SMA - Spinal Muscular Atrophy
Spinal Muscular Atrophy (SMA) is an inheritable lethal disease with an incidence of 1 in every 9 000 newborns . In SMA, patients most often begin to show signs of muscle weakness as infants or toddlers. An individual with SMA has a missing or mutated gene (SMN1, or survival motor neuron 1) that produces a protein in the body called Survival Motor Neuron (SMN) protein. This protein deficiency has its most severe affect on motor neurons. Motor neurons are nerve cells in the spinal cord which send out nerve fibers to muscles throughout the body. Since SMN protein is critical to the survival and health of motor neurons, without this protein nerve cells may atrophy, shrink and eventually die, resulting in muscle weakness.
As children with SMA develop their bodies are doubly stressed, first by the decrease in motor neurons and then by the increased demands on the nerve and muscle cells as their bodies grow larger. The resulting muscle atrophy can cause weakness and bone and spinal deformities that may lead to further loss of function, as well as additional compromise of the respiratory system. There are 4 types of SMA, SMA Type I, II and III. The determination of the type of SMA is based upon the physical milestones achieved. Type I, II and III are diagnosed respectively, before the age of 1, 2 and 3 years.
The human genome carries a close paralog of SMN1, SMN2, that differs by a C to T transition in exon 7. This single-base difference causes preferential skipping of exon 7 in SMN2 mRNA, resulting in low expression of a functional SMN2 protein. Increased inclusion of SMN2 exon 7 would result in an increase in functional SMN protein that could rescue the SMA phenotype. The onset of SMA thus apparently depends on the number of SMN2 gene copies available in the genome. Individuals with only 1 or 2 copies of the SMN2 gene will typically have the most severe expressions of SMA. Three or more copies of the SMN2 gene will typically mean a less severe expression. Today no effective cure is available for SMA.
More information about Spinal Muscular Atrophy
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SMA Foundation
The Spinal Muscular Atrophy Foundation aimes to accelerate the development of a treatment for SMA, the number 1 genetic killer of infants and toddlers.
visit www.smafoundation.org
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VSN
Dutch site aimed at providing improved standards of care, facilitating effective research, and providing advice and information to patients with a muscular disorder.
