Sickle Cell Disease Facts
November 25, 2024
This page was reviewed under our medical and editorial policy by YunZu (Michele) Wang, M.D., assistant professor, Department of Pediatrics, City of Hope® Cancer Center Duarte
Sickle cell disease is an inherited condition that affects how the body produces hemoglobin — a protein in red blood cells that helps transport oxygen throughout the body. Sometimes referred to as sickle cell anemia, this genetic blood disorder affects around 100,000 people in the United States. About 90% of patients with sickle cell disease are Black or have African-American ancestry.
What Is Sickle Cell Disease?
People with sickle cell disease inherit mutated or defective genes that cause the hemoglobin molecules inside their red blood cells to become stiff and rod-shaped. This changes the shape of their red blood cells from a flat, flexible disc to a crescent shape that looks similar to a sickle.
Changes in the shape and flexibility of the red blood cells make it harder for the cells to travel throughout the bloodstream. This can lead to blockages that may cause pain, infections or other more serious health issues. The red blood cells also break more easily, leading to anemia and fatigue.
What Causes Sickle Cell Disease?
Genes contain the “code” or instructions that determine how the body's cells develop. Sickle cell disease is caused by changes, or mutations, to the genes that provide the instructions for creating hemoglobin in red blood cells.
Scientists have identified many different types of hemoglobin gene mutations, but people with sickle cell disease have inherited two gene mutations — one from each parent — that affect how the body produces hemoglobin.
Sickle Cell Trait
If someone has only one gene mutation that can lead to sickle cell disease, this is referred to as sickle cell trait. People with sickle cell trait don’t have sickle cell disease and don’t usually have symptoms of sickle cell disease. However, they may have other problems with their kidneys, spleen and eyes, and may have to avoid dehydration and overexertion. Also, if they have a biological child with another person with sickle cell trait, their child may inherit sickle cell disease.
In the United States, sickle cell trait affects up to 10% of the Black and African American populations and around 2 million people in total.
Risk Factors
Certain factors make it more likely someone will have sickle cell disease. These include:
- Being African American or of African descent
- Being Hispanic American or from Central America
- Being of Mediterranean, Middle Eastern or Asian descent
In the United States, it’s standard for doctors to test newborns for sickle cell disease immediately after birth.
Can White People Get Sickle Cell?
It is possible for white people and people of all races and ethnicities to inherit sickle cell disease. However, the condition disproportionately affects African American and Black populations, with one in every 365 Black newborns being diagnosed with sickle cell disease at birth.
Types of Sickle Cell Disease
Sickle cell disease has various types. The type someone has depends on the number and type of gene mutations they inherit. The most common are:
HbSS: People with this type of sickle cell disease have inherited gene mutations from both parents that lead to the production of hemoglobin S — one of the abnormal types of hemoglobin that cause red blood cells to “sickle.” This is usually the most severe form of the condition.
HbSC: This type of sickle cell disease is the result of inheriting a hemoglobin S gene mutation from one parent and a hemoglobin C gene mutation from the other parent. This leads to the production of abnormal hemoglobin. HbSC is less severe than HbSS.
HbS beta thalassemia: This condition affects people who inherit a hemoglobin S gene mutation from one parent and a genetic mutation that causes beta thalassemia (another blood disorder) from the other parent. Depending on the type of beta thalassemia gene someone inherits, the condition may be mild, moderate or severe.
HbSD, HbSE and HbSO: People with these rarer forms of sickle cell disease inherit a hemoglobin S gene mutation from one parent and a hemoglobin D, E or O gene mutation from the other parent. These types of the disease can vary in severity.
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