The empty sack syndrome: a platelet storage pool deficiency associated with empty dense granules

A Morphometric Analysis of Platelet Dense Granules of Patients with Unexplained Bleeding: A New Entity of Delta-Microgranular Storage Pool Deficiency

One thousand and eighty patients, having prolonged bleeding times, frequent epistaxis, menorrhagia or easy bruising or other bleeding manifestations, and excluding those with von Willebrand's disease, were evaluated for platelet dense granule deficiency. The mean diameter of platelet dense granules was determined for all patients using image analysis. Four hundred and ninety-nine had "classic" dense (delta) granule storage pool deficiency (δ-SPD). Five hundred and eighty-one individuals (53.8%) were found to have a normal mean number of dense granules, but for some of these patients, the dense granules were smaller than for the controls. Of the patients having a normal number of dense granules, 165 (28.4%) were found to have significantly smaller granules than the platelets obtained from the control subjects. Their average granule diameter was 123.35 ± 0.86 nm, that is more than three standard deviations below the mean of the control data. Total δ-granule storage pool volumes (TDGV)/platelet were calculated using these measurements. Individuals with δ-SPD had half the number of granules (2.25 ± 0.04 DG/PL) and storage pool volume (3.88 ± 1.06 × 106 nm3) when compared to our control data (4.64 ± 0.11 DG/PL; 10.79 × 106 nm3 ± 0.42). Individuals having a bleeding history but a normal average of small dense granules had a calculated storage pool volume statistically different than controls and essentially the same storage pool volume as patients with δ-SPD. We have identified a sub-classification of δ-SPD that we have defined as micro-granular storage pool deficiency (δ-MGSPD).

Flow cytometric mepacrine fluorescence can be used for the exclusion of platelet dense granule deficiency

BACKGROUND

δ-storage pool disease (δ-SPD) is a bleeding disorder characterized by a reduced number of platelet-dense granules. The diagnosis of δ-SPD depends on the measurement of platelet ADP content, but this test is time consuming and requires a relatively large blood volume. Flow cytometric analysis of platelet mepacrine uptake is a potential alternative, but this approach lacks validation, which precludes its use in a diagnostic setting.

OBJECTIVES

To evaluate the performance of platelet mepacrine uptake as a diagnostic test for δ-SPD.

PATIENTS/METHODS

Mepacrine fluorescence was determined with flow cytometry before and after platelet activation in 156 patients with a suspected platelet function disorder and compared with platelet ADP content as a reference test. Performance was analyzed with a receiver operating characteristic (ROC) curve.

RESULTS

Eleven of 156 patients had δ-SPD based on platelet ADP content. Mepacrine fluorescence was inferior to platelet ADP content in identifying patients with δ-SPD, but both mepacrine uptake (area under the ROC curve [AUC] 0.87) and mepacrine release after platelet activation (AUC 0.80) had good discriminative ability. In our tertiary reference center, mepacrine uptake showed high negative predicitive value (97%) with low positive predictive value (35%). Combined with a negative likelihood ratio of 0.1, these data indicate that mepacrine uptake can be used to exclude δ-SPD in patients with a bleeding tendency.

CONCLUSION

Mepacrine fluorescence can be used as a screening tool to exclude δ-SPD in a large number of patients with a suspected platelet function disorder.

A simplified flow cytometric method for detection of inherited platelet disorders-A comparison to the gold standard light transmission aggregometry

Background

Flow cytometric platelet activation has emerged as an alternative diagnostic test for inherited platelet disorders. It is, however, labor intensive and few studies have directly compared the performance of flow cytometric platelet activation (PACT) to light transmission aggregometry (LTA). The aims of this study were 1/ to develop a simplified flow cytometric platelet activation assay using microtiter plates and 2/ to correlate the outcome to gold standard method LTA, and to clinical bleeding assessment tool scores (BAT score).

Methods

The PACT method was developed in microtiter plates using adenosine diphosphate (ADP), collagen-derived peptide (CRP-XL) and thrombin receptor activator for peptide 6 (TRAP-6) as agonists. Antibodies against GPIIb-IIIa activation epitope (PAC1), P-selectin (CD62P) and lysosome-associated membrane glycoprotein 3 (LAMP3; CD63) were used as platelet activation markers. Sixty-six patients referred to the coagulation unit for bleeding symptoms were included in this single-center observational study. Platelet activation was determined by PACT and LTA. The results of both methods were correlated to BAT score.

Results

A two-by-two analysis using Cohen’s kappa analysis gave moderate agreement between LTA and PACT (82%, kappa = 0.57), when PACT analysis with ADP and CRP-XL was compared to LTA. Using LTA as reference method, positive predictive value was 70% and negative predictive value was 87%. A substantial number of patients had high BAT score and normal LTA and PACT results. Patients with abnormal LTA or PACT results had higher BAT score than patients with normal results, but the difference was not significant.

Conclusions

The performance in microtiter plates simplified the PACT method and enabled analysis of more patients at the same time. Our results indicate that with modification of the current PACT assay, a higher negative predictive value can be obtained. Furthermore, with comparable result to LTA the PACT could be used as a screening assay for inherited platelet disorders.

Inherited platelet function disorders: overview and disorders of granules, secretion, and signal transduction

Inherited disorders of platelet function are characterized by highly variable mucocutaneous bleeding manifestations. The platelet dysfunction arises by diverse mechanisms, including abnormalities in platelet membrane glycoproteins, granules and their contents, platelet signaling and secretion mechanisms: thromboxane production pathways and in platelet procoagulant activities. Platelet aggregation and secretion studies using platelet-rich plasma currently form the primary basis for the diagnosis of an inherited platelet dysfunction. In most such patients, the molecular and genetic mechanisms are unknown. Management of these patients needs to be individualized; therapeutic options include platelet transfusions, 1-desamino-8d-arginine vasopressin (DDAVP), recombinant factor VIIa, and antifibrinolytic agents.

SLC35D3 delivery from megakaryocyte early endosomes is required for platelet dense granule biogenesis and is differentially defective in Hermansky-Pudlak syndrome models

Platelet dense granules are members of a family of tissue-specific, lysosome-related organelles that also includes melanosomes in melanocytes. Contents released from dense granules after platelet activation promote coagulation and hemostasis, and dense granule defects such as those seen in Hermansky-Pudlak syndrome (HPS) cause excessive bleeding, but little is known about how dense granules form in megakaryocytes (MKs). In the present study, we used SLC35D3, mutation of which causes a dense granule defect in mice, to show that early endosomes play a direct role in dense granule biogenesis. We show that SLC35D3 expression is up-regulated during mouse MK differentiation and is enriched in platelets. Using immunofluorescence and immunoelectron microscopy and subcellular fractionation in megakaryocytoid cells, we show that epitope-tagged and endogenous SLC35D3 localize predominantly to early endosomes but not to dense granule precursors. Nevertheless, SLC35D3 is depleted in mouse platelets from 2 of 3 HPS models and, when expressed ectopically in melanocytes, SLC35D3 localizes to melanosomes in a manner requiring a HPS-associated protein complex that functions from early endosomal transport intermediates. We conclude that SLC35D3 is either delivered to nascent dense granules from contiguous early endosomes as MKs mature or functions in dense granule biogenesis directly from early endosomes, suggesting that dense granules originate from early endosomes in MKs.

The use of thromboelastography for the peripartum management of a patient with platelet storage pool disorder

We describe the peripartum management of a 26-year-old primigravida with a platelet storage pool disorder who underwent spontaneous vaginal delivery of twins with epidural analgesia. Postpartum hemorrhage from uterine atony, and cervical and vaginal lacerations were treated successfully with 1-desamino-8D-arginine vasopressin and blood products. The use of thromboelastography in the assessment and management of bleeding risk in the setting of platelet storage pool disorder is described.

The value of proteomics for the diagnosis of a platelet-related bleeding disorder

Familial bleeding problems are frequently difficult to diagnose because currently used clinical tests cannot identify intracellular molecular defects of platelets. Using platelet proteomics, a comprehensive analytical tool, we diagnosed a family with severe bleeding problems of unknown origin with Quebec Platelet Disorder. Prior to proteomic analysis, we determined platelet counts, presence of glycoprotein (GP) Ib and GPIIb/IIIa, platelet aggregation, dense granule content and release, plasma levels of fibrinogen, Factor XIII and fibrin degradation products in four family members. Abnormalities were detected in platelet aggregation studies, which revealed variably reduced responses to ADP, collagen and epinephrine with concomitantly decreased ATP/serotonin secretion. In addition, D-dimer levels were significantly elevated 72 hours after in vitro thrombin stimulation of platelet-rich plasma. Together with the autosomal dominant inheritance and the delayed onset of bleeding in two of the four patients these results did not support any known platelet disorder. Therefore, the proteome of platelet lysates separated by one-dimensional SDS-PAGE was analysed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Platelet proteomics showed reduced amounts of alpha-granule proteins multimerin, fibrinogen and thrombospondin-1 in patient compared to control samples suggestive of Quebec Platelet Disorder. The diagnosis of Quebec Platelet Disorder was confirmed by urokinase-specific Western blots. Urokinase causes the degradation of alpha-granule proteins in this disorder. Diagnosis of rare bleeding disorders has important implications for prophylactic and acute treatment of bleeding patients. This is the first report using proteomics to identify a familial platelet defect.

Acute subarachnoid hemorrhage associated with platelet storage pool disease and the hemoglobinopathy caused by beta-thalassemia minor

We describe a case of acute subarachnoid hemorrhage with a complex blood-clotting mechanism and two negative angiographies. The patient was discharged from hospital with a presumptive diagnosis of idiopathic causes, but further analysis of the clinical history from the primary care provider prompted a hematologic analysis, which produced a diagnosis of platelet storage pool disease with alterations during the degranulation and aggregation functions. Electron microscopy revealed no ultrastructural abnormalities of platelet membranes, granules, or organelles. The patient had been previously diagnosed with thalassemia minor.

delta-Storage pool disease: a pitfall in the forensic investigation of sudden anal blood loss in children: a case report

We present the case of a 3.5-year-old boy with sudden anal blood loss at school. Sexual abuse was suspected, and, apart from anal fissures seen on sigmoidoscopy, no other clinical signs of any sort of disorder were present. As no medical explanation for the blood loss could be given, penetrating anal trauma was suggested. During follow-up consultations, there were complaints of occasional blood loss. Platelet aggregation tests and electron microscopy finally helped diagnose a delta-storage pool disease which is a rare haemostatic disorder involving the dense granules of the platelets. Although exclusion of well-known blood diseases through routine laboratory testing is a common practice in children with sudden blood loss, this case illustrates the value of more specialised investigation both from a diagnostic and forensic point of view.

Development of platelet secretory granules

Platelet granule exocytosis plays a critical role in thrombosis and wound healing. Platelets have three major types of secretory granules that are defined by their unique molecular contents, kinetics of exocytosis and morphologies. Although the ontogeny of platelet granules is poorly understood, a convergence of new insights into megakaryocyte development, the molecular mechanisms of vesicle trafficking and the genetic basis of platelet granule defects, is beginning to define the cellular and molecular pathways responsible for platelet granule ontogeny.

A novel immunocytochemical assay for the detection of serotonin in platelets

A method for the rapid, inexpensive and easy detection of platelet serotonin (5-hydroxytryptamine, 5-HT) is not currently available. Consequently, many patients suffering from unresolved platelet-related bleeding disorders are not examined for a possible platelet 5-HT deficiency. The direct measurement of 5-HT concentration with high-performance liquid chromatography (HPLC) or serotonin enzyme-linked immunosorbent assay (ELISA) is costly and highly demanding. Indirect methods, which determine the content of ATP or calcium with lumi-aggregometry or electron microscopy, rely upon the assumption that the ATP or calcium concentration is equivalent to that of 5-HT. We have developed a fluorescence-based assay for 5-HT that can be performed within 2 h on fresh or frozen samples using a fluorescence microscope or a flow cytometer. The assay requires only 0.2 ml of platelet-rich plasma and might therefore be of particular interest for paediatric patients. Samples from control and patient donors were analysed for 5-HT with the new immunocytochemical assay in comparison with HPLC and/or 5-HT ELISA. Patients with Hermansky-Pudlak syndrome were readily identified. The new assay was also reliable in cases where the 5-HT content of dense granules was not correlated with the calcium or ATP content, such as in calcium deficiency or in the presence of selective serotonin reuptake inhibitors.

Acquired delta-storage pool deficiency associated with idiopathic myelofibrosis

A 73-year-old woman complained of easy bruising, as a consequence of prolonged bleeding time despite normal platelet counts. Platelet aggregation profile, mepacrine fluorescence test, flow cytometry and transmission electron microscopy studies led to the diagnosis of delta-storage pool deficiency (SPD) A few months later, she developed hyperleucocytosis with immature granulocytes and erythroblasts. The presence of bone marrow fibrosis and clonal cytogenetic abnormalities led to the diagnosis of idiopathic myelofibrosis (IM). Association between SPD and IM has never been reported. The pathogenesis of this unusual association remains unclear and may involve proliferation of abnormal monoclonal stem cells with differentiation into activated megakaryocytes associated with impaired dense granule development and increased cytokines release which may be. involved in myelofibrosis.

Platelet dense granules: structure, function and implications for haemostasis

The advances that have been made over the last decade in microscopic, biochemical, molecular, and genetic techniques have led to substantial improvement in our understanding of platelet dense granule structure and function, and the implications of dense granule deficiencies for haemostasis. However, much has still to be learned. For example, what is the specific mechanism of docking and fusion that occurs during dense granule exocytosis? What are the roles of dense granule membrane proteins during exocytosis or after expression on the surface of activated platelets? Finally, how do the genetic defects identified in HPS and CHS result in the clinical phenotype of these diseases, and what does this tell us about the origin and function of the affected subcellular organelles?

Hermansky-Pudlak syndrome: report of a case with histological, immunohistochemical and ultrastructural findings

We report a 38-year-old female of Puerto Rican descent with Hermansky-Pudlak syndrome and decreased levels of von Willebrand factor. Histologic and ultrastructural findings of non-sunexposed skin showed melanocytes with short dendritic processes and decreased numbers of melanosomes. Ultrastructural examination of platelets revealed greatly reduced numbers of delta granules. Recognition of this syndrome is important because skin neoplasms, ceroid deposition and hemorrhagic manifestations can be causes of morbidity and of potential death in patients affected with this syndrome.

Storage pool disease in chronic lymphocytic leukemia: abnormal aggregation and secretion without bleeding

Although bleeding complications are relatively common in patients with chronic lymphocytic leukemia, they tend to be related to thrombocytopenia or an acquired clotting factor inhibitor. Chronic lymphocytic leukemia-associated thrombocytopenia, which may also contribute to the hemorrhagic risk, is generally caused by decreased production and immune-mediated destruction. This is the case of a 56-year-old man with longstanding chronic lymphocytic leukemia who developed thrombocytopenia (platelet counts of approximately 50,000/microL) with an associated abnormal platelet morphology. Although the patient did not suffer clinically significant bleeding, several tests of platelet function were grossly abnormal. Electron microscopic examination of the platelets revealed virtually complete absence of dense granules. Platelet aggregation did not occur with adenosine diphosphate (10 microM), collagen (2 micrograms/mL), or ristocetin (1 mg/mL). Doubling the agonist concentrations produced only minimal agglutination with ristocetin. The bleeding time was mildly prolonged at 9.0 and 10.5 minutes. Von Willebrand antigen and ristocetin cofactor levels were normal. Collagen-induced adenosine triphosphate secretion was less than 10% that of a matched normal control. In contrast, platelet force development was virtually normal, reaching 4,800 dynes at 1,200 seconds compared with 5,800 dynes for the healthy control. The patient's clots demonstrated enhanced clot modulus 44,000 dynes/cm2 versus 22,400 dynes/cm2 for the healthy control. The latter finding was primarily because of high fibrinogen concentration. This third report of storage pool disease in a patient with chronic lymphocytic leukemia demonstrates that dense granule release is not required for normal platelet-mediated force development.