Severe ADAMTS13 deficiency (the VWF cleaving protease) causes accumulation of ultra-large vWF multimers (ULVWF) that can lead to the clinical picture of thrombotic microangiopathy as seen in its most severe form in thrombotic thrombocytopenic purpura (TTP) [34]. This evidence concerns the gene ADAMTS13 and thrombotic microangiopathy.