Sickle cell disease is one of a group of disorders that affects hemoglobin. This is the molecule in red blood cells that delivers oxygen to cells throughout the body. People with this particular hemoglobinopathy (autosomal recessive) have atypical hemoglobin molecules called hemoglobin S, which can distort red blood cells into a sickle, or crescent, shape that hematologist’s label drepanocytes.