Science > The Human Genome Project and Sickle Cell Anemia

The Human Genome Project began in 1990 and lasted for 13 years. The project was organized by the U.S. Department of Energy and the National Institutes of Health. The main purpose of the Human Genome Project was to identify all genes in the human genome and to determine all 3 billion base pairs of the DNA. Other goals were to store all information in databases, to improve the tools they were using for analyzing data, to transfer technologies to the private sector and to study the ethical, legal, and social challenges (3).

At least 18 countries were involved in this project and some of the largest programs were at Australia, France, Sweden, China and the U.K. Some of the major contributors were the U.S.DOE Joint Genome Institute from Walnut Creek, California, Baylor College of Medicine Human Genome Sequencing Center, Department of Molecular and Human Genetics from Houston, Texas, The Wellcome Trust Sanger Institute, The Wellcome Trust Genome Campus from Hinxton, Cambridgeshire, U.K, Washington University School of Medicine Genome Sequencing Center from St. Louis, Missouri, USA and Whitehead Institute/MIT Center for Genome Research from Cambridge, Massachusetts, USA (4).

There are many benefits of this project for human race. All the information that biologist and researchers can use now will help to understand our DNA better and it will contribute to an easier diagnosis, treatment and hopefully in the future we can prevent all genetic diseases.

I chose to write about sickle cell anemia, which is one of the most common diseases among African Americans. I first heard about this disease on my Anthropology class and since then it interested me to study more about it. Throughout this Biology course and the help of the doegenomes.org and other websites I learned many interesting about this disease which I am going to present in my research paper.

Sickle Cell Anemia

Sickle cell anemia affects millions of people all over the world, but it is most common in Africa, India and the Mediterranean. In the United States this genetically inherited disease occurs in about 1 in every 500 African American births. In my research paper I will write about how the sickle cell anemia disease occurs, what the advantage is if you have the sickle cell trait contrast to the disadvantages when you have the anemia. I will also write what the problems and symptoms are, the cause and the treatment of this disease.

Sickle cell anemia is a genetic disease that occurs when people inherit two copies of the defective sickle cell gene, one from each unaffected but carrier parent. Individuals who have the disease suffer from sickle cell anemia because their body makes abnormally shaped red blood cells. These red blood cells, unlike the normal, smooth and round blood cells, are shaped like crescents or sickles. They often get stuck in blood vessels and block the flow of blood to the organs. This can cause pain and organ damage. This disease also cause low blood count (8). Anemia means the condition in which there is a reduction of the number of red blood corpuscles of the total amount of hemoglobin in the bloodstream (Agnes). The shortage of red blood cells occurs because sickle cells only last about 10 to 20 days compare to normal red blood cells that last about 120 days. When sickle cells die, the bone marrow, which makes new red blood cells can’t replace them fast enough, therefore it causes anemia (6).

People need two sickle cell genes to get the sickle cell anemia, but to get the sickle cell trait one copy of the sickle cell gene is enough. When people have sickle cell trait they have generally no symptoms or very little, they live normal life but unfortunately they can pass the sickle cell gene on to their children. When two people who are unaffected by the disease but carrier of the trait will have a 25% chance to have a child who will inherit two sickle cell genes and will be affected by the disease. In such a case their child will have a 50% chance to inherit one normal gene and one sickle cell gene, and will be have a sickle cell trait. Their child will also have 25% chance to inherit two normal genes and won’t have the sickle cell trait or disease (6).

“Sickle cell anemia is an autosomal recessive disease caused by a point mutation in the hemoglobin beta gene (HBB) found on chromosome 11p15.4….A mutation in HBB results in the production of a structurally abnormal hemoglobin, called HbS” (1). Hemoglobin is a protein that carries oxygen from our lungs to the rest of the body via the circulatory system. When the oxygen level is low or the hemoglobin concentration is high the person who is homozygous for HbS, this structurally abnormal hemoglobin clusters together and change the red blood cell into sickle cell. “HbS results from a switch in amino acids used to makes the beta chin. Specifically, the amino acid glutamic acid is replaced with the amino acid valine at position 6 in the beta chain. Replacing glutamic acid with valine causes the abnormal HbS chains to stick together and form long, rigid molecules” (1). “This substitution creates a hydrophobic spot on the outside of the protein structure that sticks to the hydrophobic region of an adjacent hemoglobin molecule’s beta chain” (1). This polymerization occurs after the red blood cells released all the oxygen molecules and returned to the lungs where hemoglobin can bind oxygen, the long fibers of HbS molecules depolymerize. The effects of polymerization and depolimerization cause the distorted shape in the red blood cell’s membrane (1).

According to our Essential Biology with Physiology book the sickle cell disease annually kills about 100,000 people worldwide. The signs and symptoms of the disease are many and it is different in every person because of its pleiotropy characteristic. Basically, because of the shortage of blood cells and the blocking effect of the sickle shaped red blood cells, the symptoms are various. For example, delayed growth and late puberty, fatigue, paleness and shortness of breath are the symptoms of low blood count. It can cause hand-foot syndrome, when in the hands and foot swelling occurs with fever, due to the blocked small blood vessels with sickle cells. Eye problems, sometimes blindness can be another complication resulting from not getting enough blood. Yellowing of the skin and the eyes are also due to the fast breakdown of red blood cells. The accumulation of sickled cells in spleen causes its damage and it is unable to fight against infections, therefore Pheumonia can kill infants and young children who have the disease as quickly as in a few hours. People with the disease can also easily get other infections like, meningitis, influenza and hepatitis. Other complications, like sores on the legs, acute chest syndrome which is very painful, stroke, gallstones and priapism can occur (6).

Unfortunately there is no cure for sickle cell anemia, but there are some effective treatments exist to treat people who suffer from this disease. To reduce their pain, patients use acetaminophen, nonsteroidal anti-inflammatory drugs and andopioids. On those who suffer from frequently occurred painful crises doctors give hydroxyurea to prevent the crisis. To prevent infections a daily dose of penicillin and vaccinations for influenza, pneumonia, meningitis and hepatitis is required with the combination of regular checkups with doctors. When the disease is life-threatening in some cases blood transfusion is used. Researchers think that bone marrow transplant is an effective treatment for the disease, but because of the risk of serious complications and death it is only used in special cases, such as if a young patient have severe disease (6).

All newborn babies in 44 States of the U.S, the District of Columbia, Puerto Rico, and the Virgin Islands are automatically tested for sickle cell anemia, so the children with the disease can get treatments to prevent infections and to reduce pain (7). The disease can also be diagnosed as early as the first few months of pregnancy and abortion is offered as an option if the parents decide not to have a child with such a painful disease.

Given the fatal disease associated wit HbS, geneticists were surprised to discover that certain populations, especially in Africa, had very high frequencies of HbS. Researchers eventually discovered that both HbA and HbS are maintained because selective forces in certain environments favor the heterozygote over either homozygote. For example in Africa where malaria is a killer disease, the heterozygote, with one sickle cell allele and one normal one, was the fittest phenotype. Heterozygotes have enough abnormal hemoglobin, in which malaria parasites cannot thrive, to protect against malaria. Heterozygotes also have enough normal hemoglobin to fight off sickle cell anemia. In Africa the heterozygotes survived and reproduced in greater numbers than people with any other phenotype, therefore the HbS allele has been maintained among African people (Kottak). According to our book 32% of the population in Africa benefits from the advantage of having a sickle cell trait and be defended from malaria over 4% of the population who have the sickle cell disease.

Sickle cell anemia is a painful genetic disease and sadly many people suffer from it. Diagnosis of the disease and effective treatments are available for the patients. Abortion is offered to prevent to bring a human being to this world who will suffer from many painful symptoms and complication that the disease can cause. In the United States and in many other countries we don’t have to worry about the deadly malaria disease and it is a disadvantage to have the trait, but in many other countries where malaria is present it’s an advantage to be heterozygotes because those people with the trait are protected against malaria. I am amazed by the trade-offs that environment selects for us to be the best suited genotype to survive and reproduce and how evolutionary biology relates to society.

 

Bibliography:

Agnes, Michael. Webster’s New World Dictionary & Thesaurus. Cleveland, Ohio: Wiley Publishing, Inc, 2004.

Campbell, Neil A, Reece, Jane, Simon, Eric J. Essential Biology with Physiology. Upper Saddle River, New Jersey: Prentice Hall, 2004.

Kottak, Conrad Phillip. Anthropology: The exploration of human diversity. New York: McGraw-Hill, 2004.

U.S. Department of Energy Office of Science:

1. http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/hbb.shtml
2. http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/sca.shtml
3. http://www.ornl.gov/sci/techresources/Human_Genome/project/about.shtml
4. http://www.ornl.gov/sci/techresources/Human_Genome/research/centers.shtml

U.S. Department of Health & Human Services:

5. http://www.nhlbi.nih.gov/health/dci/Diseases/Sca/SCA_Diagnosis.html
6. http://www.nhlbi.nih.gov/health/dci/Diseases/Sca/SCA_SignsAndSymptoms.html
7. http://www.nhlbi.nih.gov/health/dci/Diseases/Sca/SCA_Treatments.html
8. http://www.nhlbi.nih.gov/health/dci/Diseases/Sca/SCA_WhatIs.html

 

 

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