Spinal muscle atrophy (SMA) is a common genetic disease, which is commonly found in infants and children and rarely found in adults. In SMA, a particular section of the nervous system, which controls voluntary muscle movement, is impacted. Explained ahead are the types, causes, and symptoms associated with SMA.

1. Types of SMA
There are four types of SMA, and these types vary according to the level of severity.

• Type 1 SMA
  Type 1 SMA is the most severe type and is usually found at birth or after the first few months when the baby is approximately six months old. Any baby suffering from this type may pass away after the age of two.
• Type 2 SMA
  Type 2 is an intermediate form of SMA. It occurs when a baby is anywhere between 7 to 18 months old and the rate of progression varies from patient to patient. The life expectancy in this type of SMA can vary from early childhood to adulthood depending on the condition of the patient.
• Type 3 SMA
  Type 3 SMA is a mild form that occurs in patients that belong from a varying age group between 18 months and early adulthood. The life expectancy in this type of SMA is nearing the normal lifespan of an individual.
• Type 4 SMA
  Type 4 is the rarest type of spinal muscle atrophy. This type occurs in patients when they are in their 20s or 30s.

2. Causes of SMA
SMA is classified as a motor neuron disease, as it is identified by the loss of nerve cells in the spinal cord called motor neurons. All the aforementioned types of SMA are caused by a mutation in the survival motor neuron protein, which is essential for the normal functioning of the motor neuron.

3. Symptoms across various types of SMA

• Type 1 SMA
  The core symptoms of this SMA type include weak trunk movement and floppy limbs. Patients with Type 1 SMA have difficulty moving and are unable to sit. They face problems in holding their head up, breathing, swallowing, and feeding. As this is the most severe type of SMA, it progresses rapidly as the muscles become weaker, which results in regular respiratory infection.
• Type 2 SMA
  Children with the problem of Type 2 SMA are unable to stand and suffer from respiratory infections.
• Type 3 SMA
  Patients with this type are able to walk and stand but have difficulty in getting up from sitting position. They are at a greater probability of having respiratory infections. They may also face mild weakness.
• Type 4 SMA
  Patients with this type are able to walk during adulthood. However, they gradually experience muscle weakness and other typical symptoms.