title: Von Willebrand factor--cleaving protease activity in congenital thrombotic thrombocytopenic purpura.
abstract: Thrombotic thrombocytopenic purpura (TTP) is characterized by microangiopathic haemolytic anaemia (MAHA), thrombocytopenia, fluctuating neurological impairment, renal dysfunction and fever. Both acquired and congenital forms are recognized. Recurrent episodes, which may be predictable (occurring every 21-28 d), are seen in congenital disease and may be treated by infusion with fresh-frozen plasma (FFP). Congenital TTP has recently been associated with deficiency of a novel von Willebrand factor (VWF)-cleaving protease. To investigate whether residual protease activity dictates clinical manifestations, we determined protease activity in three patients with congenital TTP of varying severity. Intrinsic VWF-cleaving protease activity of a range of plasma-derived products was also assessed as one patient had been successfully maintained for many years, initially using an intermediate-purity factor VIII concentrate (Kryobulin) and then cryoprecipitate. All three patients had a severe absolute deficiency of VWF-cleaving protease activity (< 3%) up to 5 months after clinical symptoms. Three relatives were also found to have a mild reduction in protease activity (25-50%). Nevertheless, the intrinsic VWF-cleaving protease activity of plasma-derived products correlated with their clinical efficacy: significant (100%) protease activity was found in FFP, cryosupernatant, solvent-detergent-treated plasma, cryoprecipitate and Kryobulin. Two clinically ineffective factor VIII products (Fahndi and Haemate P) possessed only low protease activity (6.25% and 12.5% respectively). Although this suggests that VWF-cleaving protease activity is central to the pathogenesis of congenital TTP, either small differences in protease activity below 3% or hitherto unknown factors have a profound influence on clinical phenotype. The possible use of factor VIII concentrates in the treatment of this condition also warrants further investigation.
authors.affiliation: Department of Haematology, University College London, London, UK. paul.harrison@ucl.ac.uk
authors.forename: S L
authors.initials: SL
authors.lastname: Allford
authors.forename: P
authors.initials: P
authors.lastname: Harrison
authors.forename: A S
authors.initials: AS
authors.lastname: Lawrie
authors.forename: R
authors.initials: R
authors.lastname: Liesner
authors.forename: I J
authors.initials: IJ
authors.lastname: MacKie
authors.forename: S J
authors.initials: SJ
authors.lastname: Machin
mesh_terms: D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; D003450:Cryoglobulins / Q000627:therapeutic use; D005169:Factor VIII / Q000627:therapeutic use; D006801:Humans; D007223:Infant; D007770:L-Lactate Dehydrogenase / Q000097:blood; D008297:Male; D008666:Metalloendopeptidases / Q000097:blood*; D010976:Platelet Count; D011697:Purpura, Thrombotic Thrombocytopenic / Q000151:congenital* / Q000201:enzymology / Q000628:therapy; D014841:von Willebrand Factor
chemical_list: D003450:Cryoglobulins; D014841:von Willebrand Factor; D005169:Factor VIII; D007770:L-Lactate Dehydrogenase; D051722:ADAM Proteins; D008666:Metalloendopeptidases; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human