Related concepts:

Hemoglobin S

Introduction to sickle cell anemia:

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 disease, the red blood cells are brittle.

What is sickle cell anemia?

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).

Who gets sickle cell anemia?

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.

What are the symptoms of sickle cell anemia?

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.