Genetic mutations are associated with both disorders: in TTP the ADAMTS13 gene, the vWF cleaving protease, is affected, and in HUS several complement genes are mutated.
Important recent molecular and genetic insights into the pathogenesis of the three types of MPGN, of typical and atypical HUS and of TTP, i.e. dysregulation of the complement system, distinct molecular defects in C3 and factor H, the major regulatory protein of the alternative pathway of complement activation, and deficiency of a von Willebrand factor (VWF) -cleaving protease, i.e.ADAMTS13, are highlighted.
Decreased von Willebrand factor (VWF)-cleaving protease activity (<5%) has been implicated in patients with congenital thrombotic thrombocytopenic purpura-hemolytic uremic syndrome (Upshaw-Schulman syndrome) and associated with mutations within the ADAMTS13 gene.
Recent studies on the relationship between UL-vWFMs and vWF-CPase, together with its autoantibody (inhibitor) have brought about a clear discrimination between thrombotic thrombocytopenic purpura and hemolytic uremic syndrome.
Patients with thrombotic thrombocytopenic purpura (TTP) have a deficiency of von Willebrand factor (vWF)-cleaving protease, whereas patients with hemolytic-uremic syndrome (HUS) show normal activity of this protease.
In vitro proteolytic degradation of von Willebrand factor by the protease was studied in 5 patients with familial and 7 patients with nonfamilial hemolytic-uremic syndrome and was normal in all 12 patients.
In some variants of type 2A vWF, the cleavage site in the vWF subunit is more susceptible to proteolytic degradation than in normal vWF, whereas in patients with TTP or HUS the protease activity may be suppressed. vWF-degrading protease plays an important role in pathogenesis of congenital or acquired disorders of hemostasis and thrombosis.