VWF and congenital thrombotic thrombocytopenic purpura: Upshaw–Schulman syndrome (USS) is an ultrarare but life-threatening autosomal recessive disease characterized by the absence or a severe deficiency of plasma von Willebrand factor (vWF)-cleaving protease; this results in the abnormal presence of ultralarge vWF multimers and subsequent platelet adhesion to these vWF multimers, leading to the formation of circulating platelet microthrombi [1–3].