Spinal muscular atrophy Dr Trisha Macnair Leads to progressive weakness and wasting of skeletal muscles.

In this article

What is spinal muscular atrophy (SMA)? Symptoms

Causes and risk factors Treatment and recovery

Advice and support

SMA is a genetic disorder that affects nerve cells so that muscles can't be used and become wasted, or atrophied.

SMA affects the nerves in an area of the spinal cord called the anterior horn. The nerve cells become damaged, breaking the link between the brain and the muscles. As a result, the muscles can't be used and waste away. This can lead to problems with breathing as well motor activities such as crawling, walking, feeding and head control.

The severity of the symptoms depends on the type of SMA.

Type I (Werdnig-Hoffman disease) is the most severe. It may begin before birth or shortly afterwards (mothers may notice decreased movement of the foetus late in pregnancy), and affected babies are rarely able to lift their head or develop normal movement. Swallowing, feeding and breathing may be difficult, and the child rarely survives to the age of two.

Type II (moderate) usually appears in the first couple of years. The child may reach adulthood, although they may need help to sit or stand, and strain on the muscles can cause complications.

Type III (Kugelberg-Welander disease) is relatively mild and may be diagnosed as late as adolescence. Those affected may have problems walking or getting up from sitting.

Adult-onset SMA tends to progress very slowly, and it's not generally life-threatening. Symptoms are variable and depend on the muscles affected. Fatigue may be a problem, but the muscles used for swallowing and respiratory function are rarely affected.

SMA is a genetic disease and types I, II and III are autosomal recessive conditions meaning that if both your parents are carriers, you have a 1 in 4 chance of having the disease. Boys and girls are affected equally. It's estimated that about one million people in the UK are SMA carriers (about one in 50 people) and around one in 20,000 babies is affected with severe SMA.

Adult-onset SMA may be inherited in other ways. In a few cases, adult-onset SMA results from genetic mutations acquired during life rather than being inherited.

Currently, there's no cure or treatment to repair the nerve damage, but supportive care, is very important, especially physio and attention to respiratory function.

Within affected families, once the abnormal gene has been identified, carriers can be detected by a blood test, and antenatal screening using CVS (chorionic villus sampling) is available.

The Jennifer Trust for Spinal Muscular Atrophy
Helpline: 0800 975 3100
Email: jennifer@jtsma.org.uk
Website: www.jtsma.org.uk

This article was last medically reviewed by Dr Orlena Kerek in February 2009