TBL Sickle Cell flashcards

Question 1

Hb polymerization

Answer 1

In hypoxic environment HbS molecules precipitate as tactoids (long array of 14-strand helical polymers) and cause Heinz bodies. Form when Hb is in deoxygenated T-state.

Question 2

How HbS causes vaso-occlusion (3)

Answer 2

1. Sickle HbS RBCs stick to endothelial cells in capillaries and RBCs releases contents, including polymers. 2. Ruptured contents activte blood coagulation cascade and endothelial cells which leads to inflammation 3. Vessels with trapped cells occluded (involves leukocyte and RBC adhesion, ischemia, infarction leading to tissue damage from necrosis)

Question 3

Sickle cell and the brain

Answer 3

Peak incidence in children <7—have much greater risk of stroke

Question 4

Sickle cell inheritance

Answer 4

Autosomal recessive disease

Question 5

Sickle cell trait

Answer 5

Carriers with minimal clinical problems. May develop sickle cell crisis if extremely hypoxic.

Question 6

Sickle cell trait balanced polymorphism

Answer 6

Survival advantage for malaria because parasitized red cells become sequestered in hypoxic areas of liver and spleen. If these cells sickle they are destroyed by reticuloendothelial cells which destroys motile feeding stage of parasites (trophozoites).

Question 7

Solubility test for SCD

Answer 7

Blood added to solution with high ionic strength. Deoxyhemoglobin S has low solubility (will appear cloudy) but deoxyhemoglobin A is stable (not cloudy). Cannot distinguish trait from disease.

Question 8

Hemoglobin electophoresis

Answer 8

Separate proteins based on migration in electric field based on charge, mass, and shape. Does not use SDS or protein denaturation so Hb molecules migrate in 4 globin chains. Use agarose gel and buffer at pH 6.0 (can separate based on AA content). Sickle cell mutation causes loss of 2 negative charges. Gel can be scanned to look for AUC.

Question 9

SDS

Answer 9

Negatively charged detergent which coats proteins with negative charge prior to electrophoresis

Question 10

RFLP

Answer 10

More sensitive than electrophoresis alone. Uses restriction endonucleases (like MstII) to cleave specific sites within DNA sequences. Longer fragments if mutation (didn’t get cleaved). Followed by electrophoresis.

Question 11

2 groups with high prevalence of SCD

Answer 11

1. African-Americans 2. Native Americans

Question 12

3 treatments for SCD

Answer 12

1. Partial-exchange transfusion (could cause iron overload) 2. Bone marrow transplantation 3. Induction of fetal Hb synthesis (higher HbF results in milder symptoms and inhibit sickling) like with Hydroxyurea