Normal red blood cells are soft, gel-like discs that can squish as needed to slip through the tiny capillaries of the body. In sickle cell anemia, the red blood cells are brittle.
Sickle cell disease is caused by a genetic variation of hemoglobin, the molecule that carries oxygen in the red blood cell. Sickle hemoglobin (hemoglobin S) is very slightly different from normal hemoglobin (hemoglobin A); only one amino acid, the sixth from the end, is different.
When the hemoglobin is carrying oxygen it functions normally. When not carrying oxygen, however, the molecules link together to form rigid rods. The red blood cells become sickle-shaped.
These brittle blood cells are easily destroyed, leading to anemia. They can also get stuck, leading to crises where not enough oxygen gets to the tissues.
Children with two hemoglobin S genes have classic sickle cell anemia (SS). Those with one hemoglobin S gene and one normal hemoglobin gene are carriers (AS – or sickle cell trait). Those with one hemoglobin S gene and one other abnormal hemoglobin gene have a variant of sickle cell disease (such as hemoglobin SC disease or hemoglobin S beta-thalassemia).
Sickle cell disease is an inherited condition. Both parents must carry the trait. The trait is thought to be so common because it changes the red blood cells in a way that makes people resistant to malaria.
Sickle cell anemia is most common in people of African, Indian, Middle Eastern, or Mediterranean descent. Nevertheless, it can occur in all peoples.
Young babies with sickle cell anemia often have no symptoms for the first several months. Anemia develops by about 4 months of age. The first symptom is usually painful swelling of the hands and feet as a result of sickle cells being trapped in the small blood vessels of the bones.
In young children, the spleen is often enlarged, swollen by a collection of sickled red blood cells. Over time, the spleen is destroyed by this process, leaving children more susceptible to certain infections, including Haemophilus influenzae and pneumococcus. They are also particularly susceptible to salmonella bone infections.
Pain is a common feature of sickle cell anemia. It can become quite severe during pain crises. These may be triggered by fevers or other illnesses.
Acute chest syndrome is another sickle cell crisis. In this case the lung tissues receive inadequate oxygen.
A parvovirus B19 infection (fifth disease) can trigger something called an aplastic crisis. In an aplastic crisis, red blood cell production drops. Because of the already increased destruction of red blood cells that occurs in sickle cell disease, the numbers of red blood cells can plummet dangerously.
Sickle cell anemia often causes other problems as well, including jaundice, strokes, liver disease, kidney disease, gallstones, heart disease, eye problems, painful erections, and poor growth.
This is a lifelong condition, unless corrected by something such as bone marrow transplantation.
Sickle cell anemia is tested for on many newborn screening tests so that it can be diagnosed before children develop symptoms. It can also be diagnosed by specific blood tests.
Children with sickle cell anemia need close care by someone skilled at treating the condition in order to prevent and treat complications. This includes special attention to immunizations and to aggressive treatment of routine illnesses and fevers. Antibiotics are given to prevent infections as well. Staying well hydrated is important.
Each of the sickle cell crises demands prompt treatment.
A number of medicines have been used to reduce sickling or to increase levels of better functioning hemoglobin.
Newborn screening, early diagnosis, and aggressive management can prevent many of the complications of sickle cell anemia. The disease itself cannot occur unless two carriers have children together. About ½ of their children will be carriers, and another ¼ of their children will have the disease.