Spinal muscular atrophy

Spinal muscular atrophy (SMA) is a genetic disease that causes muscle weakness and progressive loss of movement.

It occurs due to deterioration in the nerve cells (motor neurones) connecting the brain and spinal cord to the body’s muscles.

As the link between the nerves and muscles breaks down, the muscles that are used for activities such as crawling, walking, sitting up, and moving the head become progressively weaker and shrink (atrophy). Mental abilities are unaffected by SMA.

There are a number of different conditions which are called SMA. The term is usually used for the most common form, which is caused by a genetic problem where one copy of the genetic error is inherited from each parent.

Read more about the causes of spinal muscular atrophy

Classification of spinal muscular atrophy

SMA is classified according to the age at which symptoms develop and how severe they are:

• Type I – the most severe type, develops in babies less than six months old
• Type II – less severe than type I, symptoms usually appear in babies 7-18 months old 
• Type III – the mildest type affecting children, symptoms usually appear after 18 months of age
• Type IV – affects adults

In the most severe cases (Type I), fatal respiratory problems mean that children rarely survive beyond two years of age.

Type II SMA may shorten life expectancy, but improvements in care standards mean that the majority of people can live long, fulfilling and productive lives.

Life expectancy is usually unaffected in more mild cases (Types III and IV).

Read more about the types of spinal muscular atrophy.

Treatment and support

There is no cure for SMA, but treatment and support can help to manage the condition. Depending on its severity, treatment may involve:

• exercises and equipment to improve mobility and breathing
• feeding tubes and nutrition advice
• bracing or surgery to treat curvature of the spine (scoliosis)

A range of healthcare professionals are involved in the care of SMA, including doctors who specialise in neurology, physiotherapists, occupational therapists, and speech and language therapists.

Read more about treating spinal muscular atrophy.

Testing for spinal muscular atrophy

If there are concerns your children may inherit SMA, for example if you have a family history of the condition, genetic testing may be recommended. This involves checking a sample of your blood for the genetic problem responsible for the condition.

It's also possible to check an unborn child for this genetic problem during pregnancy, using tests such as chorionic villus sampling (CVS) and amniocentesis.

If a child shows typical signs of SMA, such as obvious muscle weakness, a blood test can usually confirm a diagnosis.

Read more about diagnosing spinal muscular atrophy.