Body:
A carrier is someone who "carries" a variant of the gene that doesn't generally cause him or her any ill health effects because he or she does not have a second variant. This is sometimes called sickle cell trait. While sickle cell disease carriers do not have the disease, they can pass on gene variants to their children.
In rare and extreme situations of low oxygen (mountain climbing, being at high altitude, extremely hard exercise) and/or dehydration, a carrier for Hb S can have symptoms such as a pain crisis or muscle breakdown (called rhabdomyolysis).