Congenital thrombotic thrombocytopenic purpura (cTTP; Upshaw-Schulman syndrome) is an ultra-rare disorder caused by severe deficiency of ADAMTS13, the metalloprotease responsible for cleaving ultra-large von Willebrand factor (UL-VWF) multimers. The gene discussed is ADAMTS13; the disease is congenital thrombotic thrombocytopenic purpura.