Sickle cell disease is an inherited blood disorder, passed from parent to child. Children with sickle cell disease have two defective hemoglobin S genes, one from each parent. Various forms of sickle cell disorder occur when a person inherits one hemoglobin S gene (sickle cell gene) from one parent and one other type of defective hemoglobin gene from the other parent.
Normally, a person inherits two genes that tell the body to produce normal hemoglobin A. One gene comes from each parent. People who inherit one defective hemoglobin S gene and one normal hemoglobin A gene have sickle cell trait. These people don't have symptoms of sickle cell disease, and their bodies don't make sickled blood cells. But they can pass the defective hemoglobin S gene to their children.