Gray platelet syndrome in the elderly

Gray platelet syndrome: natural history of a large patient cohort and locus assignment to chromosome 3p

Gray platelet syndrome (GPS) is an inherited bleeding disorder characterized by macrothrombocytopenia and absence of platelet α-granules resulting in typical gray platelets on peripheral smears. GPS is associated with a bleeding tendency, myelofibrosis, and splenomegaly. Reports on GPS are limited to case presentations. The causative gene and underlying pathophysiology are largely unknown. We present the results of molecular genetic analysis of 116 individuals including 25 GPS patients from 14 independent families as well as novel clinical data on the natural history of the disease. The mode of inheritance was autosomal recessive (AR) in 11 and indeterminate in 3 families. Using genome-wide linkage analysis, we mapped the AR-GPS gene to a 9.4-Mb interval on 3p21.1-3p22.1, containing 197 protein-coding genes. Sequencing of 1423 (69%) of the 2075 exons in the interval did not identify the GPS gene. Long-term follow-up data demonstrated the progressive nature of the thrombocytopenia and myelofibrosis of GPS resulting in fatal hemorrhages in some patients. We identified high serum vitamin B(12) as a consistent, novel finding in GPS. Chromosome 3p21.1-3p22.1 has not been previously linked to a platelet disorder; identification of the GPS gene will likely lead to the discovery of novel components of platelet organelle biogenesis. This study is registered at www.clinicaltrials.gov as NCT00069680 and NCT00369421.

Inherited disorders of platelet alpha-granules

Platelet alpha-granules are the storage site for the internal membrane glycoprotein P-selectin and for a variety of megakaryocyte-synthesized and plasma-derived soluble proteins. Quantitative and/or qualitative abnormalities in alpha-granules are found in a number of inherited bleeding disorders, including gray platelet syndrome, alphadelta-storage pool deficiency, the Quebec platelet disorder, and in some patients with dysmegakaryopoietic thrombocytopenia. In addition, single alpha-granular protein deficiencies are seen in other bleeding disorders,including factor V deficiency, afibrinogenemia, Glanzmann's thrombasthenia, von Willebrand disease, and plasminogen-activator inhibitor-1 deficiency. The excessive bleeding that occurs in patients with inherited abnormalities of platelet alpha-granules indicates that the proteins stored within this compartment are important for normal hemostasis. The clinical and laboratory features of these different, inherited platelet storage pool disorders suggest unique molecular and biochemical defects are responsible for these conditions. However, the genetic causes of these disorders are largely unknown. This paper reviews our current knowledge of the inherited disorders of platelet alpha-granules.

The gray platelet syndrome: Clinical spectrum of the disease

The gray platelet syndrome (GPS) is a rare inherited disorder of the megakaryocyte (MK) lineage. Thrombocytopenia and enlarged platelets are associated with a specific absence of alpha-granules and their contents. GPS patients exhibit much heterogeneity both in bleeding severity and in their response to platelet function testing. A unique feature is that proteins endogenously synthesised by megakaryocytes (MK) or endocytosed by MK or platelets fail to enter into the secretable storage pools that characterise alpha-granules of normal platelets. Although the molecular basis of the disease is unknown, evidence suggests that alpha-granules simply fail to mature during MK differentiation. One result is a continued leakage of growth factors and cytokines into the marrow causing myelofibrosis. While for some patients platelet function may be only moderately affected, for others thrombin and/or collagen-induced platelet aggregation is markedly modified and an acquired lack of the GPVI collagen receptor has been reported. In this review, we document the clinical and molecular heterogeneity in GPS, a unique disease of the biogenesis of platelet alpha-granules and of the storage of growth factors and secretable proteins.

Assessment of platelet numbers and morphology in the peripheral blood smear

Automated systems are currently in widespread use for the assessment of patients' complete blood counts. The evaluation of the peripheral blood smear, however, still constitutes a pivotal tool in the evaluation of patients with hematologic disorders. This article focuses on disorders affecting the number or morphology of platelets as assessed by evaluation of a peripheral blood smear and also outlines some of their important clinical findings.

A new genetic isolate of gray platelet syndrome (GPS): clinical, cellular, and hematologic characteristics

Gray platelet syndrome (GPS) is a disorder characterized by thrombocytopenia and large platelets that lack alpha granules and their contents. We describe two siblings with GPS who are members of a Moslem Bedouin genetic isolate. The children, an 8-year-old girl and a 5-year-old boy, had characteristic pale blue platelets lacking alpha granules on electron microscopy. Platelet aggregation studies were normal. The girl underwent a bone marrow aspiration and biopsy which showed mild myelofibrosis and extensive emperipolesis, i.e., the passage of other hematopoietic cells through megakaryocytes. Both children lacked high-molecular-weight multimers of von Willebrand factor (vWF) and had reduced activity and antigens of vWf. Platelet activation was approximately normal when ADP was employed as agonist, but significantly impaired using the thrombin receptor-activating peptide (TRAP). These findings are explained in light of the mechanism of action of each agonist. In addition, we propose that the emperipolesis was caused by increased P-selectin in megakaryocytes, and resulted in release of fibroblastic growth factors, explaining the myelofibrosis. The detailed description of these cases provides a basis for future differentiation of the various types of GPS, and for our current attempts to isolate the gene causing GPS in this genetic isolate.

Anesthetic implications of the grey platelet syndrome

PURPOSE

To describe the obstetrical anesthetic care provided to two sisters with a rare qualitative platelet disorder, the grey platelet syndrome (GPS).

CLINICAL FEATURES

Both patients manifested thrombocytopenia prior to delivery without previous history of a bleeding diathesis or other abnormal laboratory tests of coagulation function. The first required emergency Cesarean section due to fetal bradycardia. Due to the thrombocytopenia and the emergency nature of the procedure, general anesthesia was used. During the C-section, 1.5-2 litres of old blood was noted in the abdominal cavity which was attributed to an old splenic capsular tear of unknown etiology. Work-up for the thrombocytopenia revealed large platelets on the peripheral smear with abnormal aggregation on platelet function studies. Electron microscopy of the platelets revealed absent alpha granules, diagnostic of GPS. The second patient, the sister of patient #1, presented in a similar fashion. However, at presentation, the platelet count was 112,000 x m(-3) and spinal anesthesia was provided without complication for Cesarean delivery. The same patient presented for a second delivery during which fetal bradycardia necessitated emergency C-section under general anesthesia. Despite administration of six units of platelets, blood loss was 5,200 mL. Her postpartum course was uncomplicated and she and the infant were discharged home on postoperative day #4.

CONCLUSION

The primary concerns for the anesthesiologist looking after patients with qualitative platelet defects are related to defective coagulation which influences the need for perioperative replacement of blood products and limits the use of regional anesthesia.

Megakaryocytes and platelets in alpha-granule disorders

This chapter summarizes research data contributing to current understanding of disorders affecting alpha-granules of megakaryocytes and platelets. Diagnostic features of the gray platelet syndrome are well defined. Combined evidence suggests a defect, specific to the megakaryocyte cell lineage, causing a cytoskeletal abnormality and defective targeting of endogenously synthesized proteins to the alpha-granule. The abnormalities linked by signal transduction pathways. von Willebrand disease and afibrinogenaemia are disorders which highlight the functional importance of platelet storage pools of von Willebrand factor and fibrinogen, essential ligands in the process of adhesion and aggregation. The abnormality in the factor V Quebec disorder leads to a degradation of most proteins contained within the alpha-granule. The familial platelet disorder Paris-Trousseau thrombocytopenia is the only alpha-granule disorder associated with a cytogenetic abnormality, and it presents a useful model for exploring the genetic influence on regulation of thrombopoiesis. Study of these syndromes has elucidated aspects of the physiology of normal megakaryocyte maturation and platelet formation, including storage organelle biosynthesis.

Inherited giant platelet disorders

Giant platelet disorders (GPD) refer to rare, usually inherited states characterized by abnormally large platelets, thrombocytopenia and bleeding tendency of variable severity. This review summarizes major clinical and laboratory features of three GPDs (Bernard-Soulier syndrome, May-Hegglin anomaly and gray platelet syndrome). Differential diagnosis between immunological thrombocytopenia and GPDs is important. Although rare, giant platelet disorders should be borne in mind, since bleeding tendency in some individuals may be severe and knowledge of bleeding diathesis is of importance before delivery or surgical procedures also in less symptomatic individuals.

Gray platelet syndrome with splenomegaly and signs of extramedullary hematopoiesis: a case report with review of the literature

Gray platelet syndrome (GPS) is a rare bleeding disorder characterized by thrombocytopenia, agranular gray platelets in blood films, and almost total absence of platelet alpha-granules and their constituents. We describe here a rare case of GPS with myelofibrosis and splenomegaly indicating extramedullary hematopoiesis. Splenectomy was followed by normalization of platelet count but the bleeding diathesis continued. Based on a follow-up of more than 15 years, the slight myelofibrosis in our patient seems to be non-progressive. We also summarize the major clinical and laboratory features of previously published cases of GPS in order to obtain more comprehensive understanding of this rare disorder. From the clinical point of view, the bleeding tendency in this syndrome generally varies from mild to moderate, and no specific treatment is usually needed. Careful examination of peripheral blood films is necessary for the diagnosis of this rare syndrome.

The functions of thrombospondin and its involvement in physiology and pathophysiology

The thrombospondin family of molecules is expressed in many different tissues. Its expression is highly regulated by different hormones and cytokines and is developmentally controlled. It can bind to many different cell types, probably via an array of receptors which are similarly regulated. The level of thrombospondins in body fluids and their distribution in tissue change in correlation with various pathological states. It is linked to the growth of primary tumors and to metastasis, to development of the atherosclerotic plaque, to malaria infection and other diseases. The role(s) of thrombospondin(s) are by and large unknown, though specific interaction seem to affect particular cell functions. The wide-spread spatial and temporal regulation, multiple interactions and correlation with major diseases imply important roles in cell function and call for concerted effort to unravel the mystery.

Platelet secreted lipoprotein-like particle is taken up by the macrophage scavenger receptor and enhances cellular cholesterol accumulation

Enhanced macrophage cholesterol accumulation is associated with foam cell formation in the atherosclerotic lesion. Since platelet activation plays an important role in atherogenesis, we questioned whether products released from activated platelets could affect macrophage cholesterol metabolism. The addition of platelet-conditioned medium (PCM, obtained from collagen activated platelets) to a J-774 macrophage cell line, enhanced cellular cholesteryl ester content by 32%. The cholesterol esterification rate was also increased by 29%. Pre-loading the macrophages with cholesterol by incubation with acetyl-LDL, resulted in a further elevation of 48% in PCM-mediated cholesterol esterification. Possible mechanisms for the enhanced cholesterol esterification by J-774 macrophages following incubation with PCM include increased cholesterol influx and/or decreased cholesterol efflux (These cells were recently shown not to synthesize cholesterol). However, both increased uptake of PCM cholesterol by the macrophages as well as increased cellular cholesterol efflux (by 22%) were noted. The enhancement of cholesterol esterification by PCM was competitively inhibited by fucoidin and polyinosinic acid, implicating PCM binding to the scavenger receptor. This was further evidenced by the observations that apolipoprotein E which reduces cellular uptake via the scavenger receptor but not via the LDL receptor, also inhibited the effect of PCM, whereas IgG C-7, the LDL receptor antibody, did not alter the effect of PCM. Lysosomal involvement in the cellular processing of PCM was observed since PCM activity was inhibited by the lysosomal inhibitor, chloroquine. Partial purification of PCM by gel filtration revealed that the cholesterol component was associated with both phospholipids and proteins in a lipoprotein-like particle. Delipidation of PCM resulted in its inactivation but both heat treatment and tryptic digestion of PCM, revealed that the protein (and not only the cholesterol) component was also essential for the effect of PCM on cellular cholesterol esterification. Furthermore, PCM prepared from platelets of a patient with Gray Platelet Syndrome that lack platelet alfa granules (which contain platelet specific proteins), failed to enhance cholesterol esterification. These results demonstrate that lipoprotein-like particles released during platelet activation can interact with the macrophage scavenger receptor thus leading to enhanced cellular cholesterol accumulation.