SMA (spinal muscular atrophy) is a disease that robs people of physical strength by affecting the motor nerve cells in the spinalcord, taking away the ability to walk, eat, or breathe. It is the number one genetic cause of death for infants. SMA is caused by a mutation in the survival motor neuron gene 1 (SMN1).
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'Spinal Muscular Atrophy'
Spinal muscular atrophy(SMA) types o,1,2,3 and 4are inherited as abnormal recessive genetic disorders are associated with abnormalities(mutations) in the SMN1 and SMN2 genes on chromosome 5 at chromosomal locus 5q11-q13. SMA1 is thought to be the primary disease causing by genes. Approximately 95-98% of affected individuals have deletions in the SMA 1 gene and 2-5% have specific mutations in the SMA 1 genes that result in a decreased production of the SMN proteins. When three or more copies of the SMA 2 gene are also present, the disease may be milder.
Genetic disease are determined by the combination of genes for a particular trait that are on the chromosome received from the father and the mother.
Recessive genetic disorders occurred when an individual inherit the same abnormal gene or the same trait from each parent. If an individual received one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore , have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
Biological or surrogate markers for Smears under development.
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This potential surrogate markers studied to date include :
- Measuring the amount and ratio of full length and truncated SMN2 RNA transcripts as well as am out of SMN proteins from white blood cells or fibroblast culture.
- Counting motor units which have shown co-relation with the SMN 2copy number, age and functions.
- Quantitative ultrasound in assessing muscle changes in patients with SMA .
- Electrical impedance.
- A longitudinally study of the surrogate markers will be necessary before any particular one can be used in an intervention studies.
