Kids Health Info

Spinal muscular atrophy

  • Spinal muscular atrophy (SMA) is a genetic disease that affects motor nerves.

    When we want to move our body, motor nerves send the message from our brain to our muscles telling the muscles to move. Spinal muscular atrophies affect the motor nerves and stop these messages getting from the nervous system to the muscles. Over time, the muscles become weak and 'atrophy'.

    Types of SMA

    Spinal muscular atrophy is usually classified by the approximate age of the child when they first have symptoms.

    Under two years old:

    Infantile SMA, or SMA1

    This is also known as Type 1 SMA, or Werdnig-Hoffman disease. Symptoms are sometimes present at birth. This is the most serious form of SMA.

    Six to 18 months old:

    Intermediate SMA, or SMA2

    Also known as Type 2 SMA or SMA2. Children with SMA2 can sit when placed, but cannot get to a sitting position by themselves.    

    After 18 months old to adulthood:

    Juvenile SMA, or SMA3                                                                      

    Also known as Type 3 SMA or Kugelberg-Welander disease. People with SMA3 are affected sometime between the age of 18 months to teens or adulthood. It is a much milder form of SMA.  Mobility is affected, however progression is at a much slower rate.

    Adult onset:

    Type 4, or SMA4

    Because SMA is a genetic disorder, there is a chance that future children born to an affected couple may also be affected. Prenatal diagnosis, to determine if a child will have SMA, is available to parents-to-be with a family history of SMA. Talk to your neurologist or geneticist about this.  

    Signs and symptoms

    Signs and symptoms of SMA include muscle weakness, poor muscle tone and floppiness. The legs are usually weaker than the arms. Babies who are affected may have feeding difficulties and a weak cry. Children who are affected are late to achieve, or do not reach, milestones such as sitting, crawling or walking. The muscles of the face are not affected, but swallowing can be weak. Children with SMA have normal intelligence.


    Symptoms are progressive. This causes increasing weakness in the muscles of the limbs and chest, making breathing progressively more difficult. Involvement of the breathing muscles is the most serious complication of all forms of SMA, especially in children.


    • Currently there is no cure for SMA.
    • Physiotherapy helps prevent contractions of muscles, but cannot restore lost muscle strength in SMA.
    • Children with some forms of SMA may have difficulty swallowing and need a feeding tube. (PEG)
    • Chest infections can be life-threatening in children with SMA, and need quick treatment with antibiotics and chest physiotherapy.  
    • Using a respirator or 'ventilator' may help children with breathing difficulties. See: 
    • Scoliosis (curvature of the spine) is common in children with SMA because of weakness in the muscles around the vertebral column. Surgery can help. See: 
    • Sodium valproate (trade-name Epilim) has been shown to slow the progression of SMA3 and this may also be helpful for the other forms of SMA. Other medications which may slow the progression of weakness in SMA include phenylbutyrate and hydroxyurea. 

    Getting support

    SMA is a difficult thing for families to deal with. Your neurologist has a lot of experience in helping families and individuals cope with diseases like SMA. He or she can also put you in touch with other families in a similar situation. This can be a great source of comfort and support.

    The internet

    While the internet can be a source of good information, it can also be a source of false hope, inaccurate and often misleading information including 'magic' pills and potions which promise to 'cure' your child's SMA. Always read this information with great scepticism. Rely on your doctor for expert and professional advice.

    Key points to remember

    • Spinal muscular atrophy (SMA) is a progressive disease of the motor nerves.
    • SMA is a genetic disorder. Parents of children with SMA have no neurological problems themselves and are generally unaware that they carry the SMA gene until they have children with SMA.
    • Good regular medical care prolongs survival and improves quality of life of children with SMA. Researchers, doctors and families hope to find effective treatments for this disorder in the years to come.

    For more information


    The content for this fact sheet has been contributed to by the RCH Neurosciences Dept and Muscular Dystrophy Australia. Published in Sept 2007. Revised October 2010.

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This information is intended to support, not replace, discussion with your doctor or healthcare professionals. The authors of these consumer health information handouts have made a considerable effort to ensure the information is accurate, up to date and easy to understand. The Royal Children's Hospital, Melbourne accepts no responsibility for any inaccuracies, information perceived as misleading, or the success of any treatment regimen detailed in these handouts. Information contained in the handouts is updated regularly and therefore you should always check you are referring to the most recent version of the handout. The onus is on you, the user, to ensure that you have downloaded the most up-to-date version of a consumer health information handout.