Sickle Cell Anemia Case Study

Alexandria Agee
Ms. Songer
AP Biology
February 16 2015
Sickle Cell Anemia: Case Study
Summary
Sickle Cell Anemia is a painful diseases that is caused by a mutation in the protein called hemoglobin which helps carry oxygen in red blood cells. Because of the mutation, the hemoglobin is shaped oddly which results in pain because it is hard for the blood to travel throughout the body and anemia because of the lack of oxygen in the blood. A person can only have this disease if both parents are carriers and they receive two recessive alleles. There are five effects of the disease at different levels. At the DNA level the mutation causes the sequence to be coded GTG, CAC instead of GAG, CTC which results in a mutant protein. At the protein level the hemoglobin clump together which makes it hard for it to travel through arteries and vessels. At the cellular level the blood cell because “sickle shaped” due to the lack of oxygen that constricts blood flow. In an organism sickle cell anemia causes pain and fatigue during exercise. The only positive effect is the resistance to malaria. These examples show how a small mutation has a very large (sometimes fatal) effect. Therefor large and small mutations can have big effects (“A case study of the effects of mutation: Sickle cell anemia,” 2015)
1. Sickle Cell Anemia is an autosomal recessive disease. These means that both parents of the offspring have to have one normal gene and one mutated gene. The mutated gene is caused by substitution in an amino acid that distinguishes if a person is normal or has the disease. During meiosis chromosomes cross over which results in many possible DNA combinations. Simply by the luck of the genetic hand the two recessive chromosomes may come together and the offspring has Sickle Cell Anemia. A person can only have this disease if and only if they have both recessive genes ( “Sickle Cell Disease,” 2015)
2. A simple mutation, typically one of substitution results in this disease. Substitution is where one base is exchanged for another therefore a codon is changed from one chemical letter to another (“Types of Mutations,” 2015). Furthermore hemoglobin consists of four subunits including two beta-globin. The HBB gene provides instruction for making the beta-globin. However the substitution in the HBB gene results in incorrect instructions which in turn causes abnormal beta-globin. These abnormal subunits is what causes the hemoglobin to be misshapen and have other inefficiencies (“Sickle Cell Disease,” 2012).
3. Sickle Cell Anemia can be tested in heterozygous parents by a simple blood test. It can also be tested in fetuses with an amniocentesis or a chorionic villus sampling (CVS). During an amniocentesis the doctor takes the amniotic fluid surrounding the baby and test for the disease. During CVS the doctor takes part of the placenta for DNA testing (“Sickle Cell Disease,” 2014). In newborns a blood sample can be used for hemoglobin electrophesis which determines if a child has it. If the parents are both carriers of the disease they can choose a more expensive option of using vitro fertilization and gene selection to make sure that their child does not have it (“Sickle Cell Disease,” 2012).
4. Although medicine is constantly improving doing amniocentesis and CVS in order to test for this disease can lead to miscarriage. There are complications with both of these test that may kill your child and these are much higher in CVS. Also if a parent finds out that their child does have this disease they may choose to abort it. This raises the question is it right to kill a child if they have a high chance but not a certainty that they may have Sickle Cell Anemia. Others have argued that abortion of a child with Sickle cell Anemia is the same as eugenics. These means that people are trying to “kill off” Sickle Cell Anemia to essentially make it nonexistent (Fadare 2009).
5. Sickle Cell Anemia is most common in people of African descent. If both parents are carriers of the recessive gene then there is a 25 percent chance of their child having it. If both parents do not have the gene then there is a 0 percent chance of their offspring having Sickle Cell Anemia. If one parent is heterozygous but the other is homozygous there is a 0 percent chance of their offspring having it because there needs to be two recessive alleles. In the rare cases that both parents have the autosomal recessive disease than there is a 100 percent chance of their offspring also having the disease (“Inheritance and Genetics of Sickle Cell Anemia,” 2014).

References
A case study of the effects of mutation: Sickle cell anemia. (2015). Retrieved February 17, 2015, from http://evolution.berkeley.edu/evolibrary/article/0_0_0/mutations_06
Fadare, J. (2009, December 7). Some Ethical Issues in the Prenatal Diagnosis of Sickle Cell Anameia. Retrieved February 17, 2015, from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4111006/
Inheritance and Genetics of Sickle Cell Anemia. (2014). Retrieved February 17, 2015, from http://www.rightdiagnosis.com/s/sickle_cell_anemia/inherit.htm
Sickle cell disease. (2012). Retrieved February 17, 2015, from http://ghr.nlm.nih.gov/condition/sickle-cell-disease
Sickle cell disease. (2014). Retrieved February 16, 2015, from http://www.babycentre.co.uk/a558112/sickle-cell-disease
Sickle Cell Disease. (2015). Retrieved February 17, 2015, from http://learn.genetics.utah.edu/content/disorders/singlegene/sicklecell/
Types of mutations. (2015). Retrieved February 17, 2015, from http://evolution.berkeley.edu/evolibrary/article/mutations_03