Sickle cell anemia

Synonyms

6

Overview

Sickle cell anemia is a disease in which the body produces abnormally shaped red blood cells that have a crescent or sickle shape. These cells do not last as long as normal, round, red blood cells, which leads to anemia (low number of red blood cells). The sickle cells also get stuck in blood vessels, blocking blood flow. Signs and symptoms of sickle cell disease usually begin in early childhood and may include anemia, repeated infections, and periodic episodes of pain (called crises). This condition is caused by mutations in the HBB gene and is inherited in an autosomal recessive pattern. Treatment typically focuses on controlling symptoms and may include pain medicines during crises; hydroxyurea to reduce the number of pain episodes; antibiotics and vaccines to prevent bacterial infections; and blood transfusions

Symptoms

Signs and symptoms of sickle cell anemia often don't appear until an infant is at least 4 months old and may include:

  • Anemia. Sickle cells are fragile. They break apart easily and die, leaving you without a good supply of red blood cells. Red blood cells usually live for about 120 days before they die and need to be replaced. But sickle cells die after an average of less than 20 days. This results in a lasting shortage of red blood cells (anemia). Without enough red blood cells in circulation, your body can't get the oxygen it needs to feel energized. That's why anemia causes fatigue.
  • Episodes of pain. Periodic episodes of pain, called crises, are a major symptom of sickle cell anemia. Pain develops when sickle-shaped red blood cells block blood flow through tiny blood vessels to your chest, abdomen and joints. Pain can also occur in your bones. The pain may vary in intensity and can last for a few hours to a few weeks. Some people experience only a few episodes of pain. Others experience a dozen or more crises a year. If a crisis is severe enough, you may need to be hospitalized.
  • Hand-foot syndrome. Swollen hands and feet may be the first signs of sickle cell anemia in babies. The swelling is caused by sickle-shaped red blood cells blocking blood flow out of their hands and feet.
  • Frequent infections. Sickle cells can damage your spleen, an organ that fights infection. This may make you more vulnerable to infections. Doctors commonly give infants and children with sickle cell anemia vaccinations and antibiotics to prevent potentially life-threatening infections, such as pneumonia.
  • Delayed growth. Red blood cells provide your body with the oxygen and nutrients you need for growth. A shortage of healthy red blood cells can slow growth in infants and children and delay puberty in teenagers.
  • Vision problems. Some people with sickle cell anemia experience vision problems. Tiny blood vessels that supply your eyes may become plugged with sickle cells. This can damage the retina — the portion of the eye that processes visual images.

Causes

Hemoglobin is a protein inside red blood cells that carries oxygen. Sickle cell anemia is caused by a mutation in the gene that tells your body to make an abnormal type of hemoglobin, called hemoglobin S. 

The fragile, sickle-shaped haemoglobin cells deliver less oxygen to the body's tissues, and can break into pieces that disrupt blood flow. Sickle cell anemia is inherited as an autosomal recessive trait. This means it occurs in someone who has inherited the hemoglobin S gene from both parents.

Sickle cell disease is much more common in people of African and Mediterranean descent. It is also seen in people from South and Central America, the Carribbean, and the Middle East. Someone who inherits hemoglobin S from one parent and normal hemoglobin (A) from the other parent will have sickle cell trait. Someone who inherits hemoglobin S from one parent and another type of abnormal hemoglobin from the other parent will have another form of sickle cell disease, such as thalassemia.

Prevention

The sickle cell gene is passed from generation to generation in a pattern of inheritance called autosomal recessive inheritance. This means that both the mother and the father must pass on the defective form of the gene for a child to be affected.

If only one parent passes the sickle cell gene to the child, that child will have the sickle cell trait. With one normal hemoglobin gene and one defective form of the gene, people with the sickle cell trait make both normal hemoglobin and sickle cell hemoglobin. Their blood may contain some sickle cells, but they generally don't experience symptoms. However, they are carriers of the disease, which means they can pass the defective gene on to their children.

With each pregnancy, two people with sickle cell traits have:

  • A 25 percent chance of having an unaffected child with normal hemoglobin
  • A 50 percent chance of having a child who also is a carrier
  • A 25 percent chance of having a child with sickle cell anemia

If you carry the sickle cell trait, you may wish to see a genetic counselor before trying to conceive a child. A genetic counselor can help you understand your risk of having a child with sickle cell anemia.

Diagnosis

A blood test can check for hemoglobin S — the defective form of hemoglobin that underlies sickle cell anemia. In the United States, this blood test is part of routine newborn screening done at the hospital. But older children and adults can be tested, too.

In adults, a blood sample is drawn from a vein in the arm. In young children and babies, the blood sample is usually collected from a finger or heel. The sample is then sent to a laboratory, where it's screened for hemoglobin S.

If the screening test is negative, there is no sickle cell gene present. If the screening test is positive, further tests will be done to determine whether one or two sickle cell genes are present. People who have one gene — sickle cell trait — have a fairly small percentage of hemoglobin S. People with two genes — sickle cell anemia — have a much larger percentage of the defective hemoglobin.

Sickle cell disease can be diagnosed in an unborn baby by sampling some of the fluid surrounding the baby in the mother's womb (amniotic fluid) to look for the sickle cell gene. If you or your partner has been diagnosed with sickle cell anemia or sickle cell trait, ask your doctor about whether you should consider this screening. Ask for a referral to a genetic counselor who can help you understand the risk to your baby.

Prognosis

Although sickle cell disease is present at birth, symptoms usually don't occur until after 4 months of age. Sickle cell anemia may become life threatening. Blocked blood vessels and damaged organs can cause acute painful episodes, or "crises." There are several types of crises:

1. Hemolytic crisis occurs when damaged red blood cells break down

2. Splenic sequestration crisis is when the spleen enlarges and traps the blood cells

3. Aplastic crisis results when an infection causes the bone marrow to stop producing red blood cells.

These painful crises, which occur in almost all patients at some point in their lives, can last hours to days, affecting the bones of the back, the long bones, and the chest. Some patients have one episode every few years, while others have many episodes per year. The crises can be severe enough to require admission to the hospital for pain control and intravenous fluids. Repeated crises can cause damage to the kidneys, lungs, bones, eyes, and central nervous system.

In the past, death from organ failure often occurred between the ages of 20 and 40 in most sickle-cell patients. More recently, because of better understanding and management of the disease, patients live into their forties and fifties. Causes of death include organ failure and infection. Some people with the disease experience minor, brief, and infrequent episodes. Others experience severe, prolonged, and frequent episodes resulting in many complications.

Treatment

Folic acid and penicillin:

Children born with sickle-cell disease undergo close observation by the pediatrician and require management by a haematologist to assure they remain healthy. These patients take a 1 mg dose of folic acid daily for life. From birth to five years of age, they also have to take penicillin daily due to the immature immune system that makes them more prone to early childhood illnesses.

Malaria chemoprophylaxis:

The protective effect of sickle-cell trait does not apply to people with sickle cell disease; in fact, they are more vulnerable to malaria, since the most common cause of painful crises in malarial countries is infection with malaria. It has therefore been recommended that people with sickle-cell disease living in malarial countries should receive anti-malarial chemoprophylaxis for life.

vaso-occlusive crisis:

Most people with sickle-cell disease have intensely painful episodes called vaso-occlusive crises. However, the frequency, severity, and duration of these crises vary tremendously. Painful crises are treated symptomatically with pain medications; pain management requires opioid administration at regular intervals until the crisis has settled. For milder crises, a subgroup of patients manage on NSAIDs (such as diclofenac or naproxen). For more severe crises, most patients require inpatient management for intravenous opioids; patient-controlled analgesia (PCA) devices are commonly used in this setting. Diphenhydramine is also an effective agent that doctors frequently prescribe to help control itching associated with the use of opioids.

Acute chest crisis:

Management is similar to vaso-occlusive crisis, with the addition of antibiotics (usually a quinolone or macrolide, since cell wall-deficient ["atypical"] bacteria are thought to contribute to the syndrome), oxygen supplementation for hypoxia, and close observation. Should the pulmonary infiltrate worsen or the oxygen requirements increase, simple blood transfusion or exchange transfusion is indicated. The latter involves the exchange of a significant portion of the patients red cell mass for normal red cells, which decreases the percent of haemoglobin S in the patient's blood. The patient with suspected acute chest syndrome should be admitted to the hospital with worsening A-a gradient an indication for ICU admission.

Hydroxyurea:

The first approved drug for the causative treatment of sickle-cell anaemia, hydroxyurea, was shown to decrease the number and severity of attacks and to possibly increase survival time  

Hydroxyurea (Droxia) - FDA-approved indication: To reduce the frequency of painful crises and to reduce the need for blood transfusions in adult patients with sickle cell anemia with recurrent moderate to severe painful crises (generally at least 3 during the preceding 12 months).

Transfusion therapy:

Blood transfusions are often used in the management of sickle-cell disease in acute cases and to prevent complications by decreasing the number of red blood cells (RBC) that can sickle by adding normal red blood cells. In children prophylactic chronic red blood cell (RBC) transfusion therapy has been shown to be efficacious to a certain extent in reducing the risk of first stroke or silent stroke when transcranial Doppler (TCD) ultrasonography shows abnormal increased cerebral blood flow velocities. In those who have sustained a prior stroke event it also reduces the risk of recurrent stroke and additional silent strokes.

Bone marrow transplants:

Bone marrow transplants have proven effective in children. Bone marrow transplants are the only known cure for SCD. However, bone marrow transplants are difficult to obtain because of the specific HLA typing necessary. Ideally, a twin family member (syngeneic) or close relative (allogeneic) would donate the bone marrow necessary for transplantation.

Resources

Refer to research Publications.