Congenital thrombotic thrombocytopenic purpura in association with a mutation in the second CUB domain of ADAMTS13

Abstract

Severe deficiency of the von Willebrand Factor (VWF)–cleaving proteinase, ADAMTS13, is associated with the development of thrombotic thrombocytopenic purpura (TTP). Several mutations spread across the ADAMTS13 gene have been identified in association with a deficiency of VWF-cleaving proteinase activity in patients with congenital TTP. The spread of these dysfunctional mutations and the domain structure of ADAMTS13 are suggestive of a complex interaction between the enzyme and its substrate. We have studied a patient with congenital TTP who is a compound heterozygote for the Thr196Ile mutation in the metalloproteinase domain and a frameshift mutation (4143-4144insA) in the second CUB domain that results in loss of the last 49 amino acids of the protein. The VWF-cleaving proteinase activity of the truncated enzyme was comparable to that of the wild-type enzyme but its secretion from transfected COS-7 cells was about 14% of the wild type.