Platelet δ-Storage Pool Disease: An Update

Neurosurgical bleeding in platelet storage pool disorder: a case report

Dense-granule deficiency (DGD) is an inherited platelet disorder due to the absence of dense granules essential for activation of platelets in the event of vascular injury. Decreased platelet dense granules can be detected by electron microscopy, while other tests of hemostasis, including platelet function analyzer (PFA®) closure times, may be normal. The present case report describes a patient with a lifelong history of mucocutaneous bleeding and excessive hemorrhage with resection of vestibular Schwannoma. After hemostasis was obtained the case was aborted and the neurosurgeon noted bleeding resembled as if patient was on an antiplatelet drug. Subsequent hematologic workup revealed a severe platelet function disorder. There is a paucity of literature on management of intracranial neurosurgery in patients with inherited platelet disorders. Patients undergoing major surgical procedures often receive tranexamic acid (TXA), desmopressin, and/or human-leukocyte antigen (HLA)-matched platelet transfusions. We review the clinical management of intracranial tumor surgery, as well as Cyberknife radiosurgery, in our patient with DGD. After diagnosis was known, thoughtful hemostatic planning with empiric platelet transfusions and TXA prevented recurrent bleeding.

Skin Telocytes Could Fundament the Cellular Mechanisms of Wound Healing in Platelet-Rich Plasma Administration

For more than 40 years, autologous platelet concentrates have been used in clinical medicine. Since the first formula used, namely platelet-rich plasma (PRP), other platelet concentrates have been experimented with, including platelet-rich fibrin and concentrated growth factor. Platelet concentrates have three standard characteristics: they act as scaffolds, they serve as a source of growth factors and cytokines, and they contain live cells. PRP has become extensively used in regenerative medicine for the successful treatment of a variety of clinical (non-)dermatological conditions like alopecies, acne scars, skin burns, skin ulcers, muscle, cartilage, and bone repair, and as an adjuvant in post-surgery wound healing, with obvious benefits in terms of functionality and aesthetic recovery of affected tissues/organs. These indications were well documented, and a large amount of evidence has already been published supporting the efficacy of this method. The primordial principle behind minimally invasive PRP treatments is the usage of the patient's own platelets. The benefits of the autologous transplantation of thrombocytes are significant, representing a fast and economic method that requires only basic equipment and training, and it is biocompatible, thus being a low risk for the patient (infection and immunological reactions can be virtually disregarded). Usually, the structural benefits of applying PRP are attributed to fibroblasts only, as they are considered the most numerous cell population within the interstitium. However, this apparent simplistic explanation is still eluding those different types of interstitial cells (distinct from fibroblasts) that are residing within stromal tissue, e.g., telocytes (TCs). Moreover, dermal TCs have an already documented potential in angiogenesis (extra-cutaneous, but also within skin), and their implication in skin recovery in a few dermatological conditions was attested and described ultrastructurally and immunophenotypically. Interestingly, PRP biochemically consists of a series of growth factors, cytokines, and other molecules, to which TCs have also proven to have a positive expression. Thus, it is attractive to hypothesize and to document any tissular collaboration between cutaneous administered PRP and local dermal TCs in skin recovery/repair/regeneration. Therefore, TCs could be perceived as the missing link necessary to provide a solid explanation of the good results achieved by administering PRP in skin-repairing processes.

ISTH bleeding assessment tool and platelet function analyzer in children with mild inherited platelet function disorders

OBJECTIVES

To evaluate the diagnostic performance of platelet function analyzer (PFA) and The International Society on Thrombosis and Hemostasis bleeding-assessment-tool (ISTH-BAT) in detecting mild inherited platelet function disorders (IPFDs) in children with suspected bleeding disorders.

METHODS

Prospective single-center diagnostic study including consecutive patients <18 years with suspected bleeding disorder and performing a standardized workup for platelet function defects including ISTH-BAT, PFA, platelet aggregation testing, blood smear-based immunofluorescence, and next-generation sequencing-based genetic screening for IPFDs.

RESULTS

We studied 97 patients, of which 34 von Willebrand disease (VWD, 22 type-1, 11 type-2), 29 IPFDs (including delta-/alpha-storage pool disease, Glanzmann thrombasthenia, Hermansky-Pudlak syndrome) and 34 with no diagnosis. In a model combining PFA-adenosine diphosphate (ADP), PFA-epinephrine (EPI), and ISTH-BAT overall performance to diagnose IPFDs was low with area under the curves of 0.56 (95% CI 0.44, 0.69) compared with 0.84 (95% CI 0.76, 0.92) for VWD. Correlation of PFA-EPI/-ADP and ISTH-BAT was low with 0.25/0.39 Spearman's correlation coefficients. PFA were significantly prolonged in patients with VWD and Glanzmann thrombasthenia. ISTH-BAT-scores were only positive in severe bleeding disorders, but not in children with mild IPFDs or VWD.

CONCLUSION

Neither ISTH-BAT nor PFA or the combination of both help diagnosing mild IPFDs in children. PFA is suited to exclude severe IPFDs or VWD and is in this regard superior to ISTH-BAT in children.

Frequency, clinical, and laboratory findings of platelet secretion disorders in patients referred to the specialized coagulation laboratory of the Iranian Blood Transfusion Organization

OBJECTIVES

Platelet secretion disorders (PSDs) are a subgroup of platelet function disorders (PFDs) caused by defects in the content or release of platelet granules. These patients have a variable degree of mucocutaneous bleeding tendency. The diagnostic facilities of PSDs are imitated in Iran, even in specialized coagulation laboratories. The present study aims to estimate the frequency of PSDs among patients referred to the Iranian Blood Transfusion Organization (IBTO).

METHODS

The research population includes all patients referred to the specialized coagulation laboratory of IBTO and requested platelet function and von Willebrand testing by their physicians. They were recruited between May 2022 and October 2022 if they were not diagnosed as having procoagulant defects, von Willebrand disease (VWD), Glanzmann thrombasthenia (GT), Bernard-Soulier syndrome (BSS), and platelet count <100 × 10 9 (except in the syndromic forms). Patients with a defect in response to at least two agonists in Light transmission aggregometry (LTA), one agonist in the ATP-secretion study, and/or impairment in the expression of CD62P are considered PSDs.

RESULTS

Among 121 cases referred to our center over 6 months, 40 patients fulfilled the inclusion and exclusion criteria. Ten patients were diagnosed with PSDs. Six were classified as δ-platelet secretion disorders (δ-PSD), two α-platelet secretion disorders (α-PSD), and two αδ-platelet secretion disorders (αδ-PSD).

CONCLUSIONS

The prevalence of PSDs in our population study was 25% (10/40), which seems highly prevalent. Therefore, expanding laboratory approaches to platelet function defects is necessary as a routine in our country.

Experience With Pre-procedural Hemostatic Medications versus Platelet Transfusion in Patients With Platelet Storage Pool Deficiency

BackgroundStorage pool deficiency (SPD) is a rare bleeding disorder characterized by reduction in the number of delta granules within platelets, interfering with hemostasis. Current literature lacks well-designed studies from which to draw concrete conclusions regarding pre-procedural management of bleeding complications. Objective: The purpose of this study is to describe bleeding and safety outcomes of SPD patients receiving either pre-procedural platelet transfusions or platelet-sparing regimens. Methods: An exploratory retrospective cohort study was conducted among SPD patients, comparing major bleeding events between those who received platelet transfusion and those who received desmopressin, tranexamic acid, and/or aminocaproic acid within 24 hours prior to procedure. Results: Rates of major bleeding were not found to be higher among patients who received a platelet-sparing regimen [platelet-sparing: 2/25 (8%); platelet transfusion: 2/29 (6.9%); P = .99]. Incidence of non-major bleeding was higher in the platelet transfusion group, but this was not statistically significant [platelet-sparing: 0/25 (0%); platelet transfusion: 3/29 (10.3%); P = .24]. Treatment-related adverse effects were observed following 8 of 54 procedures (14.8%). Conclusion: Use of a platelet-sparing regimen was not associated with a significantly higher incidence of major or non-major bleeding events. Future prospective trials are recommended to compare outcomes between therapies.

Delta Storage Pool Deficiency: A Pediatric Case Report and Review of the Literature

Platelet storage deficiencies are a heterogeneous group of bleeding disorders of variable severity caused by decreased number or content of platelet granules. We present the case of a 10-year-old patient with no personal history of previous bleeding who was admitted to the emergency department due to menorrhagia and mucocutaneous pallor. Common disorders of primary and secondary hemostasis were ruled out. Subsequently, a study of electron microscopy of platelets was performed, which reported the presence of alpha granules with a decreased number of dense granules. Currently, the patient receives treatment with tranexamic acid during menstrual periods, supplementation with ferrous sulfate, and oral contraceptives, achieving control of bleeding episodes.

Expanding applications of allogeneic platelets, platelet lysates, and platelet extracellular vesicles in cell therapy, regenerative medicine, and targeted drug delivery

Platelets are small anucleated blood cells primarily known for their vital hemostatic role. Allogeneic platelet concentrates (PCs) collected from healthy donors are an essential cellular product transfused by hospitals to control or prevent bleeding in patients affected by thrombocytopenia or platelet dysfunctions. Platelets fulfill additional essential functions in innate and adaptive immunity and inflammation, as well as in wound-healing and tissue-repair mechanisms. Platelets contain mitochondria, lysosomes, dense granules, and alpha-granules, which collectively are a remarkable reservoir of multiple trophic factors, enzymes, and signaling molecules. In addition, platelets are prone to release in the blood circulation a unique set of extracellular vesicles (p-EVs), which carry a rich biomolecular cargo influential in cell-cell communications. The exceptional functional roles played by platelets and p-EVs explain the recent interest in exploring the use of allogeneic PCs as source material to develop new biotherapies that could address needs in cell therapy, regenerative medicine, and targeted drug delivery. Pooled human platelet lysates (HPLs) can be produced from allogeneic PCs that have reached their expiration date and are no longer suitable for transfusion but remain valuable source materials for other applications. These HPLs can substitute for fetal bovine serum as a clinical grade xeno-free supplement of growth media used in the in vitro expansion of human cells for transplantation purposes. The use of expired allogeneic platelet concentrates has opened the way for small-pool or large-pool allogeneic HPLs and HPL-derived p-EVs as biotherapy for ocular surface disorders, wound care and, potentially, neurodegenerative diseases, osteoarthritis, and others. Additionally, allogeneic platelets are now seen as a readily available source of cells and EVs that can be exploited for targeted drug delivery vehicles. This article aims to offer an in-depth update on emerging translational applications of allogeneic platelet biotherapies while also highlighting their advantages and limitations as a clinical modality in regenerative medicine and cell therapies.

Platelet Delta (δ)-Storage Pool Deficiency: A Case Series and Review of the Literature

Hereditary platelet delta (δ)-storage pool deficiency is a rare condition in which there are fewer dense granules in platelets disrupting primary hemostasis. It can cause a mild-moderate bleeding tendency with normal coagulation studies; hence, it is an underdiagnosed diagnostic challenge. The authors present three patients with hereditary platelet delta (δ)-storage pool deficiency who had heavy menstrual bleeding, excessive bleeding following surgery, mucocutaneous bleeding, and a bleeding score greater than or equal to 6. These cases reveal the susceptibility of underdiagnosing platelet disorders and the significance of utilizing a bleeding assessment tool to help guide further workup with transmission electron microscopy to visualize the fewer dense granules in platelets. Although bleeding is typically moderate, it can be severe in certain scenarios, like after mucosal surgeries, and can lead to death, highlighting the importance of the condition's recognition and prophylactic treatment.

A Case Report of Rotational Thromboelastometry-Assisted Decision Analysis for Two Pregnant Patients With Platelet Storage Pool Disorder

Platelet storage pool disorders (PSPDs) constitute a diverse group of hematologic abnormalities, which share the common feature of a deficiency in the ability of platelets to aggregate. Parturients with PSPD can present management challenges to their care team when they present for childbirth, especially with regard to neuraxial anesthesia. We report a series of 2 deliveries from unrelated patients affected by PSPD. In particular, we highlight the utility of rotational thromboelastometry (ROTEM) and the need for a multidisciplinary approach to the care of patients with this hematologic abnormality.

Supplementation with omega-3 or omega-6 fatty acids attenuates platelet reactivity in postmenopausal women

Postmenopausal women are at increased risk for a cardiovascular event due to platelet hyperactivity. There is evidence suggesting that ω-3 polyunsaturated fatty acids (PUFAs) and ω-6 PUFAs have cardioprotective effects in these women. However, a mechanistic understanding of how these fatty acids regulate platelet function is unknown. In this study, we supplemented postmenopausal women with fish oil (ω-3 fatty acids) or evening primrose oil (ω-6 fatty acids) and investigated the effects on their platelet activity. The effects of fatty acid supplementation on platelet aggregation, dense granule secretion, and activation of integrin αIIbβ3 at basal levels and in response to agonist were tested in postmenopausal women following a supplementation and washout period. Supplementation with fish oil or primrose oil attenuated the thrombin receptor PAR4-induced platelet aggregation. Supplementation with ω-3 or ω-6 fatty acids decreased platelet dense granule secretion and attenuated basal levels of integrin αIIbβ3 activation. Interestingly, after the washout period following supplementation with primrose oil, platelet aggregation was similarly attenuated. Additionally, for either treatment, the observed protective effects post-supplementation on platelet dense granule secretion and basal levels of integrin activation were sustained after the washout period, suggesting a long-term shift in platelet reactivity due to fatty acid supplementation. These findings begin to elucidate the underlying mechanistic effects of ω-3 and ω-6 fatty acids on platelet reactivity in postmenopausal women. Hence, this study supports the beneficial effects of fish oil or primrose oil supplementation as a therapeutic intervention to reduce the risk of thrombotic events in postmenopausal women. https://clinicaltrials.gov/ct2/show/NCT02629497.

Expert opinion on the use of platelet secretion assay for the diagnosis of inherited platelet function disorders: Communication from the ISTH SSC Subcommittee on Platelet Physiology

Assessment of platelet secretion is crucial for diagnosing suspected inherited platelet function disorders (IPFD). A previous survey of the SSC on Platelet Physiology of the ISTH and a comprehensive review highlighted that most of the platelet secretion assays (PSAs) lack standardization and validation. The aim of this study was to provide expert consensus guidance on the use of PSAs for IPFD diagnosis. We surveyed 26 experts from 10 different countries using the RAND/UCLA methodology, to attain a consensus on sensitivity, specificity, feasibility, time to readout, and cost of most PSAs. Answers were then graded in three categories: appropriate, uncertain, and inappropriate. Equivocal or misinterpretable statements required a second and third round survey involving 14 of the original 26 experts. We report here the consolidated results of the entire procedure. There was uniform agreement on several general statements, including that PSAs should be performed in hemostasis laboratories as first line diagnostic tests even in patients with normal platelet aggregation, and should include a δ-granule secretion marker. Among the specific assays examined, lumiaggregometry, other luciferin/luciferase-based assays, high-performance liquid chromatography methods, radiolabeled-serotonin based assays, and whole-mount transmission electron microscopy were rated as appropriate for the measurement of δ-granule release, and platelet P-selectin expression by flow cytometry and released proteins by ELISA for α-granule release. For most of the other PSAs, the expert opinions were widely dispersed. Lack of expert consensus on many PSAs clearly indicates an unmet need for rigorous standardization, multicenter comparison of results, and validation of PSAs for clinical laboratory practice.

Screening platelet function in blood donors

Background

Transfusion of defective platelets could contribute to the inefficiency of platelet transfusion in preventing or stopping bleeding.

Study Design and Methods

This single‐center prospective study aimed to determine the prevalence of functional platelet abnormalities in a population of blood donors with a clinical history of bleeding diathesis or with history of hematoma (>4 cm) during blood donation. Donors with positive bleeding screening questionnaire were referred to the reference center for rare platelet diseases at La Timone University Hospital (Marseille) to confirm the bleeding tendency using a more extensive bleeding questionnaire (MCMDMscore) and to assess hemostasis, including a comprehensive platelet analysis.

Results

One hundred and ninety‐five donors identified based on a history of hematoma and 2434 blood donors were included in the study. Eighty‐eight donors (3.6%) had a bleeding score indicating a potential bleeding disorder. Five donors with a history of hematoma (2.5%) and 15 (17%) donors with a confirmed bleeding score underwent hemostatic analysis, including two men and 18 women with average age of 33.9 years. Minor hemostatic abnormalities were observed in three donors. Two donors exhibited accelerated fibrinolysis with reduced euglobulin lysis time and increased D‐dimer levels in serum. Two donors had a platelet granule defect, without identification of genetic abnormality.

Conclusion

The bleeding questionnaire proved to be a valuable tool to screen blood donors for potential platelet defects. Platelet dysfunction was rare in the blood donor population assessed. Additional studies are necessary to understand the clinical impact that the transfusion of platelets with qualitative defects has on recipients.

Insights Into Platelet-Derived MicroRNAs in Cardiovascular and Oncologic Diseases: Potential Predictor and Therapeutic Target

Non-communicable diseases (NCDs), represented by cardiovascular diseases and cancer, have been the leading cause of death globally. Improvements in mortality from cardiovascular (CV) diseases (decrease of 14%/100,000, United States) or cancers (increase 7.5%/100,000, United States) seem unsatisfactory during the past two decades, and so the search for innovative and accurate biomarkers of early diagnosis and prevention, and novel treatment strategies is a valuable clinical and economic endeavor. Both tumors and cardiovascular system are rich in angiological systems that maintain material exchange, signal transduction and distant regulation. This pattern determines that they are strongly influenced by circulating substances, such as glycolipid metabolism, inflammatory homeostasis and cyclic non-coding RNA and so forth. Platelets, a group of small anucleated cells, inherit many mature proteins, mRNAs, and non-coding RNAs from their parent megakaryocytes during gradual formation and manifest important roles in inflammation, angiogenesis, atherosclerosis, stroke, myocardial infarction, diabetes, cancer, and many other diseases apart from its classical function in hemostasis. MicroRNAs (miRNAs) are a class of non-coding RNAs containing ∼22 nucleotides that participate in many key cellular processes by pairing with mRNAs at partially complementary binding sites for post-transcriptional regulation of gene expression. Platelets contain fully functional miRNA processors in their microvesicles and are able to transport their miRNAs to neighboring cells and regulate their gene expression. Therefore, the importance of platelet-derived miRNAs for the human health is of increasing interest. Here, we will elaborate systematically the roles of platelet-derived miRNAs in cardiovascular disease and cancer in the hope of providing clinicians with new ideas for early diagnosis and therapeutic strategies.

Circumcision bleeding rates in patients diagnosed with delta-storage pool deficiency later in life

BACKGROUND

Male circumcision is a common procedure, generally performed during the newborn period. Bleeding is an uncommon but feared complication of circumcision. Few reports have evaluated circumcision bleeding rates in patients with bleeding disorders.

OBJECTIVES

To study circumcision bleeding rates in male subjects who were diagnosed later in life with delta-storage pool deficiency (δ-SPD).

METHODS

We retrospectively reviewed the medical records of male subjects (≤18 years of age) who were circumcised without hemostatic prophylaxis prior to δ-SPD diagnosis from 2000 to 2020. Bleeding rates and severity were the main outcomes evaluated. We collected demographic data, bleeding scores using a validated assessment tool, laboratory data, and platelet electron microscopy results. A descriptive analysis was performed.

RESULTS

Twenty-five male subjects were included. The median bleeding score at presentation was 3.5 (range: 2-9). The diagnosis was confirmed using platelet electron microscopy. A value of <2 dense granules/platelet was considered abnormal. Circumcision was performed at a median age of 2 days (range: 1 day to 4 months). None of the subjects had intraoperative or postoperative bleeding. With a bleeding rate of zero, we suggest that newborn males with a family history of δ-SPD may be safely circumcised without hemostatic prophylaxis.

Current methods to analyze lysosome morphology, positioning, motility and function

Since the discovery of lysosomes more than 70 years ago, much has been learned about the functions of these organelles. Lysosomes were regarded as exclusively degradative organelles, but more recent research has shown that they play essential roles in several other cellular functions, such as nutrient sensing, intracellular signalling and metabolism. Methodological advances played a key part in generating our current knowledge about the biology of this multifaceted organelle. In this review, we cover current methods used to analyze lysosome morphology, positioning, motility and function. We highlight the principles behind these methods, the methodological strategies and their advantages and limitations. To extract accurate information and avoid misinterpretations, we discuss the best strategies to identify lysosomes and assess their characteristics and functions. With this review, we aim to stimulate an increase in the quantity and quality of research on lysosomes and further ground-breaking discoveries on an organelle that continues to surprise and excite cell biologists.

Platelet Storage Pool Deficiency and Elevated Inflammatory Biomarkers Are Prevalent in Postural Orthostatic Tachycardia Syndrome

A significant number of postural orthostatic tachycardia syndrome (POTS) patients have platelet delta granule storage pool deficiency (δ-SPD). The etiology of POTS is unknown but a number of laboratories, including ours, have reported elevations of G-protein-coupled adrenergic receptor and muscarinic acetylcholine receptor autoantibodies in POTS patients, detected by a variety of techniques, suggesting that the disorder is an autoimmune condition. Thus, it could also be considered an inflammatory disease. In a pilot study, we investigated a limited number of platelet-related cytokines and chemokines and discovered many that were elevated. This case−control study validates our pilot study results that POTS patients have an activated innate immune system. Plasma of 35 POTS patients and 35 patients with unexplained bleeding symptoms and categorized as “non-POTS” subjects was analyzed by multiplex flow cytometry to quantify 16 different innate immune system cytokines and chemokines. Electron microscopy was used to quantify platelet dense granules. Ten of 16 biomarkers of inflammation were elevated in plasma from POTS patients compared to non-POTS subjects, with most of the differences extremely significant, with p values < 0.0001. Of particular interest were elevations of IL-1β and IL-18 and decreased or normal levels of type 1 interferons in POTS patients, suggesting that the etiology of POTS might be autoinflammatory. All POTS patients had δ-SPD. With a growing body of evidence that POTS is an autoimmune disease and having elevations of the innate immune system, our results suggest a potential T-cell-mediated autoimmunity in POTS characteristic of a mixed-pattern inflammatory disease similar to rheumatoid arthritis.

An Investigation of ABO Blood Type and the Platelet Delta Granule Storage Pool

Individuals with bleeding tendencies are more likely to have blood type O than blood types A, B, or AB. Platelet storage pool deficiencies are a lesser-known group of bleeding disorders which often go undiagnosed and may account for a significant number of patients with unexplained bleeding defects. We hypothesized that patients with platelet δ-storage pool deficiency might also have a predominance of type O blood. A retrospective review of medical records of 2,020 patients with unexplained bleeding and evaluated for δ-storage pool deficiency was performed. Correlations between dense granule numbers, blood type, and von Willebrand factor were analyzed for statistical differences. 51.5% of blood samples were blood type O compared to an incidence of 44.0% in the U.S. population. There was a significant association of vWF and blood type O but not with the delta storage pool. There is a preponderance of blood type O in the study population compared to the U.S. population. There is no statistically significant link between blood type O and lower dense granule numbers in this study.

Cryptogenic oozers and bruisers

Bleeding disorders with normal, borderline, or nondiagnostic coagulation tests represent a diagnostic challenge. Disorders of primary hemostasis can be further evaluated by additional platelet function testing modalities, platelet electron microscopy, repeat von Willebrand disease testing, and specialized von Willebrand factor testing beyond the usual initial panel. Secondary hemostasis is further evaluated by coagulation factor assays, and factor XIII assays are used to diagnose disorders of fibrin clot stabilization. Fibrinolytic disorders are particularly difficult to diagnose with current testing options. A significant number of patients remain unclassified after thorough testing; most unclassified patients have a clinically mild bleeding phenotype, and many may have undiagnosed platelet function disorders. High-throughput genetic testing using large gene panels for bleeding disorders may allow diagnosis of a larger number of these patients in the future, but more study is needed. A logical laboratory workup in the context of the clinical setting and with a high level of expertise regarding test interpretation and limitations facilitates a diagnosis for as many patients as possible.

Hepatocyte-specific glucose-6-phosphatase deficiency disturbs platelet aggregation and decreases blood monocytes upon fasting-induced hypoglycemia

OBJECTIVE

Glycogen storage disease type 1a (GSD Ia) is a rare inherited metabolic disorder caused by mutations in the glucose-6-phosphatase (G6PC1) gene. When untreated, GSD Ia leads to severe fasting-induced hypoglycemia. Although current intensive dietary management aims to prevent hypoglycemia, patients still experience hypoglycemic events. Poor glycemic control in GSD Ia is associated with hypertriglyceridemia, hepatocellular adenoma and carcinoma, and also with an increased bleeding tendency of unknown origin.

METHODS

To evaluate the effect of glycemic control on leukocyte levels and coagulation in GSD Ia, we employed hepatocyte-specific G6pc1 deficient (L-G6pc-/-) mice under fed or fasted conditions, to match good or poor glycemic control in GSD Ia, respectively.

RESULTS

We found that fasting-induced hypoglycemia in L-G6pc-/- mice decreased blood leukocytes, specifically proinflammatory Ly6Chi monocytes, compared to controls. Refeeding reversed this decrease. The decrease in Ly6Chi monocytes was accompanied by an increase in plasma corticosterone levels and was prevented by the glucocorticoid receptor antagonist mifepristone. Further, fasting-induced hypoglycemia in L-G6pc-/- mice prolonged bleeding time in the tail vein bleeding assay, with reversal by refeeding. This could not be explained by changes in coagulation factors V, VII, or VIII, or von Willebrand factor. While the prothrombin and activated partial thromboplastin time as well as total platelet counts were not affected by fasting-induced hypoglycemia in L-G6pc-/- mice, ADP-induced platelet aggregation was disturbed.

CONCLUSIONS

These studies reveal a relationship between fasting-induced hypoglycemia, decreased blood monocytes, and disturbed platelet aggregation in L-G6pc-/- mice. While disturbed platelet aggregation likely accounts for the bleeding phenotype in GSD Ia, elevated plasma corticosterone decreases the levels of proinflammatory monocytes. These studies highlight the necessity of maintaining good glycemic control in GSD Ia.

Cardiovascular serotonergic system: Evolution, receptors, transporter, and function

The serotonergic system, serotonin (5HT), serotonin transporter (SERT), and serotonin receptors (5HT-x), is an evolutionarily ancient system that has clear physiological advantages to all life forms from bacteria to humans. This review focuses on the role of platelet/plasma serotonin and the cardiovascular system with minor references to its significant neurotransmitter function. Platelets transport and store virtually all plasma serotonin in dense granules. Stored serotonin is released from activated platelets and can bind to serotonin receptors on platelets and cellular components of the vascular wall to augment aggregation and induce vasoconstriction or vasodilation. The vascular endothelium is critical to the maintenance of cardiovascular homeostasis. While there are numerous ligands, neurological components, and baroreceptors that effect vascular tone it is proposed that serotonin and nitric oxide (an endothelium relaxing factor) are major players in the regulation of systemic blood pressure. Signals not fully defined, to date, that direct serotonin binding to one of the 15 identified 5HT receptors versus the transporter, and the role platelet/plasma serotonin plays in regulating hypertension within the cardiovascular system remain important issues to better understand many diseases and to develop new drugs. Also, expanded research of these pathways in lower life-forms may serve as important model systems to further our understanding of the evolution and mechanisms of action of serotonin.

Platelet Aggregation Assays Do Not Reliably Diagnose Platelet Delta Granule Storage Pool Deficiency

Background

Patients with platelet dysfunction disorders present with a variety of mucocutaneous bleeding symptoms including easy bruising, frequent epistaxis, bleeding gums upon tooth brushing and for women, heavy menstrual bleeding. Available laboratory assays to evaluate platelet function include the platelet function analyzer (PFA) and in larger centers with coagulation laboratories, light transmission platelet aggregometry (LTA) analyses. Both assays are known to have a number of limitations, especially in the diagnosis of platelet delta granule storage pool deficiency (δ-SPD). δ-SPD is an underdiagnosed condition caused by decreased numbers of platelet dense granules (DGs) and is best diagnosed by electron microscopy (EM). Patients with platelet δ-SPD have a decreased response to low levels of the agonist adenosine diphosphate (ADP) in the second wave of light transmittance with LTA or decreased ADP secretion by fluorescence lumiaggregometry. There are few reports that have evaluated patients with δ-SPD and their respective LTA results. One report published in 1987 described normal LTA assays in 23% of patients with δ-SPD; a more recent report described LTA as having the sensitivity to detect only about 52% of patients with δ-SPD. The purpose of our study was intended to review the LTA and EM results of patients suspected of having a platelet function disorder at our institution for comparison with previously published studies.

Methods

Our study included 344 patients who had been evaluated by both LTA and whole mount EM. Aggregometry utilized five agonists: ADP, epinephrine, collagen, arachidonic acid, and ristocetin. DGs were enumerated in 100 whole-mounted platelets to determine a mean number of dense granules per platelet (DGs/PL).

Results

Seventy-seven percent of our patients were found to have δ-SPD (264/344); 68% (179/264) of these subjects had an abnormal platelet LTA. Thirty-two percent (85/264) of our patients had normal LTA results but were found to have δ-SPD with a mean of 2.54 ± 0.15 DG/PL (normal = 4 - 6 DG/PL).

Conclusion

These data confirm previous reports suggesting the utilization of LTA alone in patients with histories of unexplained bleeding may miss the diagnosis of platelet δ-SPD. It is, therefore, prudent to assess platelet DG number by EM, especially if platelet LTA assessment is normal.

Diagnosing Inherited Platelet Disorders: Modalities and Consequences

Inherited platelet disorders (IPDs) are a group of rare conditions featured by reduced circulating platelets and/or impaired platelet function causing variable bleeding tendency. Additional hematological or non hematological features, which can be congenital or acquired, distinctively mark the clinical picture of a subgroup of patients. Recognizing an IPD is challenging, and diagnostic delay or mistakes are frequent. Despite the increasing availability of next-generation sequencing, a careful phenotyping of suspected patients-concerning the general clinical features, platelet morphology, and function-is still demanded. The cornerstones of IPD diagnosis are clinical evaluation, laboratory characterization, and genetic testing. Achieving a diagnosis of IPD is desirable for several reasons, including the possibility of tailored therapeutic strategies and individual follow-up programs. However, detailed investigations can also open complex scenarios raising ethical issues in case of IPDs predisposing to hematological malignancies. This review offers an overview of IPD diagnostic workup, from the interview with the proband to the molecular confirmation of the suspected disorder. The main implications of an IPD diagnosis are also discussed.

Platelet storage pool disorder: multidisciplinary planning in pregnancy

A 32-year old primigravida woman presented for antenatal care giving a history that her mother had platelet storage pool disorder (PSPD). The patient was subsequently diagnosed with PSPD during her pregnancy and had a caesarean delivery for breech presentation at 39 weeks. In this paper, we discuss the basic science, inheritance pattern, symptoms and management of this condition, alongside the antenatal and intrapartum and postnatal management specific to it, highlighting the need for a multidisciplinary approach to care. PSPD refers to a group of rare conditions involving defects in platelet granule storage or secretion, which leads to abnormal aggregation and activation of platelets. There are both genetic and acquired forms of the condition. It is a functional platelet disorder, meaning platelet counts will usually remain in the normal range. The diagnosis may be suspected due to characteristic signs and symptoms, but patients may also be asymptomatic. There have been only a few documented cases of pregnant women with PSPD; therefore, management is not clear. Vaginal delivery is not contraindicated, however, postpartum haemorrhage should be anticipated and planned for the use of deamino D-arginine vasopressin (DDAVP), tranexamic acid, prophylactic oxytocics and prompt access to blood products, including platelets, if required. This case highlights the need for effective multidisciplinary teamwork between obstetricians, anaesthetists and haematologists to ensure high-quality care and enable careful intrapartum management planning.

Inherited Platelet Disorders: An Updated Overview

Platelets play a major role in hemostasis as ppwell as in many other physiological and pathological processes. Accordingly, production of about 10¹¹ platelet per day as well as appropriate survival and functions are life essential events. Inherited platelet disorders (IPDs), affecting either platelet count or platelet functions, comprise a heterogenous group of about sixty rare diseases caused by molecular anomalies in many culprit genes. Their clinical relevance is highly variable according to the specific disease and even within the same type, ranging from almost negligible to life-threatening. Mucocutaneous bleeding diathesis (epistaxis, gum bleeding, purpura, menorrhagia), but also multisystemic disorders and/or malignancy comprise the clinical spectrum of IPDs. The early and accurate diagnosis of IPDs and a close patient medical follow-up is of great importance. A genotype-phenotype relationship in many IPDs makes a molecular diagnosis especially relevant to proper clinical management. Genetic diagnosis of IPDs has been greatly facilitated by the introduction of high throughput sequencing (HTS) techniques into mainstream investigation practice in these diseases. However, there are still unsolved ethical concerns on general genetic investigations. Patients should be informed and comprehend the potential implications of their genetic analysis. Unlike the progress in diagnosis, there have been no major advances in the clinical management of IPDs. Educational and preventive measures, few hemostatic drugs, platelet transfusions, thrombopoietin receptor agonists, and in life-threatening IPDs, allogeneic hematopoietic stem cell transplantation are therapeutic possibilities. Gene therapy may be a future option. Regular follow-up by a specialized hematology service with multidisciplinary support especially for syndromic IPDs is mandatory.

Platelet Phenotyping and Function Testing in Thrombocytopenia

Patients who suffer from inherited or acquired thrombocytopenia can be also affected by platelet function defects, which potentially increase the risk of severe and life-threatening bleeding complications. A plethora of tests and assays for platelet phenotyping and function analysis are available, which are, in part, feasible in clinical practice due to adequate point-of-care qualities. However, most of them are time-consuming, require experienced and skilled personnel for platelet handling and processing, and are therefore well-established only in specialized laboratories. This review summarizes major indications, methods/assays for platelet phenotyping, and in vitro function testing in blood samples with reduced platelet count in relation to their clinical practicability. In addition, the diagnostic significance, difficulties, and challenges of selected tests to evaluate the hemostatic capacity and specific defects of platelets with reduced number are addressed.

Oral Squamous Cell Carcinoma Is Associated with a Low Thrombosis Risk Due to Storage Pool Deficiency in Platelets

Venous thrombo-embolism (VTE) disease is the second most common cause of mortality in cancer patients, and evaluation and prevention of thrombosis risk is essential. VTE-associated risk varies according to the type of tumor disease. Oral cancer is the most frequent type of head and neck cancer, and it represents approximately 2.1% of all cancers worldwide. Most tumors are squamous cell carcinomas and are mainly due to tobacco and alcohol abuse. VTE risk associated with oral squamous cell carcinoma (OSCC) is low. However, many studies have shown that OSCC has the following biological features of cancers associated with a high thrombosis risk: modified thrombosis and fibrinolysis mechanisms; strong expression of procoagulant proteins; secretion of procoagulant microparticles; and production of procoagulant cytokines. Using an original mouse model of tongue squamous cell carcinoma, our study aimed to clarify this paradoxical situation. First, we showed that OSCC tumors have a pro-aggregatory phenotype and a high local thrombosis risk. Second, we found that tongue tumor mice do not have an elevated systemic thrombosis risk (the risk of an "at distance" thrombosis event such as lower extremity deep venous thrombosis or pulmonary embolism) and even show a reduction in risk. Third, we demonstrated that tongue tumor mice show a reduction in platelet reactivity, which explains the low systemic thrombosis risk. Finally, we found that tongue tumor mice present granule pool deficiency, thereby explaining the reduction in platelet reactivity and systemic thrombosis risk.

Thrombocytopathies: Not Just Aggregation Defects-The Clinical Relevance of Procoagulant Platelets

Platelets are active key players in haemostasis. Qualitative platelet dysfunctions result in thrombocytopathies variously characterized by defects of their adhesive and procoagulant activation endpoints. In this review, we summarize the traditional platelet defects in adhesion, secretion, and aggregation. In addition, we review the current knowledge about procoagulant platelets, focusing on their role in bleeding or thrombotic pathologies and their pharmaceutical modulation. Procoagulant activity is an important feature of platelet activation, which should be specifically evaluated during the investigation of a suspected thrombocytopathy.

Prospective Therapeutic Applications of Platelet Extracellular Vesicles

There is much interest in the use of extracellular vesicles (EVs) as a subcellular therapy for regenerative medicine and drug delivery. Blood-borne platelets represent a source of therapeutic EVs that is so far largely unexplored. Advantages of platelets as a cellular source of EVs include their established clinical value, regulated collection procedures, availability in a concentrated form, propensity to generate EVs, and unique composition and tissue-targeting capacity. This review analyzes the unique potential of platelet-derived (p-) EVs as therapeutic modalities and presents their inherent translational advantages for hemostasis, for regenerative medicine, and as drug-delivery vehicles.