Thrombotic disorders Flashcards
Briefly describe the 5 major causes of hereditary
thrombophilia (blood forms clots easily)
• Deficiency of naturally occuring anticoagulants:
- antithrombin (AT)
- Protein C
- Protein S
• Factor V Leiden (FVL)
• Prothrombin Gene Mutation (G20210A)
a) background on Antithrombin (function, mechanism)
b) pathophysiology Antithrombin deficiency (hereditary thrombophilia)
a) AT inhibits serine proteases: targets activated II (thrombin), X, IX, XI, XII. & enhanced by heparin
b) mutation in reactive site &/ Heparin binding = dec activity = thrombophilia
Lab Ix/test of Antithrombin deficiency (hereditary thrombophilia)
*functional-heparin co-factor assay (for Type 2 def)
- Pt plasma mixed w/ heparin & thrombin
- clot based assay
- residual thrombin activity
• Antigenic: ELISA or latex agglutination (for Type 1 def)
Describe the protein C / protein S system
Contains:
• Protein C (PC): Vit K dependent >aPC inactivates FVa/FVIIIa
• Protein S (PS): Vit K dependent
• Thrombomodulin (TM) on Endoth.C > binds free thrombin & changes thrombin substrate specificity
• Endothelial Protein C Receptor (EPCR) on EC > binds to PC
describe the activity assays of protein C
- *Chromogenic assay: not detect PC w/ abnormal PL / Ca2+ binding
- Clot-based (aPTT): normal plasma prolonged time vs PC def. plasma has normal time (unreliable to chrome. assay)
list 3 the assays of protein S
- *Free PS antigenic assay
- Total PS antigenic assay
- PS functional assay
Describe the 3 types of deficiency in PS
T1: Normal PS but dec no. made = dec Ag lvl & functional PS
T2: Normal PS w/ dec functional activity = normal Ag lvl & dec functional lvls
T3: Dec free PS Ag, normal TOTAL PS Ag
PC and AT have 2 types of deficiencies, what are they
T1: dec Ag lvl of functional protein
T2: normal Ag lvls of protein w/ dec function
a) Describe the prothrombin gene mutation (G20210A)
b) type of testing it’s ID
- mutation in 3’ UTR of F2 gene = inc stability of F2 mRNA
- (hetero) elevated plasma prothrombin => inc thrombin generation
b) molecular testing
a) describe how factor V is activated
b) describe how factor V is INactivated
a)Thrombin of fXa cleave fV = remove B-domain
+ Remaining peices of fV joined by Ca2+ = fVa
b) (w/out PS) aPC cleaves afV at 506, 306, 679 aa. OR (w/ PS) aPC can cleave 306aa (skip 506)
how can PS & fV act as co-factor for aPC (> inhibit factor VIII)
fV is cleaved at aa506 AND fV retains C-terminal portion of B-domain
*note FVL NOT act as aPC co-factor
describe Factor V Leiden (FVL)
- mutation in F5 = changes aa (Arg->Glut) @ 506 in fV protein
- aPC doesn’t recognise Glut @ 506 so not cleaved
=> aFVL will be inactivated by aPC @ slower rate than fVa
Lab Ix/test of Factor V Leiden (hereditary thrombophilia)
Molecular testing OR aPC resistance test
Briefly describe the APC resistance test and how it can be modified to specifically measure FV Leiden or other causes of APC resistance
- sample is diluted in fV deficient plasma
- diluted sample is tested for aPTT, w/ & w/out addition of aPC
- WT fV: clotting time is prolonged when aPC is added
- FVL: time is NOT prolonged bc fVL is more slowly activated by aPC
Briefly describe the pathogenesis of heparin-induced thrombocytopenia (HIT)
- activated plt release PF4 from alpha granule
- PF4 + heparn => PF4-heparin complex
3*. complex recognised as foreign => Aby made - Aby bind to complex => activate plts = aggregation
- HIT => thrombosis
OR
*3. complex binds to a monocyte = release tiss. factor - activate endothelial cells = express TF
- HIT => thrombosis
