A child's risk of getting sickle cell disorder occurs when he or she inherits one sickle cell gene and one other type of defective hemoglobin gene.
People who inherit one defective hemoglobin S gene and one normal hemoglobin A gene have sickle cell trait. They don't have symptoms of sickle cell disease, and their bodies don't make sickled blood cells. But they have a 1-out-of-2 (50%) chance of passing the defective hemoglobin S gene to each of their children.
- If both parents have sickle cell trait, each of their children will have a 1-out-of-4 (25%) chance of having sickle cell disease.
- If one parent has sickle cell disease (has two genes for making hemoglobin S) and the other has sickle cell trait (has one hemoglobin S gene and one normal hemoglobin A gene), each of their children will have a 1-out-of-2 (50%) chance of having sickle cell disease and a 1-out-of-2 (50%) chance of having sickle cell trait.
- If one parent has sickle cell disease (two hemoglobin S genes) and the other has two normal hemoglobin A genes, each of their children will have sickle cell trait. None of the children will have sickle cell disease.
People whose ancestors were from Africa, India, the Middle East, the Mediterranean (Turkey, Italy, Greece), and some Latin American countries are more likely to inherit the gene that can cause sickle cell disease. In the United States, about 2,000 children are born each year with sickle cell disease.2
For more information, see a picture of the risk of passing on an autosomal recessive disease such as sickle cell disease.