Sickle cell disease (SCD) – medical revision notes
In this article, we will describe 10 medical revision notes about sickle cell disease (SCD).
Sickle cells in human blood film – both normal red blood cells and sickle-shaped cells are present.
Key Points
- Sickle cell disease (SCD; a haemoglobinopathy) causes a chronic haemolytic anaemia occurring commonly in people with African ancestry
- SCD is a group of genetic blood disorders caused by a mutation in the haemoglobin-Beta gene found on chromosome 11
- Sickle-shaped red blood cells cause vaso-occlusion and are prone to haemolysis, leading to severe pain crises, organ ischaemia, and other systemic complications
- Infection, bone marrow aplasia, or lung involvement (acute chest syndrome) can develop acutely and be fatal
- Sickle cells are seen on the peripheral blood smear. Diagnosis requires haemoglobin electrophoresis
- Vaccines against bacterial infections, prophylactic antibiotics, and aggressive treatment of infections prolong survival. Hydroxyurea can decrease the frequency of crises and the acute chest syndrome.
1. Definition
- Sickle Cell Disease (SCD) is a group of inherited blood disorders caused by a mutation in the haemoglobin-Beta gene on chromosome 11. They cause a chronic haemolytic anaemia
- The most severe forms include haemoglobin SS (the most common) and sickle beta-zero thalassaemia (Sβ0-thalassaemia), while haemoglobin SC and sickle beta-plus thalassaemia (Sβ+-thalassaemia) are less severe.
In SCD, red blood cells become abnormally shaped like a sickle or crescent, impairing their oxygen-carrying capacity. These distorted cells can block small blood vessels, leading to painful episodes and complications.
2. Epidemiology
- Though most common among people of African descent, SCD also affects individuals from Central and South America, the Middle East, India, Mediterranean regions, and Asia
- The disease is now present globally, including in the UK.
3. Risk factors
As outlined in epidemiology, SCD affects individuals of various ethnic backgrounds worldwide.
4. Cause
SCD is inherited in an autosomal recessive pattern. A child inherits SCD if both parents carry a sickle cell trait gene. This means:
- A person with two defective genes (one from each parent) will have SCD
- A person with one defective gene is a carrier (sickle cell trait) but will not develop the disease
- Parents who are both carriers have a 25% chance of having a child with SCD.
5. Symptoms
- Sickle cell crises: Episodes of severe pain caused by blocked blood flow
- Chronic anaemia
- Frequent infections: Resulting from spleen dysfunction
- Chronic pain, gallstones, delayed growth, vision issues, and eye disease.
6. Diagnosis
Newborn screening detects SCD through blood tests identifying the presence of sickle haemoglobin. This is part of routine UK screening programmes.
7. Treatment
Short-term (management of crises)
- Pain relief: Often opioids or other analgesics
- Antibiotics: For infections
- IV fluids and oxygen: To manage vaso-occlusive crises and hypoxia
- Blood transfusions: In severe cases.
Long-term management
- Immunisations: Particularly to prevent infections due to spleen dysfunction
- Folic acid
- Hydroxyurea: To reduce the frequency of crises and complications
- Stem cell transplantation: Considered for advanced cases.
New treatments
Recent advances include gene-editing therapies like Casgevy (exagamglogene autotemcel) and Lyfgenia (lovotibeglogene autotemcel).
8. Complications
- Stroke and acute chest syndrome
- Organ damage: Particularly AKI, CKD, and ESRF in some patients
- Infections: Increased risk due to splenic dysfunction or removal
- Splenic sequestration: Sudden pooling of blood in the spleen leading to severe anaemia, which can be life-threatening. Repeated episodes often result in spleen damage, causing it to lose function by age 8 in most affected children.
9. Prognosis
- With modern treatments, life expectancy for people with SCD has improved significantly, with many living into their 50s or beyond
- However, SCD still causes considerable morbidity and impacts quality of life, necessitating lifelong medical care.
10. Prevention
- Vaccination and long-term antibiotics (e.g. penicillin) to reduce infection risk
- Regular monitoring and management of complications with appropriate interventions.
Additional information
Malaria connection
Sickle cell trait provides some protection against malaria, which explains its higher prevalence in regions where malaria is endemic. However, this protection is incomplete, and individuals can still contract malaria.
Racism and stigma in SCD
SCD disproportionately affects people of African descent, and individuals with SCD may face racism and stigma in healthcare settings. Patients presenting with pain crises are often accused of drug-seeking behaviour or have their pain underestimated. It is essential to recognise these biases and ensure appropriate, compassionate care.
In the UK, studies have shown that SCD patients experience longer wait times in A&E compared to other groups, emphasising the need for awareness and better management practices.
Summary
We have described 10 medical revision notes about sickle cell disease (SCD). We hope it has been helpful.
Other resources
Sickle cell disease (NHS England)
Sickle cell disease (NHS Scotland)
