In about 5 percent of people with this disorder, one copy of the SMN1 gene is missing a section, and the other copy has a different kind of mutation that disrupts the production or function of the SMN protein. As a result, SMN protein production is impaired. About 95 percent of individuals with spinal muscular atrophy have mutations that delete a piece of the SMN1 gene in both copies of the gene in each cell. There are many types of spinal muscular atrophy that differ in age of onset and level of muscle functioning however, there is overlap among the types. Spinal muscular atrophy has a wide range of severity. This condition is characterized by a loss of motor neurons that leads to weakness and wasting (atrophy) in muscles used for movement (skeletal muscles) that worsens with age. Many mutations in the SMN1 gene have been found to cause spinal muscular atrophy. Several different versions of the SMN protein are produced from the SMN2 gene, but only one version is functional the other versions are smaller and quickly broken down.
Dendrites and axons are required for the transmission of impulses between neurons and from neurons to muscles.Ī small amount of SMN protein is produced from a gene similar to SMN1 called SMN2. The SMN complex is also important for the development of specialized outgrowths from nerve cells called dendrites and axons. The SMN complex helps to assemble the cellular machinery needed to process pre-mRNA. Messenger RNA begins as a rough draft (pre-mRNA) and goes through several processing steps to become a final, mature form. In cells, the SMN complex plays an important role in processing molecules called messenger RNA (mRNA), which serve as genetic blueprints for making proteins. Motor neurons transmit signals from the brain and spinal cord that tell skeletal muscles to tense (contract), which allows the body to move. These cells are located in the spinal cord and the part of the brain that is connected to the spinal cord (the brainstem). This protein is one of a group of proteins called the SMN complex, which is important for the maintenance of specialized nerve cells called motor neurons. The SMN protein is found throughout the body, with highest levels in the spinal cord. The SMN1 gene provides instructions for making the survival motor neuron (SMN) protein.
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