Spinal muscle atrophy, or SMA, is a genetic disorder that affects the nervous system. This is an autosomally recessive trait that causes damage to the motor neuron supplying the spinal cord. This, in turn, disrupts the functioning and movement of the voluntary muscle. This is primarily caused as the muscle does not get the natural nerve stimulation that enables them to coordinate. Atrophy means shrinking or reducing in size, which happens in muscle as a small portion of the muscle is active.

SMA is mainly caused by the mutation of chromosome 5 that translates an SMN protein, which is essential for the function of the motor neurons. This protein is necessary so that the motor neuron is able perform the motor transmission with impulse. The most common genetic cause is an SMN1 gene on chromosome 5. This may be caused due to epigenetic alteration, meaning the non-chromosomal part adjacently placed to the SMN causes the disease.

SMA is classified in types ranging from 1 to 4 as follows:

1. Type 1 SMA

Also called infantile onset SMA, or Werdnig- Hoffmann syndrome, type 1 SMA is generally diagnosed from birth to 6 months of age. Prime symptoms of SMA type 1 include muscle weakness, breathing trouble, weak cry, and trouble swallowing and sucking. In many cases, affected babies may not be able to sit without support. Children with SMA type 1 often suffer significantly short lifespans.

2. Type 2 SMA

With type 2 SMA, the onset occurs within 7 to 18 months of age. This type is often termed intermediate SMA. The symptoms include arm and leg weakness, weakness in the respiratory system, and the lower torso. The spinal curvature may also suffer scoliosis, which may require surgery and/or a brace. Many children with SMA type 2 can sit without support, but they often cannot walk independently. Respiratory complications may also persist. Although mortality rate in this type is low, many patients live into adulthood.

3. Type 3 SMA

Type 3 SMA begins within 18 months to 15 years of age and is also known as Kugelberg- Welander syndrome. This is the mildest form of SMA as lifespan remains healthy. The symptoms cause respiratory issues, as well as muscle, leg, shoulder, arm and hip weakness.

4. Type 4 SMA

In the fourth stage of SMA, the onset of symptoms occurs between 18 and 50 years of age presenting in muscle weakness, twitching and tremors. Life expectancy is not affected and the muscle that is responsible for breathing and swallowing remains unaffected. Only a small group of people affected with this type of SMA needs the assistance of a wheelchair.