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Spinal muscular atrophy (SMA)

3-minute read

Spinal muscular atrophy (SMA) is a rare condition that causes muscles to gradually become weak and waste away. Although there is no cure for SMA, there are treatments and support available to help those living with SMA to have the best quality of life possible.

What is SMA?

SMA is an inherited (genetic) condition that affects the nerves leading to your muscles, known as motor nerves. SMA prevents your muscles from receiving messages from your brain. Over time, the muscles become weaker and waste away. This process is known as atrophy.

SMA affects muscles you can see, such as those in your arms and legs, and also muscles you don’t see, such as those used in breathing, coughing and swallowing.

Types of SMA

There are 4 types of SMA based on the types of symptoms and the age at which those symptoms first appear.

Type 1 SMA

Type 1 SMA (also known as Werdnig-Hoffman disease) is the most common type, affecting about 6 out of 10 people with SMA. The symptoms first appear in babies under 6 months old. Type 1 SMA is the most severe type.

Symptoms include:

  • weak and floppy arms and legs
  • problems with coughing, breathing and swallowing
  • lack of head control

Babies with type 1 SMA usually face a difficult fight for survival.

Type 2 SMA

Type 2 SMA affects about 3 out of 10 people with SMA. It appears in children between 6 and 18 months old and is less severe than type 1 SMA.

Some children with type 2 may be able to sit without support when placed in a sitting position. They are usually unable to walk, and may have problems with coughing, breathing and swallowing. They may later develop a curved spine (scoliosis).

Type 2 SMA may shorten life expectancy but many children live well into adulthood.

Type 3 SMA

Type 3 SMA is a milder form of SMA. People with type 3 usually first develop symptoms some time between the age of 18 months and their teens.

Most children with type 3 SMA can walk but may develop problems walking later on. They may also experience problems with breathing and swallowing but these are less common than with type 2. Many children with type 3 SMA have a normal life expectancy.

Type 4 SMA

In type 4 SMA, symptoms start in adulthood. People with type 4 may experience muscle twitches, muscle weakness and difficulty walking. They don’t usually have problems with breathing or swallowing and they usually have a normal life expectancy.

What causes SMA?

SMA is a genetic condition. Both parents of a person with SMA will carry the SMA gene.

Diagnosis of SMA

SMA is usually diagnosed through a genetic blood test. Other tests may also be done to rule out other conditions.

Treatments for SMA

Because there is a wide range of symptoms and severity in SMA, treatments will be different for different people. A team of healthcare professionals with different types of expertise is usually needed to manage SMA.

Treatments may include the following:

  • help with breathing, such as a machine that helps to clear the throat (a cough assist machine)
  • help with feeding, such as providing a dietitian for advice and using feeding tubes
  • mobility equipment, such as a wheelchair or walking frame
  • physiotherapy
  • treatments for scoliosis.

Living with SMA

SMA is a physical condition and does not affect intelligence. Children and adults with SMA need to be encouraged and supported to participate in activities where possible and to live a full life.

More information

For more information and support, visit Spinal Muscular Atrophy Australia.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: July 2018

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