Darnell Tyler is a 24-year-old Black male client with a history of sickle cell disease who presents to the emergency department, or ED, with a report of sudden, severe pain, rated a 9/10 that started late last night in his back, hands and feet.
He says he has been nauseous and vomiting for the last few days. After blood is drawn for culture, IV fluids and antibiotics are started. Then Darnell is admitted to the medical unit for further treatment and evaluation.
Sickle cell disease is a group of genetic conditions that affect hemoglobin, which can cause red blood cells to take the shape of a sickle or crescent. As a result, these red blood cells are more fragile and can be destroyed more easily, which can cause anemia.
Normally, red blood cells are able to carry oxygen from the lungs to peripheral tissues because they contain hemoglobin A, or HbA for short. Now, hemoglobin A is made up of two α-globin and two β-globin peptide chains, giving red blood cells a characteristic flexible biconcave shape that allows them to travel easily through blood vessels.
With this in mind, sickle cell disease is caused by a mutation in the HBB gene, which almost always results in the 6th amino acid of beta globin being a valine instead of glutamic acid.
As a result, two normal α-globin and two mutated β-globin peptide chains give rise to an abnormal hemoglobin called hemoglobin S for sickle, or HbS for short.
Now, under normal conditions, HbS is also able to carry oxygen quite well. However, under conditions such as hypoxia, acidosis, or dehydration, HbS forms long chains within the red blood cells.
This ultimately distorts the red blood cells into a rigid and fragile crescent shape that looks like a sickle. Now, sickle cell disease is autosomal recessive, so both parents must pass the mutated HBB gene to their child, so they will be homozygous for HbS.
This is especially common in individuals whose ancestors came from Sub-Saharan Africa, as well as South America, the Caribbean, and Central America. The mutated gene is also quite common among individuals of Mediterranean, Middle Eastern, Indian, and Asian descent.