SMA (spinal muscular atrophy) is a genetic disease that robs people of physical strength by affecting the motor nerve cells in the spinal cord, taking away the ability to walk, eat, or breathe. It is the number one genetic cause of death for infants. SMA is caused by a mutation in the survival motor neuron gene 1 (SMN1).
Spinal muscular atrophy (SMA) causes muscle weakness and progressive loss of movement. It is caused by deterioration in the nerve cells (motor neurons) 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 disorder is caused by a genetic defect in the SMN1 gene, which encodes SMN, a protein widely expressed in all eukaryotic cells and necessary for survival of motor neurons. Lower levels of the protein results in loss of function of neuronal cells in the anterior horn of the spinal cord and subsequent system-wide muscle wasting (atrophy).
Spinal muscular atrophy manifests in various degrees of severity, which all have in common progressive muscle wasting and mobility impairment. Proximal muscles and lung muscles are affected first. Other body systems may be affected as well, particularly in early-onset forms of the disorder. SMA is the most common genetic cause of infant death. Spinal muscular atrophy is an inherited disorder and is passed on in an autosomal recessive manner.
SMA manifests over a wide range of severity, affecting infants through adults. The disease spectrum is variously divided into 3–5 types, in accordance either with the age of onset of symptoms or with the highest attained milestone of motor development.