PT-VWD posing diagnostic and therapeutic challenges – small case series

Treatment of Inherited Platelet Disorders: Current Status and Future Options

Inherited platelet disorders (IPDs) comprise a heterogeneous group of entities that manifest with variable bleeding tendencies. For successful treatment, the underlying platelet disorder, bleeding severity and location, age, and sex must be considered in the broader clinical context. Previous information from the AWMF S2K guideline #086-004 (www.awmf.org) is evaluated for validity and supplemented by information of new available and future treatment options and clinical scenarios that need specific measures. Special attention is given to the treatment of menorrhagia and risk management during pregnancy in women with IPDs. Established treatment options of IPDs include local hemostatic treatment, tranexamic acid, desmopressin, platelet concentrates, and recombinant activated factor VII. Hematopoietic stem cell therapy is a curative approach for selected patients. We also provide an outlook on promising new therapies. These include autologous hematopoietic stem cell gene therapy, artificial platelets and nanoparticles, and various other procoagulant treatments that are currently tested in clinical trials in the context of hemophilia.

Guidance on the diagnosis and management of platelet-type von Willebrand disease: A communication from the Platelet Physiology Subcommittee of the ISTH

Platelet-type von Willebrand disease (PT-VWD) is a rare autosomal dominant platelet bleeding disorder, with 55 patients reported worldwide so far, probably frequently misdiagnosed. Currently, there are no clear guidelines for the diagnosis and management of PT-VWD and this may contribute to misdiagnosis and thus to inappropriate treatment of these patients. This report provides expert opinion-based consensus recommendations for the standardized diagnostic and management approach to PT-VWD. Tests essential in the diagnostic workup are platelet count and size, ristocetin-induced platelet agglutination with mixing studies, and sequencing of platelet GP1BA gene. Platelet transfusions and von Willebrand factor-rich concentrates (if VWF is low) are the most effective treatments. This consensus may help to avoid misdiagnosis and guide appropriate management of patients with this disease.

Menstrual and obstetrical bleeding in women with inherited platelet receptor defects-A systematic review

INTRODUCTION

Women with inherited platelet receptor defects (IPRD) may have an increased risk of heavy menstrual bleeding (HMB) and postpartum haemorrhage (PPH).

AIM

To present a systematic overview of the literature on the prevalence and management of menstrual and obstetrical bleeding in women with IPRD.

METHODS

Electronic databases were searched for original patient data on the prevalence and management of HMB and PPH in women with known IPRD or who were being investigated for IPRD.

RESULTS

Sixty-nine papers (61 case reports/series and 8 cohort studies) were included. Overall, studies were rated as 'poor quality'. The included cohort studies reported HMB in 25% (13/52) of women with Bernard-Soulier syndrome and in 22.1% (34/154) of women with Glanzmann thrombasthenia. In total, 164 deliveries in women with IPRD were described. Excessive bleeding occurred in 16.9% (11/65) of deliveries described in the largest cohort. PPH occurred in 63.2% (55/87) of deliveries described in case reports/series. PPH occurred in 73.7% (14/19) of deliveries that were not covered by prophylaxis compared with 54.2% (32/59) of deliveries that were (OR = 2.36, 95% CI 0.75-7.40). Neonatal bleeding complications were reported in 10.0% (8/80) of deliveries. In all (6/6) deliveries with neonatal bleeding complications wherein the presence of alloantibodies was investigated, either antiplatelet or anti-HLA antibodies were detected.

DISCUSSION/CONCLUSION

Menstrual and particularly obstetrical bleeding problems frequently occur in women with IPRD, based on small case reports and series of poor quality. International collaboration, preferably on prospective studies, is needed to improve clinical management of women-specific bleeding in IPRD.

Mechanisms of thrombocytopenia in platelet-type von Willebrand disease

Platelet-type von Willebrand disease is an inherited platelet disorder characterized by thrombocytopenia with large platelets caused by gain-of-function variants in GP1BA leading to enhanced GPIbα-von Willebrand factor (vWF) interaction. GPIbα and vWF play a role in megakaryocytopoiesis, thus we aimed to investigate megakaryocyte differentiation and proplatelet-formation in platelet-type von Willebrand disease using megakaryocytes from a patient carrying the Met239Val variant and from mice carrying the Gly233Val variant. Platelet-type von Willebrand disease megakaryocytes bound vWF at an early differentiation stage and generated proplatelets with a decreased number of enlarged tips compared to control megakaryocytes. Moreover, they formed proplatelets upon contact with collagen, differently from normal megakaryocytes. Similarly, collagen triggered megakaryocytes showed defective activation of the RhoA-MLC2 axis, which prevents proplatelet formation, and increased phosphorylation of Lyn, which acts as a negative regulator of GPVI signaling, thus preventing ectopic proplatelet-formation on collagen. Consistently, human and murine bone marrow contained an increased number of extravascular platelets compared to controls. In addition, platelet survival of mutant mice was shortened compared to control mice, and the administration of desmopressin, raising circulating vWF, caused a marked drop in platelet count. Taken together, these results show for the first time that thrombocytopenia in platelet-type von Willebrand disease is due to the combination of different pathogenic mechanisms, i.e. the formation of a reduced number of platelets by megakaryocytes, the ectopic release of platelets in the bone marrow, and the increased clearance of platelet/vWF complexes.

Inherited platelet functional disorders: General principles and practical aspects of management

Platelets are a critical component for effecting hemostasis and wound healing. Disorders affecting any platelet pathway mediating adhesion, activation, aggregation and procoagulant surface exposure can result in a bleeding diathesis. Specific diagnosis even with advanced techniques which are unavailable to most centers is often difficult. Inherited platelet function disorders therefore represent a heterogeneous and complex collection of disorders with a spectrum of bleeding severity, from relatively mild (and easily missed or misdiagnosed) to severe bleeding phenotype with salient diagnostic features. We advocate the use of bleeding assessment tools to help identification of patients and more importantly for assessment of individual patient bleeding phenotype to guide management decisions for treating and preventing bleeding. The complex management of these patients is best coordinated in a multidisciplinary comprehensive care clinic setting expert in managing bleeding disorders and associated complications, with particular attention to the physical and psychosocial health of patients and their families. Depending on the bleeding phenotype, the location and severity of bleeding, and the nature of an invasive procedure, available treatment modalities range from conservative measures using local pressure, topical thrombin, fibrin sealant, antifibrinolytics etc. to the use of systemic haemostatics such as desmopressin (DDAVP), platelets and recombinant human activated factor VII (rFVIIa). This review will provide opinions on the practical aspects and general management of inherited platelet function disorders, with discussion on the mechanism of action, and the pros and cons of various hemostatic agents. Finally, the prospect of curative treatment for patients with severe bleeding phenotype refractory to available treatments and with poor quality of life will be briefly discussed.

Thrombocytopathy leading to impaired in vivo haemostasis and thrombosis in platelet type von Willebrand disease

Platelet defects due to hyper-responsive GPIbα causing enhanced VWF interaction, counter-intuitively result in bleeding rather than thrombosis. The historical explanation of platelet/VWF clearance fails to explain mechanisms of impaired haemostasis particularly in light of reported poor platelet binding to fibrinogen. This study aimed to evaluate the defects of platelets with hyper-responsive GPIbα and their contribution to impaired in vivo thrombosis. Using the PT-VWD mouse model, platelets from the hTg^G233V were compared to control hTg^WT mice. Platelets' pro-coagulant capacity was evaluated using flowcytometry assessment of P-selectin and annexin V. Whole blood platelet aggregation in response to ADP, collagen and thrombin was tested. Clot kinetics using laser injury thrombosis model and the effect of GPIbα inhibition in vivo using 6B4; a monoclonal antibody, were evaluated. Thrombin-induced platelet P-selectin and PS exposure were significantly reduced in hTg^G233V compared to hTg^WT and not significantly different when compared to unstimulated platelets. The hTg^G233V platelets aggregated normally in response to collagen, and had a delayed response to ADP and thrombin, when compared to hTg^WT platelets. Laser injury showed significant impairment of in vivo thrombus formation in hTg^G233V compared to hTg^WT mice. There was a significant lag in in vitro clot formation in turbidity assay but no impairment in thrombin generation was observed using thromboelastography. The in vivo inhibition of GPIbα facilitated new - unstable - clot formation but did not improve the lag. We conclude platelets with hyper-responsive GPIbα have complex intrinsic defects beyond the previously described mechanisms. Abnormal signalling through GPIbα and potential therapy using inhibitors require further investigations.