Sickle Cell Anemia Case Study:
Hemoglobin is a protein found in red blood cells (RBCs) that transports oxygen throughout the body. Sickle cell disease (also called sickle cell anemia) is caused by a genetic mutation in the DNA sequence that codes for the hemoglobin protein. The mutation causes an amino acid substitution. Due to this change in amino acid sequence, the hemoglobin tends to precipitate (or clump together) within the RBC after releasing its oxygen. This clumping causes the RBC to assume an abnormal “sickled” shape.
Individuals who are homozygous for the normal hemoglobin allele (HBA) receive a normal hemoglobin allele from each parent and are designated AA genotype. People who are homozygous for normal hemoglobin do not have any sickled RBCs.
Individuals who receive one normal hemoglobin allele from one parent and one mutant hemoglobin, or sickle cell allele (HBS), from the other parent are heterozygous and are said to have sickle cell trait. Their genotype is AS. Heterozygous individuals produce both normal and mutant hemoglobin proteins. These individuals do not have sickle cell disease, and most of their RBCs are normal. However, due to having one copy of the sickle cell allele, these individuals do manifest some sickling of their RBCs in low-oxygen environments.
People with sickle cell disease are homozygous for the sickle cell allele (SS genotype); they have received one copy of the mutant hemoglobin allele from each parent. The resulting abnormal, sickle-shaped RBCs in these people block blood flow in blood vessels, causing pain, serious infections, and organ damage.
Normal = AA (Homozygous dominant)
Mostly Normal (Sickle Cell Trait) = AS (Heterozygous)
Sickle Cell Disease = SS (Homozygous recessive)
