Sickle Cell Anemia

Front 1

Globin gene and dev.hemoglobin

Back 1

1. Chromosome 16: alpha globin gene zeta, alph1, alpha 2

2. Chromosome 11: beta globin gene: episilon, gamma, delta, beta

1. embryonic hemoglobin:
(a) zeta2epsilon2 OR zeta2gamma2
2. HbF: alpha2gamma2
3. HbA1 (98%): alpha2beta2
4. HbA2 (2%): alpha2delta2
*adult RBC has some HbF

HbC: beta6glu -> lys
- in low O2 environment, form cyrstalloids

HbS: beta 6glu ->val

Front 2

HbS

Back 2

HbS: beta 6glu ->val
(a) hydorphobic patch form at mutation site
(b) low O2 environment, HbS aggregate into tactoid.
(c) tacoid: long hemoglobin polymer when hemoglobin in T state -> damage RBC membrane (heinz bodies) --> sickle shape
- not pass freely through microciruculation and become trapped and stick to endothelia cells
- trapped and damaged RBC release cellular contents including polymerize hemoglobin -> activation of coagulation and vascular endothelial cell -> inflammation.
(d) consequences:
- hemolysis: due to membrane disruption and adhesions to endothelial surfaces --> anemia
- vaso-occlusions: involves endothelial activaiton, leukocyte and red cell adhesion, ishemia and infarction leading to tissue damage from necrosis
- affect organs esp. with large blood supply: liver, spleen, kidney
- hyperbilirubinemia (bilirubin accumulation in plasma), heptaomegaly (impaired live function, cardiomegly.

Front 3

Sickle cell mutation - autosomal recessive

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1. homozygous - SS: sickle cell disease
2. heterozygous: sickle cell trait (AS):
- not devleop sickle cell crises unless very hypoxis
- balanced polymorphism: survival advantage: parasitized REB sequestere in hypoxic areas of liver and sleepn, cells sickle, destryed by reticuloendotheliall and motile feeding stage of parasties.
3. heterozygous AA: no malaria protect

Front 4

diagnosis of sickle cell

Back 4

(1). initial: symptoms/liquid chromatography assay (show pt's hemoglobin has different charges, and thus mutation
(2). solubility test
- blood add to high ionic solution
- deoxuhemoglobin S has low solubilty and deoxyhemoglobin A is soluble
- precipitation --> difference in solubility but cannot distinguish trait form disease.
(3). hemoglobin eletrophoresis
- definitive diagnosis
- lysed REB use citrate buffer at pH6.0, Hb can be separated byed on aa contact and mass
- S mutation -> loss of two negative charges (glu- val) -> move slower
- HbF -> lower mass -> move faster than HbA
- HbC -> more positive and bigger than HbA HbS HbF
- quantificaiton of A:S

Front 5

II

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4). DNA analyses (restriction fragment length polymorphism)
- sensitive test for little bit of cell from amniotic fluid
- based on ability of restriction endonuclease to cleave specific sites in DNA
- if cleavage site contains mutation, resitrction endonucleases can no longer cleave -> larger DNA fragment to normal sequence
- electrophoresis after DNA cleavage: AA, single band with faster movement, AS two bands, SS one back

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Distribution of Sickle cell

Treatment

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US: African American, second largest Native American

Treatment:
1. partial exchange transftion: used selectively due to complicaiton of iron overload (transuison -induced hemosidrosis --> no excretory pathway in body for elimination excess iron -> organ failure

2. bone marrow transplantiaon : repopulate bone marrow tih normal donor cells
3 induciton of fetal Hb syntehsis
- RBC wtih HbF and HbS survive longer than only with HbS), higher HbF have milder symptoms
- HbF inhibit sickling - RBC not deformed, no vaso occlusive crsies
- hydroxyurea increase expression of fetal hemoglobin - determine efficacy of using HU in chidlren with sickle cell