Flashcards in Hemoglobinopathies Deck (11):
On what chromosome is the alpha globin gene cluster located?
On what chromosome is the beta globin gene cluster located
What is the amino acid substitution that causes sickle cell disease?
Glutamic acid (hydrophilic) changed to valine (hydrophobic)
What is the amino acid substitution that causes HbC (mild sickle cell disease)?
Glutamic acid changed to lysine
How is sickle cell disease diagnosed?
(1) Hb electrophoresis
(2) Molecular detection of HbS and HbC mutant alleles
What are four forms of therapy for sickle cell disease?
(1) Preventative - penicillin prophylaxis, vaccination, avoidance of hypoxia
(2) Hydroxyurea - induce HbF production
(3) Chronic RBC transfusion
(4) Analgesics for pain
What does α thalassemia result from?
Gene deletion on chromosome 16
What does β thalassemia result from?
Point mutation on chromosome 11
What are the consequences of varying numbers of α gene deletions?
(1) αα/α- - silent carrier
(2) αα/-- or α-/α- - α-thalassemia trait (mild anemia, microcytosis)
(3) α-/-- - HbH disease (β4, moderate to severe hemolytic anemia)
(4) --/-- - Hydrops fetalis, homozygous α thalassemia (Hb Bart's: γ4)
What is the clinical presentation of β thalassemia?
(1) Microcytic anemia
(2) Target cells on histology from central blebbing due to low Hb and RBC deflation
(3) Crewcut appearance on x-ray and chipmunk facies from extramedullary hematopoiesis