What is Spinal Muscular Atrophy?


Approximately one in 10,000 live births have a case of Spinal Muscular Atrophy (SMA) (Lunn & Wang, 2020). Unfortunately, despite being the leading genetic cause of infant deaths, SMA is not well known. SMA is an autosomal recessive disorder, meaning there is a genetic defect in both copies of an autosomal gene (Torgerson & Ochs, 2014). This disorder is a result of deteriorating, or degenerating, motor neurons, which are nerve cells that control voluntary muscle movement located in the spinal cord (Lunn & Wang, 2020 and Spinal Muscular Atrophy (SMA)). This leads to individuals with SMA experiencing atrophy, or the weakening and shrinking of their muscles (Spinal Muscular Atrophy (SMA)). Additionally, individuals with SMA often face hypotonia, or the reduction of tension in their muscles while they stretch, resulting in muscle fatigue and weakness (Lunn & Wang, 2020). SMA normally occurs in children at any age, however, children from infancy to early childhood often experience worsened symptoms of the disorder. It is possible, however, for patients to develop SMA later in childhood, adolescence, and into adulthood, but in these cases individuals tend to have a more positive prognosis (Spinal Muscular Atrophy (SMA)). 

There are four types of SMA that are caused due to a genetic mutation in the survival motor neuron 1 gene (SMN1) located on the fifth chromosome. Type I, or Werdnig-Hoffmann disease, is the most severe and common type. It often occurs before six months of infancy and unfortunately oftentimes results in death within the first two years of the child’s life. Patients diagnosed with type one SMA experience hypotonia, lack of control of head movement, inability to sit up without support, weakened intercostal muscles, and paradoxical breathing. Paradoxical breathing is reverse breathing, so as one breathes in, their chest contracts, and as one breathes out it expands (Lunn & Wang, 2020). 

Type II SMA is of intermediate severity and normally occurs between seven to eighteen months. Patients are able to sit up without support, and some are able to walk with supporting leg braces. Unfortunately, no patients can walk without support, and there may also be difficulty with coughing, fine tremors, as well as kyphoscoliosis. Kyphoscoliosis is when the spine curves in an outward direction (Lunn & Wang, 2020). 

SMA patients with type III, or Kugelberg-Welander disease, tend to have less severe symptoms, and are mostly able to walk independently. Individuals with type III SMA often experience muscle weakness as a result of joint overuse and may develop scoliosis as well. Patients with type IV SMA are often diagnosed in their twenties or thirties and are able to walk independently as adults without experiencing too much motor impairment (Lunn & Wang, 2020). Lastly, other forms of SMA that occur are not caused by the genetic mutation on the SMN1 gene. Some of these types of SMA include “spinal muscular atrophy with respiratory distress (SMARD), spinal and bulbar muscular atrophy (Kennedy’s disease), and distal spinal muscular atrophy” (Lunn & Wang, 2020). 

Unfortunately, there are no current medications or treatments to cure SMA. However, there are supporting methods to lessen the severity of symptomatic pains. For instance, braces and wheelchairs are often used to assist patients in walking or other types of muscle movement. Patients can also receive support for muscle movement through physical and occupational therapy. Lastly, ventilation assistance helps for patients with symptoms such as breathing difficulties (Spinal Muscular Atrophy (SMA)). Although there are no medications and permanent treatments for SMA as of now, there remains hope for further advances in the future as many medications are currently in clinical trials. As more people are educated about SMA, more research advances will be attempted and progress for treatments will be made. 

 

References

Johns Hopkins Medicine. 2020. Spinal Muscular Atrophy (SMA). [online] Available at: <https://www.hopkinsmedicine.org/health/conditions-and-diseases/spinal-muscular-atrophy-sma> [Accessed 11 October 2020]. 

Lunn, M.R. & Wang, C.H., 2008. Spinal muscular atrophy. Lancet, 371, pp. 2120-2133.

Oquendo, C., 2019. Low Angle Shot Of A Child Held by Woman and Man On Each Hand Walking On An Unpaved Pathway Outdoors. [image] Available at: <https://www.pexels.com/photo/low-angle-shot-of-a-child-held-by-woman-and-man-on-on-each-hand-walking-on-an-unpaved-pathway-outdoors-3038455/> [Accessed 11 October 2020]. 

Torgerson, T. & Ochs, H., 2014. Autosomal Recessive Disorders. Stiehm’s Immune Deficiencies 5th Edition.

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