Effect of Five Therapeutic Strategies on the Coagulation Defect Induced By the Thrombomodulin C.1611C>a Mutation

A novel autosomal dominant bleeding disorder characterized by trauma- and surgery-induced severe bleeding despite normal coagulation factor levels, platelet functional tests and fibrinolysis was recently described by two independent groups (1, 2). The genetic cause of this bleeding disorder was identified as a nonsense mutation in the THBD gene (c.1611C>A,p.Cys537Stop), resulting in very highlevels of soluble thrombomodulin (TM) in plasma. Extremely elevated plasma TM levelsenhance APC generation and down-regulate factor (F)Va, FVIIIa and thrombin generation (TG). This rare bleeding disorder is caused by a gain-of-function mutation in an anticoagulant factor. The clinical management of bleeding episodes in patients with this disorder remains challenging. The aim of this in-vitro study was to evaluate the ability of five haemostatic agents to restore the coagulation capacity of patients with TMc.1611C>A mutation.

We compared the in-vitro efficacy of five haemostatic agents to restore thrombin generation in plasma of a patient affected by the disease.

The addition of APCC in patient's plasma showed a dose dependent improvement of TG. A full normalization of ETP (1698nM.min) and peak thrombin (270nM) was observed with the lowest concentration of FEIBA. There was over-correction of TG at higher concentrations of FEIBA, which may represent a risk of thrombosis. In contrast, the haemostatic effect of PCC evaluated in the same experimental conditions showed no significant modification of TG with any concentration of PCC tested. No improvement of TG was observed with any concentration of rFVIIa added.

In our patient, life-threatening hemorrhage could be stopped by the combined administration of platelet concentrates and fresh frozen plasma (2). This can be explained by considering that platelets contain and release at the site of injury, a form of FV which is partially activated and resistant to APC-mediated inactivation and therefore relatively insensitive to the anticoagulant effects of soluble TM. Since soluble TM and APC target not only FVa generation but also FVIIIa generation, and since platelets do not contain FVIII, we speculated that using FVIII concentrates in combination with platelet concentrates might be clinically even more effective in preventing bleeding in the patient. Our in vitro results showed a partial correction of TG with increasing concentrations of rFVIII concentrate. After addition of control platelets (50 - 100-150 x10⁹/L) to the patient's plasma, TG was dose-dependently improved and normalized. The presence of functionally active TM in platelets might explain the need for exogenous platelets to normalize TG.The association of rFVIII concentrate 50 IU/dL with fresh PRP containing 50 - 100-150 x10⁹ platelets/L, improved further the coagulation capacity of the patient and fully normalized TG at all tested concentrations. No over correction of TG was observed with this strategy.

Our in vitro data suggest that APCC, platelet transfusion or the combined use of FVIII and platelet concentrates might be helpful to restore haemostasis in patients presenting this rare bleeding disorder. The clinical haemostatic efficacy of these therapeutic strategies needs to be confirmed during acute bleeding episodes or surgery.

1. Langdown J, Luddington RJ, Huntington JA, Baglin TP. A hereditary bleeding disorder resulting from a premature stop codon in thrombomodulin (p.Cys537Stop). Blood 2014; 124:1951-1956

2. Dargaud Y, Scoazec JY, Wielders SJ, Trzeciak C, Hackeng TM, Négrier C, Hemker HC, Lindhout T, Castoldi E. Characterization of an autosomal dominant bleeding disorder caused by a thrombomodulin mutation. Blood 2015; 125 :1497-501