ADAMTS13 and systemic sclerosis: ADAMTS13, which cleaves unusually large (and hyperreactive) von Willebrand factor (ULVWF) released from activated endothelial cells to smaller and less active forms, is a metalloproteinase involved in von Willebrand factor coagulation and platelet activation pathways, and is possibly related to the vasculopathy and endotheliopathy present in SSc 23,24.