Severe deficiency of von Willebrand factor (VWF)-cleaving protease (ADAMTS-13) activity (<5% of normal) is a specific finding for acute idiopathic thrombotic thrombocytopenic purpura (TTP), a disorder that presents as thrombocytopenia, microangiopathic hemolytic anemia, and often organ dysfunction such as neurological disturbances or renal failure, and fever.
In two male sons, this mutation caused a severe (< 3%) deficiency of ADAMTS-13 activity and antigen level, associated with periodic thrombocytopenia, haemolytic anaemia and mild mental confusion.
Initial investigations revealed severe thrombocytopenia, a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) activity level of less than 1%, and strongly elevated D-dimer and lactate dehydrogenase levels.