ADAMTS13 and thrombotic thrombocytopenic purpura: To date, more than 100 mutations in ADAMTS13 have been reported.7 However, mutations in the CUB domains are rare, and how these mutations affect the biosynthesis and function of ADAMSTS13 remains unclear.8 We discovered two novel mutations in the ADAMSTS13 CUB domains in a sibling pair who displayed significantly reduced ADAMTS13 activity, although only the female developed acute TTP episodes.