what is an sma
Introduction. Spinal muscular atrophy (SMA) is a genetic disease that causes muscle weakness and progressive loss of movement. SMA is caused by deterioration in the nerve cells (motor neurones) connecting the brain and spinal cord to the body's muscles.ntroduction. Spinal muscular atrophy (SMA) is a genetic disease that causes muscle weakness and progressive loss of movement. SMA is caused by deterioration in the nerve cells (motor neurones) connecting the brain and spinal cord to the body's muscles.