Its activity is often <10% in TTP, and can be used to distinguish between typical and atypical HUS; notably, atypical HUS often exhibits a high level of serum ADAMTS13.[5] Herein, we have described a patient who had anemia, thrombocytopenia, and acute kidney failure, as well as absence of diarrhea, absence of E coli or other pathogens on stool culture, and serum ADAMTS13 activity of 49.4%. The gene discussed is ADAMTS13; the disease is thrombotic thrombocytopenic purpura.