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Spinal muscular atrophy (SMA)

4-minute read

What is SMA?

Spinal muscular atrophy (SMA) is an inherited (genetic) condition that affects the nerves leading to the muscles, known as motor nerves. SMA prevents the muscles from receiving messages from the 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 the arms and legs, and also muscles you don’t see, such as those used in breathing, coughing and swallowing.

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 are the types of SMA?

There are 5 types of SMA based on the types of symptoms and the age at which those symptoms first appear.

Type 0 SMA

The rarest and most severe form, this affects babies in the womb. Unfortunately, they usually don’t survive more than 12 months.

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.

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 7 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 sometime 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.

How is SMA diagnosed?

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

How is SMA treated?

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

Some new medications have recently been developed to treat people with SMA, called Spinraza and Zolgensma. Spinraza is available to patients in Australia via the Pharmaceutical Benefits Scheme, which means the Government subsidises most of the cost.

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.

Resources and support

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

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Last reviewed: July 2021

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