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Spinal muscular atrophy (SMA)

  • Spinal muscular atrophy (SMA) is a rare genetic disorder that affects the part of the nervous system that controls muscle movement.

    SMA affects the motor nerves (neurons) of the spinal cord. Usually, when we want to move our body, motor nerves send the message from our brain to our muscles, telling the muscles to move. In children with SMA, these messages do not reach the muscles. This causes muscle weakness, muscle damage, muscle wasting (atrophy) and eventual loss of function.

    Children with SMA may have difficulty crawling, sitting, walking and moving their limbs and neck. Their ability to breathe and swallow may also be affected. 

    Types of SMA

    SMA is a very complex disorder, affecting each child differently. There are three common types of SMA affecting children. 

    • SMA type 1: This is the most severe form of SMA. Symptoms may be present at birth or develop within the first few weeks or months. They include severe weakness or 'floppiness', poor head control, weak cry and cough, and difficulty with swallowing and feeding. 
    • SMA type 2: This develops within the first three years of life. Children with SMA type 2 can usually sit when placed in a sitting position, but cannot get to a sitting position by themselves. They have delayed motor (physical) milestones, poor weight gain, weak cough, hand tremors, contractures (fixed deformities of joints) and scoliosis (curved spine).
    • SMA type 3: Children with SMA type 3 develop symptoms sometime between the age of 18 months and adolescence. It is a much milder form of SMA. Mobility is affected, but the progression of the condition is much slower than types 1 and 2. SMA type 3 causes variable muscle weakness, cramps and fatigue. Some people with SMA type 3 can walk independently; others may require assisted mobility devices, such as scooters or walking frames.

    Signs and symptoms of SMA

    How SMA affects a child depends on when the disorder first causes symptoms. Early signs of SMA include:

    • muscle weakness and poor muscle tone (a lack of tension in the muscles, which can cause floppiness)
    • the child's legs are usually weaker than the arms
    • babies may have feeding difficulties and a weak cry
    • young children are late to achieve, or do not reach, milestones such as sitting, crawling or walking
    • the muscles of the face are not affected, but the child may have difficulty swallowing.

    The symptoms of SMA are progressive, which means that they get worse over time. The muscles of the limbs and chest become weaker, gradually making breathing more difficult. Weakness of the breathing muscles is the most serious complication of all forms of SMA, especially in children.

    It is important to note that SMA does not affect all parts of the body. Intelligence is unaffected and children with SMA attend mainstream schools.

    When to see a doctor

    If your child shows any signs or symptoms of SMA, or you are concerned that your child is not reaching their motor milestones, see your Maternal and Child Health Nurse or GP. You may be referred to a paediatrician or paediatric neurologist.

    Treatment for SMA

    Currently there is no cure for SMA, but there are many ways to help your child. Your child will be under the care of a team made up of different medical professionals.

    In the past, the treatment of SMA has been based on management of the complications of weakness, feeding problems and breathing difficulties. However, there are some new medications that in recent years have been proven to improve strength, motor function, breathing and feeding in children with SMA. These medications should become increasingly available in the future and will change the focus of SMA management. 

    Medical care for children with SMA aims to prolong survival and improve quality of life. 

    • Physiotherapy helps maintain muscle function as long as possible but cannot restore lost muscle strength in SMA.
    • Children with some forms of SMA may have difficulty swallowing and need a feeding tube or suctioning.
    • Chest infections can be life-threatening in children with SMA. They need to be treated quickly with antibiotics and chest physiotherapy.  
    • Your child may need to use a respirator (ventilator) if they are having breathing difficulties.  
    • Scoliosis (curvature of the spine) is common in children with SMA because of weakness in the muscles around the spine. Sometimes surgery can help correct this.

    Getting support

    SMA can be very difficult for families to deal with. Your multidisciplinary care team has a lot of experience in helping families and children cope with diseases like SMA, and they can also put you in touch with other families in a similar situation. This can be a great source of comfort and support.

    Spinal Muscular Atrophy Australia and Muscular Dystrophy Australia provide support, assistance and information for people and families affected by SMA.

    While the internet can be a source of good information, it can also be a source of false hope and inaccurate information. Be cautious of misleading claims about treatments that promise to 'cure' your child's SMA. Rely on your doctor for expert and professional advice.

    What causes SMA?

    SMA is a genetic condition caused by a mutation (change) in the survival motor neuron (SMN) gene. Parents of children with SMA have no signs or symptoms themselves and are generally not aware that they carry the mutated SMA gene until they have a child with SMA. If both parents are carriers, their children each have a one-in-four chance of inheriting SMA. 

    Couples with a family history of SMA can have prenatal genetic testing to determine if an unborn child has SMA. Talk to your obstetrician, neurologist or geneticist about this. 

    Key points to remember

    • Spinal muscular atrophy (SMA) is a progressive disorder affecting the motor (movement) nerves.
    • SMA is a very complex disorder, and there are three common types of SMA affecting children. SMA type 1 is the most serious form.
    • Children with SMA may have muscle weakness and poor muscle tone, and may not reach milestones such as sitting or crawling.
    • There is currently no cure for SMA, but medical care aims to improve the quality of life of children with SMA and prolong survival.
    • New medications are expected to become available that have been shown to improve strength, motor function, breathing and feeding in children with SMA.

    For more information

    Common questions our doctors are asked

    What is the long-term outlook for a child with SMA?

    SMA progresses differently for each child with the disorder. The severity usually depends on the type of SMA your child has. SMA type 1 is the most serious; children with this form of SMA have a significantly shortened life expectancy.

    How far off is a cure for SMA?

    Although no cure currently exists for SMA, research is currently underway. Researchers, doctors and families hope to find effective treatments for this disorder in the near future.

    Developed by The Royal Children's Hospital Neurology department with input from Muscular Dystrophy Australia. We acknowledge the input of RCH consumers and carers.

    Reviewed September 2018.

    This information is awaiting routine review. Please always seek the most recent advice from a registered and practising clinician.

    Kids Health Info is supported by The Royal Children’s Hospital Foundation. To donate, visit


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