Originally appeared: January 2021 Newsletter
SMA is caused by both copies of the survival motor neuron 1 (SMN1) gene on chromosome 5 being deleted or mutating. This gene is responsible for producing survival motor neuron (SMN) protein, which maintains the health and normal function of motor neurons.
In someone with SMA, both copies of the SMN1 gene are deleted or mutated, leading to less SMN protein being produced. In almost all cases (more than 95%), the child inherits the genetic cause of SMA from their parents. However, in a very small percentage of children (about 2%), the deletion or mutation in the SMN1 gene happens and is not present in either parent.
Without the correct level of SMN protein, motor neurons in the spinal cord are lost, preventing the muscles from receiving proper signals from the brain. The deterioration of motor neurons leads to the gradual reduction in the mass and strength of muscles (atrophy).
REFERENCES:
Kolb S, Kissel J. Spinal Muscular Atrophy. Neurol Clin. 2015;33(4):831-846.
Markowitz J, Singh P, Darras B. Spinal Muscular Atrophy: A Clinical and Research Update. Pediatr Neurol. 2012;46(1):1-12.
Mercuri E, Finkel R, Muntoni F et al. Diagnosis and management of spinal muscular atrophy: Part 1: Recommendations for diagnosis, rehabilitation, orthopedic and nutritional care. Neuromuscular Disorders. 2018;28(2):103-115.