What is spinal muscular atrophy and how is it treated?

Baby Arthur underwent gene therapy infusion at the Evelina London Children's Hospital on May 25.
Arthur Morgan suffers from SMA and has become the first NHS patient to receive gene therapy treatment. Credit: PA

Five-month-old baby Arthur Morgan has become the first NHS patient treated with a drug for the rare genetic condition, spinal muscular atrophy (SMA).

Between 600 and 1,200 children and adults are currently living with the condition in England and Wales.

SMA most often affects babies and children and makes it hard for them to use their muscles.

It causes the nerves that control muscle strength and movement to break down.

As it progressively destroys motor neurons - nerve cells in the brain stem and spinal cord - people with SMA will have issues with speaking, walking, breathing, and swallowing.

What is SMA and what treatments are available to treat it?

Dr Elizabeth Wraige, consultant paediatric neurologist who treated Baby Arthur, explains what spinal muscular atrophy is

What is SMA?

SMA is a genetic condition that makes the muscles weaker and affects movement and, in some cases, breathing. There are four types of SMA and symptoms will depend on which type a person has.

There is a wide spectrum of how severely children, young people and adults are affected, but it's a serious condition that gets worse over time.

Increasingly, there are treatments to help manage the symptoms.

How is it inherited?

Around 1 in every 40 to 60 people is a carrier of the main faulty gene (SMN1 ) that causes SMA.

This faulty gene does not make enough of a protein needed for the motor neurons to work properly, and when the motor neurons break down, they can't send signals to the muscles.

In most cases, a child can only be born with SMA if both of their parents have a faulty gene that causes the condition, although they will not usually have SMA themselves.

If both parents are carriers, there's a 25% chance their child will have SMA; 50% chance their child will be a carrier of the faulty gene, but not have SMA; 25% chance their child will not have SMA and will not be a carrier

His father Reece Morgan was by Arthur's side. Credit: PA

What are the different types of SMA?SMA Type 1: The symptoms and effects of SMA Type 1 usually begin from birthor within the first few weeks or months of life. Generally, the earlier the onset of symptoms, the more severe the condition. This is the most severe type and life expectancy for babies with SMA type 1 has been usually only a few years, but treatments, such as that being given to five-month-old Arthur Morgan, are helping affected babies live longer.SMA Type 2: Symptoms usually appear between seven and 18 months of age. Babies and toddlers with type 2 are usually able to sit but not walk independentlySMA Type 3: There are two types of SMA Type 3:– SMA Type 3a: Symptoms usually begin between 18 months and three years of age.

– SMA Type 3b: Symptoms will usually begin after three years of age.

Children with both types are usually able to walk, though they may lose this ability overtime. Difficulties usually appear later than for children who develop symptoms earlier.

SMA Type 4: Symptoms begin in adulthood and will affect the ability to walk

What are the symptoms of SMA?Symptoms will vary depending on the type of SMA. Some babies with SMA are often described as "floppy" and don't learn to roll or sit at the expected age.

Other symptoms include:

  • weak arms and legs

  • movement difficulties, such as being unable to sit up, crawl or walk

  • twitching or shaking muscles 

  • bone and joint problems – such as an unusually curved spine (scoliosis)

  • difficulties breathing

  • swallowing problems

  • breathing difficulties

How does Zolgensma work to treat SMA? Dr Elizabeth Wraige explains

What treatments are available?

While there is no cure for SMA, treatments can help children with SMA live a better life.

Until two years ago, there were no treatment options available for children with spinal muscular atrophy (SMA), which is the leading genetic cause of death for children.

But babies could potentially have the ability to sit, crawl and walk after being treated with US gene therapy Zolgensma, which has been called the most expensive drug in the world.

Zolgensma, which has a list price of £1.79 million per dose, was made available on the NHS after the health service struck a deal with manufacturers Novartis Gene Therapies in March.

Breathing exercises and equipment can help people manage the symptoms, while physical therapy, occupational therapy, and rehabilitation can help to improve posture and mobility. Braces or surgery can be used to treat problems with the spine or joints.

The earlier Zolgensma is given for SMA the better, with pre-symptomatic treatment shown to give the very best possible outcomes. Early diagnosis and treatment is vital and campaigners are calling for newborn screening for SMA to be introduced in the UK.