Spinal muscular atrophy


Spinal muscular atrophy (SMA) is a genetic condition that makes the muscles weaker and causes problems with movement.

It's a serious condition that gets worse over time, but there are treatments to help manage the symtoms.

Symptoms of SMA

The symptoms of SMA and when they first appear depend on the type of SMA you have.

Typical symptoms include:

  • floppy or weak arms and legs
  • movement problems - such as difficulty sitting up, crawling or walking
  • twitching or shaking muscles (tremors)
  • bone and joint problems - such as an unusually curved spine (scoliosis)
  • swallowing problems
  • breathing difficulties

SMA does not affect intelligence or cause learning disabilities.

Types of SMA

There are several types of SMA, which start at different ages.  Some types cause more serious problems than others.

The main types are:

  • type 1 - develops in babies less than 6 months old and is the most severe type
  • type 2 - appears in babies who are 7 to 18 months old and is less severe than type 1
  • type 3 - develops after 18 months of age and is the least severe type affecting children
  • type 4 - affects adults and usually only causes mild problems

In the past, babies with type 1 rarely survived beyond the first few years of life. But in recent years outcomes have improved with early diagnosis and treatment.

Most children with type 2 survive into adulthood and can live long, fulfilling lives.  Types 3 and 4 do not usually affect life expectancy.

Treatments for SMA

It's not currently possible to cure SMA, but research is ongoing to find possible new treatments.

Treatment and support is available to manage the symptoms and help people with SMA have the best possible quality of life.

Treatment may involve:

  • excercises and equipment to help with movement and breathing
  • feeding tubes and dietary advice
  • braces or surgery to treat problems with the spine or joints
  • medicines that target the faulty genes that cause the condition

A range of healthcare professionals may be involved in your care, including specialist doctors, physiotherapists, occupational therapists, and speech and language therapists.

Tests for SMA

The genetic problem than causes SMA is passed on to a child by their parents.

Speak to a GP if you're planning a pregnancy and:

  • you've had a child with SMA before
  • you have a history of the condition in your family
  • your partner has a history of the condition in their family

The GP may refer you to a genetic counsellor to discuss the risk of the condition affecting a future pregnancy and any tests you can have.

If you're pregnant and there's a chance your baby could have SMA, tests can be carried out to check if they'll be born with the same condition.

Tests can also be done after birth to diagnose SMA in children and adults.

How SMA is inherited

In most cases, a child can only be born with SMA if both of their parents have a faulty gene than causes the condition.

The parents will not usually have SMA themselves, which is known as being a carrier.  Around 1 in every 40 to 60 people is a carrier of the main faulty gene that causes SMA.

If 2 parents who are carriers have a baby, there's a:

  • 1 in 4 (25%) chance their child will have SMA
  • 1 in 2 (50%) chance their child will be a carrier of the faulty gene, but will not have SMA
  • 1 in 4 (25%) chance their child will not have SMA and will not be a carrier

Some rarer types of SMA are inherited in a slightly different way, or may not be passed on at all. 

Speak to a doctor if you or your partner has a family history of SMA and you're worried your children might get it.

Read more about how SMA is inherited on the Spinal Muscular Atrophy UK website

National Congenital Anomaly and Rare Disease Registration Service

If you or your child has spinal muscular atrophy, your clinical team will pass on information about you or your child to the National Congenital Anomaly and Rare Disease Registration Service (NCARDRS).

The NCARDRS helps scientists look for better ways to prevent and treat spinal muscular atrophy. You can opt out of the register at any time.


There are several types of spinal muscular atrophy (SMA), which start at different ages.

They can all cause weakness and difficulty moving, but how bad these problems are varies.

Intelligence and learning ability are not affected by any type of SMA.

Type 1 SMA (young babies)

Children with type 1 SMA show symptoms in the first 6 months of life.

Babies with the condition:

  • have very weak and floppy arms and legs (hypotonia)
  • have problems moving, eating, breathing, and swallowing
  • are unable to raise their head or sit with support

Spinal Muscular Atrophy UK has more information about type 1 SMA.

Type 2 SMA (older babies and toddlers)

Children with type 2 SMA usually show symptoms when they're 7 to 18 months old. The symptoms are less severe than type 1.

Children with the condition may:

  • be able to sit up without help, but not stand or walk
  • have weak arms or legs
  • have shaking (tremors) in their fingers and hands
  • later develop problems with their joints, such as an unusually curved spine (scoliosis)
  • have weak breathing muscles and difficulty coughing – this can put them at risk of chest infections

Spinal Muscular Atrophy UK has more information about type 2 SMA.

Type 3 SMA (children and young adults)

People with type 3 SMA usually develop symptoms after 18 months of age, but this is very variable and sometimes it may not appear until late childhood or early adulthood.

People with the condition:

  • are able to stand and walk without help, although they may find walking or getting up from a sitting position difficult
  • may have balance problems, difficulty running or climbing steps, and a slight shaking in their fingers
  • may find walking gets gradually harder over time, and they may eventually lose the ability to walk when they're older

Spinal Muscular Atrophy UK has more information about type 3 SMA.

Type 4 SMA (adults)

Type 4 SMA, also called adult-onset SMA, usually begins in early adulthood.

Someone with the condition may have:

  • weakness in the hands and feet
  • difficulty walking 
  • shaking and twitching muscles

Type 4 SMA gets slowly worse over time, but does not normally cause problems with breathing or swallowing.

Spinal Muscular Atrophy UK has more information about type 4 SMA.

Other types of SMA

There are several other types of SMA, including:


Tests can be carried out to check if you or your child has spinal muscular atrophy (SMA), or if you're at risk of having a child with the condition.

Tests before getting pregnant

Speak to a GP if you're planning a pregnancy and:

  • you've had a child with SMA before
  • you have a history of the condition in your family
  • your partner has a history of the condition in their family

The GP may refer you for genetic counselling to help you understand the risk of your child having SMA.  You can have a genetic test to see if you have the faulty gene linked to the condition.

If you're at risk of having a child with SMA, talk to your genetic counsellor about your options.

These may include:

  • getting pregnant and waiting to see if your child is born with SMA, or having tests during pregnancy to see if they will have it
  • using donated sperm or eggs to get pregnant
  • pre-implantation genetic diagnosis (PGD) - where a woman's eggs are fertilised in a laborotary and the resulting embryos are tested for SMA before being put in the womb.

Tests during pregnancy

If you're pregnant and there's a risk you could have a child with SMA, tests can be carried our to check for the condition.

The 2 main tests are:

  • chorionic villus sampling (CVS) – a sample of cells from the placenta are tested, usually during weeks 11 to 14 of pregnancy
  • amniocentesis – a sample of amniotic fluid is tested, usually during weeks 15 to 20 of pregnancy

Both these tests can slightly increase your chances of a miscarriage.

If tests show your baby is likely to have SMA, talk to your doctor about what this means and what your options are.

Tests after birth

If you or your child has typical symptoms of SMA, a genetic blood test can be done to confirm the condition.

You may also be asked if anyone in your family has a condition that affect their nerves and muscles.

A physical examination may be done to look for signs of SMA or similar conditions.

Very occasionally, other tests may be needed, too. For example:

  • electromyography – thin needles are inserted into a muscle to detect how well it's working
  • muscle biopsy – a small sample of muscle is taken for analysis

The charity Spinal Muscular Atrophy UK provides more information and advice if your child has recently been diagnosed with SMA.


It's not currently possible to cure spinal muscular atrophy (SMA), but research is ongoing to find new treatments.

Treatment and support is available to manage the symptoms and help people with the condition have the best possible qualiy of life.

A team of different healthcare professionals will be involved in your or your child's care.  They'll help make a care plan outlining the support and treatments you may need.

Feeding and diet help

It is important for people with SMA, especially children, to get the right nutrients.This will help with healthy growth and development.

A dietitian can offer advice about feeding and diet.

If you or your child has difficulty feeding or swallowing, a feeding tube may sometimes be needed.

Several types of tube can be used, such as a tube attached directly to the stomach through the skin of the tummy (gastrostomy tube), ot a tube passed through the nose and down the throat (nasogastric tube).

Breathing help

There are several treatments for the breathing problems that can affect people with SMA.

These include:

  • breathing excercises to strengthen the breathing muscles and make coughing easier
  • a suction machine to help clear the throat if needed - this involves passing a thin, plastic tube to the back of the throat to suck away any mucus
  • in more severe cases, a special machine that provides air through a mask or tube

You may be advised to have vaccinations against flu and pneumonia to reduce your risk of becoming seriously ill from these infections.

Assistive equipment

If you or your child have difficulty moving, an occupational therapist or physiotherapist can provide advice and support.

For example, they can advise about things such as:

  • mobility equipment - including walking frames and wheelchairs
  • supports for the arms and legs (splints or braces)
  • shoe inserts that make walking easier (orthotics)

The Spinal Muscular Atrophy UK charity also has more advice about day-to-day living with SMA.

Excercises and stretches

Exercises and stretches can help maintain strength and stop joints becoming stiff.

A physiotherapist can suggest some exercises to try.

The amount of exercise you or your child can do will depend on your condition, but it's best to try to stay as active as possible.

Treatments for spine problems

Some children with SMA develop an unusually curved spine (scoliosis).

Treatments for this include:

  • a specially made back brace to help support the back and encourage the spine to grow correctly
  • spinal surgery – where the spine is straightened using metal hooks and rods, before being fused into place with pieces of bone

Read more about treatments for scoliosis in children.


Medicines that are used to treat some types of SMA include:

  • nusinersen (Spinraza) – a medicine that targets the faulty gene, given as an injection into the spine, every few months
  • risdiplam (Evrysdi) – a medicine that targets the back-up copy of the faulty gene, given as a liquid once a day
  • onasemnogene abeparvovec (Zolgensma) – a gene therapy medicine that delivers a healthy copy of the gene that causes the condition, given as a single injection

Your treatment team will advise on whether these medicines are suitable for you or your child. This depends on the type of SMA and you or your child's age and symptoms.

Read more about medicines for SMA from Spinal Muscular Atrophy UK

Research into new treatments

Research is being carried out into possible new treatments for SMA.

You can ask your medical team about ongoing clinical trials into new treatments. You can also check the database of clinical trials for SMA to find out about current research.

The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website nhs.uk
Last Updated: 22/12/2022 12:10:59