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.
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-1||SMA Type-2||SMA Type-3|
|Werdnig-hoffmann disease||Dubowitz disease||Kugelberg-welander disease|
|Birth to 6 Months||7 to 18 Months||2 to 17 Years|
|Severe||Less Severe||Less Severe|
|Hypertonia, symmetrical flaccid paralysis||Joint contractures||No ambulation|
|Poor antigravity movements||Kyphoscoliosis, tremors of upper extremity||Restricted to wheel chair|
|Scoliosis absent||Scoliosis Present||Scoliosis 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 years||Patient can survive for 5-6 years||Patient can survive a normal life period on wheel chair|
|Death occurs due to chest infection||Death occurs due to chest infection||Normal 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.
- Swallowing problem
- Scoliosis occurs after sitting milestone has achieved
- Spontaneous tongue movements.
- Delayed gross motor skills (fine movements)
- Flaccid loose body (4 limbs are involved)
- Weak cry (not loud)
- Weak sucking
- Recurrent chest infections
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
- 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
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.
- Non-invasive positive pressure ventilation.