What is Sickle Cell Anemia?

Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene. This is responsible for making the protein hemoglobin that carries oxygen in red blood cells. This mutation leads to the production of abnormal hemoglobin molecules, known as hemoglobin S. This causes red blood cells to become stiff and sickle-shaped instead of their normal round shape. These sickle-shaped cells can become trapped in blood vessels. And this leads to reduced blood flow and oxygen supply to various parts of the body. It also causes a range of health problems.

The mutation responsible for sickle cell anemia is a single-nucleotide substitution in the beta-globin gene, which encodes the beta subunit of hemoglobin. Specifically, the mutation changes the amino acid at position 6 of the beta-globin protein from glutamic acid to valine. This results in the formation of hemoglobin S. This mutation is inherited in an autosomal recessive pattern. This means that an individual must inherit two copies of the mutated gene (one from each parent) to develop sickle cell anemia.

Individuals who inherit only one copy of the sickle cell mutation and one normal copy of the beta-globin gene have a condition known as sickle cell trait. While they are generally healthy, they can still experience some symptoms associated with sickle cell anemia under certain conditions, such as high altitudes, dehydration, or extreme exercise. Additionally, people with sickle cell trait can pass on the mutated gene to their offspring, making sickle cell trait and sickle cell anemia more prevalent in certain populations.

What are the Symptoms and Complications of Sickle Cell Anemia 

Sickle cell anemia is a condition that affects the production of hemoglobin, the protein in red blood cells that carries oxygen throughout the body. The abnormal hemoglobin in sickle cell anemia causes red blood cells to become stiff and sickle-shaped, which can lead to a range of symptoms and complications. The severity of these symptoms can vary widely among individuals, depending on factors such as the number of sickle cells in the blood and the degree of anemia.

Some of the most common symptoms and complications of sickle cell anemia include:

• Pain: The sickle-shaped cells can become trapped in blood vessels, leading to reduced blood flow and oxygen supply to various parts of the body, causing severe pain crises. These painful episodes can affect the bones, joints, and other tissues, and can last for several hours to several weeks.
• Anemia: Sickle cell anemia can cause a chronic shortage of red blood cells, leading to anemia, a condition in which the body doesn’t have enough red blood cells to carry oxygen to the body’s tissues. This can cause fatigue, weakness, and shortness of breath.
• Increased Risk of Infections: Sickle cells can damage the spleen, an organ that helps filter out bacteria and other harmful substances from the blood, leading to increased risk of infections, particularly from certain types of bacteria.
• Delayed Growth and Development: Sickle cell anemia can interfere with the normal growth and development of children, and can cause delayed puberty and delayed onset of menstruation in girls.
• Eye Problems: Sickle cell anemia can cause damage to the blood vessels in the retina, leading to vision problems and even blindness.
• Pulmonary Complications: Sickle cell anemia can cause a variety of respiratory problems, including acute chest syndrome, a condition similar to pneumonia that can be life-threatening.
• Stroke: Sickle cell anemia can increase the risk of stroke, particularly in children.
• Organ Damage: Over time, the sickle-shaped cells can cause damage to various organs in the body, including the liver, kidneys, and spleen.

Diagnosis of sickle cell anemia

Sickle cell anemia is typically diagnosed through a combination of physical exams, laboratory tests, and genetic testing. The diagnosis is important to help manage symptoms and prevent complications associated with the condition.

Here are some of the methods used to diagnose sickle cell anemia:

• Blood tests: Blood tests can be used to check the levels of hemoglobin and other blood components. In individuals with sickle cell anemia, the levels of hemoglobin are typically low, and the blood may also contain a higher than normal number of immature red blood cells.
• Sickle Cell Screening: A sickle cell test can be done to check if an individual has the sickle cell trait or sickle cell anemia. The test involves collecting a small sample of blood and examining it under a microscope to look for sickle-shaped cells. This test can be performed at birth as part of routine newborn screening in many countries.
• Hemoglobin Electrophoresis: This test can determine the type of hemoglobin present in the blood, including the presence of abnormal hemoglobin S. The test involves separating different types of hemoglobin by electrical charge, which allows for the detection of abnormal hemoglobin.
• DNA Testing: Genetic testing can be used to confirm a diagnosis of sickle cell anemia and determine the specific genetic mutation responsible for the condition. This type of testing is particularly useful in cases where the diagnosis is unclear or in families with a history of the condition.
• Prenatal Testing: Prenatal testing can be used to detect sickle cell anemia in a developing fetus. Testing can be done through chorionic villus sampling (CVS) or amniocentesis, which involve sampling cells from the placenta or amniotic fluid respectively.

If a diagnosis of sickle cell anemia is confirmed, healthcare professionals will provide guidance on managing symptoms and preventing complications, such as regular blood transfusions or stem cell transplantation. In addition, genetic counseling may be recommended for families to discuss the implications of the diagnosis and inheritance patterns.

What are Sickle Traits?

Sickle cell trait is a genetic condition in which an individual inherits one copy of the sickle hemoglobin gene and one normal hemoglobin gene. Unlike sickle cell anemia, in which an individual inherits two copies of the sickle hemoglobin gene, sickle cell trait usually does not cause any health problems.

Individuals with sickle cell trait are typically asymptomatic and have normal hemoglobin levels, but they can pass the sickle hemoglobin gene on to their children. However, under certain circumstances, sickle cell trait can lead to complications.

Here are some of the factors that can increase the risk of complications in individuals with sickle cell trait:

• Extreme Physical Exertion: Intense exercise, such as marathon running, can cause dehydration and changes in blood flow, which can lead to the sickling of red blood cells and the release of myoglobin, a protein that can damage the kidneys.
• High Altitude: At high altitudes, there is less oxygen in the air, which can trigger sickling of red blood cells and cause complications such as pain crises.
• Surgery and Anesthesia: General anesthesia and surgery can be stressful on the body, and can increase the risk of complications such as blood clots.
• Pregnancy: Women with sickle cell trait can have an increased risk of certain pregnancy-related complications, such as pre-eclampsia and preterm delivery.
• Infections: In rare cases, individuals with sickle cell trait can be at increased risk of certain infections, such as severe pneumococcal disease.

Global Prevalence of Sickle Cell Anemia

Sickle cell anemia is a genetic blood disorder that is most common among people of African descent, although it can also affect people from other ethnic groups, including those of Hispanic, Middle Eastern, and Mediterranean origin.

Here are some key facts about the global prevalence of sickle cell anemia:

• The World Health Organization estimates that sickle cell anemia affects approximately 300,000 to 400,000 babies born each year worldwide.
• The majority of individuals with sickle cell anemia live in sub-Saharan Africa, where the prevalence of the condition is highest. An estimated 60% to 80% of all cases of sickle cell anemia occur in Africa.
• Sickle cell anemia is also common in other regions of the world, including parts of India, the Middle East, and the Caribbean. In these regions, the prevalence of sickle cell anemia is generally lower than in sub-Saharan Africa.
• In the United States, sickle cell anemia affects approximately 100,000 individuals, most of whom are of African descent. The condition is also relatively common among people of Hispanic, Middle Eastern, and Mediterranean origin.

• The global prevalence of sickle cell anemia is expected to increase in the coming years due to factors such as population growth, urbanization, and increased migration. However, improved screening, early diagnosis, and access to appropriate treatment can help to reduce the burden of the condition and improve outcomes for affected individuals.
• Overall, sickle cell anemia is a significant public health concern, particularly in regions where it is highly prevalent. Efforts to raise awareness about the condition, increase access to screening and diagnostic services, and improve care and treatment for affected individuals are critical to reducing the impact of sickle cell anemia on individuals, families, and communities worldwide.

Current Research and Future Directions for Sickle Cell Anemia

Research on sickle cell anemia is ongoing, with a focus on developing new treatments, improving outcomes for affected individuals, and ultimately finding a cure for the condition. Here are some recent advances and future directions in sickle cell anemia research:

• Gene Therapy: One promising approach to treating sickle cell anemia is gene therapy, which involves modifying the patient’s own stem cells to produce normal hemoglobin. In 2019, the US Food and Drug Administration approved the first gene therapy for sickle cell anemia, called Zynteglo. Clinical trials are ongoing to further evaluate the safety and efficacy of gene therapy for sickle cell anemia.
• New Drug Therapies: Several new drug therapies are being developed for sickle cell anemia, including medications that can help to reduce the frequency and severity of pain crises, prevent complications such as strokes and organ damage, and improve overall quality of life for affected individuals. One example is voxelotor, a drug that can increase the amount of oxygen that hemoglobin can carry, which was approved by the FDA in 2019.
• Precision Medicine: There is growing interest in using precision medicine approaches to tailor treatments to the individual needs of patients with sickle cell anemia. This could involve using genetic testing to identify specific mutations that are causing the disease, and developing personalized treatment plans based on these findings.
• Improved Screening and Diagnosis: Early diagnosis and treatment are critical to improving outcomes for individuals with sickle cell anemia. Efforts are underway to improve screening and diagnostic tools, particularly in regions where the condition is highly prevalent.
• Patient-Centered Research: There is a growing emphasis on involving patients and families in the research process, to ensure that research is focused on the needs and priorities of those most affected by sickle cell anemia.

References

- https://www.sicklecelldisease.org/research-and-treatment/

- https://www.nhlbi.nih.gov/health-topics/sickle-cell-anemia

- https://www.fda.gov/news-events/press-announcements/fda-approves-gene-therapy-patients-sickle-cell-disease

Hsieh MM, Kang EM, Fitzhugh CD, et al. Allogeneic hematopoietic stem-cell transplantation for sickle cell disease. N Engl J Med. 2009;361(24):2309-2317. doi:10.1056/NEJMoa0904971