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Boston, MA 02115
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My Child Has:
Spinal Muscular Atrophy
Programs that treat this condition
Neuromuscular Program   Spinal Muscular Atrophy Program  
What is spinal muscular atrophy (SMA)?
Spinal Muscular Atrophy (SMA) is a genetic condition in which the muscles throughout the body are weakened because the cells in the spinal cord and motor nerves do not work properly. Approximately 10-16 people out of every 100,000 children are born with this condition.
What are the symptoms of spinal muscular atrophy?
SMA is characterized by muscle weakness and decreased muscle tone. This weakness affects legs more than arms and proximal muscles (those closest to the body like hips and shoulders) more than distal muscles (those farthest from the body like fingers and toes).

This weakness tends to be equal between the right and left sides of the body. In addition to the muscles we have in our arms and our legs, we also have muscles in our chest which help us with breathing. In many cases of SMA these muscles are also affected, leading to some breathing problems.

The severity of this condition varies greatly between individuals, so the disease is broken up into three main groups. These are referred to as SMA type I, SMA type II, and SMA type III. The type of SMA a child has is determined by the highest motor function a child achieves.

  • SMA type I, also known as Werdnig-Hoffmann Disease
    • The most severe form of SMA
    • Defined as children who are not able to sit independently.
    • Usually present to the doctors before six months of age 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).
    • Due to respiratory problems, children with SMA type I often have a significantly shortened life span.
  • SMA type II
    • An intermediate form of SMA
    • Defined as children who can sit unassisted but cannot walk or stand.
    • Usually present to the doctors before 18 months of age because of low muscle tone and delayed gross motor skills. Individuals with SMA type II can also have the typical tongue movements and/or a minor tremor of both hands. SMA type II can cause varying degrees of breathing difficulties.
    • In many cases of SMA type II children and adults also experience a shortened lifespan.
  • SMA type III, also known as Kugelberg-Welander Disease
    • The least severe form of SMA
    • Defined as individuals who are able to stand and walk unassisted.
    • Usually individuals with this form of SMA have limited, if any, breathing difficulties, and may show little or no decline. This form of SMA often resembles muscular dystrophy but can be identified by specialized testing.
While these three forms are considered one disease with one genetic cause, there is great variability in the severity of the condition and the challenges a child or individual faces.
What causes spinal muscular atrophy?
SMA is a genetic disease. SMA is an autosomal recessive disease. This means that both males and females are equally affected, and that two copies of the nonworking gene, one inherited from each parent, are necessary to have the condition.

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.

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 for the general population is technically difficult and usually available only if a previously affected child in the family has been studied.

How is spinal muscular atrophy diagnosed?
Spinal muscular atrophy is sometimes difficult to diagnose, as symptoms can resemble other conditions or medical problems. The diagnosis is usually made after the sudden or gradual onset of muscle weakness and decreased muscle tone.

The work-up for a child with muscle weakness, suspicious for SMA, would include:

  • A detailed physical exam
  • Gathering of past medical history
  • Gathering of family history information
  • Diagnostic testing
    • An EMG is a test that measures the electrical activity of a muscle or a group of muscles. This testing can detect abnormalities due to neuromuscular conditions, like SMA.
    • Genetic blood tests
    • In exceptionally rare cases a muscle biopsy may be needed.
What is the treatment for spinal muscular atrophy?
At this time there is no cure for spinal muscular atrophy. The goal of treatment however is to prevent respiratory problems and provide adequate nutritional care to the child. This may involve a breathing machine in severe cases. However, the specific treatment for each child will vary based on the child's age, overall health, medical history, extent of the condition, type of SMA, and the families' goals for the child.

In efforts to move us further towards a cure, research has begun at Children's Hospital Boston for children with SMA. This is a collaborative effort with Columbia University, New York and Children's Hospital of Philadelphia as part of the Pediatric Neuromuscular Clinical Research (PNCR) Network.

More information about this network and these research opportunities can be found at: http://www.urmc.edu/sma/.

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