Having a "sickle cell trait" means that a person has inherited the sickle cell gene from one parent. This differs from sickle cell disease, in which a person inherits the gene from both parents, notes WebMD. People with only one sickle cell gene can still pass it to their children.
People with sickle cell disease have only the abnormally shaped hemoglobin S, while those with sickle cell trait have both normal hemoglobin A and the abnormal hemoglobin S, explains WebMD. While they do not have sickle cell disease, in rare cases, people with sickle cell trait experience muscle pain or other problems, usually when engaging in intense exercise, when overheated or at high altitudes.