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Spinal muscular atrophy (SMA)

7-minute read

Key facts

  • Spinal muscular atrophy (SMA) is a genetic condition.
  • It affects the nerves called motor neurons.
  • SMA is the childhood version of motor neurone disease.
  • Although there is no cure for spinal muscular atrophy, there are new treatments available.

What is spinal muscular atrophy ?

Spinal muscular atrophy (SMA) is a genetic condition. It affects the nerves leading to your muscles. These nerves are known as motor neurons.

Over time, your muscles become weaker and atrophy (waste away).

Spinal muscular atrophy affects the muscles used for:

  • movement — in your arms, legs and head
  • breathing, coughing and swallowing

Although there is no cure for spinal muscular atrophy, there are new treatments available.

Spinal muscular atrophy is the childhood version of motor neurone disease.

What are the types of spinal muscular atrophy ?

There are 5 types of spinal muscular atrophy. These are based on the age when symptoms first appear.

  • Type 0 — symptoms are present at birth
  • Type 1 — symptoms usually develop during the first few months of life
  • Type 2 — symptoms usually appear between 7 to 18 months
  • Type 3 — symptoms usually appear after 18 months
  • Type 4 — symptoms usually appear from early adulthood

Type 1 SMA is the most common type, affecting about 7 in 10 people with SMA.

What are the symptoms of spinal muscular atrophy?

The symptoms of spinal muscular atrophy depend on its type.

Type 0 spinal muscular atrophy

Type 0 is the rarest and most severe form of SMA. It affects babies in the womb.

Symptoms include:

  • less movement in the womb
  • joint deformities at birth
  • extremely weak muscle tone at birth

Unfortunately, babies born with Type 0 SMA usually don’t survive more than 12 months.

Type 1 spinal muscular atrophy

Type 1 SMA is also called Werdnig-Hoffman disease. The symptoms include:

  • weak muscle tone
  • poor head control
  • a weak cry and cough
  • difficulty swallowing

Currently, babies with type 1 SMA usually do not live past their second birthday.

Type 2 spinal muscular atrophy

Type 2 SMA affects about 3 in 10 people with SMA. It is less severe than type 1 SMA.

Children with Type 2 SMA may:

  • not reach their motor (movement) milestones on time
  • have poor weight gain
  • have a weak cough
  • have fine hand tremors
  • have joint contractures
  • have scoliosis (curvature of the spine)

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

Type 3 spinal muscular atrophy

Type 3 SMA is a milder form of SMA.

Symptoms can include:

  • muscle weakness and cramps
  • loss of the ability to walk

People with type 3 SMA have a normal life expectancy.

Type 4 spinal muscular atrophy

People with type 4 may have:

  • mild to moderate muscle weakness
  • tremors
  • mild breathing problems

People with Type 4 SMA have a normal life expectancy.

What causes spinal muscular atrophy?

Spinal muscular atrophy is a genetic condition.

It is a recessive disorder. This means that you need to inherit a copy of the faulty gene from both of your parents.

As many as 1 in 35 people in Australia have a faulty SMA gene.

When should I see my doctor?

See your doctor if you have concerns about your child’s:

  • muscle tone — they may seem floppy
  • head control
  • feeding difficulties

Newborn screening for SMA is being rolled out across Australia. This helps children get care and treatment as soon as possible.

FIND A HEALTH SERVICE — The Service Finder can help you find doctors, pharmacies, hospitals and other health services.

How is spinal muscular atrophy diagnosed?

Your doctor will examine your child. They will also arrange for genetic testing. Other tests may also be done to rule out other conditions.

ASK YOUR DOCTOR — Preparing for an appointment? Use the Question Builder for general tips on what to ask your GP or specialist.

How is spinal muscular atrophy treated?

Recently, some new medicines have become available that treat spinal muscular atrophy types 1-3. While they don’t cure the disease, they help stop further decline.

However, the long-term effects of these treatments aren’t yet known.

Living with SMA

A team of healthcare professionals with different types of expertise is needed to manage spinal muscular atrophy. These professionals should include a:

Management goals will depend on your current symptoms.

Children and adults with spinal muscular atrophy need to live a full life.

Can SMA be prevented?

There is no cure for SMA.

However, from November 2023, Medicare will cover the cost of reproductive carrier testing. You may have this test:

  • before you become pregnant
  • in the early stages of pregnancy

These tests allow you to make choices about having children and help identify babies at risk of SMA.

Newborns with SMA can be started on treatment before symptoms appear. This can improve both their functioning and survival.

Research is looking at ways to prevent, diagnose and treat spinal muscular atrophy.

Complications of SMA

Some types of SMA are fatal (cause death).

Spinal muscular atrophy is a physical condition and does not affect your intelligence.

Resources and support

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

You may also be interested in learning more about the Australian Neuromuscular Disease Registry (ANMDR). ANDMR collects information from patients to improve the understanding of neuromuscular disease.

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with 24 hours a day, 7 days a week.

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

Last reviewed: November 2023

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