ADAMTS13 and congenital thrombotic thrombocytopenic purpura: Congenital TTP has been reported to be associated with severe deficiency of the plasma activity of ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type I domain 13), which is reduced to <5% of normal by mutation of the ADAMTS13 gene, and this is known as the Upshaw–Schulman syndrome (USS) [1,2].