Hb disease Flashcards
Hb abnormal types
HbS, HbC, HbE, HbCS, HbH (HbH disease, HbH Barts)
HbS
predominant in people with “sickle cell” disease
Glu–Val position 6
HbC
Glu–Lys position 6
HbC precipitates as crystals → ↑ RBC rigidity and ↓ deformability → extravascular hemolysis
β-globin mutation (glutamate replaced by lysine)
HbC is less soluble than HbA and tends to form hexagonal crystals, which lead to RBC dehydration (↑ MCHC).
RBCs have reduced oxygen-binding capacity and a shorter lifespan.
HbE
Glu–Lys
alternating splicing codon 26
HbCS
long alpha globin chain—causes alpha thalassemia
HbH
3 alpha globin genes deleted, leaving 4 beta globin chains
HbH disease vs HbH barts
HbH disease: bbbb
HbH barts: yyyy
3 reasons for defects in the Hb gene that cause abnormal hemoglobin and anemia
- Structural defects in the Hb (maybe due to mutational change in the amino acid residue …like sickle cell anemia)
- Reduced production of one of two subunits of Hb (all 4 subunits of Hb are required for proper function ie. thalassemia’s)
- Abnormal association of Hb subunits: paucity of one subunit leads to association of same subunits and inactive functioning of Hb leading to anemia ie alpha-thalassemia
Normal Hb types
Hb A- Normal Hb that exists after birth. It’s a tetramer with 2 alpha and 2 beta subunits
Hb A2- Less than 3% of Hb found in red cells after birth that consists of 2 alpha and 2 delta chains
Hb F- predominant during Fetal development and consists of 2 alpha and 2 gamma subunits.
Types of Thalassemia
- Beta thalassemia, which includes the subtypes Major and Intermedia
- Alpha thalassemia, which include the subtypes hemoglobin H and hydrops fetalis
- thalassemia minor
Anemia
A decrease in the number of circulating red blood cells (RBC), represented by a reduction in hemoglobin concentration (Hb), hematocrit (Hct), or RBC count. May be due either to inadequate RBC production, excessive RBC destruction, or blood loss.
