Sickle Cell Disease

Sickle cell disease (SCD) is a group of inherited blood disorders which affect hemoglobin, a protein that helps red blood cells carry oxygen throughout the body and gives the cells their color. Healthy red blood cells with normal hemoglobin are round and move easily through small blood vessels.

Red blood cells with the abnormal hemoglobin S variant become sticky and sickle-shaped. These sickle cells tend to live only about 16 days compared to 120 days for normal red blood cells, causing a constant shortage of red blood cells (known as anemia). Also, the more rigid sickle-shaped cells may have difficulty passing through small blood vessels and block normal blood flow. Blockages cause pain and damage tissue, and ultimately lead to many of the complications of sickle cell disease.

A child must inherit abnormal hemoglobin genes from both parents to have SCD. People who inherit only one abnormal hemoglobin gene have sickle cell trait. While they don’t have the disease, they are carriers and can pass the gene on to their children. Generally, people with sickle cell trait don’t experience symptoms, however, extreme conditions (increased atmospheric pressure, high altitudes, low oxygen levels, high-intensity physical activities, or severe dehydration) can lead to complications including sudden death.

Symptoms

  • Anemia: Causes a shortage of red blood cells and the hemoglobin they carry created by the short lifespan of affected red blood cells.
  • Pain Episodes: Pain occurs when sickle cells block the flow of blood. The intensity varies and can last for hours or weeks.
  •  Swelling in the hands and feet: Swelling occurs when sickle cells block the flow of blood to extremities and is often accompanied by fever.
  • Frequent Infections: Sickle cells can damage the spleen, an organ that fights infection, leaving patients at a higher risk of infection.
  • Delayed growth: SCD causes a shortage of healthy red blood cells which carry oxygen throughout the body. Oxygen is required by the body for growth.
  • Vision Loss: Sickle cells can block the flow of blood through the tiny vessels that supply oxygen to the eyes resulting in retinal damage and problems processing visual images.

Types

Sickle cells are red blood cells with abnormal hemoglobin and there are several variations. The type of sickle cell disorder is based on the types of abnormal hemoglobin genes inherited. The most common are:

  • Sickle Cell Trait (HbAS). People with sickle cell trait inherit an abnormal hemoglobin “S” gene from one parent and a normal hemoglobin gene (“A”) from the other parent. While people with HbAS carry an abnormal “S” gene, they normally will not experience any symptoms of the disease, except as a result of some extreme environmental condition (see above).
  • Sickle Cell Disease (HbSS). Also known as sickle cell anemia, this is the most common and most severe type of sickle cell disorder. People with HbSS inherit the hemoglobin “S” gene mutation from both parents.
  • Sickle-Hemoglobin C Disease (HbSC). People with sickle-hemoglobin C disease inherit the abnormal hemoglobin “C” variant from one parent and the “S” variant from the other parent. This is a milder sickling disorder, and symptoms are similar to SCD but less frequent and less severe.
  • Sickle Thalassemia Disease (HbSß). There are two types: HbSß0-thal and HbSß+-thal. People inherit the “S” variant from one parent and the ß -thalassemia variant from the other. HbSß0-thal is usually a severe form of SCD.

Causes

Sickle cell disease is caused by a mutation in the hemoglobin gene, a genetic disorder passed down by parents. The disease is absolutely not contagious and cannot be transmitted from an affected person to a non-affected person. A child must inherit an abnormal hemoglobin gene from both their mother and their father to have the disease. If the sickle cell gene is inherited from only one parent, the child has sickle cell trait.

Risks/Complications

There are a variety of complications associated with SCD:

  • Stroke: If sickle cells block the flow of blood to  an area of the brain, stroke can occur.
  • Acute Chest Syndrome: This is a life-threatening condition which can be caused by sickle cells blocking blood vessels in the lungs. Symptoms include chest pain, fever, and difficulty breathing.
  • Pulmonary Hypertension: High blood pressure in the lungs can be fatal.
  • Organ Damage: Organs including the kidneys, liver, and spleen are damaged when chronically deprived of oxygen-rich blood due to sickle cell-clogged blood vessels.
  • Blindness: Over time, sickle cell damage to the tiny vessels that supply blood to the eyes can result in blindness.
  • Leg Ulcers: SCD can cause open sores on the legs.
  • Gall Stones: Bilirubin is created by the breakdown of red blood cells and high levels can cause gall stones to form.
  • Painful, Long-Lasting Erections: When sickle cells block blood vessels in the penis, damage and impotence can occur.

Diagnosis

SCD is diagnosed with a simple blood test. Children with SCD have an increased risk of infection and other health problems so early diagnosis (preferably as a newborn) is important for initiating life-saving health maintenance therapies. Sickle Cell Trait is not a disease, however, carriers should be identified for genetic counseling and family planning purposes and also cautioned about situations that place them at risk for complications.

Treatment

The only potential cure for SCD is bone marrow transplant, also known as stem cell transplant. This procedure replaces the bone marrow of the person with SCD with the healthy bone marrow from a matched donor, such as a sibling who doesn’t have SCD. Stem cells from umbilical cord blood can also be used. Finding a suitable bone marrow donor isn’t always possible, and the procedure has many risks, including death.

The risks increase for people over age 16. Other treatments include blood transfusions and medications to help reduce pain, relieve symptoms, and prevent complications. Blood transfusions relieve anemia by increasing the number of normal red blood cells in the body and can also decrease the risk of stroke. Penicillin, the pneumococcal vaccination, and flu shot help prevent infections. Hydroxyurea is a daily medication that reduces the frequency of pain crises and may reduce the need for blood transfusions. Folic acid supplementation encourages the creation of new red blood cells.

Prevention

A genetic counselor can help sickle cell trait carriers understand their risk of having a child with SCD. Counselors can also explain reproductive options and preventive measures.

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