What is SMA?

SMA stands for Spinal Muscular Atrophy, a genetic disease that is currently incurable and often fatal. One person in every forty is a carrier of the defective gene that causes SMA and if both parents are a carrier, their child has a 1 in 4 chance of having the disease. This would usually be due to the SMN1 (Survival of Motor Neuron) gene, on Chromosome 5, being "altered" or missing altogether.


The absence or abnormality of the SMN1 gene results in production of low levels of the SMN protein which is essential for the survival of motor neurons. SMA affects these motor neurons in the spinal cord, which are called anterior horns cells. Messages travel from the brain, down the spinal cord, through these horn cells and along motor neurons to the muscles, which are then told to move. In a person with SMA, these messages cannot get through as they should as the anterior horn cells cannot provide an effective link between the brain and the muscles. This means the ability to control the muscles gets less and less to the point where they get weak and waste away. In general the higher the level of SMN protein and later onset of symptoms the less severe the SMA is.


There are around 100 new cases of Spinal Muscular Atrophy each year in the UK alone, and approximately 1 in 6,500 children are affected. SMA is autosomal recessive which means for a child to be affected BOTH parents must be a carrier of the faulty gene.


The diagram to the right shows the chances of a child having SMA if both parents are a carrier.