Understanding Sickle Cell Disease, Pathophysiology, and Its Treatments

Mohamad-Ali Salloum, PharmD • July 12, 2024

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Sickle Cell Disease (SCD) is a genetic disorder that affects the red blood cells in our body. These cells, which are usually round and flexible, become rigid and take on a sickle or crescent moon shape in individuals with SCD. This change in shape can cause these cells to block blood flow, leading to various complications. 


Pathophysiology and Molecular Biology 


The pathophysiology of SCD is characterized by the polymerization of deoxygenated intracellular sickle hemoglobin, causing the red blood cells to sickle. This can be likened to a gelatin dessert setting in a mold, taking on a specific shape as it solidifies. Similarly, the abnormal hemoglobin in SCD solidifies, causing the red blood cells to take on a sickle shape. 

On a molecular level, SCD is caused by a mutation in the beta globin gene, which leads to the production of an abnormal hemoglobin protein, called hemoglobin S. This is akin to a typo in a recipe that results in a dish with a different taste and texture. In the case of SCD, the ‘typo’ in the gene results in the production of abnormal hemoglobin, which changes the shape and flexibility of the red blood cells. 


Causes 


SCD is an inherited disorder, meaning it is passed down from parents to their children through genes. If both parents carry the sickle cell trait, there is a 25% chance that their child will have SCD. This is similar to how certain physical traits, like eye color or height, are passed down from parents to their children. 


Diagnosis 


SCD is usually diagnosed through a blood test. In the United States, this test is part of routine newborn screening. However, older children and adults can also get tested. In some cases, SCD can even be diagnosed before a baby is born through a sample of amniotic fluid or tissue from the placenta. 


Current Treatments 


The management of SCD focuses on preventing complications, relieving symptoms, and improving the quality of life for patients. Here are some of the current treatments: 


  1. Hydroxyurea: This medication increases the production of fetal hemoglobin (HbF), a type of hemoglobin that does not sickle. By increasing HbF levels, hydroxyurea reduces the frequency of pain crises and the need for blood transfusions. For example, a patient taking hydroxyurea may experience fewer episodes of severe pain compared to someone not on the medication. 
  2. Blood Transfusions: Regular blood transfusions can help reduce the risk of stroke and other complications by increasing the number of normal red blood cells in circulation. For instance, a child with a high risk of stroke may receive monthly blood transfusions to lower this risk. 
  3. Pain Management: Pain crises are a common and debilitating symptom of SCD. Pain management strategies include over-the-counter pain relievers like ibuprofen, prescription opioids, and non-pharmacological methods such as heating pads and hydration. For example, a patient experiencing a pain crisis might use a combination of ibuprofen and a heating pad to alleviate pain. 
  4. Bone Marrow Transplant: This is currently the only potential cure for SCD. It involves replacing the patient’s bone marrow with healthy marrow from a compatible donor. However, this procedure carries significant risks and is not suitable for all patients. For instance, a young patient with a severe form of SCD might undergo a bone marrow transplant if a suitable donor is found. 

Potential Treatments 


Research is ongoing to find new and more effective treatments for SCD. Some of the promising potential treatments include: 


  1. Gene Therapy: This approach aims to correct the genetic mutation responsible for SCD. One method involves using a virus to deliver a normal copy of the HBB gene to the patient’s bone marrow cells. For example, a patient undergoing gene therapy might have their bone marrow cells modified to produce normal hemoglobin, potentially curing the disease. 
  2. CRISPR-Cas9: This gene-editing technology can precisely target and modify specific genes. Researchers are exploring its use to correct the sickle cell mutation or to increase the production of fetal hemoglobin. For instance, a patient treated with CRISPR-Cas9 might have their genes edited to produce more HbF, reducing the severity of their symptoms. 
  3. Voxelotor: This medication works by increasing the affinity of hemoglobin for oxygen, preventing the polymerization of HbS and the sickling of red blood cells. For example, a patient taking voxelotor might experience fewer vaso-occlusive crises compared to someone not on the medication. 
  4. L-glutamine: This amino acid supplement has been shown to reduce the frequency of pain crises in patients with SCD. For instance, a patient taking L-glutamine might have fewer hospitalizations due to pain crises. 


Comparison of Treatment Mechanisms 


To better understand the mechanisms of action of these treatments, let’s compare hydroxyurea and voxelotor: 


  1. Hydroxyurea: This medication increases the production of fetal hemoglobin (HbF), which does not sickle. By increasing HbF levels, hydroxyurea reduces the frequency of pain crises and the need for blood transfusions. For example, a patient taking hydroxyurea may experience fewer episodes of severe pain compared to someone not on the medication. 
  2. Voxelotor: This medication works by increasing the affinity of hemoglobin for oxygen, preventing the polymerization of HbS and the sickling of red blood cells. For example, a patient taking voxelotor might experience fewer vaso-occlusive crises compared to someone not on the medication. 

Both medications aim to reduce the complications of SCD, but they do so through different mechanisms. Hydroxyurea increases the production of a non-sickling form of hemoglobin, while voxelotor prevents the sickling of red blood cells by stabilizing hemoglobin in its oxygen-bound state. 


Conclusion 


Sickle Cell Disease is a complex genetic disorder with significant impacts on patients’ lives. Understanding its pathophysiology, molecular biology, and causes helps us appreciate the challenges faced by those with the disease. Current treatments focus on managing symptoms and preventing complications, while potential treatments offer hope for more effective and curative options in the future. Through continued research and innovation, we can improve the quality of life for individuals with SCD and move closer to finding a cure. 


Resources:

  1. Mayo Clinic. Sickle cell anemia - Symptoms & causes: https://www.mayoclinic.org/diseases-conditions/sickle-cell-anemia/symptoms-causes/syc-20355876.
  2. Cleveland Clinic. Sickle Cell Disease (SCD): Types, Symptoms & Causes: https://my.clevelandclinic.org/health/diseases/12100-sickle-cell-disease
  3. Johns Hopkins Medicine. Sickle Cell Disease: https://www.hopkinsmedicine.org/health/conditions-and-diseases/sickle-cell-disease
  4. CDC. About Sickle Cell Disease: https://www.cdc.gov/sickle-cell/about/index.html 
  5. NHLBI, NIH. Sickle Cell Disease - Causes and Risk Factors: https://www.nhlbi.nih.gov/health/sickle-cell-disease/causes
  6. Oxford Academic. Sickle-Cell Anemia Hemoglobin: The Molecular Biology of the First: https://academic.oup.com/genetics/article/167/1/1/6050610
  7. Blood Advances. Metabolomic and molecular insights into sickle cell disease and innovative therapies: https://ashpublications.org/bloodadvances/article/3/8/1347/260127/Metabolomic-and-molecular-insights-into-sickle
  8. Science News Explores. Explainer: What is sickle cell disease?: https://www.snexplores.org/article/explainer-what-is-sickle-cell-disease 
  9. NHS. Sickle cell disease - Diagnosis: https://www.nhs.uk/conditions/sickle-cell-disease/diagnosis/ 
  10. Springer. Pathophysiology and recent therapeutic insights of sickle cell disease: https://link.springer.com/article/10.1007/s00277-020-03977-9 
  11. Drugs.com. How does Endari work to treat sickle cell disease?: https://www.drugs.com/medical-answers/endari-work-treat-sickle-cell-disease-3323440/ 


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    ABOUT THE AUTHOR

    Mohamad-Ali Salloum, PharmD

    Mohamad Ali Salloum LinkedIn Profile

    Mohamad-Ali Salloum is a Pharmacist and science writer. He loves simplifying science to the general public and healthcare students through words and illustrations. When he's not working, you can usually find him in the gym, reading a book, or learning a new skill.

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