Hemoglobin S

Hemoglobin S is a variant of hemoglobin, the protein in red blood cells that carries oxygen throughout the body. It differs from normal hemoglobin (hemoglobin A) due to a genetic mutation. Individuals with two copies of the gene for hemoglobin S have sickle cell disease, which causes red blood cells to become rigid and shaped like a sickle or crescent. This can lead to blockages in blood vessels, pain, and various health complications. People with one copy of hemoglobin S have sickle cell trait, which usually doesn't cause symptoms but can be passed to offspring.