner with other hospitals and pharmaceutical companies to combine our resources and expertise to help find a cure for SMA.

    Children’s Hospital Partners with Isis Pharmaceuticals

    We are starting a phase I drug study with Isis Pharmaceuticals to help test the safety of a new drug that could help people with SMA. This study will look at the safety and tolerability of a drug that has been shown to increase survival of motor neuron (SMN) protein production. In 95 percent of SMA cases, the SMN1 gene is absent.  This drug could potentially have beneficial therapeutic outcomes for people with SMA, meaning it could help reduce the symptoms of SMA by inducing a second gene, known as SMN2, to produce more protein.

    Children's Hospital joined large research network to study SMA in 2004

    Boston Children's Hospital is one of four sites - along with Columbia University Medical Center in New York, the Children's Hospital of Philadelphia, and University of Rochester Medical Center - that make up the Pediatric Neuromuscular Clinical Research Network (PNCR) for SMA.

    At these hospitals, individuals have participated in a major natural history study of SMA that looks at strength, movement, quality of life and medical history of people with the disease. The study's purpose was to better understand how the disorder progresses and to prepare for potential medication trials. Additionally, there is an ongoing study collecting blood, urine, saliva and tissue samples of people with SMA to create a bio-repository to help with future SMA research. Basil Darras, MD, leads Children’s Hospital Boston’s SMA research program.

    If you are interested in participating in SMA research, please contact:

     Rebecca Parad, Clinical Research Coordinator

     T: 617-355-2752, e: rebecca.parad@childrens.havard.edu


     Elizabeth Shriber, Clinical Research Coordinator

     T: 857-218-4677,  e: elizabeth.shriber@childrens.harvard.edu

    Testing a new way to track SMA's course

    Researchers at Children's Hospital has been evaluating a new method aimed at reliably measuring nerve changes in individuals with SMA , using a technique known as electrical impedance myography (EIM).

    Understanding the development of SMA

    Mustafa Sahin, MD, PhD, is studying the molecular pathology of SMA, or how the disease develops. Specifically, his lab is testing and exploring the role of axonal RNA regulation in SMA. Learn more about SMA research at the Sahin lab.

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