Sickle cell disease is a hereditary blood disorder that affects the red blood cells. People with this disease have red blood cells that mostly contain an abnormal type of hemoglobin. Hemoglobin is the main substance of the red blood cells, helping them carry oxygen from the air in our lungs to the different parts of the body. Normal red blood cells are smooth and round, like doughnuts, so they can squeeze through the blood vessels; they also live for about 120 days before new cells replace them.
People with sickle cell disease have misshapen red blood cells, usually hard and pointed, and shaped like a sickle (crescent). This makes it more difficult for them to pass through the small blood vessels; they tend to get stuck and block the flow of blood, so that tissue throughout the body becomes oxygen deprived and damaged. These abnormal red blood cells also don't live as long as normal ones -- only about 16 days -- and the body simply can't make enough new red blood cells to keep up. So there are fewer red blood cells in the body, causing anemia, gallstones, and jaundice, among other complications.
Sickle cell disease is not the same thing as sickle cell trait. People with sickle cell trait are generally healthy; they don't have the disease, they merely carry the gene that causes the disease. And they can pass this gene on to their children. All sickle cell conditions are inherited from parents, just like blood type, and hair and eye color.
If one of the parents has sickle cell anemia and the other is normal, all of the children will have sickle cell trait. If one parent has sickle cell anemia and the other has sickle cell trait, there is a 50 percent (1 in 2) chance of having a baby with either condition. And if both parents have sickle cell trait, they have a 25 percent (1 in 4) chance of having a baby with sickle cell anemia.