Hb SS-disease, also known as sickle cell anemia, is the most common disorder affecting hemoglobin. This condition is a form of sickle cell disease. People with this disorder have atypical hemoglobin molecules called hemoglobin S, which can distort red blood cells into a sickle (crescent) shape. Characteristic features of sickle cell anemia include anemia, repeated infections, and periodic episodes of pain and organ damage.