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About Spinal Muscular Atrophy

Spinal muscular atrophy is a degenerative problem that affects the motor nerves, resulting in muscle wasting and weakness. Spinal muscular atrophy occurs in approximately one in 6,000-10,000 live births.


SMA is an autosomal recessive disease. This means that two abnormal copies of the gene, one inherited from each parent, are necessary to have the condition. Boys and girls are affected with equal frequency. A child who inherits only one abnormal gene copy is a carrier and is not at risk to develop symptoms. When both parents are carriers, there is a one in four, or 25 percent, chance with each pregnancy, to have a child with SMA. Carrier testing of parents can help determine the recurrence risk in a specific family. A gene called survival motor neuron (or SMN) is found to have an abnormal area (called a deletion) in over 95 percent of cases of SMA. Symptomatic individuals of all ages can be tested through DNA studies typically done from a blood sample.

Virtual Visits for Returning Neurology Patients

Virtual Visits are conducted as follow up appointments for patients who are already registered within the Neurology department. If you are an existing patient of one of the Mass General Neurology outpatient clinics and would like to request that your next follow up appointment be conducted virtually, please refer to the TeleHealth website to sign up.

New Neurology Patients

If you would like to be referred (or refer a patient) and become a new patient of the SMA Clinic in the Mass General Department of Neurology, please contact us.


Spinal muscular atrophy is sometimes difficult to diagnose, as symptoms can resemble other conditions or medical problems. Each child may experience symptoms differently. There are several types of spinal muscular atrophy based on symptoms and age of onset.

Type I (Werdnig-Hoffman)
This is the most severe type of SMA, and unfortunately, the most common. Symptoms may be present at birth or develop within the first few weeks or months after birth. Infants have difficulty holding up their head, sucking, feeding, swallowing and often move very little. The legs are more severely affected than the arms. The muscles of the chest that help to expand the lungs are affected, and the chest may appear small or “bell-shaped”. They have a weak cough, and are prone to respiratory infections. The tongue may demonstrate “worm-like” movements, and they may demonstrate a tendency to choke while feeding. Complications from breathing problems often lead to death or dependence on some form of respiratory support by 2 to 3 years of age.

Type II (Intermediate Form)
This form of SMA most commonly becomes evident in children between 6 months to 2 years of age. They may show delays in acquiring motor skills such as rolling, sitting or crawling. They are unable to walk independently without support. They typically have generalized muscle weakness and may require braces, walkers or a wheelchair for assistance. Life expectancy varies greatly in this group of children, since they demonstrate a very wide range in degree of weakness. However, complications commonly include weakness of chest muscles involved in breathing, resulting in a weak cough and tendency for pneumonia. Scoliosis develops in virtually all children at some point, and they are prone to bone fractures.

Children who are unable to bear weight often develop hip dislocation. Contractures of the muscles and joints can limit function over time. Children in this group may also demonstrate difficulties in swallowing and chewing and require close monitoring of nutrition. Lifespan in this group depends on the severity of respiratory muscle weakness, but many children survive well into adulthood.

Type III (Kugelberg-Welander)
This form of SMA most commonly becomes evident in children between 2 and 17 years of age. These children may show delays in motor development, difficulty walking, trouble getting up from the floor, mild muscle weakness and frequent falls. Fatigue can be a significant problem, which limits the ability to walk long distances. A tremor involving the hands is common. Scoliosis is frequent in later childhood. Respiratory muscle involvement is much less often a problem, and difficulty swallowing is rare.

Type IV
This form of SMA includes those individuals who don’t develop symptoms of weakness until they reach adulthood. Usually, this results in muscle weakness predominantly affecting the legs and manifests as a walking disability. The symptoms of spinal muscular atrophy may resemble other problems or medical conditions and can be confused with other muscle or nerve conditions, including muscular dystrophy, myopathy, other spinal muscular atrophy variants or even forms of amyotrophic lateral sclerosis (ALS). Another closely related condition, known as spinobulbar muscular atrophy (Kennedy’s disease), can also present in late childhood or adulthood.


The diagnosis of spinal muscular atrophy may be suspected if you or your child demonstrate specific symptoms or demonstrate signs on examination that are consistent with the pattern of weakness seen in this disorder. During the physical examination, your child’s physician will obtain a complete medical history, and he/she may also ask if there is a family history of any medical problems.

Diagnostic tests that can help to confirm the diagnosis of spinal muscular atrophy include the following:

Blood tests
Genetic testing can confirm a suspected diagnosis in most cases. Sometimes the initial genetic test is negative, and additional genetic testing or other testing may be needed to confirm a diagnosis.


Electromyogram (EMG)
An EMG is a test that measures the electrical activity of a muscle or a group of muscles. An EMG can detect abnormal electrical muscle activity due to diseases and neuromuscular conditions. A small sample of the muscle is removed and examined to determine and confirm a diagnosis or condition. Learn more about our EMG lab.


MRI or imaging studies
Imaging studies of the brain or spine to help rule out other conditions.


While there are as yet no specific, confirmed pharmaceutical therapies that can either extend lifespan or increase strength in SMA subjects, the identification of compounds that can increase SMN protein in cells from SMA subjects and in genetic animal models of SMA is promising. Moreover, proactive management strategies to optimize lung function, physical mobility and nutrition can help preserve motor function, improve quality of life and extend survival, particularly in more severely affected SMA infants and young children.

Following diagnosis in children with milder forms of SMA, including the infant with an as yet uncertain prognosis, it is important to work closely with parents in order to anticipate problems and pursue management aggressively to optimize outcomes. Because of the tremendous variability in severity of muscle weakness, an individualized approach is often necessary. Far too often, respiratory, nutritional and even physical rehabilitation interventions are reactive rather than proactive. Treatment for the intermediate or milder forms of SMA should be focused on preserving mobility and minimizing respiratory complications, particularly restrictive pulmonary disease or respiratory compromise due to progressive scoliosis. Specific interventions can be helpful in optimizing the individual’s health and helping to maintain motor function.

Management Strategies

Find information, guides and more resources on each of the following topics to aid you in planning a management strategy:

  • Respiratory
  • Nutrition
  • Exercise & Mobility
  • Orthopedic
  • Special Considerations in SMA Infants
  • Dental Care

The first medication for SMA, Spinraza (Nusinersen), was approved by the FDA in December 2016. We’re here to help answer any questions you may have about this new treatment for SMA. For more information, please contact our Clinical Program Coordinator at 617-726-5732, Monday through Friday, 8:30 to 5:00 pm U.S. Eastern time.

Other than Spinraza, medical care is primarily supportive, focused on respiratory support, nutritional support, and musculoskeletal management.

Respiratory Management

Pulmonary Management
Since respiratory management can impact lifespan considerably, physicians should support families in implementing a proactive approach. While pulmonary management is often demanding, it is also the therapeutic modality that will most likely enhance quality of life and prolong lifespan. Pulmonary medicine consultation is recommended to assist in making decisions regarding long-term respiratory management.

Exercises & Aids
To maintain lung capacity, breathing exercises and supplementary aids may be helpful. Incentive spirometry and “breath-stacking” can be implemented at an early age but require discipline to perform on a daily basis. Aerosol therapy with nebulizers may be helpful in some settings and can be initiated at the onset of respiratory symptoms.

Steroid Treatments, Cough Assist Devices, Vest Therapy, and Manual Percussion
Benefit from the routine use of mucolytics, bronchodilators or steroid treatments is unclear and should be dictated by individual circumstances. Cough assist devices, such as the inexsufflator (cough machine), are essential when ineffective cough inhibits adequate removal of bronchial secretions in the lower airways. Vest therapy or manual percussion techniques to help mobilize secretions, when used in conjunction with the cough assist machine, can be additionally helpful in some patients. Regular use of such therapies, most importantly the cough assist machine, are invaluable in the setting of a superimposed respiratory illness and can help prevent a simple cold or bronchitis from evolving into pneumonia or a collapsed lung resulting in respiratory crisis. Even when children are well, daily use of such a regimen can help minimize atelectasis and chest wall contractures and deformity. In many children and young adults, nocturnal hypoventilation with and without obstructive apnea necessitates assisted ventilation.

BiPAP is recommended whenever the vital capacity falls to less than 40 percent. However, in infants and young children who can’t cooperate with formal pulmonary function testing, doctors must use other signs and symptoms to help decide when a child might benefit from BiPAP support. Recurrent nighttime awakenings are often an indication that patients may not be optimally breathing during sleep. A sleep study may help to determine whether or not there is an obstructive component (due to low muscle tone or enlarged tonsils or adenoids), or whether nocturnal hypoventilation (shallow-breathing resulting in low oxygen levels or increased carbon dioxide levels) is present. BiPAP is often recommended for use only at night, but can be invaluable to use for longer periods of time when an upper respiratory infection or other illness results in increased work of breathing and fatigue.

Flu Prophylaxis
Flu prophylaxis is recommended annually. In younger infants and children with significant intercostal weakness (all type I and weak type II subjects), prophylaxis for respiratory syncytial virus (RSV) is also recommended.

Oxygen Therapy
Oxygen therapy should only be used in conjunction with assisted ventilation in such patients, as it can suppress respiratory drive, resulting in atelectasis and hypercarbia.

Respiratory Infection
Aggressive treatment of respiratory infection is essential. Antibiotic use is of value when symptoms arising from a presumed viral upper respiratory infection persist longer than expected or new fever or altered secretions appear in the midst of an apparent viral illness. Since recurrent or prolonged antibiotic treatment can predispose patients to yeast infections or even enterocolitis, a balanced approach is needed. In the severely compromised infant or child, a lower threshold for administering antibiotics may be warranted. If illness results in persistent hypoxemia below 93 percent, the need for hospitalization and potential intubation should be discussed, although many such patients can be managed effectively in hospital using a non-invasive respiratory protocol.


Nutrition is critically important for maintaining muscle mass and strength and minimizing fatigue in SMA patients. Intermittent monitoring of dietary intake in consultation with a dietician experienced in management of patients with neuromuscular conditions or metabolic disorders can be extremely helpful. Children may be deficient in carnitine due to decreased intake of meat related to jaw contractures interfering with chewing. Swallowing problems sometimes be difficult to detect, and in weaker children or in those with borderline nutritional status or frequent respiratory illness, swallowing studies should be performed on a regular basis to ensure that silent aspiration isn’t contributing to respiratory problems.

Maintenance of appropriate nutrition is especially critical during illness. SMA subjects have diminished lean body mass and a secondary defect in fatty acid oxidation that limits their reserve in the setting of prolonged fasting. Thus, when concerns regarding the ability to safely administer oral feeds develop, alternative forms of nutrition should be considered. Options include temporary nasogastric or nasojejunal feeds, or peripheral or total parenteral nutrition (PPN or TPN).