ALS: DNA, mutation and enzymes

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ALS: DNA, mutation and enzymes

ALS: DNA, Mutation, and Enzymes

Gene: Recent study has shown that FALS, familial amyotrophic lateral sclerosis is caused by a mutation in a gene called superoxide dismutase 1 (SOD1). This mutation can be caused by gene inheritance through autosominal dominant genes (familial ALS) or through other, not fully discovered environmental factors (sporadic ALS). SOD1 is located in chromosome 21 of the 22 pairs of chromosome in our body and its main function is to create “superoxide dismutase” enzymes. Superoxide dismutase enzymes are abundant in cells throughout the body and its main job is to break down hazardous oxygen molecules called superoxide radicals in cells, as an excess of such radicals can damage the cell and must be broken down.

BibliographyWilliam Mullen, Chicago Tribune News, 08/22/2011, "Cause of ALS is found, Northwestern team says" Mayo Clinic, 12/02/2010, "Amyotrophic Lateral Sclerosis"ALS Association, 03/03/2013, "What is ALS?", "Study Discovers How Gene Mutations Cause ALS and Other Brain, Muscle and Bone Diseases"National Institude of Neurological Disorders and Stroke, 12/02/2013 "Amyotrophic Lateral Sclerosis (ALS) Fact Sheet"

Mutation: A mutation in the SOD1 gene could altar the amino acid lineup in the resulting superoxide dismutase enzyme created. However, there are more than 170 known mutations for causing ALS and each mutation shows prevalence in a different race of ALS patients in the world. The most common mutation in the United States, A4V, involves a point mutation in the SOD1 gene DNA. Then, through the process of protein synthesis of the mutated gene, amino acid alanine (GCG, GCA, GCC, GCU) is replaced with valine (GUG, GUA, GUC, GUU) in position 4 of the enzyme chain, thus creating an altered enzyme with new and perhaps harmful properties.

Developing ALS: It is still unclear how nerve cells in the motor neuron are so strongly affected by a gene mutation in SOD1. However, scientists, specifically researchers from the ALS association, speculate that the altered enzyme may have its “superoxide-radical-breaking” abilities lessened, therefore creating an influx of toxic superoxide radical molecules in the nerve cell and potentially killing the cell. Another theory is that the superoxide dismutase enzymes have simply lost its purpose, and clogs up nerve cells without doing any work, and may also kill the cell.

Why the mutation occurs…Though around 90 percent of all ALS cases appeared in patients with no family history of having ALS, all ALS patients receive the disease through a mutation in the SOD1 gene. Whilst familial ALS cases are confirmed to be inherited in the autosomal dominant matter through parents to offspring, sporadic ALS has no clear cause for mutation of SOD1. Environmental factors such as chemical, radiation exposure or food contamination have all been suggested but not yet proved. However, an interesting case of ALS-like nerve disease epidemic occurred in the Chamorro people of Guam Island during the 1950s, and scientists have discovered that the reason due to the spread of this disease is because of the indirect consumption of the cycad nut; fruit bats are considered a delicacy amongst the Chamorro people, and is part of their daily diet, and the fruit bats eat cycad nuts which contain neurotoxins that harms nerve cells of humans. The concentrated diet of fruit bats of the Chamorro people, to an extent where fruit bats of Guam have been eaten to extinction, led to a buildup of toxins that led to harmful effects to nerves, causing diseases such as ALS or Parkinsons.

A flow chart of offsprings of heterozygous affected male (Aa) and homozygous recessive unaffected female (aa). The genotypic ratio would be 2Aa:2aa, therefore a fifty percent chance of a child recieving familial ALS from their parents. There is also speculation that familial ALS in Asia is inherited through a different manner, possibly sex linked, as ALS was a disease known to only affect males in Asia.

Glog by Sean YangFor Honors Bio D block

A codon wheel to clearly demonstrate how a single letter switch in the codon alanine can mutate it into valine, thus triggering ALS

A delicacy of the Chamorro people, Fruitbats, next to its favorite food, the cycad nut.

A comparison of an ALS affected nerve cell in the lower motor neuron and an healthy ALS nerve cell.

To learn more about ALS, visit the ALS association. Click on the logo to the left to access to ALS association's website


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