Thalassemia and Sickle Cell Anemia

Vocabulary flashcards covering quantitative hemoglobinopathies (alpha- and beta-thalassemias) and qualitative hemoglobin variants (HbS, HbC, and HbE), including genetic mutations, clinical findings, peripheral blood morphology, and electrophoretic patterns.

Quantitative Hemoglobin Defect

A genetic abnormality resulting in reduced or absent synthesis of structurally normal globin chains (such as in thalassemias), typically producing microcytic hypochromic red blood cells.

Qualitative Hemoglobin Defect

A genetic mutation that produces structurally altered globin chain variants (such as HbS, HbC, or HbE), typically presenting as normocytic normochromic red blood cells.

Hemoglobin Electrophoresis (pH 8.6)

An alkaline laboratory assay used as a confirmatory test to separate and quantify normal and variant hemoglobin molecules based on their electrical charges.

Alpha-Thalassemia Major

The most severe form of alpha-thalassemia characterized by deletion of all four $\alpha$-globin genes, leading to an absence of functional adult or fetal hemoglobin and resulting in fatal hydrops fetalis with high concentrations ($80\text{--}90\%$) of Hb Bart.

Hemoglobin Bart (Hb Bart)

An abnormal hemoglobin tetramer composed of four gamma chains ($\gamma_4$) that has an extremely high affinity for oxygen, preventing oxygen release to fetal tissues and causing severe hypoxia.

Hydrops Fetalis

A condition associated with alpha-thalassemia major manifesting as massive edema, severe abdominal swelling, and liver enlargement, leading to fetal demise in utero or death within hours of birth.

Alpha-Thalassemia Intermedia (Hemoglobin H Disease)

A clinical condition resulting from the deletion of three of the four $\alpha$-globin genes, presenting with microcytic hypochromic anemia, hemoglobin levels of $8\text{--}10\text{ g/dL}$, target cells, hepatosplenomegaly, and chronic hemolysis.

Hemoglobin H (HbH)

An unstable, high-affinity hemoglobin tetramer formed by excess beta chains ($\beta_4$) in alpha-thalassemia intermedia that precipitates in red blood cells and precipitates chronic hemolytic episodes.

"Golf Ball" Appearance

The distinctive stippled appearance of erythrocytes when unstable HbH precipitates are incubated with supravital stains such as new methylene blue.

Alpha-Thalassemia Minor

A condition caused by the deletion of two of the four $\alpha$-globin genes, presenting with mild microcytic hypochromic red blood cells, hemoglobin levels $> 10\text{ g/dL}$, few target cells, and an essentially asymptomatic clinical course.

Silent Carrier (Alpha-Thalassemia)

An asymptomatic state caused by the loss of one $\alpha$-globin gene out of four, resulting in normal hemoglobin synthesis and no detectable abnormal bands on electrophoresis.

$\beta^0$ Allele

A mutant allele of the beta-globin gene on chromosome 11 characterized by the complete absence of $\beta$-chain synthesis.

$\beta^+$ Allele

A mutant allele of the beta-globin gene on chromosome 11 that results in a partial reduction or block in $\beta$-chain synthesis.

$\beta^{SC}$ Allele

A silent-carrier beta-globin allele on chromosome 11 in which $\beta$-chain synthesis is only minimally affected.

Beta-Thalassemia Major (Cooley's Anemia)

A severe homozygous or compound heterozygous condition ($\beta^0/\beta^0$, $\beta^0/\beta^+$) marked by absent or markedly decreased HbA, elevated HbF and $\text{HbA}_2$, profound microcytic hypochromic anemia ($\text{Hb } 2\text{--}3\text{ g/dL}$), skeletal deformities, and transfusion dependency.

Frontal Bossing

An enlargement and prominence of the forehead resulting from massive expansion of the cranial erythroid bone marrow to compensate for profound anemia in beta-thalassemia major.

"Hair-on-End" Appearance

A classic radiographic finding of the skull in severe beta-thalassemia major caused by trabeculae radiating perpendicularly to accommodate extreme marrow erythroid hyperplasia.

Nucleated Red Blood Cell (nRBC)

An immature, erythroblast-stage red cell seen in peripheral blood during states of severe bone marrow stress and extramedullary hematopoiesis; normal reference interval in peripheral blood is $0\text{ / none}$.

Hemoglobin S (HbS)

A hemoglobin variant generated by a point mutation ($\text{GAG} \rightarrow \text{GUG}$) in the beta-globin gene that substitutes valine for glutamic acid ($\beta\text{ Glu} \rightarrow \text{Val}$).

Sickling Mechanism

The process occurring when deoxygenated HbS molecules polymerize into insoluble fibrous rods at oxygen saturation levels $<85\%$, deforming the red cell into a rigid crescent or sickle shape.

Vaso-occlusion

The obstruction of microvascular capillary beds by rigid, sickled red blood cells, causing acute ischemia, severe tissue pain, inflammation, and potential organ infarction.

Reticulocyte Production Index (RPI) in SCA

A measure of bone marrow erythropoietic response that is characteristically $>2$ in sickle cell anemia, reflecting intact bone marrow compensation for accelerated peripheral hemolysis.

Hemoglobin C (HbC)

A common hemoglobin variant found in West Africa resulting from a point mutation substituting lysine for glutamic acid ($\beta\text{ Glu} \rightarrow \text{Lys}$), causing normocytic normochromic anemia with target cells and folded, irregularly contracted cells.

Hemoglobin E (HbE)

A hemoglobin variant prevalent in Southeast Asia (Burma, Thailand, Cambodia, Malaysia, Indonesia) caused by a $\beta\text{ Glu} \rightarrow \text{Lys}$ point mutation, typically presenting with microcytic hypochromic anemia and numerous target cells.

Erythrocytapheresis

A therapeutic apheresis procedure that selectively extracts rigid sickle cells from the patient's blood while returning normal donor red blood cells to reduce blood viscosity and prevent vaso-occlusion.