Alloantibody developed in a factor XIII A subunit deficient patient during substitution therapy; characterization of the antibody

Abstract

Introduction: In factor XIII A subunit (FXIIIA) deficiency, the development of alloantibodies is extremely rare. Only four reports have been published and the antibodies were not characterized. Aim: The aim of this study was to describe the clinical course and the laboratory diagnosis of a FXIII-A deficient patient who developed alloantibodies. Methods: FXIII activity was assessed with an ammonia release assay. FXIII-A, FXIII B subunit (FXIII-B) and the complex plasma FXIII (FXIII-A2B2) antigens were determined by ELISA. The causative mutation was detected by fluorescent DNA sequencing. The binding of alloantibody to FXIII-A2 and FXIII-A2B2 was studied by surface plasmon resonance. The cleavage of FXIII-A by thrombin and Ca2+-induced activation of thrombin-cleaved FXIII were followed by western blotting and activity measurement, respectively. Results: FXIII activity, FXIII-A2B2 and FXIII-A antigens were below the limit of detection in the patient's plasma. The severe FXIII-A deficiency was due to a novel homozygous mutation resulting in early stop codon (c.127C>T, p.Gln42STOP). The alloantibody bound to FXIII-A2 and FXIII-A2B2 with equally high affinity (Kd~10-8). It accelerated the elimination of administered FXIII concentrate from the circulation, interfered with thrombin and Ca2+-induced activation and inhibited FXIII activity. Attempts to eliminate the alloantibody resulted only in transient improvement. Patient developed intracerebral haemorrhage after a minor trauma and died in spite of aggressive replacement therapy with FXIII concentrate. Conclusion: The anti-FXIII-A alloantibody caused an unmanageable bleeding complication. The antibody was of combined subtype which accelerated the elimination of FXIII and exerted a multiple inhibitory effect on FXIII activation/activity.