How Mutation Causes Genetic Disorders


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In 1908, the Hardy-Weinberg Theorem was introduced in evolutionary genetics. It postulates about the population equilibrium that occurs in an infinitely large population. The population has to not only be large, but it also has to have a randomness factor that comes from random mating. It should be free of migration to prevent the loss of any particular gene or group from the gene pool. Consequently, there should not be any influx of one gene. When the population reaches equilibrium, it should be devoid of any mutations. In my opinion, mutations are part of natural selection. They are what leads to genetic diversity and create variation among us.

Many of the diseases that exit in our world have a genetic component to them. Despite common belief, not all mutations are bad. Some mutations have no effect on us and may remain dormant through our entire lifespan. Others are beneficial to us. An example would be the mutation that causes Hemoglobin S to be produced. When you only have one copy of mutated gene, you get resistance to malaria. Whereas if you receive two copies of the mutated gene, you get the genetic disorder known as Sickle Cell Anemia. A less extreme example would be the mutated gene that causes some people to be born with red hair. No harm comes from this mutation but it s irreversible.

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In popular media and research, we hear a lot about the harmful mutations and their detrimental effects. We discussed many of them in this lecture such as Tay-Sachs, Cystic fibrosis, Phenylketonuria, Sickle Cell Anemia, and Achondroplasia. One common characteristic among these genetic disorders is that they are inherited. They can be passed from generation to generation within families. It s important to that note that most inherited genetic disorders are recessive. Thus, in order for you to inherit the genetic disorder, you have to have two copies of the mutated gene. The genetic disorders that are caused by only one mutated gene tend to occur less often. An example would be Huntington s disease, which is a rare disorder. Most carriers pass before being able to reproduce. Due to this fact, this mutated gene is weeded out from the gene pool thanks to evolutionary genetics.

The first genetic disorder that I wanted to research was Tay-Sachs. Tay-Sachs is a genetic disorder that affects your nerve cells. Overtime, a degradation of your nerve cells occurs. This is due to a mutation on the Chromosome 15. A gene known as HEXA caused by the mutation to not be present. The enzyme, пЃў-hexosaminidase A, is found in the lysosomes in your nerve cells. Its purpose is to break down the GM2 gangliosides in neurons. But due to its absence, a buildup of gangliosides takes place and causes damage to your neurons. Tay-Sachs can be diagnosed early on during infancy. Doctors tend to check for a specific eye normality known as cherry red spot. This helps to diagnose Tay-Sachs. In terms of treating those affected with this genetic disorder, a ganglioside synthesis inhibitor is prescribed. The progression of the Tay-Sachs disease will be slowed, but nothing can be done to reverse loss of nerve cells. This is why it is best to diagnose while still in the early stages of the disorder.

Next, I wanted to discuss Cystic fibrosis. Cystic fibrous is a genetic disorder that causes damage to your lungs, digestive system, and other organ systems. A mutation has occurred on your Chromosome 7 that causes an absence or defective protein known as Cystic Fibrous Transmembrane Regulator (CFTR). Without this enzyme present in your body, the secretions in these organ systems become thick and sticky. The passageways are then likely to become blocked. Those affected by Cystic fibrous are able to maintain it. Doctors prescribe anti-inflammatory drugs to reduce any swelling. Also, bronchodilators will help to prevent lung infections which those with this genetic disorder are prone to getting. The goal is to help reopen the passageways that were blocked and thin out the viscous secretions such as mucus in your lungs.

The mutated gene that causes Sickle Cell Anemia is found on Chromosome 11 known as hemoglobin beta (HBB). Sickle Cell Anemia is a genetic disorder where due to a mutated HBB gene, Hemoglobin S in present in your body. It s a protein that causes your red blood cells to deform. They take on a crescent-like shape (sickle). Once the red blood cells are deformed, they tend to clump together and can cause blockages in your arteries. People with Sickle Cell Anemia are at higher risk to have heart issues, such as heart attacks or strokes. The mutation of your HBB gene occurs when an alanine base is changed to thymine in your DNA sequence. This causes the coded amino acid to be changed from the desired glutamic acid to valine. The change in amino acids is what causes your body to produce Hemoglobin S. The symptoms for Sickle Cell Anemia show early on in a person s life. They suffer from anemia (low RBC) and pain. A form of treatment that is used in extreme cases is using a medication known as hydroxcarbamide. This drug stimulates the production of fetal hemoglobin in your system. The newly formed fetal hemoglobin will not be affected by the mutation and can take the place of the mutated adult hemoglobin.

Phenylketonuria is a genetic disorder where the levels of phenylalanine in your body are at toxic levels. A mutation has occurred on Chromosome 12 in the gene that is responsible for the protein phenylalanine hydrolase. Due to this mutated gene, the phenylalanine in your body is unable to convert into tyrosine. Serious effects can occur when a high concentration of phenylalanine is allowed for a long period of time. People with phenylketonuria suffer from intellectual disabilities, seizures, and behavioral problems. Phenylalanine is one of the building blocks of proteins. It s a major amino acid that is obtained through our diet. Because of this, people with phenylketonuria are mindful with their food intake. Their PHE blood levels can be monitored using a blood testing device similar to what diabetics use.

Achondroplasia is a genetic disorder that is a form of dwarfism. The bone growth has been stunted due to this mutation. Typically, people with this disorder have short limbs and enlarged heads. A mutation has occurred on their Chromosome 4 in the FGFR3 gene. This gene encodes the instructions for making the protein, Fibroblast Growth Factor Receptor 3. FGFR protein is responsible for controlling bone growth. The mutation caused the glycine in the DNA sequence to be replaced with arginine. The result is a problem in the bone development where the cartilage fails to develop in to bone. Many with achondroplasia live normally without any afflictions. There are some cases where people suffer from apnea (breathing slows) or bowed legs. Others suffer from severe back pain due to the abnormality in the curvature of the spine. As far as treatment goes, there is no cure. It has found that providing children with achondroplasia with growth hormone helps their bone development. But it does not prove to be effective.

Hemophilia is a genetic disorder that affects the clotting process in your blood. A natural immune system response for us that when a wound occurs your body clots in order to prevent you from losing further blood. Those individual with Hemophilia lacks this immune response. They tend to bruise easily and can even suffer from continuous bleeding if a serious injury occurs. There are two types of Hemophilia: Hemophilia A and B. This mutation occurs on the X chromosome and involves the F8 and F9 genes, respectively. It is more common to occur in males than in females since the disorder requires two mutated X chromosomes. A well-known case of a person with Hemophilia was in the last royal family of Russia. The youngest child and son, Alexei Nikolaevich, was born with the genetic disorder. It was later discovered that the Empress was carrier with the recessive gene. Alexei had a severe case of Hemophilia. He was sheltered most his life. They went to extreme lengths to protect him; even so far as to carry the child wherever he went. Due to the mutated genes, your Factor VIII and IX are affected. They are important in the blood clotting process. A treatment that is sometime used for those with Hemophilia is transfusions of the Factor VIII and XI.

The topic of genetic disorders and the mutations behind them interested me because I, myself, was born with a mutation. It s interesting how some mutations can be inherited while other mutations are not. Also, the fact that my mutation did not present itself till later in life was fascinating. I believe that if I did not have such a passion for pharmacy, I would have enjoyed becoming a research biologist. So, I could further study all the different types of disorders that can be caused by mutations.

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