SMA affects the part of the nervous system that controls voluntary muscle movement.1 In spinal muscular atrophy, there is a loss of important cells in the spinal cord—called motor neurons—which are essential for muscle strength and movement. These motor neurons regulate muscle activity by sending signals from the central nervous system (CNS), which is the part of the body’s nervous system that includes the brain and spinal cord.1,2
The loss of functioning motor neurons leads to progressive muscle weakness and atrophy (the gradual decrease in the mass and strength of muscles), as muscles stop receiving signals from the CNS.3
Unlike many other rare neuromuscular diseases, there is a clear understanding of the specific genetic cause of spinal muscular atrophy. SMA is caused by a mutation in the survival motor neuron 1 (SMN1) gene, which is responsible for producing survival motor neuron (SMN) protein. This protein maintains the health and normal function of motor neurons.
In people with spinal muscular atrophy, both copies of the SMN1 gene are mutated, leading to a decreased production of SMN protein. Without a proper level of SMN protein, motor neurons in the spinal cord will be lost, preventing the muscles from receiving proper signals from the brain.4
SMA is divided into different types according to the age of onset and functional ability. There is also a range of severity within each type.5
The characters shown are real patients and the required consent to use their stories has been obtained from the patients and families. Photographs are for illustrative purposes only.
1. Lunn MR, Wang CH. Spinal muscular atrophy. Lancet. 2008;371(9630):2120-2133.
2.Wang CH, et al. Consensus statement for standard of care in spinal muscular atrophy. J Child Neurol. 2007;22(8):1027-1049.
3. National Institute of Neurological Disorders and Stroke. Motor Neuron Disease Fact Sheet. 2012.
Available at: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Motor-Neuron-Diseases-Fact-Sheet. Accessed January 9, 2017.
4. Genetics Home Reference. SMN2 gene. 2012. Available at: https://ghr.nlm.nih.gov/gene/SMN2. Accessed January 9, 2017.
5. Kolb SJ, Kissel JT. Spinal muscular atrophy. Arch Neurol. 2011;68(8):979-984.