Spinal muscular atrophy (SMA) diagnosis, treatment

What is spinal muscular atrophy?

Spinal muscular atrophy or SMA is a group of hereditary diseases which progressively destroys motor neurons and cause muscle wasting. Reflexes are absent as connection from spinal cord is poor. Brain and muscles are normal. SMA is a lower motor neuron lesion. In spinal cord degeneration of alpha motor neurons occurs which affects skeletal muscle movements. It is a genetic autosomal recessive disease. SMN1 and SMN2 genes are involved. Patient is flaccid, atrophy of muscles occur and breathing muscles are also affected. SMN1 and SMN2 genes are responsible for protein SMN. In this inherited disease one or both genes are absent.

spinal muscular atrophy

Types of Spinal Muscular Atrophy:

There are many types of spinal muscular atrophy depending upon the age difference, here we will discuss the major ones:

SMA Type-1SMA Type-2SMA Type-3
Werdnig-hoffmann diseaseDubowitz diseaseKugelberg-welander disease
Birth to 6 Months7 to 18 Months2 to 17 Years
SevereLess SevereLess Severe
Hypertonia, symmetrical flaccid paralysisJoint contracturesNo ambulation
Poor antigravity movementsKyphoscoliosis, tremors of upper extremityRestricted to wheel chair
Scoliosis absentScoliosis PresentScoliosis Present
By birth child is normal, delayed milestone (sitting)By birth child is normal, delayed milestone (standing)By birth child is normal, delayed milestone (walking)
Patient can survive for 2 yearsPatient can survive for 5-6 yearsPatient can survive a normal life period on wheel chair
Death occurs due to chest infectionDeath occurs due to chest infectionNormal Death

Function Loss in SMA:

Patient suffering from Spinal muscular atrophy have difficulty in crawling, sitting, standing, head movements, breathing, swallowing, and speaking.

Causes of Spinal muscular atrophy:

It is a genetic disorder in which duplication of SMN-1 do not occur. So, to compensate its function another protein replaces it and causes mutations and function of protein is disturbed.

  • Genetic Problem
  • Loss of motor neurons
  • Both copies of survival motor neuron protein SMN-1 on chromosome 5q are defected.
  • Lack of protein SMN.
  • Weakness, and wasting of skeletal muscles

Symptoms of spinal muscular atrophy:

Spinal muscular atrophy patients presents with the following symptoms:

  • Muscle weakness
  • Decreased Muscle tone
  • Limited mobility
  • Frog leg, like appearance
  • Impaired function and endurance.
  • Breathing problems due to weak diaphragm and intercostals.
  • Fatigue
  • Swallowing problem
  • Scoliosis occurs after sitting milestone has achieved
  • Spontaneous tongue movements.
  • Tremors
  • Delayed gross motor skills (fine movements)
  • Flaccid loose body (4 limbs are involved)
  • Weak cry (not loud)
  • Weak sucking
  • Recurrent chest infections

Diagnostic Method:

Spinal muscular atrophy can be diagnosed by using following diagnostic procedures:

  • Prenatal screening
  • Gene panel investigation
  • Muscle biopsy
  • Absence of anti gravity movements
  • Creatine kinase blood test
  • Electromyography
  • Nerve conduction study
  • Genetic testing

Treatment for SMA:

No cure, but treatment can improve symptoms. Gene replacement therapy called Zolgensma.


  • Prevent contractures
  • Help prevent joint tightness
  • Increase flexibility
  • ROM exercises
  • Positioning exercises to prevent bed sores and skin itching.
  • Regular stretching
  • Splints, braces, standing devices
  • Orthosis
  • Taping

Respiratory Care:

In SMA respiratory system is most commonly affected. Respiratory failure is the most common reason for death rate in SMA. So, respiratory care can increase the lifetime. Following measure is taken to prevent chest infection:

  • Airway clearance
  • High frequency chest wall oscillations.
  • Suctioning
  • Non-invasive positive pressure ventilation.

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