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Questions and Answers
What is typically observed in a patient with Thalassemia Minor?
What is typically observed in a patient with Thalassemia Minor?
Which laboratory finding reflects a bone marrow response to hemolysis?
Which laboratory finding reflects a bone marrow response to hemolysis?
Which of the following findings is NOT associated with Homozygous β-Thalassemia?
Which of the following findings is NOT associated with Homozygous β-Thalassemia?
What does the Alkali Denaturation Test primarily measure?
What does the Alkali Denaturation Test primarily measure?
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What is a common symptom of Hb H disease?
What is a common symptom of Hb H disease?
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Which of the following findings is associated with a low MCHC?
Which of the following findings is associated with a low MCHC?
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In which condition may reticulocyte counts reach 5-10%?
In which condition may reticulocyte counts reach 5-10%?
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Which hemoglobin variant test differentiates RBCs based on their resistance to elution?
Which hemoglobin variant test differentiates RBCs based on their resistance to elution?
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What is a distinguishing characteristic of Hgb H disease?
What is a distinguishing characteristic of Hgb H disease?
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Which condition is characterized by the deletion of one alpha gene?
Which condition is characterized by the deletion of one alpha gene?
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What is one possible symptom of Hgb S/Beta-thalassemia?
What is one possible symptom of Hgb S/Beta-thalassemia?
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Which population is most likely to exhibit Hgb S/Alpha-thalassemia?
Which population is most likely to exhibit Hgb S/Alpha-thalassemia?
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What laboratory finding is often associated with Hgb C/Beta-thalassemia?
What laboratory finding is often associated with Hgb C/Beta-thalassemia?
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What is a common feature of patients with Hgb E/Beta-thalassemia?
What is a common feature of patients with Hgb E/Beta-thalassemia?
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What is indicated by a low reticulocyte count in patients with Hgb S/Alpha-thalassemia?
What is indicated by a low reticulocyte count in patients with Hgb S/Alpha-thalassemia?
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What laboratory method might be necessary to diagnose a Silent Carrier of Alpha-thalassemia?
What laboratory method might be necessary to diagnose a Silent Carrier of Alpha-thalassemia?
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What is the primary characteristic of individuals with sickle cell trait?
What is the primary characteristic of individuals with sickle cell trait?
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Which hemoglobin variant is characterized by lysine replacing glutamic acid at position 6 on both beta chains?
Which hemoglobin variant is characterized by lysine replacing glutamic acid at position 6 on both beta chains?
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Which symptom is typically absent in individuals with heterozygous Hgb C trait?
Which symptom is typically absent in individuals with heterozygous Hgb C trait?
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What is a common laboratory finding in individuals with Hemoglobin C disease?
What is a common laboratory finding in individuals with Hemoglobin C disease?
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Which population has the highest prevalence of Hemoglobin C disease?
Which population has the highest prevalence of Hemoglobin C disease?
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In patients with Hemoglobin SC disease, which percentage of Hemoglobin is typically Hgb S?
In patients with Hemoglobin SC disease, which percentage of Hemoglobin is typically Hgb S?
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What is the expected hemoglobin composition in individuals with Homozygous Hemoglobin C disease?
What is the expected hemoglobin composition in individuals with Homozygous Hemoglobin C disease?
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What tests are used to differentiate between Hemoglobin variants?
What tests are used to differentiate between Hemoglobin variants?
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Study Notes
Hemoglobinopathies
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Inherited disorders causing structurally abnormal globin chains
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Qualitative defects due to amino acid substitutions
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Changes in red blood cell (RBC) deformability and electrophoretic mobility can occur
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Homozygous condition (both globin chains affected) is more serious than heterozygous (only one globin chain affected)
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Target cells are associated with hemoglobinopathies
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Diagnosis confirmed via hemoglobin electrophoresis, isoelectric focusing, or DNA analysis
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Hgb S formation (most common amino acid substitution) is the most common cause
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Hgb C (second) and Hgb E (third) are also common
Sickle Cell Disease (Hgb SS)
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Valine replaces glutamic acid at position 6 on both beta chains
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Results in decreased hemoglobin solubility and function
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Defect inherited from both parents
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Primarily present in sub-Saharan Africa (64.4%)
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Other regions include Arab-India (22.7%), The Americas (7.4%), Eurasia (5.4%), and Southeast Asian (0.1%)
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Approximately 230,000 babies are born with sickle cell disease in sub-Saharan Africa each year
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Production of Hgb A is absent with ~80% Hgb S and 20% Hgb F compensation
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Hgb insolubility results in crystallization within erythrocytes, creating characteristic sickled shapes
Sickle Cell Trait (Hgb AS)
- Valine replaces glutamic acid at position 6 on one beta chain
- Inherited from one parent
- Produces approximately 60% Hgb A and 40% Hgb S
- Common hemoglobinopathy in the USA
Hemoglobin C Disease (Hgb CC)
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Lysine replaces glutamic acid at position 6 on both beta chains
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Inherited from both parents
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Found in African Americans (2-3%) and West Africans (17-28%)
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Approximately 90% Hgb C, 2% Hgb A2 and 7% Hgb F
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Mild anemia is possible
Hemoglobin C-Harlem (Hgb C-George town)
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Double substitution on beta chain (Valine for glutamic acid at position 6 and aspartic acid for asparagine at position 73)
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Heterozygous forms are asymptomatic
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Compound heterozygosity (HbS and HbC-Harlem) is similar to Hgb SS disease
Hemoglobin SC Disease
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Abnormal sickle gene from one parent and abnormal C gene from the other parent
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Glutamic acid replaced by valine in one beta chain, and by lysine in the other
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Common in West African, Mediterranean and Middle Eastern populations
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Approximately 50% Hgb S and 50% Hgb C are produced
Hemoglobin E (HbEE)
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Lysine replaces glutamic acid at position 26 on the beta chain
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Common in Southeast Asian, African, and African-American populations
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Homozygous form results in mild anemia with microcytes and target cells
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Heterozygous forms are usually asymptomatic
Hemoglobin D
- Glycine replaces glutamic acid at position 121 on the beta chain
- Found predominantly in Middle Eastern and Indian populations
- Most variants are named for the region of discovery.
- Homozygous and heterozygous forms are usually asymptomatic
Hemoglobin G
- Lysine replaces asparagine at position 68 in alpha chain
- Common variant in African-Americans
Hemoglobin M
- Point mutations in alpha or beta globin genes result in methemoglobin production
Hemoglobin-Arab
- Lysine replaces glutamic acid at position 121
- In Kenya, Israel, Egypt, and Bulgaria; it represents a prevalence of 0.4% in African-Americans
- No clinical symptoms; only mild splenomegaly in homozygotes
Thalassemias
- Group of inherited disorders characterized by a decreased rate of synthesis of normal globin chains.
- Grouped by affected globin chains:
- Alpha Thalassemias
- Beta Thalassemias
- Varying severity in affected population, ranging from asymptomatic conditions to severe transfusion-dependent disease.
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Description
Explore the inherited disorders of hemoglobin such as sickle cell disease. This quiz covers the structural abnormalities of globin chains, methods of diagnosis, and geographic prevalence. Test your knowledge on the qualitative defects related to hemoglobinopathies and their implications.
