VWF and congenital thrombotic thrombocytopenic purpura: Hereditary thrombotic thrombocytopenic purpura (hTTP), also known as Upshaw–Schulman syndrome, is a rare genetic disorder caused by mutations in the ADAMTS13 gene that leads to decreased or absent production of the plasma von Willebrand factor (VWF)-cleaving metalloprotease ADAMTS13.