What is Spinal Muscular Atrophy?

Spinal muscular atrophy is a genetic disease that affects the nervous system. It generally affects the part of the nervous system which regulates the voluntary movements, and most of them are located in the spinal cord. In this situation; the muscle cells do not receive the signals from the spinal cord and as a result; it leads to atrophy of voluntary muscles.spinal-muscular-atrophy

The disease is caused by a genetic defect in SMN 1 gene, which codes for a protein SMN.

There are various degrees of severity in spinal muscular atrophy. Muscle impairment and muscle wasting are the common symptoms of this disease.

The spinal muscular atrophy is the most common cause of infant death caused by the genetic disease.


There is a high range of severity in spinal muscular disorder from infants to adults. 4 types of spinal muscular disorder are known:-

  • SMA1 (infantile) – The common age for the onset of this disease is 0-6 months. SMA manifests itself in the first month of life. Rapid death of motor neurons causes loss of function of major organs especially of the respiratory system that leads to pneumonia and finally leads to death due to respiratory failure. Baby having SMA1 cannot live more than 2 years of age; the death generally occurs in few weeks.
  • SMA2 (intermediate) – The most common age of onset is 6-18 months. The intermediate form generally affects those children who cannot walk and stand during their life, but they can maintain a sitting position. The weakness generally noticed between 6-18 months, body muscles are weakened and the main problems are associated with the respiratory system.
  • SMA3 (juvenile) – The usual age of onset is after 12 months of life. In this type; a person can walk properly but he/she can lose this ability later in the life. There are no such problems with the respiratory system and life expectancy is normal.
  • SMA4 (adult-onset) – The usual age of onset is in adulthood, it leads to gradual weakening of muscles of proximal body parts.

Signs and symptoms 

  • Areflexia (particularly in extremities).
  • Muscle weakness all over the body.
  • Poor muscle tone.
  • Difficulty in sitting, walking, standing and achieving developmental milestones.
  • The most severe symptom of SMA is that it affects the respiratory muscles that lead to a weak cough, weak cry in infants, and accumulation of secretions in lungs or throat.
  • Difficulty in sucking or swallowing and poor feeding.
  • Twitching of the tongue.


Spinal muscular atrophy is linked to a genetic mutation in the SMN1 gene.


  • The absence of reflexes.
  • Electromyogram.
  • Serum creatine kinase may be normal or increased.


There is no such cure for the spinal muscular disease.

The only drug that is used is Nusinersen.

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