Thrombotic Thrombocytopenic Purpura (TTP) is associated with formation of microthrombi in the microcirculation. A deficiency in the protein ADAMTS13 has been found in patients with TTP and is believed to be fundamental in its pathogenesis.


Features of ADAMTS13:

(1) acronym for " A D istinegrin A nd M etaloprotease with T hrombo S pondin Type 1 motif"

(2) The protein is a protease that degrades unusually large von Willebrand Factor (vWF) multimers. Left intact these multimers bind platelets to form microthrombi that lodge in the micro-circulation.

(3) The activity of ADAMTS13 can be measured using an ELISA assay that measures binding of degraded vWF to collagen.


Causes of a deficiency in ADAMTS13 activity:

(1) familial, associated with a genetic mutation in the protein (homozygous patients may have spontaneous and recurrent episodes of TTP)

(2) acquired, associated with a functional inhibitor


Features of TTP associated with a deficiency of ADAMTS13:

(1) presence of vWF-rich microthrombi

(2) thrombocytopenia, microangiopathic hemolytic anemia and organ dysfunction

(3) deficiency in ADAMTS13 activity

(4) clinical improvement with increased ADAMTS13 activity, typically achieved by plasma exchange (removes inhibitors) replaced with fresh frozen plasma or cryoprecipitate (replaces ADAMTS13)


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