Spinal Muscular atrophy

Spinal muscle atrophy, also called as Spino-muscular atrophy is a type of Motor neuron disease. In motor neuron diseases, there is degeneration of either upper or lower motor neurons. Specific point to note about motor neuron diseases is there is no sensory involvement.

Watch a heart wrenching story of a family and their son’s fight against Spinal muscular atrophy which is a number one genetic killer of kids under the age of 2.

Spinal muscle atrophy predominantly affects lower motor neurons i.e. the lesion involves anterior horn of the spinal cord and lower part. Important point to note here is, motor neuron involvement in motor neuron disease is not only limited to motor neurons of spinal cord but they also involve the motor neurons of brainstem.

Spinal muscle atrophy has an autosomal recessive inheritance and selectively affects SMN1 gene located on chromosome number 5. This gene codes for a protein that is necessary for the survival of motor neurons. Spinal muscle atrophy has been divided into four types depending on the age of onset of the disease. The types are as follows –

  1. Infantile – Has an ago of onset of zero to six months and is also called as Werdnig-Hoffman disease. This is a very aggressive type of SMA. It is seen in the very first month of life and leads to poor working of important body parts due to motor neuron death. Respiratory system is severely affected and respiratory failure due to pneumonia is the typical reason of death. Babies with infantile spinal muscule atrophy usually do not survive beyond 2 years.
  2. Intermediate – This type has an age of onset of 6-18 months. Children affected with this disease will never be able to stand or walk but can maintain sitting posture. Life expectancy is up to adulthood.
  3. Juvenile – Age of onset for juvenile type is beyond 18 months and patients with Juvenile type Spinal Muscle atrophy can move or walk without using any help for some time but they may lose this ability after some time. Life expectance is almost normal.
  4. Adult –Age of onset for this form is third decade and mainly affects proximal muscles resulting in patient to be wheel chair bound. Life expectancy is unaffected.

Lower motor neuron lesion produces flaccid paralysis and fasciculation’s are the most common symptom. The severity of involvement of the lower motor neurons varies and hence also the severity of symptoms. The predominant features of spinal muscular atrophy as per the level of involvement are –

  • Feature due to anterior horn cell involvement –
  1. Initially asymmetric paralysis.
  2. Fasciculation’s.
  3. Progressive muscular atrophy.
  • Features due to Brainstem nuclei involvement –
  1. Difficulty in chewing, swallowing and movement of face and tongue.
  2. Fasciculation’s of tongue.
  • Other common features of the disease are-
  1. Areflexia.
  2. lower weight and growth.
  3. Weak pulmonary muscles which lead to weak cough, weak cry and

respiratory distress.

  1. Head often tilted to one side.
  2. Milestones are delayed or never achieved.
  3. Poor muscle tone (This feature gave it the name ‘Floppy baby syndrome’)

Like other Motor neuron diseases following features will never be seen in spinal muscle atrophy –

  1. Ocular involvement.
  2. Bladder involvement.
  3. Sensory involvement.
  4. Cognitive features.

Currently there is no cure for spinal muscle atrophy, but research on this matter has gained considerable momentum.