Cell Surface Platelet Tissue Factor Expression: Regulation by P2Y12 and Link to Residual Platelet Reactivity.

BACKGROUND: ADP-induced platelet activation leads to cell surface expression of several proteins, including TF (tissue factor). The role of ADP receptors in platelet TF modulation is still unknown. We aimed to assess the (1) involvement of P2Y1 and P2Y12 receptors in ADP-induced TF exposure; (2) modulation of TFpos-platelets in anti-P2Y12-treated patients with coronary artery disease. Based on the obtained results, we revisited the intracellular localization of TF in platelets. METHODS: The effects of P2Y1 or P2Y12 antagonists on ADP-induced TF expression and activity were analyzed in vitro by flow cytometry and thrombin generation assay in blood from healthy subjects, P2Y12-/-, and patients with gray platelet syndrome. Ex vivo, P2Y12 inhibition of TF expression by clopidogrel/prasugrel/ticagrelor, assessed by VASP (vasodilator-stimulated phosphoprotein) platelet reactivity index, was investigated in coronary artery disease (n=238). Inhibition of open canalicular system externalization and electron microscopy (TEM) were used for TF localization. RESULTS: In blood from healthy subjects, stimulated in vitro by ADP, the percentage of TFpos-platelets (17.3±5.5%) was significantly reduced in a concentration-dependent manner by P2Y12 inhibition only (-81.7±9.5% with 100 nM AR-C69931MX). In coronary artery disease, inhibition of P2Y12 is paralleled by reduction of ADP-induced platelet TF expression (VASP platelet reactivity index: 17.9±11%, 20.9±11.3%, 40.3±13%; TFpos-platelets: 10.5±4.8%, 9.8±5.9%, 13.6±6.3%, in prasugrel/ticagrelor/clopidogrel-treated patients, respectively). Despite this, 15% of clopidogrel good responders had a level of TFpos-platelets similar to the poor-responder group. Indeed, a stronger P2Y12 inhibition (130-fold) is required to inhibit TF than VASP. Thus, a VASP platelet reactivity index <20% (as in prasugrel/ticagrelor-treated patients) identifies patients with TFpos-platelets <20% (92% sensitivity). Finally, colchicine impaired in vitro ADP-induced TF expression but not α-granule release, suggesting that TF is open canalicular system stored as confirmed by TEM and platelet analysis of patients with gray platelet syndrome. CONCLUSIONS: Data show that TF expression is regulated by P2Y12 and not P2Y1; P2Y12 antagonists downregulate the percentage of TFpos-platelets. In clopidogrel good-responder patients, assessment of TFpos-platelets highlights those with residual platelet reactivity. TF is stored in open canalicular system, and its membrane exposure upon activation is prevented by colchicine.

Platelets and Neurodegenerative Diseases: Current Knowledge and Future Perspectives.

Platelets have a fundamental role in mediating hemostasis and thrombosis. However, more recently, a new idea is making headway, highlighting the importance of platelets as significant actors in modulating immune and inflammatory responses. In particular, platelets have an important role in the development of vascular amyloid-b-peptide(ab) deposits, known to play a relevant role in Alzheimer's disease (AD) through accumulation and deposition within the frontal cortex and hippocampus in the brain. The involvement of platelets in the pathogenesis of AD opens up the highly attractive possibility of applying antiplatelet therapy for the treatment and/or prevention of AD, but conclusive results are scarce. Even less is known about the potential role of platelets in mild cognitive impairment (MCI). The aim to this brief review is to summarize current knowledge on this topic and to introduce the new perspectives on the possible role of platelet activation as therapeutic target both in AD and MCI.

Novel manifestations of immune dysregulation and granule defects in gray platelet syndrome.

Gray platelet syndrome (GPS) is a rare recessive disorder caused by biallelic variants in NBEAL2 and characterized by bleeding symptoms, the absence of platelet α-granules, splenomegaly, and bone marrow (BM) fibrosis. Due to the rarity of GPS, it has been difficult to fully understand the pathogenic processes that lead to these clinical sequelae. To discern the spectrum of pathologic features, we performed a detailed clinical genotypic and phenotypic study of 47 patients with GPS and identified 32 new etiologic variants in NBEAL2. The GPS patient cohort exhibited known phenotypes, including macrothrombocytopenia, BM fibrosis, megakaryocyte emperipolesis of neutrophils, splenomegaly, and elevated serum vitamin B12 levels. Novel clinical phenotypes were also observed, including reduced leukocyte counts and increased presence of autoimmune disease and positive autoantibodies. There were widespread differences in the transcriptome and proteome of GPS platelets, neutrophils, monocytes, and CD4 lymphocytes. Proteins less abundant in these cells were enriched for constituents of granules, supporting a role for Nbeal2 in the function of these organelles across a wide range of blood cells. Proteomic analysis of GPS plasma showed increased levels of proteins associated with inflammation and immune response. One-quarter of plasma proteins increased in GPS are known to be synthesized outside of hematopoietic cells, predominantly in the liver. In summary, our data show that, in addition to the well-described platelet defects in GPS, there are immune defects. The abnormal immune cells may be the drivers of systemic abnormalities such as autoimmune disease.

Does chronic oral anticoagulation reduce in-hospital mortality among COVID-19 older patients?

BACKGROUND: Patients hospitalized with COVID-19 experienced an increased risk of venous thromboembolism. AIMS: To evaluate the effect of chronic oral anticoagulation (OAC) therapy, both with vitamin K antagonists (VKAs) or direct oral anticoagulants (DOACs), on prognosis of COVID-19 older patients. METHODS: Single-center prospective study conducted in the Emergency Department (ED) of a teaching hospital, referral center for COVID-19 in central Italy. We evaluated all the patients ≥ 65 years, consecutively admitted to our ED for confirmed COVID-19. We compared the clinical outcome of those who were on chronic OAC at ED admission with those who did not, using a propensity score matched paired cohort of controls. The primary study endpoint was all-cause in-hospital death. Patients were matched for age, sex, clinical comorbidities, and clinical severity at presentation (based on NEWS ≥ 6). Study parameters were assessed for association to all-cause in-hospital death by a multivariate Cox regression analysis to identify independent risk factor for survival. RESULTS: Although overall mortality was slightly higher for anticoagulated patients compared to controls (63.3% vs 43.5%, p = 0.012), the multivariate adjusted hazard ratio (HR) for death was not significant (HR = 1.56 [0.78-3.12]; p = 0.208). Both DOACs (HR 1.46 [0.73-2.92]; p = 0.283) and VKAs (HR 1.14 [0.48-2.73]; p = 0.761) alone did not affect overall survival in our cohort. CONCLUSIONS: Among older patients hospitalized for COVID-19, chronic OAC therapy was not associated with a reduced risk of in-hospital death. Moreover, our data suggest similar outcome both for patients on VKAs or in patients on DOACs.

Eltrombopag for the treatment of inherited thrombocytopenias: a phase II clinical trial.

Patients with inherited thrombocytopenias often require platelet transfusions to raise their platelet count before surgery or other invasive procedures; moreover, subjects with clinically significant spontaneous bleeding may benefit from an enduring improvement of thrombocytopenia. The hypothesis that thrombopoietin-mimetics can increase platelet count in inherited thrombocytopenias is appealing, but evidence is scarce. We conducted a prospective, phase II clinical trial to investigate the efficacy of the oral thrombopoietin-mimetic eltrombopag in different forms of inherited thrombocytopenia. We enrolled 24 patients affected by MYH9-related disease, ANKRD26-related thrombocytopenia, X-linked thrombocytopenia/ Wiskott-Aldrich syndrome, monoallelic Bernard-Soulier syndrome, or ITGB3-related thrombocytopenia. The average pre-treatment platelet count was 40.4 ×109/L. Patients received a 3- to 6-week course of eltrombopag in a dose-escalated manner. Of 23 patients evaluable for response, 11 (47.8%) achieved a major response (platelet count >100 ×109/L), ten (43.5%) had a minor response (platelet count at least twice the baseline value), and two patients (8.7%) did not respond. The average increase of platelet count compared to baseline was 64.5 ×109/L (P<0.001). Four patients with clinically significant spontaneous bleeding entered a program of long-term eltrombopag administration (16 additional weeks): all of them obtained remission of mucosal hemorrhages, with the remission persisting throughout the treatment period. Treatment was globally well tolerated: five patients reported mild adverse events and one patient a moderate adverse event. In conclusion, eltrombopag was safe and effective in increasing platelet count and reducing bleeding symptoms in different forms of inherited thrombocytopenia. Despite these encouraging results, caution is recommended when using thrombopoietinmimetics in inherited thrombocytopenias predisposing to leukemia. ClinicalTrials.gov identifier: NCT02422394.

Antithrombotic prophylaxis for surgery-associated venous thromboembolism risk in patients with inherited platelet disorders. The SPATA-DVT Study.

Major surgery is associated with an increased risk of venous thromboembolism (VTE), thus the application of mechanical or pharmacologic prophylaxis is recommended. The incidence of VTE in patients with inherited platelet disorders (IPD) undergoing surgical procedures is unknown and no information on the current use and safety of thromboprophylaxis, particularly of low-molecular-weight-heparin in these patients is available. Here we explored the approach to thromboprophylaxis and thrombotic outcomes in IPD patients undergoing surgery at VTE-risk participating in the multicenter SPATA study. We evaluated 210 surgical procedures carried out in 155 patients with well-defined forms of IPD (VTE-risk: 31% high, 28.6% intermediate, 25.2% low, 15.2% very low). The use of thromboprophylaxis was low (23.3% of procedures), with higher prevalence in orthopedic and gynecological surgeries, and was related to VTE-risk. The most frequently employed thromboprophylaxis was mechanical and appeared to be effective, as no patients developed thrombosis, including patients belonging to the highest VTE-risk classes. Low-molecular-weight-heparin use was low (10.5%) and it did not influence the incidence of post-surgical bleeding or of antihemorrhagic prohemostatic interventions use. Two thromboembolic events were registered, both occurring after high VTE-risk procedures in patients who did not receive thromboprophylaxis (4.7%). Our findings suggest that VTE incidence is low in patients with IPD undergoing surgery at VTE-risk and that it is predicted by the Caprini score. Mechanical thromboprophylaxis may be of benefit in patients with IPD undergoing invasive procedures at VTE-risk and low-molecular-weight-heparin should be considered for major surgery.

Carbamazepine interaction with direct oral anticoagulants: help from the laboratory for the personalized management of oral anticoagulant therapy.

Current guidelines recommend caution in prescribing concomitant use of direct-acting oral anticoagulants (DOACs) and antiepileptic drugs due to drug-drug interactions leading to potential risk of DOACs subtherapeutic concentration and treatment failure. Herein we report a significant interaction between carbamazepine (CZP) and apixaban, causing subtherapeutic concentration of the drug in a patient with atrial fibrillation who had a transient ischemic attack (TIA) episode. Another anti-Xa DOAC, edoxaban, administered to the patient after TIA occurrence did not show significant interaction with CZP. In addition to confirm that cautions should be used when antiepileptic and DOACs are concomitantly prescribed, the present case also demonstrates that, in the management of certain subsets of patients who need anticoagulant treatment, measurement of DOAC plasma concentration can help guide a personalized management and avoid adverse clinical outcomes.

Bleeding risk of surgery and its prevention in patients with inherited platelet disorders.

Excessive bleeding at surgery is a feared complication in patients with inherited platelet disorders. However, very few studies have evaluated the frequency of surgical bleeding in these hemorrhagic disorders. We performed a worldwide, multicentric, retrospective study to assess the bleeding complications of surgery, the preventive and therapeutic approaches adopted, and their efficacy in patients with inherited platelet disorders: the Surgery in Platelet disorders And Therapeutic Approach (SPATA) study. We rated the outcome of 829 surgical procedures carried out in 423 patients with well-defined forms of inherited platelet disorders: 238 inherited platelet function disorders and 185 inherited platelet number disorders. Frequency of surgical bleeding was high in patients with inherited platelet disorders (19.7%), with a significantly higher bleeding incidence in inherited platelet function disorders (24.8%) than in inherited platelet number disorders (13.4%). The frequency of bleeding varied according to the type of inherited platelet disorder, with biallelic Bernard Soulier syndrome having the highest occurrence (44.4%). Frequency of bleeding was predicted by a pre-operative World Health Organization bleeding score of 2 or higher. Some types of surgery were associated with a higher bleeding incidence, like cardiovascular and urological surgery. The use of pre-operative pro-hemostatic treatments was associated with a lower bleeding frequency in patients with inherited platelet function disorders but not in inherited platelet number disorders. Desmopressin, alone or with antifibrinolytic agents, was the preventive treatment associated with the lowest bleedings. Platelet transfusions were used more frequently in patients at higher bleeding risk. Surgical bleeding risk in inherited platelet disorders is substantial, especially in inherited platelet function disorders, and bleeding history, type of disorder, type of surgery and female sex are associated with higher bleeding frequency. Prophylactic pre-operative pro-hemostatic treatments appear to be required and are associated with a lower bleeding incidence.

Platelet diameters in inherited thrombocytopenias: analysis of 376 patients with all known disorders.

Abnormalities of platelet size are one of the distinguishing features of inherited thrombocytopenias (ITs), and evaluation of blood films is recommended as an essential step for differential diagnosis of these disorders. Nevertheless, what we presently know about this subject is derived mainly from anecdotal evidence. To improve knowledge in this field, we evaluated platelet size on blood films obtained from 376 patients with all 19 forms of IT identified so far and found that these conditions differ not only in mean platelet diameter, but also in platelet diameter distribution width and the percentage of platelets with increased or reduced diameters. On the basis of these findings, we propose a new classification of ITs according to platelet size. It distinguishes forms with giant platelets, with large platelets, with normal or slightly increased platelet size, and with normal or slightly decreased platelet size. We also measured platelet diameters in 87 patients with immune thrombocytopenia and identified cutoff values for mean platelet diameter and the percentage of platelets with increased or reduced size that have good diagnostic accuracy in differentiating ITs with giant platelets and with normal or slightly decreased platelet size from immune thrombocytopenia and all other forms of IT.

Megakaryocytic emperipolesis and platelet function abnormalities in five patients with gray platelet syndrome.

The gray platelet syndrome (GPS) is a rare congenital platelet disorder characterized by mild to moderate bleeding diathesis, macrothrombocytopenia and lack of azurophilic α-granules in platelets. Some platelet and megakaryocyte (MK) abnormalities have been described, but confirmative studies of the defects in larger patient cohorts have not been undertaken. We studied platelet function and bone marrow (BM) features in five GPS patients with NBEAL2 autosomal recessive mutations from four unrelated families. In 3/3 patients, we observed a defect in platelet responses to protease-activated receptor (PAR)1-activating peptide as the most consistent finding, either isolated or combined to defective responses to other agonists. A reduction of PAR1 receptors with normal expression of major glycoproteins on the platelet surface was also found. Thrombin-induced fibrinogen binding to platelets was severely impaired in 2/2 patients. In 4/4 patients, the BM biopsy showed fibrosis (grade 2-3) and extensive emperipolesis, with many (36-65%) MKs containing 2-4 leukocytes engulfed within the cytoplasm. Reduced immunolabeling for platelet factor 4 together with normal immunolabeling for CD63 in MKs of two patients demonstrated that GPS MKs display an alpha granule-specific defect. Increased immunolabeling for P-selectin and decreased immunolabeling for PAR1, PAR4 and c-MPL were also observed in MKs of two patients. Marked emperipolesis, specific defect of MK alpha-granule content and defect of PAR1-mediated platelet responses are present in all GPS patients that we could study in detail. These results help to further characterize the disease.

Impact of Gut Microbiota on Obesity, Diabetes, and Cardiovascular Disease Risk.

Gut microbiota has been recently established to have a contributory role in the development of cardiometabolic disorders, such as atherosclerosis, obesity, and type 2 diabetes. Growing interest has focused on the modulation of gut microbiota as a therapeutic strategy in cardiovascular diseases and metabolic disorders. In this paper, we have reviewed the impact of gut microbiota on metabolic disorders and cardiovascular disease risk, focusing on the newest findings in this field.

MYH9-related disease: a novel prognostic model to predict the clinical evolution of the disease based on genotype-phenotype correlations.

MYH9-related disease (MYH9-RD) is a rare autosomal-dominant disorder caused by mutations in the gene for nonmuscle myosin heavy chain IIA (NMMHC-IIA). MYH9-RD is characterized by a considerable variability in clinical evolution: patients present at birth with only thrombocytopenia, but some of them subsequently develop sensorineural deafness, cataract, and/or nephropathy often leading to end-stage renal disease (ESRD). We searched for genotype-phenotype correlations in the largest series of consecutive MYH9-RD patients collected so far (255 cases from 121 families). Association of genotypes with noncongenital features was assessed by a generalized linear regression model. The analysis defined disease evolution associated to seven different MYH9 genotypes that are responsible for 85% of MYH9-RD cases. Mutations hitting residue R702 demonstrated a complete penetrance for early-onset ESRD and deafness. The p.D1424H substitution associated with high risk of developing all the noncongenital manifestations of disease. Mutations hitting a distinct hydrophobic seam in the NMMHC-IIA head domain or substitutions at R1165 associated with high risk of deafness but low risk of nephropathy or cataract. Patients with p.E1841K, p.D1424N, and C-terminal deletions had low risk of noncongenital defects. These findings are essential to patients' clinical management and genetic counseling and are discussed in view of molecular pathogenesis of MYH9-RD.

Analysis of 339 pregnancies in 181 women with 13 different forms of inherited thrombocytopenia.

Pregnancy in women with inherited thrombocytopenias is a major matter of concern as both the mothers and the newborns are potentially at risk of bleeding. However, medical management of this condition cannot be based on evidence because of the lack of consistent information in the literature. To advance knowledge on this matter, we performed a multicentric, retrospective study evaluating 339 pregnancies in 181 women with 13 different forms of inherited thrombocytopenia. Neither the degree of thrombocytopenia nor the severity of bleeding tendency worsened during pregnancy and the course of pregnancy did not differ from that of healthy subjects in terms of miscarriages, fetal bleeding and pre-term births. The degree of thrombocytopenia in the babies was similar to that in the mother. Only 7 of 156 affected newborns had delivery-related bleeding, but 2 of them died of cerebral hemorrhage. The frequency of delivery-related maternal bleeding ranged from 6.8% to 14.2% depending on the definition of abnormal blood loss, suggesting that the risk of abnormal blood loss was increased with respect to the general population. However, no mother died or had to undergo hysterectomy to arrest bleeding. The search for parameters predicting delivery-related bleeding in the mother suggested that hemorrhages requiring blood transfusion were more frequent in women with history of severe bleedings before pregnancy and with platelet count at delivery below 50 × 10(9)/L.

Safety and effectiveness of oral anticoagulants in patients with atrial fibrillation and stage 4 chronic kidney disease: a real-world experience.

It is still uncertain whether direct oral anticoagulants (DOACs) perform better than vitamin K antagonists (VKAs) in subjects with non-valvular atrial fibrillation (NVAF) and advanced chronic kidney disease (CKD). The aim of the study was to compare safety and effectiveness of DOACs and VKAs in patients with NVAF and stage 4 CKD (creatinine clearance 15-29 mL/min). We searched the hospital databases of two academic centers to retrospectively identify patients with stage 4 CKD who were on treatment with DOACs or VKAs for NVAF. Safety was the primary outcome of the study and was assessed in terms of incidence of major bleeding (MB). Secondary outcomes were clinically relevant non-major bleeding (CRNMB) and death for any cause. A total of 176 patients (102 on DOACs and 74 on VKAs) were found and included in the analysis. The incidence rate of MB was not statistically different between groups (8.6 per 100 patients-year in the DOAC group and 5.6 per 100 patients-year in the VKA group). Rates of IS/SSE and CRNMB were statistically similar in the two treatment groups, as well. There were less deaths for any cause in the DOAC group than in the VKA group (8.6 and 15.8 per 100 patients-year, respectively), but the difference was not statistically significant. This study found no difference in terms of safety and effectiveness between patients with NVAF and stage 4 CKD treated with DOACs and VKAs. Larger prospective or randomized studies are needed to confirm these findings.

Association of laboratory test results with the bleeding history in patients with inherited platelet function disorders (the Bleeding Assesment Tool - LABoratory tests substudy): communication from the Platelet Physiology ISTH-SSC.

Background: In hemophilia and von Willebrand disease, the degree of alteration of laboratory assays correlates with bleeding manifestations. Few studies have assessed the predictive value for bleeding of laboratory assays in patients with inherited platelet function disorders (IPFDs). Objectives: To assess whether there is an association between platelet function assay results and bleeding history, as evaluated by the International Society on Thrombosis and Haemostasis (ISTH) bleeding assessment tool (BAT). Methods: Centers participating in the international ISTH-BAT validation study were asked to provide results of the diagnostic assays employed for the patients they enrolled, and the association with the individual patients' bleeding score (BS) was assessed. Results: Sixty-eight patients with 14 different IPFDs were included. Maximal amplitude of platelet aggregation was significantly lower in patients with a pathologic BS and correlated inversely with the BS, a finding largely driven by the subgroup of patients with Glanzmann thrombasthenia and CalDAG-GEFI deficiency; after their exclusion, TRAP-induced aggregation remained significantly lower in patients with a pathologic BS. Bleeding time was significantly more prolonged in patients with a high BS than in those with a normal BS (27.1 ± 6.2 minutes vs 15.1 ± 10.6 minutes; P < .01). Reduced α-granule content was significantly more common among patients with a pathologic BS than among those with a normal BS (80% vs 20%; P < .05). Receiver operating characteristic curve analysis revealed a significant discriminative ability of all the aforementioned tests for pathologic BS (P < .001), also after exclusion of patients with Glanzmann thrombasthenia and CalDAG-GEFI deficiency. Conclusion: This study shows that altered platelet laboratory assay results are associated with an abnormal ISTH-BAT BS in IPFD.

MORE EARLY BLEEDS ASSOCIATED WITH HIGH BASELINE DIRECT ORAL ANTICOAGULANT LEVELS IN ATRIAL FIBRILLATION: THE MAS STUDY.

Treatment with direct oral anticoagulants (DOAC) in atrial fibrillation (AF) patients is effective and safe. However, bleeding complications still occur. Whether the measurement of DOAC levels may further improve treatment efficacy and safety is still an open issue. In the "Measure and See" (MAS) Study (#NCT03803579) venous blood was collected 15-30 days after DOAC initiation in AF patients who were then followed for one year to record the occurrence of major and clinically relevant non-major bleeding. DOAC plasma levels were measured in one laboratory, and results were kept blind to patients and treating doctors. Trough DOAC levels were assessed in 1657 patients [957 (57.7%) and 700 treated with standard and low-dose, respectively]. Fifty bleeding events were recorded during 1606 years of follow-up (3.11% pt/yrs). Fifteen bleeding events (4.97% pt/yrs) occurred in patients with C-trough standardized values in the highest activity class (> 0.50); whereas 35 events (2.69% pt/yrs) occurred in those with values in the two lower classes ( 0.50, p= 0.0401). Increasing DOAC levels and low-dose DOAC use were associated with increased bleeding risk in the first three months of treatment. 19% of patients receiving low doses had standardized activity values in the highest class. More bleeding occurred in patients treated with low (4.3% pt/yrs) than standard (2.2% pt/yrs; p= 0.0160) dose DOAC. Early measurement of DOAC levels in AF patients identified many subjects with high activity levels despite the low doses use and had more bleeding risk during the first 3 months of treatment.

Thrombotic events associated with low baseline direct oral anticoagulant levels in atrial fibrillation: the MAS study.

ABSTRACT: Although effective and safe, treatment with direct oral anticoagulants (DOAC) in atrial fibrillation (AF) is still associated with thrombotic complications. Whether the measurement of DOAC levels may improve treatment efficacy is an open issue. We carried out the observational, prospective, multicenter Measure and See (MAS) study. Blood was collected 15 to 30 days after starting DOAC treatment in patients with AF who were followed-up for 1 year. Plasma samples were centralized for DOAC level measurement. Patients' DOAC levels were converted into drug/dosage standardized values to allow a pooled analysis in a time-dependent, competitive-risk model. The measured values were transformed into standardized values (representing the distance of each value from the overall mean) by subtracting the DOAC-specific mean value from the original values and dividing by the standard deviation. Trough and peak DOAC levels were assessed in 1657 and 1303 patients, respectively. In total, 21 thrombotic complications were recorded during 1606 years of follow-up (incidence of 1.31% of patients per year). Of 21 thrombotic events, 17 occurred in patients whose standardized activity levels were below the mean of each DOAC (0); the incidence was the highest (4.82% of patients per year) in patients whose standardized values were in the lowest class (-1.00 or less). Early measurement of DOAC levels in patients with AF allowed us to identify most of the patients who, having low baseline DOAC levels, subsequently developed thrombotic complications. Further studies are warranted to assess whether thrombotic complications may be reduced by measuring baseline DOAC levels and modifying treatment when indicated. This trial was registered at www.ClinicalTrials.gov as #NCT03803579.

Correlation between platelet phenotype and NBEAL2 genotype in patients with congenital thrombocytopenia and α-granule deficiency.

The gray platelet syndrome is a rare inherited bleeding disorder characterized by macrothrombocytopenia and deficiency of alpha (α)-granules in platelets. The genetic defect responsible for gray platelet syndrome was recently identified in biallelic mutations in the NBEAL2 gene. We studied 11 consecutive families with inherited macrothrombocytopenia of unknown origin and α-granule deficiency. All of them underwent NBEAL2 DNA sequencing and evaluation of the platelet phenotype, including a systematic assessment of the α-granule content by immunofluorescence analysis for α-granule secretory proteins. We identified 9 novel mutations hitting the two alleles of NBEAL2 in 4 probands. They included missense, nonsense and frameshift mutations, as well as nucleotide substitutions that altered the splicing mechanisms as determined at the RNA level. All the individuals with NBEAL2 biallelic mutations showed almost complete absence of platelet α-granules. Interestingly, the 13 individuals assumed to be asymptomatic because carriers of a mutated allele had platelet macrocytosis and significant reduction of the α-granule content. However, they were not thrombocytopenic. In the remaining 7 probands, we did not identify any NBEAL2 alterations, suggesting that other genetic defect(s) are responsible for their platelet phenotype. Of note, these patients were characterized by a lower severity of the α-granule deficiency than individuals with two NBEAL2 mutated alleles. Our data extend the spectrum of mutations responsible for gray platelet syndrome and demonstrate that macrothrombocytopenia with α-granule deficiency is a genetic heterogeneous trait. In terms of practical applications, the screening of NBEAL2 is worthwhile only in patients with macrothrombocytopenia and severe reduction of the α-granules. Finally, individuals carrying one NBEAL2 mutated allele have mild laboratory abnormalities, suggesting that even haploinsufficiency has an effect on platelet phenotype.