Thrombotic thrombocytopenic purpura (TTP), caused by a genetic or autoimmune‐driven lack of ADAMTS‐13 activity, leads to high levels of the ultra‐large von Willebrand factor (VWF) multimers produced by endothelial cells, causing excess platelet recruitment into forming thrombi, often with mortal consequences. The gene discussed is ADAMTS13; the disease is thrombotic thrombocytopenic purpura.