Learn About Spinal Muscular Atrophy (SMA)
Spinal muscular atrophy (SMA) is a group of disorders of the motor neurons (motor cells). These disorders are passed down through families (inherited) and can appear at any stage of life. The disorder leads to muscle weakness and atrophy.
Werdnig-Hoffmann disease; Kugelberg-Welander disease
SMA is a collection of different motor nerve (or neuron) diseases. The disease is caused by a lack of a protein (SMN) due to defective genes.
Most of the time, a person must get one copy of the defective gene from both parents to be affected. The most severe form is SMA type I, also called Werdnig-Hoffman disease. Infants with SMA type II have less severe symptoms during early infancy, but they become weaker with time. SMA type III is a less severe form of the disease.
In rare cases, SMA begins in adulthood. This is the mildest form of the disease.
A family history of SMA in an immediate family member (such as brother or sister) is a risk factor for all types of the disorder.
Symptoms of SMA may vary depending on the SMA type.
- Infants with SMA type I are born with very little muscle tone, weak muscles, and feeding and breathing problems.
- In infants with SMA type II, symptoms may not appear until age 6 months to 2 years.
- Type III SMA is a milder disease that starts in childhood or adolescence and slowly gets worse.
- Type IV is even milder, with weakness starting in adulthood.
Often, weakness is first felt in the shoulder and leg muscles. Weakness gets worse over time and eventually becomes severe.
Symptoms in an infant:
- Breathing difficulty with shortness of breath and labored breathing, leading to a lack of oxygen
- Feeding difficulty (food may go into the windpipe instead of the stomach)
- Floppy infant (poor muscle tone)
- Lack of head control
- Little movement
- Weakness that gets worse
Symptoms in a child:
- Frequent, increasingly severe respiratory infections
- Nasal speech
- Posture that gets worse
With SMA, the nerves that control feeling (sensory nerves) are not affected. So, a person with the disease can feel things normally.
There is no treatment to cure SMA. However, there are now three drugs approved by the FDA that slow how fast the muscle weakness progresses:
- Onasemnogene abeparvovec-xioi (Zolgensma)
- Risdiplam (Evrysdi)
- Nusinersen (Spinraza)
These drugs work by increasing the amount of the SMN protein produced. Talk with your provider to see if either of these medicines is right for you or your child.
Supportive care is important. Breathing complications are common in the more severe forms of SMA. To help with breathing, a device or machine called a ventilator may be needed.
People with SMA also need to be watched for choking. This is because the muscles that control swallowing are weak.
Physical therapy is important to prevent contractions of muscles and tendons and abnormal curvature of the spine (scoliosis). Bracing may be needed. Surgery may be needed to correct skeletal deformities, such as scoliosis.
Johns Hopkins Outpatient Center
Dr. Charlotte Sumner is a Professor of Neurology and Neuroscience at Johns Hopkins University School of Medicine. Dr. Sumner cares for patients with genetically-mediated neuromuscular diseases. Her practice is notable for a focus on individuals with inherited neuromuscular disorders of peripheral nerves and motor neurons, including spinal muscular atrophy (SMA) and Charcot-Marie-Tooth (CMT) disease. She co-directs the Johns Hopkins Muscular Dystrophy Association Care Center, the Spinal Muscular Atrophy (SMA), and the Charcot-Marie-Tooth (CMT) clinics, which deliver multidisciplinary clinical care, engage in international natural history studies, and provide cutting edge therapeutics. Dr. Sumner’s research focuses on developing treatments for degenerative disorders of motor neurons and peripheral nerves. Her laboratory uses human tissues and induced pluripotent cell lines, mouse models and cultured cells to characterize disease mechanisms and develop treatments. Dr. Charlotte Sumner received her medical degree from the University of Pennsylvania School of Medicine following undergraduate studies at Princeton University. She completed internal medicine internship and neurology residency at the University of California San Francisco, after which she returned to the east coast for a neuromuscular fellowship at Johns Hopkins and a neurogenetics fellowship in the Neurogenetics Branch at the National Institute of Neurological Disorders and Stroke. She joined the neurology faculty at Johns Hopkins in 2006. Dr. Sumner is rated as an Elite provider by MediFind in the treatment of Spinal Muscular Atrophy (SMA). Her top areas of expertise are Spinal Muscular Atrophy (SMA), Charcot-Marie-Tooth Disease, Primary Lateral Sclerosis, Spinal Muscular Atrophy Type 2, and Gastrostomy.
Johns Hopkins Outpatient Center
Dr. Tom Crawford has been a member of the Department of Neurology since 1987. He is co-director of the MDA clinic for Neuromuscular Disorders and Neurologist for the Ataxia Telangiectasia Clinical Center at Johns Hopkins. His practice involves general child neurology with a principal interest in caring for children with neuromuscular, neuromotor, and ataxic disorders. Primary research interests involve the basic science and clinical characterization of two important neurologic disorders that affect children: Spinal Muscular Atrophy and Ataxia Telangiectasia. He is also actively involved in the Biology of neurofilaments by characterization of transgenic animal models. He is on the Medical and Scientific Advisory Boards of Families of Spinal Muscular Atrophy, and the Medical Advisory Committee for the Muscular Dystrophy Association. He is the Neurologist for the Ataxia Telangiectasia Clinical Center at Johns Hopkins, which has evaluated almost half of the known patients with this disorder in the United States. Additional specific clinical interests include evaluation and treatment of children with brachial plexus palsies. Dr. Crawford received his medical degree from the University of Southern California. He completed a pediatric internship and residency at the Pediatric Pavilion of the Los Angeles County / University of Southern California Medical Center, followed by a pediatric chief residency. He completed his training in Neurology with Special Qualification in Child Neurology at the Los Angeles Childrens Hospital. He then traveled east to the laboratory of Dr John Griffin at Johns Hopkins for a fellowship in Neuromuscular Disorders. Prior to medical training and Neurology residency, he majored in Psychology and Religion at Yale College. Dr. Crawford has published extensively and presented nationally and internationally. He has an active role in teaching medical students and residents in neurology. In addition, Dr. Crawford has special interest and experience in EMG studies of children and adults. Dr. Crawford is rated as an Elite provider by MediFind in the treatment of Spinal Muscular Atrophy (SMA). His top areas of expertise are Primary Lateral Sclerosis, Spinal Muscular Atrophy (SMA), Ataxia-Telangiectasia, and Spinal Muscular Atrophy Type 2.
Richard Finkel is a Pediatric Neurologist and a Pediatrics provider in Memphis, Tennessee. Dr. Finkel is rated as an Elite provider by MediFind in the treatment of Spinal Muscular Atrophy (SMA). His top areas of expertise are Spinal Muscular Atrophy (SMA), Primary Lateral Sclerosis, Spinal Muscular Atrophy Type 3, and Spinal Muscular Atrophy Type 2. Dr. Finkel is currently accepting new patients.
Without treatment, children with SMA type I rarely live longer than 2 to 3 years because of respiratory problems and infections. Survival time with type II is longer, but the disease kills most of those who are affected while they are still children. New therapies that increase the amount of SMN protein have resulted in infants and children living much longer.
Children with type III disease may survive into early adulthood. But, people with all forms of the disease have weakness and disability that gets worse over time. Adults who develop SMA often have a normal life expectancy.
Complications that may result from SMA include:
- Aspiration (food and fluids get into the lungs, causing pneumonia)
- Contractions of muscles and tendons
- Heart failure
- Scoliosis
Contact your provider if your child:
- Appears weak
- Develops any other symptoms of SMA
- Has difficulty feeding
Breathing difficulty can rapidly become an emergency condition.
Genetic counseling is recommended for people with a family history of SMA who want to have children.
Summary: The Active NBS Liege study is a monocentric, academic, fully remote, observational study designed to validate digital measures of motor development in children with spinal muscular atrophy (SMA) or Duchenne muscular dystrophy (DMD) identified through newborn screening, family testing, or incidental diagnosis. The study will enroll 100 children and follow them longitudinally for up to 30 months. Pa...
Summary: This is an open-label, single-arm, multicenter clinical study to evaluate the effectiveness and safety of risdiplam administered as an early intervention in pediatric participants with spinal muscular atrophy (SMA) and 2 SMN2 copies who have previously received onasemnogene abeparvovec. Participants are children \< 2 years of age genetically diagnosed with SMA.
Published Date: December 31, 2023
Published By: Joseph V. Campellone, MD, Department of Neurology, Cooper Medical School at Rowan University, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
Fearon C, Murray B, Mitsumoto H. Disorders of upper and lower motor neurons. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 97.
Manzur AY. Evaluation and investigation of neuromuscular disorders. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 647.
NIH-National Institute of Neurological Disorders and Stroke website. Spinal muscular atrophy. www.ninds.nih.gov/health-information/disorders/spinal-muscular-atrophy. Updated November 28, 2023. Accessed March 14, 2024.