Spinal Muscle Atrophy (SMA) Types

Spinal muscle atrophy (SMA) is a genetic disorder that’s referred to as a fatal autosomal recessive disorder. It attacks the nerves cell system, leading to progressive weakening of the motor neurons. Patients suffering from SMA may experience difficulties standing, walking dressing, swallowing, and breathing.

Ideally, SMA symptoms are noticeable when the child is under 6-months old. Statistically, one in every 10,000 children are born with SMA. While the cause of SMA is unknown, almost 95% of SMA cases disorder are the result of the inadequate production of a specific protein known as survival motor neuron protein (or SMN). Patients with spinal muscular atrophy lack SMN1 and SMN2 genes found in chromosome 5, which produces survival neuron protein (SMN). Also, alteration of SMN1 and SMN genes may cause SMA. Primarily motor neuron cells are found in the spinal cord. These cells control skeletal muscle within the body, however, if there are low survival motor neuron proteins, the motor neuron located in spinal cord shrink and dies resulting in spinal cord complications. The SMA symptoms are:

  • Difficulties swallowing food
  • Breathing problems
  • Mobility issues (i.e., difficulty walking)
  • Frequent and uncontrolled tongue movement
  • Abnormal bending of the spinal cord (causing standing issues)

SMA occurs in several main types, which are determined by the onset of symptoms, they include:

1. SMA: Type I
Also referred to as Werdnig-Hoffmann disease, patients suffering from this form of the disorder can neither walk nor sit up without being supported. They may also have breathing and eating challenges. Werdnig-Hoffmann is diagnosed through muscle biopsy test or electromyography test. The best method to detect is by taking a DNA test. Approximately 80% of individuals with SMA type 1 are infants and fall into the severe category. Most importantly, respiratory check ups help to ensure the patients are not prone to respiratory infection.

2. SMA: Type II
SMA type II often develops between 7 to 18 months of age. This type of the disease affects the leg movements more than the arms, meaning SMA type 2 patients can never stand. Respiratory infections are frequent and life expectancy is typically early childhood to adulthood, depending on the severity of SMA.

3. SMA: Type III
Also known as Kugelberg-Welander disease, or juvenile SMA, symptoms tend to display between 18 months of age into early adulthood. Life expectancy with SMA type 3 is fairly normal. Patients with SMA type 3 can stand and walk, but may have trouble moving from sitting to standing, trouble running, and climbing stairs. Mild muscle weakness and respiratory infections are also common.

4. SMA: Type IV
SMA type 4 results due to a mutation of SMN1. Type IV disorders appear in patients older than 35-years old. They usually cause mild weakness in the legs, arms, and joints. The majority of victims can walk, but some have to use wheelchairs. Ideally, in every 300,000 individual with SMA suffers from type IV. Nusinersen injection and consistent therapy relieves the effects