By Jonny Lupsha, Wondrium Staff Writer
Sickle cell disease affects approximately 100,000 Americans. It’s a genetic issue that centers around the red blood cells in the human bloodstream. What does sickle cell disease do to sufferers?
Millions of people worldwide suffer from sickle cell disease. The genetic disorder leads to sickle-shaped red blood cells circulating throughout the bloodstream, with very dangerous outcomes. These sickle-shaped cells can block blood flow, which in turn can permanently damage parts of the body or even be fatal. Those living with sickle cell disease often face life-threatening emergencies and need regular blood transfusions.
Two drug companies recently announced that they’re seeking gene therapy approval from the Food and Drug Administration (FDA) that could provide a cure for sickle cell disease, making the disease become a thing of the past. In the meantime, let’s brush up on your knowledge of how the disorder works.
In his video series Understanding Genetics: DNA, Genes, and Their Real-World Applications, Dr. David Sadava, Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center, breaks down the fundamentals of sickle cell disease.
What Does Sickle Cell Disease Do to the Body?
Sickle cell disease wreaks havoc in the bloodstream. In order to get a clearer picture, consider this portrait of healthy red blood cells.
“Normal red blood cells carry hemoglobin and they’re donut shaped,” Dr. Sadava said. “They’re flexible so they can pass through narrow blood channels called capillaries, so they can kind of squeeze their way through. Red blood cells have a lifetime of about 120 days in the bone marrow, and then they die and new cells are made afterwards to replace them.”
Sickle red blood cells, however, are very different. They get their name from their shape, and they’re also very brittle. These cells can clump together and block the capillaries. This starves tissues of the oxygen they need, which is usually carried by the other, healthy red blood cells. Sickle cells also die after just 16 days, and bone marrow can’t replace blood cells that quickly, causing sufferers to have low blood counts—in other words, anemia. In fact, the disease used to be called sickle cell anemia.
Anemia is far from the only symptom.
“People with sickle cell disease have lung damage, spleen damage, and kidney damage,” Dr. Sadava said. “They have abdominal pain; they have pain in the legs and in the chest.”
Tragically, many people with sickle cell disease have strokes and even die at an early age.
How Is Sickle Cell Disease Contracted?
“The allele for sickle cell disease is inherited as a recessive,” Dr. Sadava said. “Of the 1,100 children born in the United States every year who have sickle cell disease, in most cases, their parents were healthy carriers. That is, they were healthy carriers of the harmful allele, and they had a normal allele, as well. Of course, they have a one in four chance, if they are carriers, of having a child with [the] disease.”
At the same time, the population distribution of sickle cell disease is very unusual. It originated in Africa and is still common there. In the United States, as Dr. Sadava mentioned, 1,100 children are born with sickle cell disease every year. Nigeria, by contrast, has just one-third of the U.S. population but 80,000 children per year are born with sickle cell disease.
“In 1954, a geneticist, Anthony Allison, found a similarity in the geographic distribution of sickle cell disease in Africa and Asia and malaria,” he said. “Knowing that the organism that causes malaria reproduces in part inside of red blood cells […] Allison proposed that people who are carriers of the sickle cell allele, or are homozygous for the allele, would be at a selective advantage for being resistant to malaria because their hemoglobin, in part or in whole, would be sickled, and would be abnormally shaped, so maybe the parasite can’t get in and reproduce.”
This phenomenon is known as a balanced polymorphism, or a balance between the good and the bad.
Understanding Genetics: DNA, Genes, and Their Real-World Applications is now available to stream on Wondrium.