About Sickle Cell Disease

Sickle Cell Disease: Overview

Sickle cell disease is a group of inherited red blood cell disorders. Healthy red blood cells are doughnut-shaped, soft, flexible, and contain normal hemoglobin A. They flow easily through small blood vessels and carry oxygen to tissues throughout the body. In sickle cell disease, red blood cells contain abnormal hemoglobin molecules, called hemoglobin S, for sickle hemoglobin. Red blood cells in sickle cell disease become hard, sticky, and take on the shape of a C shaped farmers tool called the sickle.

Diagram of sickle cell diseaseSickle cells live a short time, causing a shortage of red blood cells, or anemia. When sickle cells travel through small blood vessels, they can get stuck and clog the blood flow. This causes pain episodes, called a sickle cell pain crisis, often in the arms, legs, chest, back, or abdomen. Constant sickling also causes blood vessel damage and injuries to the organs in the body.

Sickle cell anemia is an inherited disease. It occurs most frequently in the African-American population, and less frequently in Hispanic and Middle Eastern populations. There are about 70,000 to 100,000 people with sickle cell disease in the United States. One per 350 to one per 500 (1/350 - 1/500) African-American newborns has sickle cell disease. The incidence of sickle cell disease among Hispanics is one in a 1,000 (1/1000).

Sickle cell trait is common among African-Americans. One out of 12, or about 10 percent of African-Americans have the sickle cell trait. When both parents carry sickle cell trait, their child has a one in four chance of being born with sickle cell disease. People with sickle cell trait do not have symptoms and lead a normal life.

There are several forms of sickle cell disease. The most common type is Hemoglobin SS disease, in which the patient carries two copies of the abnormal hemoglobin S gene. The second-most common form is Hemoglobin SC disease, in which the patient has one copy of hemoglobin S and one copy of hemoglobin C. Another type of sickle cell disease, sickle/beta-thalassemia is made up of one copy of hemoglobin S and one copy of hemoglobin A is not working normally. A genetic counselor or a hematologist can help you understand how the different forms of sickle cell disease are inherited and the risks of having a child with sickle cell disease.

Types of Sickle Cell Disease

  • Hemoglobin SS
  • Hemoglobin SC
  • Hemoglobin S/beta-thalassemia plus
  • Hemoglobin S/beta-thalassemia zero
  • Hemoglobin SD
  • Hemoglobin SOArab

Symptoms of Sickle Cell Disease

Anemia

This is a very common complication of sickle cell disease. Normal red blood cells live 120 days in the blood stream, but sickle red blood cells last only 7-14 days. This means there are not enough healthy red blood cells to carry oxygen throughout the body. When this happens, a person might have the following symptoms:

  • Fatigue
  • Irritability
  • Exercise intolerance
  • Dizziness and lightheadedness
  • Fast heart rate
  • Difficulty breathing
  • Pale skin color
  • Jaundice (yellow color in the whites of the eyes from red cell breakdown)
  • Slow growth
  • Delayed puberty

Blood transfusions can be used to treat a sudden worsening of anemia resulting from infection or enlargement of the spleen. The medication hydroxyurea is used to treat chronic anemia due to sickle cell disease.

The Sickling Problem
The Sickling Problem (Inspired by graphic from Joint Center for
Sickle Cell and Thalassemic Disorders, Brigham and Women's
Hospital, Boston,
Massachusetts)

Hand-Foot Syndrome (Dactylitis)
This symptom of sickle cell disease usually occurs in babies and can be the first symptom of sickle cell disease. Swelling in the hands and feet, often along with fever, is caused by sickle cells getting stuck in the blood vessels or the marrow of the small bones of the hands and feet. Treatment includes pain medication and fluids.

Pain Crisis (Vaso-occlusive crisis)

This is the most common complication of sickle cell disease, and it is the most frequent reason that people with sickle cell disease go to the emergency room or are admitted to the hospital. Sickle cell pain is caused by sickle cells clogging the blood flow of small vessels. The pain can start suddenly, be mild or severe, and can last for a short time or several days. Sickle cell pain is treated with pain medication and hydration, at home or in the hospital. The medication Hydroxyurea prevents sickle cell pain crisis.

Acute chest syndrome

When sickle cells block flow blood flow in the lungs, usually when there is also a lung infection, this can cause chest pain, fluid build up in the chest, and insufficient oxygen delivered to the body. This is called acute chest syndrome, which is treated by antibiotics, giving extra oxygen through a mask, blood transfusion, and pain medication. Hydroxyurea can reduce the frequency and severity of acute chest syndrome.

Stroke

Damaged blood vessels in the brain increases the chances for sickle cells to block flow. When brains cells do not get enough oxygen, they may die, causing some parts of the body not to work normally. This is called a stroke. Patients who suffer a stroke are treated with scheduled, long-term blood transfusions to prevent another stroke. A test called Transcranial Doppler Ultrasound (TCD) measures the velocity of blood flow in the large arteries in the brain and identifies children who are at increased risk for stroke. Chronic blood transfusion program or hydroxyurea therapy is offered to children who have abnormal TCDs.

Preventing Sickle Cell Symptoms

Complications of sickle cell disease can be avoided by preventing red blood cells from becoming sickle-shaped. Ways to help sickle cells stay round include:

  • Drinking plenty of water
  • Avoiding extremely hot or cold temperatures.
  • Avoiding places or situations with low oxygen, such as high altitudes, military boot camp, or strenuous athletic training.
  • Getting plenty of rest and taking frequent breaks during exercise.
  • Taking the medicine Hydroxyurea. People taking hydroxyurea must be monitored regularly by a doctor to ensure the right dose is given for the best effect.

Hydration

One of the best things you can do to prevent sickle cell symptoms is to stay hydrated by drinking water.

Hydroxyurea

Hydroxyurea is a medication that can help many sickle cell patients. It does not cure sickle cell disease, but it can improve many symptoms, by:

  • preventing pain episodes
  • preventing acute chest syndromes
  • decreasing the need for blood transfusions
  • decreasing the number of hospitalizations
  • improving survival

How Hydroxyurea Works

Hemoglobin F (or fetal hemoglobin) protects against sickle cell symptoms. It prevents hemoglobin S from sticking together and decreases the sickling of red blood cells. Patients with high hemoglobin F levels have fewer symptoms and do better than those patients with low hemoglobin F levels. Hydroxyurea increases hemoglobin F and keeps the red blood cells round.

How Hydroxyurea works

Hydroxyurea is not a drug that works immediately after one or two doses. For it to work, hydroxyurea must be taken everyday, along with folic acid. Since the body makes new sickle cells every day, hydroxyurea must also be taken every day to combat the hemoglobin S-containing cells from sickling. The effect of hydroxyurea will be felt after one or two months. Patients will begin to feel more energetic. The maximum benefit of hydroxyurea will be reached after approximately 6 months.

Hydroxyurea is a safe drug, but the dose for each patient must be carefully adjusted. Too small a dose will not have the desired effect; too large a dose will cause all blood cell counts to drop, even the good cells. Therefore, its use must be monitored by frequent blood counts in the clinic.

Hydroxyurea is usually prescribed for patients with frequent pain episodes, very low red blood cell count, acute chest syndrome, or other sickle cell problems. It is not known yet whether hydroxyurea can prevent strokes.

What Is Sickle Cell Trait?

Sickle cell trait is not sickle cell disease. Having sickle cell trait, (SCT) means that a person has inherited the sickle cell gene from a parent. Other genes you inherit from a parent are for things such as eye color or hair texture. Except in rare cases, people with sickle cell trait do not have symptoms. Many people with SCT never know they are a carrier.

One out of 12, or about ten percent of African-Americans have the sickle cell trait. When both parents carry sickle cell trait, their child has a 1 in 4 chance of being born with sickle cell disease. About three million people in the United States have sickle cell trait.

Parents can determine the odds that their children will have sickle cell disease or sickle cell trait if they know their own SCT status. A simple blood test can discover if someone has sickle cell trait.

Can Sickle Cell Anemia Be Cured?

Currently, the only known cure for sickle cell disease is bone marrow or stem cell transplant. Bone marrow is the soft tissue inside the bones that makes blood cells. A bone marrow transplant is a procedure that takes healthy bone marrow cells from a person who does not have sickle cell disease (the donor) and gives them to the person who has sickle cell disease (the recipient) to replace the bone marrow that is making sickle cells.

Bone marrow transplantation is a major undertaking and can have serious side effects. As medical advances are made, bone marrow transplantation for sickle cell disease has become increasingly safe.For the transplant to work, the bone marrow must come from someone who is a close match, usually a healthy sibling who has the same set of parents as the person with sickle cell disease.

To learn more about bone marrow transplantation for sickle cell anemia, please contact a member of the Sickle Cell Anemia and Hemoglobinopathy Program or the Stem Cell Transplant Program.