Sickle cell anemia

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at November 3, 2016
StartDiseasesSickle cell anemia

Sickle cell anemia which is also called sickle cell disease is a rare form of inherited anemia. This often painful condition marked by misshapen red blood cells is diagnosed in fewer than 200,000 cases per year in the United States.

Contents

Definition & Facts

Normal red blood cells are round and shaped like discs with a slightly indented middle. These healthy blood cells are flexible and soft, allowing them to travel throughout the body easily. This is important as they travel through tiny blood vessels to deliver oxygen throughout the body. Unlike these healthy cells, sickle cells are shaped like crescents and are very rigid and stiff.

Healthy red blood cells contain the protein hemoglobin A (HbA), which is responsible for carrying oxygen to each part of the body. sickle cells contain a different protein known as hemoglobin S (HbS.) The molecules in HbS clump together and cause the cells to become sticky and clump together.

This abnormality causes the cells to curve and become much more fragile. The clumped together cells become clogged in blood vessels, depriving organs and tissues of oxygen. While healthy red blood cells have a lifespan of about four months, sickle cells last a maximum of 10-20 days. This breakdown of cells creates an abnormally low concentration of red blood cells, known as anemia.

Symptoms & Complaints

  • Chronic anemia. The constant breakdown of red blood cells causes an ongoing shortage of red blood cells. This causes an overall lack of oxygen to the body, resulting in fatigue and pale skin and/or nail beds.
  • Pain. When blood vessels become clogged with the sticky sickle cells, blood cannot flow through them. This frequently happens in the blood vessels in the chest, joints, and abdomen. These episodes of pain are known as pain crises (or vaso-occlusive crisis). They can be severe and last for weeks. The frequency of crises depends on the severity of the patient. Some experience only a few crises per year, where others experience more than 12 per year.
  • Swollen hands and feet. This is often the first sign of sickle cell anemia in infants. The sickle cells block blood flow out of the hands and feet, causing them to swell frequently. 
  • Frequent infections. As organs are deprived of oxygen, they become damaged. Often times with sickle cell anemia, the spleen becomes damaged. This lowers the body’s ability to fight infection. Vaccinations are given to help prevent life-threatening infections. 
  • Growth and development delays. The body needs oxygen and nutrients to grow properly. A chronic shortage in healthy red blood cells prohibits the normal growth in infants and children. This often causes puberty to be delayed in teenagers.
  • Impaired vision. The retina of the eyes can become impaired due to the tiny blood vessels supplying them with oxygen being clogged due to sickle cell. Because the retina is responsible for processing visual images, this can lead to vision impairment and/or loss of vision.

Causes

Sickle cell anemia is a hereditary condition caused by a mutation in the gene responsible for creating hemoglobin. This mutation is passed down through generations through an inheritance pattern known as autosomal recessive inheritance. This means if a child inherits the gene from one parent, they will become a genetic carrier of the sickle cell trait. If the other parent is not a carrier, the child will have mostly normal red blood cells and hemoglobin with some sickle cells mixed in.

Typically, there are not enough of the sickle cells to cause symptoms in these children. Even though these children may remain asymptomatic, it is important to note that they can still pass the gene to their future children. When both parents are carriers of the gene mutation, there is a 50% chance of their child being a carrier, a 25% chance of the child developing sickle cell and a 25% chance of the child being completely unaffected. Sickle cell anemia is not contagious and can only be passed genetically. In the United States, African-American families are most commonly affected.

Diagnosis & Tests

The defective form of hemoglobin, HbS, can be detected in a blood test. This blood test is now done routinely at birth in the United States. In children or adults born before this became part of the routine screening for infants, blood is drawn from a vein in the arm or in small children, the heel or finger to check for the mutated cells. A laboratory will screen the sample for the presence of HbS.

In the event of a positive result, more tests will be performed to determine if one sickle cell gene is present or if two are present, indicating both parents to be carriers of the mutated gene. Further testing will be performed to determine the number of sickle cells present, indicating whether the patient is a carrier, or if they are found to have sickle cell anemia.

Families are usually sent to a genetic counselor, and further testing may be required periodically to check for complications of sickle cell anemia. If parents are aware they are carriers or are unsure, diagnostic tests can be performed during pregnancy by testing the fluid surrounding the baby in the womb. 

Treatment & Therapy

There is no cure for the majority of sickle cell anemia cases. The only possible option for a cure is a bone marrow transplant. This is not a very common practice due to the difficulty in finding a suitable donor who is not a carrier of sickle cell, and the serious risks involved with a transplant.

Treatment options are primarily used to treat the symptoms associated with sickle cell as well as avoid crises and prevent complications. Frequent visits with a physician are required to assess current symptoms and crises and alter treatment accordingly. Common treatments include antibiotics, typically given to infants with sickle cell from around two months of age to five years old. This is to prevent infections that may become life threatening in small children with compromised immune systems due to sickle cell. Antibiotics are also given to adults to help fight certain infections.

Pain medications are frequently used to alleviate pain associating with crises. Hydroxyurea is a daily medication used lower the frequency of crises by stimulating the body to produce hemoglobin; however, it also increases the risk of infection. The risks and benefits of this therapy are discussed between the patient and physician on a case by case basis. Other treatment options include blood transfusions and supplemental oxygen to maintain proper oxygen levels and red blood cell concentration.

Prevention & Prophylaxis

If a patient has not been tested for the sickle cell gene mutation, they may opt to be tested prior to planning a family in order to make an informed decision about having children. Among couples, if one person is a carrier, they may choose to seek genetic counseling to determine if both are carriers.

The counselor can help determine the likelihood of a potential child being born with sickle cell. If there is a chance of the mutated gene being passed to the child, the counselor will advise potential treatments and preventative measures that may be taken.