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OVERVIEW OF SICKLE CELL DISEASE

Written Dr. Uzoamaka Ugeh, M.B.CHB (OAU Ile - Ife)

Outline

What is SCD?

Sickle cell disease is the most common of the hereditary blood disorders. It is a disorder that affects hemoglobin, the molecule/protein in the red blood cells that delivers oxygen to cells throughout the body.

Abnormal blood cell

Sickle cell disease causes abnormal blood cells that are sickle shaped

People with this disorders have a typical hemoglobin molecule called hemoglobin S, which can distort red blood cells into a sickle or crescent shape. This is where the disorder gets its name.

Epidemiology

Sickle cell disease (SCD) affects millions of people worldwide. It is most common among people from Africa, Mediterranean countries such as Greece, Turkey and Italy, the Arabian Peninsula, India and Spanish - speaking regions in South America, Central America and parts of the Caribbean.

Sickle cell disease is the most common inherited blood disorder in the United States, affecting 70,000 - 80,000 Americans, estimated to occur in 1 in every 500 African American.

Causes

Mutations in the of HBB gene (hemoglobin subunit beta).

Hemoglobin consists of four protein subunit typically two subunits called alpha - globin and two subunits called beta - globin. HBB gene provides instructions for making a protein called beta globin.

Various versions of of beta - globin results from different mutation in the HBB gene. One particular HBB gene mutation produces an abnormal version of beta globin . known as hemoglobin S (HbS).

Other mutations in the HBB gene lead to additional abnormal versions of beta - globin such as C (HbC) and hemoglobin E (HbE).

HBB gene mutation can also result in an unusually low level of beta - globin; this abnormality is called beta thalassemia. In people with sickle cell disease, at least one of the beta - globin subunit in hemoglobin is replaced with hemoglobin S. In sickle cell anemia which is a common form of sickle cell disease, hemoglobin Sreplaces both beta globin subunit in hemoglobin(HbSS).

In other types of sickle cell disease, just one beta - globin subunit is replaced with a different abnormal variant such as hemoglobin C.

For example, people with sickle - hemoglobin C (HbSC) disease have hemoglobin molecules with hemoglobin S and hemoglobin C instead of beta - globin. If mutations that produce hemoglobin S and beta thalassemia occur together individuals have hemoglobin S - beta thalassemia (Hbs Beta Thal) disease.

Abnormal versions of beta - globin can distort red blood cells into a sickle shape. The sickle - shaped red blood cells die prematurely, which can lead to anemia. Sometimes the inflexible, sickle - shaped cells get stuck in small blood vessels and cause serious medical complication.

An example of a mutation is a change in the gene that codes for one of the polypeptides in a Hb molecule. In the genetic disease Sickle Cell Anaemia, the geans that coades fot the - polypeptide has the base T where it should have the base A. this means that one triplet is different, so a diferent amino acid is used when the polypeptides chain is constructed on a ribosome.

The abnormal - polypeptides has the amino acid valine where it should have the amino acid glutamic acid. The normal form of Hb is called HbS, the abnormal Hb is called sickle cell Hb (HbS).

cells stuck in capillaries

Sickle cell obstructing normal flow in capillaries

Glutamic acid is a hydrophilic amino acid. It interacts with water molecules helping to make hemoglobin molecule soluble.

Valine is hydrophobic amino acid. It does not interact with water molecules making the hemoglobin molecule less soluble.

When the abnormal hemoglobin is in an area of low oxygen concentration, the hemoglobin molecules stick to one another forming a big chain of molecules that is not soluble and therefore forms long fibers. This pulls the red blood cells out of shape making them sickle - shaped instead of round. They are no longer able to move easily through the blood system and may get stuck in capillaries.

Signs and Symptoms

Sickle cell disease (SCD is usually diagnosed at birth with standard new born screening. New born have high level of protective fetal hemoglobin, so babies that have sickle cell disease usually do not have any symptoms until5 - 6 months of age. Some children with SCD will start to have problems early on and some later. Early symptoms of SCD may include ;

The signs and symptoms of Sickle Cell Disease will vary from person to person and can change over time. Most of the signs and symptoms of SCD are related to complications of the disease.

Body painSickling in blood vessel.
Body pain Acute chest syndrome
  1. Acute Pain (Sickle Cell or Vaso - occlusive crisis) - Pain episodes can occur without warning when sickle cells block blood flow and decrease oxygen delivery. People describe this pain as sharp, intense, stabbing.

    Pain can strike almost anywhere in the body and in more than one spot at a time. The pain often occurs in the lower back, legs, arms, abdomen, chest. A crisis can be brought on by;

    1. Illness
    2. Temperature changes
    3. Stress
    4. Dehydration (not drinking enough).
    5. Being at high altitudes.
    Body painOften a person does not know what triggers or causes the crisis.
  2. Severe Anemia - People with SCD usually have mild to moderate anemia. At times, however they can have severe anemia. Severe anemia can be life threatening. In infant or child, it may be caused by splenic sequestration crisis.

    1. A splenic sequestration crisis occurs when red blood cells get stuck in the spleen making it enlarge quickly. Since the red blood cells are trapped in the spleen, fewer cells circulate in the blood. This causes severe anemia (Reduction in the blood level).
    2. A big spleen may cause pain in the left side of the belly. A parent can usually palpate or feel the enlarged spleen in the belly of his/her child.
  3. Aplastic crisis - This crisis is usually caused by parvo virus B19 infection also called fifth disease or slapped cheek.

    In SCD , it can cause the bone marrow to stop producing new red cells for a while leading to severe anemia. Severe anemia may lead to symptoms that include :

    1. Shortness of breath
    2. Being very tired
    3. Feeling dizzy
    4. Having pale skin

    Babies and infants with severe anemia may feed poorly and seem very sluggish.

    Body painSluggish looking Kid
  4. Infections - The spleen is important for protection against certain kinds of germs. Sickle cells can damage the Spleen and weaken or destroy its function early in life.
    Bacteria can cause:

    1. Blood infection (septicemia)
    2. Lung infection (Pneumonia)
    3. Infection of the covering of the brain and spinal cord (meningitis)
    4. Bone infection (Osteomyelitis)

  5. Acute Chest Syndrome - Sickling in blood vessels of the lungs can deprive a person's lung of oxygen. When this happens, areas of lung tissue are damaged and cannot exchange oxygen property. This condition is known as acute chest syndrome. It often starts a few days after a painful crisis begins. A lung infection may accompany acute chest syndrome. Symptoms are: Chest pain, Fever, Shortness of breath, Rapid breathing and Cough.
  6. Brain Complication(Clinical Stroke) - A stroke occurs when blood flow is blocked to a part of the brain. When this happens, brain cells can be damaged or can die. Symptoms of stroke may include:
    1. Weakness of an arm or leg on one side of the body
    2. Trouble speaking, walking or understanding
    3. Loss of balance
    4. Severe headache
  7. Priapism - Males with SCD can have unwanted, sometimes prolonged painful erections. This condition is called priapism. It occurs when blood flow out of the erect penis is blocked by sickled cells. If it goes on for a long period of time priapism can cause permanent damage to the penis and lead to impotence.
  8. Eye problems - Sickle cell disease can injure blood vessels in the eye. Usually the retina (Light - sensitive layer of tissue that lines the inside of the eye). Where blood vessels can over grow, get blocked or bleed. Detachment of retina can occur.
  9. Heart Disease - Problems with blood vessels - Enlargement - Pul.Hypertension.
  10. Kidney problems - kidneys have trouble making the urine as concentrated as it should be.
  11. Liver Complication - Sickled red cells block blood vessels in the liver. These blockages prevent enough oxygen from reaching liver tissue. These episodes are usually sudden and may recur. Frequent blood transfusion - Liver damage - Iron overload.
  12. Body pain Leg ulcer
  13. Joint Complications - Sickling in the bones of the hip and less commonly the shoulder joints, knees and ankles can decrease oxygen flow and result in severe damage known as avascular necrosis usually found in adolescents and adults. Symptoms include pain and problems with walking and joint movement.
  14. Delayed growth and puberty.
  15. Pregnancy - Risky to both mother and the baby. Complications - infection, High Blood Pressure, Increased pain episode.
  16. Higher Risk - Premature birth, Miscarriages, Small for date baby.

Diagnosis and Treatment

All new born in the United States are screened for SCD. Pre-birth testing looks for the sickle cell gene in your amniotic fluid.

In children and adults, one or more of the following procedures may also be used to diagnose SCD.

  1. Detailed patient history - This condition often first appears as acute pain in the hands and feet.
    1. Ask for the following symptoms;
       a.  Pain in the bone
       b.  Difficulty in breathing
       c.  Failure to thrive (growth problem)
       d.  Ulcers in the leg
       e.  Painful enlarge spleen
    2. Your Doctor may want to test for sickle cell anemia
    3. Blood test - Several blood test can be used to look for blood counts - it can reveal an abnormal Hb level in the range of 6 to 8g/dl
    4. Blood film may show RBCs that appears as irregularly contracted cells.
    5. Sickle solubility rests look for the presence of Hbs.
  2. Hb Electrophoresis

    This is needed to confirm the diagnosis of SCD. It measures the different types of hemoglobin in the blood.

    Treatment is usually aimed at avoiding crises, treatment are available for SCD.

    1. Rehydration with intravenous fluids helps red blood cells return to a normal state. The red blood cells are more likely to deform and assume the sickle shape if you're dehydrated.
    2. Treating underlying or associated infections is an important part of managing crisis as the stress of an infection can result in sickle cell crisis.
    3. Blood transfusion improve transport of oxygen and nutrients as needed.
    4. Supplemental oxygen is given through a mask. It makes breathing easier and improve oxygen levels in the blood.
    5. Pain medication is used to relieve the pain during a sickle crisis. You may need over the counter drugs or strong prescription pain medication by your Doctor.
  3. Hydroxyurea - Helps to increase production of fetal hemoglobin. It may also reduce the no of blood transfusion.
  4. Immunization - Can help prevent infections. Patient tend to have lower immunity.
  5. Bone marrow transplant- has been used to treat sickle cell anemia. Children younger than 16 years of age who have severe complications and have a matches donor are the best candidate for bone marrow transplant.
  6. Home care

    1. Use heating pads for pain relief
    2. Avoid temperature extreme (extreme heat/extreme cold)
    3. Eat an adequate amount of fruits, vegetables and whole - wheat grains. In doing so, you help your body make more RBCs
    4. Drink more water to reduce the chance of sickle cell crisis.
  7. Exercise regularly but don't overdo it. Reduce - stress.
  8. Contact your Doctor immediately if you think you have any type of infection.
  9. Early treatment of an infection may prevent a full blown crisis.

What is the long term outlook for SCD

The prognosis (outcome) of the disease varies.
Some patients have frequent and painful sickle cell crises. Others only rarely have attacks.

Sickle cells anemia is an inherited disease. Always feel free to talk to your Doctor. This will help you understand possible treatment, preventive measures and reproductive option.

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