Dr Jefferies and Partners, NHS Doctors in Fulham.

Spinal muscular atrophy

Introduction

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 symptoms.

This page covers:

Symptoms

Types of SMA

Treatments

Tests and diagnosis

How it's inherited

Further information and advice

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 doesn't 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 six months old and is the most severe type
  • type 2 – appears in babies who are 7-18 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

Babies with type 1 rarely survive beyond the first few years of life. Most children with type 2 survive into adulthood and can live long, fulfilling lives. Types 3 and 4 don't usually affect life expectancy.

Read more about the types of SMA.

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:

  • exercises and equipment to help with movement and breathing
  • feeding tubes and diet advice
  • braces or surgery to treat problems with the spine or joints

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

Read more about treatments for SMA.

Tests for SMA

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

Speak to your 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

Your 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 condition. 

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

Read more about tests for SMA.

How SMA is inherited

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

The parents won't 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 two 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 won't have SMA
  • 1 in 4 (25%) chance their child won't have SMA and won't be a carrier

Some rarer types of SMA are inherited in a slightly different way, or may not be passed on at all. SMA Support UK has more information about how SMA is inherited.

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

Further information and advice

The charity SMA Support UK can provide more information and advice for people with SMA, their families and their carers.