Sickle cell disease is inherited, not caught. You can only get it by being born with two copies of an abnormal hemoglobin gene, one from each biological parent. It is not contagious and cannot spread through blood transfusions, physical contact, or any other means. The only way sickle cell disease enters a family is through genetics.
The Gene Behind Sickle Cell
Sickle cell disease starts with a single change in the HBB gene, which tells your body how to build hemoglobin, the protein in red blood cells that carries oxygen. In this mutation, one DNA letter (a T) replaces another (an A) at a critical spot in the gene. That tiny swap produces an abnormal version of hemoglobin called hemoglobin S. When red blood cells carry hemoglobin S instead of normal hemoglobin, they become rigid and bend into a crescent or sickle shape. These misshapen cells don’t flow smoothly through blood vessels and break down far faster than normal red blood cells, leading to anemia, pain, and organ damage over time.
Everyone carries two copies of the HBB gene. To develop sickle cell disease, a person needs to inherit a faulty copy from both parents. One abnormal copy alone is not enough to cause the disease.
How Parents Pass It On
Sickle cell follows an autosomal recessive pattern, meaning both parents must contribute an abnormal gene for a child to be affected. The math is straightforward. If both parents carry one copy of the sickle cell gene (known as sickle cell trait), each pregnancy has a 25% chance of producing a child with sickle cell disease, a 50% chance of producing a child who carries the trait like the parents, and a 25% chance of producing a child with two normal copies of the gene.
If only one parent carries the trait, none of their children will have sickle cell disease, though up to half could inherit the trait. If one parent has sickle cell disease (two abnormal copies) and the other has no abnormal gene at all, every child will be a carrier but none will have the disease.
Sickle Cell Trait vs. Sickle Cell Disease
Carrying one copy of the sickle cell gene is called sickle cell trait. About 1 in every 13 Black or African American babies is born with it. People with sickle cell trait are carriers, not patients. They typically have no symptoms, live normal lifespans, and may never know they carry the gene unless they’re tested. Sickle cell trait does not turn into sickle cell disease over time.
In rare cases, carriers can experience complications when the body is under unusual stress: intense physical exertion, high altitudes, dehydration, or extreme temperatures. Some people with the trait develop kidney or spleen problems. But for the vast majority, carrying one copy of the gene has no noticeable health impact.
The distinction matters most when two carriers have children together. Many people don’t realize they carry the gene until a child is born with sickle cell disease, which is why screening programs exist.
Different Types of Sickle Cell Disease
Not all sickle cell disease looks the same. The type depends on which two abnormal genes a person inherits.
- HbSS (sickle cell anemia): The most common and usually the most severe form. The child inherits a hemoglobin S gene from each parent.
- HbSC: The child inherits hemoglobin S from one parent and a different abnormal hemoglobin called hemoglobin C from the other. This form is generally milder.
- HbS beta thalassemia: The child inherits hemoglobin S from one parent and a beta thalassemia gene from the other. The severity depends on the type of thalassemia gene involved. The “zero” version tends to be severe, while the “plus” version is usually milder.
All of these count as sickle cell disease because they all result in the body producing enough abnormal hemoglobin to cause red blood cells to sickle. The key point is that sickle cell disease can result from combinations of different hemoglobin mutations, not just two copies of hemoglobin S.
Why Certain Populations Are More Affected
Sickle cell disease occurs in about 1 out of every 365 Black or African American births and about 1 out of every 16,300 Hispanic American births. It is also common among people with ancestry from Mediterranean countries like Turkey, Greece, and Italy, as well as parts of the Middle East and India. More than 90% of people living with sickle cell disease in the United States are Black or African American.
This geographic pattern exists because carrying one copy of the sickle cell gene offers protection against malaria. In regions where malaria was historically common, carriers were more likely to survive and have children, so the gene became more frequent in those populations over thousands of years. Red blood cells containing some hemoglobin S are harder for the malaria parasite to thrive in. Parasitized cells from carriers tend to sickle and get cleared by the body’s filtering system more quickly, limiting the infection. This survival advantage kept the gene circulating even though inheriting two copies causes serious disease.
How Sickle Cell Is Detected
In the United States, every newborn is screened for sickle cell disease through a simple blood test, usually a heel prick done within the first day or two of life. The blood sample is analyzed to identify which types of hemoglobin are present. Newborns naturally have high levels of fetal hemoglobin, so the lab looks at what other hemoglobin types appear alongside it. If hemoglobin S shows up without normal adult hemoglobin, the baby likely has sickle cell disease. If both hemoglobin S and normal hemoglobin appear, the baby has sickle cell trait.
Adults who haven’t been tested can find out their status through a standard blood test called a hemoglobin electrophoresis, which separates the different types of hemoglobin in a sample. This is especially useful for people planning to have children who want to know if they’re carriers.
Testing During Pregnancy and Before
If both parents carry the sickle cell gene, it’s possible to test a developing baby during pregnancy. Chorionic villus sampling can be done between weeks 10 and 13 of pregnancy. During this procedure, a small tissue sample is taken from the placenta, either through a thin tube inserted through the cervix or through a needle in the abdomen. The sample contains enough genetic material to determine whether the baby has inherited two abnormal genes, one, or none. Amniocentesis, performed later in pregnancy, is another option.
For couples who want to prevent passing on sickle cell disease entirely, in vitro fertilization with preimplantation genetic testing is an option. Embryos created through IVF are tested at the earliest stage of development, and only embryos without two copies of the sickle cell gene are selected for transfer. This approach is considered highly effective at preventing the birth of an affected child, though it carries the cost and physical demands of IVF.
Knowing your carrier status before starting a family gives you the full picture of your options. A simple blood test is all it takes to find out.