Spinal+Muscular+Atrophy+(SMA)

**Spinal Muscular Atrophy**
====A genetic disease characterized by progressive loss of lower motor neurons (anterior horn cells) in the spinal cord, resulting in symmetric muscle weakness and atrophy. The onset of the progressive muscle weakness ranges greatly in age from before birth to adulthood. The muscle weakness is progressive. Molecular genetics studies have disclosed that spinal muscular atrophy (SMA), irrespective of the age at the onset of symptoms, is due to mutation of one gene called the SMN gene. - medterms.com====



Figure 1: Will and Emma. Emma has Spinal Muscular Atrophy and requires a motorized wheel chair to move around.

Defects in the Survival Motor Neuron 1 (SMN1) gene that encodes the SMN protein. SMA is an autosomal recessive genetic disease, which means that a person must have both copies of their SMN1 gene mutated in order to be affected. The gene is located on chromosome 5, along with its similar counterpart, SMN2. The second gene is nearly identical to a normal SMN1 gene with a few point mutations. This results in irregular splicing of mRNA’s and defective proteins most of the time. The occasional functioning protein is created, but it is not enough to save the motor neurons from being degraded. Figure 1 shows a possible hereditary pattern for SMA. Figure 1: One in about every 40-50 persons is a carrier for SMA. This figure shows a possible genetic map for SMA. The mother is a carrier, and has one mutated copy of the SMN1 gene. The father has two normal copies. They, as a couple, have a 1 in 4 chance of having a child with SMA of any type, and have a 1 in 2 chance of having a child who is also a carrier for SMA. The chances of having a normal, healthy child for this couple is 1 in 4.
 * Root cause of disease:**


 * Affected cell types/tissues/organs/systems:** Spinal cord nerve cells which are responsible for muscle contraction, called motor neurons. The disease may also affect synapses.

In the 1980s, two scientists (Werdnig and Hoffman) described a disorder of progressive muscular weakness beginning in infancy that resulted in early death, though the age of death was variable. Due to the disease’s nature, most severe cases occur too young to become famous. I personally know my cousin’s 3 year old boy has spinal muscular atrophy and has his own motor wheel chair. I believe he has type II SMA.
 * Historical background:**

According to the ISMAC system, the age of onset for spinal muscular atrophies is as follows:
 * Common symptoms:** Fatigue and weakness at a young age, facial drooping, trouble swallowing.
 * SMA type I (acute infantile or Werdnig Hoffman): Onset is from birth to 6 months.
 * SMA type II (chronic infantile): Onset is between 6 and 18 months.
 * SMA type III (chronic juvenile): Onset is after 18 months.
 * SMA type IV (adult onset): Onset is in adulthood (mean onset, mid 30s).

media type="custom" key="24658848" media type="custom" key="24658854" media type="custom" key="24658868" Standard treatments involve symptomatic treatments, which assure the affected child has enough nutrients without being too heavy (too burdensome for weakened muscles). Unfortunately, not many treatments are available for the reversal of degeneration of the motor neurons or to create more of the functioning SMN protein. Current research is working on the latter. “While SMA patients lack the functional SMN1 gene, they do have a “backup” gene, SMN2. SMN2 also makes SMN protein, but at greatly reduced efficiency, leading to lower than normal levels of the protein. SMN2 provides an attractive target for developing SMA therapeutics, and the majority of drug development efforts in the field are focused on increasing SMN protein production from this gene.” Research is currently focused on injecting a good copy of the SMN1 gene into patients. They do this in the hope that the SMN protein can be made at a normal rate, and save the undamaged motor neurons from further deterioration.
 * Standard treatments and research:**

[] [] [|www.smafoundation.org/about-sma/] []
 * References:**