Spinal muscular atrophy (SMA) is a genetic disease that causes muscle weakness and progressive loss of movement. It is caused by 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 used for activities such as crawling, walking, sitting up, moving the head and even swallowing, become progressively weaker and shrink (atrophy).
The muscles closest to the centre of the body, such as the shoulders, hips and back (proximal muscles), are usually affected first and most severely. However, in time, all voluntary muscles, as well as muscles responsible for breathing, get significantly weaker. As a result, respiratory complications occur frequently.
SMA is a progressive disorder and everyone affected by it deteriorates over time.
Mental abilities are unaffected by SMA.
For more information see NHS Spinal Muscular Atrophy Site.