Hemoglobin S (HbS) is a variant of normal hemoglobin, the oxygen-carrying protein found in red blood cells. It results from a genetic mutation in the HBB gene, which encodes the beta-globin subunit of hemoglobin. This mutation leads to the production of an abnormal form of hemoglobin, which can cause red blood cells to assume a sickle shape, particularly under low oxygen conditions.
