The Different Types Of Spinal Muscular Atrophy

Category: Spine | Author: Stefano Sinicropi

spinal muscular atrophy

Spinal muscular atrophy (SMA) is a genetic condition that affects the motor nerve cells in the spinal cord, impacting the way a person moves, eats and breathes. The disease is caused by a mutation of the survival motor neuron gene 1 (SMN1). This genetic defect is a cause of death among infants. There are a number of different variations of the condition which can set in at different ages, and we explain the different types of spinal muscular atrophy in this blog.

Spinal Muscular Atrophy Types

There are five basic types of SMA. Here’s a closer look at each condition:

  • Type 1 SMA – Type 1 SMA is the most common and earliest onset form of spinal muscular atrophy. In type 1 SMA, symptoms are present at birth or within the first six months of life. Infants with type 1 SMA typically experience muscle weakness, weak vocal muscles and breathing distress. They also tend to have difficulty swallowing and sitting up unassisted. This is also coined as Type 0 or floppy baby syndrome.
  • Type 2 SMA – Type 2 spinal muscular atrophy sets in a little later in life, between seven and 18 months of age. Symptoms set in right before a child learns to stand or walk independently, and inhibits these behaviors. Children with type 2 SMA typically live to young adulthood or even longer.
  • Type 3 SMA – Type 3 spinal muscular atrophy occurs after 18 months of age, but typically sets in during adolescence and the teenage years. Symptoms set in after children have learned to stand and walk on their own, and this may require them to transition to walking aides. Although muscle weakness occurs, the average lifespan isn’t affected much.
  • Type 4 SMA – This type of SMA develops during adulthood. Patients may experience leg or arm weakness and eventually breathing issues, but overall, life expectancy remains unchanged.
  • Rare SMAs – The types of spinal muscular atrophy involve a genetic mutation of chromosomes. A geneticist would be involved in identifying the chromosomes that have caused the symptoms.  The types 1-4 should not be confused with spinal muscular atrophy with respiratory distress (SMARD) and Distal SMA.

Treatment of Spinal Muscular Atrophy

Muscle weakness that contributes to breathing issues is the main concern in patients with spinal muscular atrophy, but another medical complication of SMA is an abnormal curvature of the spine. Oftentimes scoliosis is present in patients with Type 3 or Type 4 SMA. The condition sets in because the muscles that normally support the spine are weakened, allowing the spine to form an abnormal curvature. Scoliosis can impact a person’s mobility, and in severe cases it can make breathing more difficult.

Scoliosis as a result of spinal muscular atrophy is generally treated with bracing in children and teens. The goal is to correct the curvature of the spine until it has stopped growing. Surgeons that specialize in corrective deformity surgeries should be consulted to evaluate the timing of any type of spine surgery once the diagnosis of scoliosis is made. Consult with your surgeon for more information.

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