Some people inherit one sickle cell gene and one other defective hemoglobin gene, resulting in various types of sickling disorders. These disorders range from mild to severe.

• Sickle cell disease (hemoglobin SS disease) occurs when both genes produce hemoglobin S. This person typically has symptoms of anemia, mild to life-threatening complications, and a shortened life span.
• Sickle beta-thalassemia occurs when a person has one hemoglobin S gene and another gene that causes the body to produce less hemoglobin than normal. This person may have mild to severe sickle cell disease.
• Hemoglobin SC disease occurs when a person has one hemoglobin S gene and one abnormal hemoglobin C gene. This person may have generally milder symptoms and a longer life span than a person with sickle cell disease but still may become seriously ill.
• Hemoglobin SO disease and hemoglobin SD disease occur when a person has one hemoglobin S gene and one abnormal hemoglobin O or hemoglobin D gene. This person may experience all sickle cell disease symptoms, ranging from mild to severe.