Sickle cell anemia is inherited. You get it by receiving two copies of a specific mutated gene, one from each biological parent. It is not contagious, not caused by diet or lifestyle, and not something that develops later in life. A person is born with it.
The Genetic Mutation Behind Sickle Cell
Sickle cell anemia traces back to a single change in the gene responsible for producing part of hemoglobin, the protein in red blood cells that carries oxygen. In that gene, one amino acid (a building block of protein) gets swapped for another: valine replaces glutamic acid at a specific position. That tiny substitution produces an abnormal form of hemoglobin called hemoglobin S.
Hemoglobin S behaves normally when it’s carrying oxygen. But when oxygen levels drop, as they do when blood circulates through smaller vessels and tissues, hemoglobin S molecules stick together and form rigid, rod-like chains inside the red blood cell. This process, called polymerization, warps the normally round, flexible red blood cell into a stiff crescent or “sickle” shape. Those misshapen cells can’t flow smoothly through blood vessels. They clump, block blood flow, break apart prematurely, and trigger inflammation and tissue damage throughout the body.
How It’s Passed From Parent to Child
Sickle cell anemia follows an autosomal recessive inheritance pattern. That means two things: the gene sits on a non-sex chromosome (so males and females are equally likely to inherit it), and a child needs two copies of the mutated gene to develop the disease. One copy from mom, one from dad.
If both parents carry one copy of the sickle cell gene (known as sickle cell trait), here’s what happens with each pregnancy:
- 25% chance the child inherits two sickle cell genes and has sickle cell disease.
- 50% chance the child inherits one sickle cell gene and has sickle cell trait (a carrier, but not sick).
- 25% chance the child inherits no sickle cell genes at all.
These odds apply independently to each pregnancy. Having one child with sickle cell disease doesn’t change the probability for the next child. If only one parent carries the trait and the other has two normal hemoglobin genes, none of their children will have sickle cell disease, though some may carry the trait.
Sickle Cell Trait vs. Sickle Cell Disease
People often confuse sickle cell trait with the disease, but they are fundamentally different. Sickle cell trait means you carry one copy of the sickle cell gene and one normal hemoglobin gene. Your body still produces enough normal hemoglobin to keep red blood cells functioning properly. Most people with the trait have no symptoms, lead normal lives, and have a normal lifespan. The trait does not turn into sickle cell disease over time.
Sickle cell disease, by contrast, means you have no gene producing normal adult hemoglobin. Without that backup, red blood cells are loaded with hemoglobin S. They break down quickly, causing chronic anemia, and their sickle shape triggers episodes of blocked blood flow that can damage organs, cause strokes, and produce intense pain crises. The distinction is stark: one copy of the gene is generally harmless, two copies cause serious, lifelong illness.
Some forms of sickle cell disease involve inheriting one hemoglobin S gene and one gene for a different abnormal hemoglobin. These compound forms also cause disease, though severity can vary.
Who Is Most Likely to Carry the Gene
The sickle cell gene is most common in populations whose ancestors came from regions where malaria has historically been widespread. Carrying one copy of the gene (sickle cell trait) actually provides some protection against severe malaria, which is why natural selection preserved it in these populations over thousands of years.
Regions with the highest prevalence include sub-Saharan Africa, South America, the Caribbean, Central America, Saudi Arabia, India, and Mediterranean countries like Turkey, Greece, and Italy. In the United States, more than 90% of people with sickle cell disease are Black or African American, and an estimated 3% to 9% are Hispanic or Latino.
The numbers are significant. About 1 in every 365 Black or African American births results in sickle cell disease. About 1 in 13 Black or African American babies is born with sickle cell trait. Among Hispanic Americans, sickle cell disease occurs in roughly 1 in 16,300 births. These statistics reflect ancestry patterns, not race as a biological category. Anyone whose family roots trace to malaria-endemic regions could carry the gene.
How Sickle Cell Is Detected
Every state in the U.S. screens newborns for sickle cell disease as part of routine testing. Within the first day or two after birth, a few drops of blood are collected from a heel prick and sent to a lab. The lab analyzes the types of hemoglobin present in the sample, which reveals whether the baby has normal hemoglobin, sickle cell trait, or sickle cell disease. Results go to the baby’s healthcare provider, typically within a few weeks.
Adults who weren’t screened at birth, or who want to know their carrier status before having children, can get a simple blood test. This is particularly useful for couples planning a pregnancy, since knowing whether both partners carry the trait tells you the odds of having a child with the disease. Prenatal testing can also detect sickle cell disease during pregnancy by analyzing fetal DNA from a sample of placental tissue or amniotic fluid.
What Happens Inside the Body
The core problem in sickle cell disease is that hemoglobin S polymerizes, or clumps together, inside red blood cells whenever oxygen levels dip. This doesn’t just distort the cell’s shape. Polymerized hemoglobin has dramatically lower oxygen-carrying capacity than normal hemoglobin, so the cells become less effective at their primary job. Cells packed with polymerized hemoglobin deliver less oxygen to tissues, which can trigger further sickling in a vicious cycle.
Normal red blood cells live about 120 days. Sickled cells are fragile and often survive only 10 to 20 days, which is why the body can’t keep up with production and chronic anemia results. The rigid cells also stick to blood vessel walls, promoting inflammation and clotting. Over time, repeated episodes of blocked blood flow damage the spleen, kidneys, lungs, brain, and other organs. This is why early detection matters: treatments that reduce sickling episodes can slow organ damage and significantly improve quality of life.