Spinal Muscle Atrophy (SMA) is a neuromuscular disease that causes muscle degeneracy in humans. SMA is a genetic disorder that can affect people during birth. In some cases, the condition may go undetected until adulthood. It is also known as autosomal recessive proximal spinal muscular atrophy, which causes severe muscle twitching and extreme weakness. It is an autosomal recessive disorder which is also the primary cause of neonatal death or newborn mortality.

This complex genetic disorder, which affects the muscles, is caused by the homozygous mutation in the survival motor neuron 1, located on chromosome 5q. The loss or deletion of the SMN1 causes severe muscle degeneracy, thereby affecting the limbs and the respiratory system.

The symptoms may vary depending on the type of Spinal Muscle Atrophy (SMA) one suffers from. Besides that, the affected person’s age, stage or severity of the disorder, as well as the body’s metabolism also make a difference.

• In children or infants, the symptoms may vary from flexed knees to hips shifted from the midline while the child adopts a frog-leg sitting position.
• In infants, a weak sound of wailing may indicate SMA.
• In general, the patient may have severe respiratory congestion. This is a result of accumulated secretions inside the alveoli of the lungs, which causes respiratory muscle weakness, feeble breathing, light cough, etc.
• Tongue fasciculations
• Strained body movement
• Strained or painful peristaltic, causing serious swallowing.

There are four Spinal Muscle Atrophy (SMA) types, they include:

1. SMA Type 0 or Type 1
Also known as the Werdnig–Hoffmann disease, SMA type 1 affects infants within the first six months from when they are born. Severe muscle weakening causes a series of symptoms usually detected as the floppy baby syndrome. Motor neurons die rapidly, thereby causing inefficient body functioning and respiratory weakening followed by pneumonia and eventually infant death in most cases.

2. SMA Type 2
It is termed as the Dubowitz disease which affects children between six to eighteen months of age. Since it attacks growing infants, the affected babies are mostly unable to stand. Though cases of walking are negligible, such infants may be able to sit as they grow. Scoliosis may be observed, but it can also be rectified. Progression of muscle degeneracy can be prevented if detected early. Besides the strained respiratory system, such infants can successfully live until adulthood.

3. SMA Type 3
Also known as the Kugelberg–Welander syndrome, this particular Spinal Muscle Atrophy (SMA) type affects children older than 12 months. Patients may be able to walk if detected early. Besides, the respiratory system is almost unaffected and the person suffering from this condition has an average lifespan.

4. SMA Type 4
Also recognized as late-onset, the condition affects adults who are older than 30 years and has lesser complications. Among the various Spinal Muscle Atrophy (SMA) types, SMA Type 4 does not affect the lifespan of the individual. However, muscle degeneracy may leave the patient wheelchair-bound.

Anatomically, all Spinal Muscle Atrophy (SMA) types affect the motor neurons situated at the anterior horn of the grey matter in the spinal cord. In severe cases, it may be accompanied by joint contractures, areflexia scoliosis, and pneumonia.