Autosomal dominant macrothrombocytopenia in Italy is most frequently a type of heterozygous Bernard-Soulier syndrome

Inherited Platelet Disorders: A Short Introduction

Platelets play an important role regarding coagulation by contributing to thrombus formation by platelet adhesion, aggregation, and α-/δ-granule secretion. Inherited platelet disorders (IPDs) are a very heterogeneous group of disorders that are phenotypically and biochemically diverse. Platelet dysfunction (thrombocytopathy) can be accompanied by a reduction in the number of thrombocytes (thrombocytopenia). The extent of the bleeding tendency can vary greatly. Symptoms comprise mucocutaneous bleeding (petechiae, gastrointestinal bleeding and/or menorrhagia, epistaxis) and increased hematoma tendency. Life-threatening bleeding can occur after trauma or surgery. In the last years, next-generation sequencing had a great impact on unrevealing the underlying genetic cause of individual IPDs. Because IPDs are so diverse, a comprehensive analysis of platelet function and genetic testing is indispensable.

Biological, clinical features and modelling of heterozygous variants of glycoprotein Ib platelet subunit alpha (GP1BA) and glycoprotein Ib platelet subunit beta (GP1BB) genes responsible for constitutional thrombocytopenia

Constitutional thrombocytopenias are rare disorders, often difficult to discriminate from acquired thrombocytopenias. More than 80 genes have been described as being at the origin of these diseases. Among them, several variants of the glycoprotein Ib platelet subunit alpha (GP1BA) and glycoprotein Ib platelet subunit beta (GP1BB) genes, coding for the GpIb-IX-V glycoprotein complex, have been reported in the literature. The study reported here aimed at describing newly identified monoallelic anomalies affecting the GP1BA and GP1BB genes on a clinical, biological and molecular level. In a cohort of nine patients with macrothrombocytopenia, eight heterozygous variants of the GP1BA or GP1BB genes were identified. Five of them had never been described in the heterozygous state. Computer modelling disclosed structure/function relationships of these five variants.

A GP1BA Variant in a Czech Family with Monoallelic Bernard-Soulier Syndrome

Bernard-Soulier syndrome (BSS) is a rare inherited disorder characterized by unusually large platelets, low platelet count, and prolonged bleeding time. BSS is usually inherited in an autosomal recessive (AR) mode of inheritance due to a deficiency of the GPIb-IX-V complex also known as the von Willebrand factor (VWF) receptor. We investigated a family with macrothrombocytopenia, a mild bleeding tendency, slightly lowered platelet aggregation tests, and suspected autosomal dominant (AD) inheritance. We have detected a heterozygous GP1BA likely pathogenic variant, causing monoallelic BSS. A germline GP1BA gene variant (NM_000173:c.98G > A:p.C33Y), segregating with the macrothrombocytopenia, was detected by whole-exome sequencing. In silico analysis of the protein structure of the novel GPIbα variant revealed a potential structural defect, which could impact proper protein folding and subsequent binding to VWF. Flow cytometry, immunoblot, and electron microscopy demonstrated further differences between p.C33Y GP1BA carriers and healthy controls. Here, we provide a detailed insight into its clinical presentation and phenotype. Moreover, the here described case first presents an mBSS patient with two previous ischemic strokes.

Pathogenic Aspects of Inherited Platelet Disorders

Inherited platelet disorders (IPDs) constitute a large heterogeneous group of rare bleeding disorders. These are classified into: (1) quantitative defects, (2) qualitative disorders, or (3) altered platelet production rate disorders or increased platelet turnover. Classically, IPD diagnostic is based on clinical phenotype characterization, comprehensive laboratory analyses (platelet function analysis), and, in former times, candidate gene sequencing. Today, molecular genetic analysis is performed using next-generation sequencing, mostly by targeting enrichment of a gene panel or by whole-exome sequencing. Still, the biochemical and molecular genetic characterization of patients with congenital thrombocytopathias/thrombocytopenia is essential, since postoperative or posttraumatic bleeding often occurs due to undiagnosed platelet defects. Depending upon the kind of surgery or trauma, this bleeding may be life-threatening, e.g., after tonsillectomy or in brain surgery. Undiagnosed platelet defects may lead to additional surgery, hysterectomy, pulmonary bleeding, and even resuscitation. In addition, these increased bleeding symptoms can lead to wound healing problems. Only specialized laboratories can perform the special platelet function analyses (aggregometry, flow cytometry, or immunofluorescent microscopy of the platelets); therefore, many IPDs are still undetected.

A novel mutation in GP1BA gene in a family with autosomal dominant Bernard Soulier syndrome variant: A case report

Classic Bernard-Soulier syndrome (BSS) is a rare form of autosomal recessive disorder that is caused by mutations in the GP1BA gene that encode the GPIb-V-IX complex, a receptor of von Willebrand factor. BSS characterized by macrothrombocytopenia and excessive bleeding. The present study reports a single case (18-month Chinese girl) diagnosed with BSS. The patient suffered mild thrombocytopenia, giant platelets and normal platelet aggregation. In addition, mild bleeding and thrombocytopenia were also indicated in thirteen family members, including the proband and her father. Gene sequence analysis identified a monoallelic missense mutation in GP1BA (c.97T>A), which encodes a p.C33R substitution in the N-terminal domain of glycoprotein (GP)Ibα that may disrupt the protein structure. To the best of our knowledge, this dominant variant has not been reported previously. BSS's autosomal dominant inheritance mode is rarely identified and can be easily misdiagnosed as immune thrombocytopenia. For patients with giant platelets, thrombocytopenia and positive family history, next-generation sequencing for inherited thrombocytopenia, especially disorders that are caused by mutations in glycoprotein Ib-IX-V complex, is required.

Structure-function of platelet glycoprotein Ib-IX

The glycoprotein (GP)Ib-IX receptor complex plays a critical role in platelet physiology and pathology. Its interaction with von Willebrand factor (VWF) on the subendothelial matrix instigates platelet arrest at the site of vascular injury and is vital to primary hemostasis. Its reception to other ligands and counter-receptors in the bloodstream also contribute to various processes of platelet biology that are still being discovered. While its basic composition and its link to congenital bleeding disorders were well documented and firmly established more than 25 years ago, recent years have witnessed critical advances in the organization, dynamics, activation, regulation, and functions of the GPIb-IX complex. This review summarizes important findings and identifies questions that remain about this unique platelet mechanoreceptor complex.

Inherited Platelet Disorders: Diagnosis and Management

Inherited platelet disorders are rare but they can have considerable clinical impacts, and studies of their causes have advanced understanding of platelet formation and function. Effective hemostasis requires adequate circulating numbers of functional platelets. Quantitative, qualitative and combined platelet disorders with a bleeding phenotype have been linked to defects in platelet cytoskeletal elements, cell surface receptors, signal transduction pathways, secretory granules and other aspects. Inherited platelet disorders have variable clinical presentations, and diagnosis and management is often challenging. Evaluation begins with detailed patient and family histories, including a bleeding score. The physical exam identifies potential syndromic features of inherited platelet disorders and rules out other causes. Laboratory investigations include a complete blood count, blood film, coagulation testing and Von Willebrand factor assessment. A suspected platelet function disorder is further assessed by platelet aggregation, flow cytometry, platelet dense granule release and/or content, and genetic testing. The management of platelet function disorders aims to minimize the risk of bleeding and achieve adequate hemostasis when needed. Although not universal, platelet transfusion remains a crucial component in the management of many inherited platelet disorders.

Novel Compound Heterozygous Mutations in Two Families With Bernard-Soulier Syndrome

Background: Bernard-Soulier Syndrome (BSS) is a rare autosomal recessive bleeding disorder with large platelets and thrombocytopenia. It is caused by homozygous or compound heterozygous mutations in the GP1BA, GP1BB, or GP9 genes, which together encode the platelet surface receptor glycoprotein complex GPIb-IX-V. Objectives: We report two novel heterozygous mutations in the GP1BA and the GP9 genes, respectively. Patients/Methods: We analyzed the platelet glycoprotein expression by flow cytometry and screened the relevant genes for responsible mutations in two unrelated families. Results: Flow cytometric analyses revealed the absence of CD42a (GPIX) and CD42b (GPIb) on the platelets in the two affected siblings of family 1 and a significantly reduced expression of CD42b (GPIb) in the patient of family 2. In the two siblings, we identified a known frameshift (c.1601_1602delAT) and a novel nonsense mutation (c.1036C>T) in the GP1BA gene that abrogated the production of GP1bα. In the other patient, we found a novel missense mutation (c.112T>C) that was co-inherited with a common one (c.182A>G) in the GP9 gene, respectively. All analyzed heterozygous carriers were asymptomatic and had a normal GPIb-IX-V expression. Conclusions: The two novel GP1BA and GP9 mutations reported herein increment the number of causative genetic defects in BSS.

A novel mutation in the GP1BA gene in Bernard-Soulier syndrome

: The Bernard-Soulier syndrome (BSS) is a rare disease with a prevalence of 1/1000 000; it is characterized by macrothrombocytopenia. BSS develops as a result of a defect in the glycoprotein GPIb-IX-V complex on the platelet surface. In this article, we present a pediatric patient with the novel mutation that has been identified for the first time in BSS. A 13-month-old male patient was admitted with severe thrombocytopenia unresponsive to intravenous immunoglobulin in the neonatal period and recurrent mucocutaneous bleeding which initiated at 5 months of age. glycoprotein (GP) IX (CD42a) expression was normal as per flow cytometry results. Genetic analysis revealed a homozygous c.243C>A (p.Cys81) (p.C81) mutation. This novel mutation identified by us presents with severe thrombocytopenia and normal GPIX (CD42a) expression and is mistaken for immune thrombocytopenia in the neonatal period. This mutation creates an early stop codon and possibly leads to loss of function of the receptor.

Leucine Rich Repeat Proteins: Sequences, Mutations, Structures and Diseases

Mutations in the genes encoding Leucine Rich Repeat (LRR) containing proteins are associated with over sixty human diseases; these include high myopia, mitochondrial encephalomyopathy, and Crohn's disease. These mutations occur frequently within the LRR domains and within the regions that shield the hydrophobic core of the LRR domain. The amino acid sequences of fifty-five LRR proteins have been published. They include Nod-Like Receptors (NLRs) such as NLRP1, NLRP3, NLRP14, and Nod-2, Small Leucine Rich Repeat Proteoglycans (SLRPs) such as keratocan, lumican, fibromodulin, PRELP, biglycan, and nyctalopin, and F-box/LRR-repeat proteins such as FBXL2, FBXL4, and FBXL12. For example, 363 missense mutations have been identified. Replacement of arginine, proline, or cysteine by another amino acid, or the reverse, is frequently observed. The diverse effects of the mutations are discussed based on the known structures of LRR proteins. These mutations influence protein folding, aggregation, oligomerization, stability, protein-ligand interactions, disulfide bond formation, and glycosylation. Most of the mutations cause loss of function and a few, gain of function.

A large deletion in the GP9 gene in Cocker Spaniel dogs with Bernard-Soulier syndrome

Inherited bleeding disorders including abnormalities of platelet number and function rarely occur in a variety of dog breeds, but are probably underdiagnosed. Genetically characterized canine forms of platelet disorders provide valuable large animal models for understanding similar platelet disorders in people. Breed-specific disease associated genetic variants in only eight different genes are known to cause intrinsic platelet disorders in dogs. However, the causative genetic variant in many dog breeds has until now remained unknown. Four cases of a mild to severe bleeding disorder in Cocker Spaniel dogs are herein presented. The affected dogs showed a platelet adhesion defect characterized by macrothrombocytopenia with variable platelet counts resembling human Bernard-Soulier syndrome (BSS). Furthermore, the lack of functional GPIb-IX-V was demonstrated by immunocytochemistry. Whole genome sequencing of one affected dog and visual inspection of the candidate genes identified a deletion in the glycoprotein IX platelet (GP9) gene. The GP9 gene encodes a subunit of a platelet surface membrane glycoprotein complex; this functions as a receptor for von Willebrand factor, which initiates the maintenance of hemostasis after injury. Variants in human GP9 are associated with Bernard-Soulier syndrome, type C. The deletion spanned 2460 bp, and included a significant part of the single coding exon of the canine GP9 gene on dog chromosome 20. The variant results in a frameshift and premature stop codon which is predicted to truncate almost two-thirds of the encoded protein. PCR-based genotyping confirmed recessive inheritance. The homozygous variant genotype seen in affected dogs did not occur in 98 control Cocker Spaniels. Thus, it was concluded that the structural variant identified in the GP9 gene was most likely causative for the BSS-phenotype in the dogs examined. These findings provide the first large animal GP9 model for this group of inherited platelet disorders and greatly facilitate the diagnosis and identification of affected and/or normal carriers in Cocker Spaniels.

Prevalence of Macrothrombocytopenia in Healthy College Students in Western India

Macrothrombocytopenia is being increasingly described across the globe. There is paucity of data on the prevalence of this condition from different parts of India. 10,047 healthy college students from the city of Surat in western India were investigated for macrothrombocytopenia i.e. those with Mean platelet Volume of > 11 fL and platelet count of less than 150 × 10⁹/L. ABO blood groups, complete blood counts, peripheral smear examination and haemoglobinopathy work up was also done. Siblings and parents of the macrothrombocytopenic individuals were also studied when available. Bleeding assessment tool of International society of thrombosis and haemostasis were applied to see if there were excessive bleeding in macrothrombocytropenia patients. One hundred and ninety-six students (1.95%) had asymptomatic macrothrombocytopenia. More female students (P < 0.0001) had this condition and blood group A was under represented (P = 0.019) with this condition. Prevalence of macrothrombocytopenia was not related to ethnic subgroups to which the students belonged to, nor was it linked to presence of any haemoglobinopathy gene. In 38 of the 52, 1st degree relatives studied macrothrombocytopenia was confirmed at least in one of them. Excessive bleeding in none of the individuals with macrothrombocytopenia was noted. Asymptomatic macrothrombocytopenia is rare in western parts of India and affects 1.95% of the healthy population. Females were over represented with this condition raising a suspicion of X linked dominant inheritance. Underrepresentation of blood group A in this condition requires further study.

Hemizygosity for the gene encoding glycoprotein Ibβ is not responsible for macrothrombocytopenia and bleeding in patients with 22q11 deletion syndrome

Essentials How thrombocytopenia relates to bleeding in 22q11 deletion syndrome (22q11DS) is not clear. Bleeding severity, platelet count and volume, and GPIBB were examined in patients with 22q11DS. Macrothrombocytopenia and bleeding typified imperfectly overlapping subsets of 22q11DS patients. GPIBB hemizygosity does not cause macrothrombocytopenia or bleeding in patients with 22q11DS. SUMMARY: Background and objectives Macrothrombocytopenia and bleeding are frequently associated with 22q11 deletion syndrome (22q11DS). GPIBB, which encodes the glycoprotein (GP) Ibβ subunit of GPIb-IX-V, is commonly deleted in patients with 22q11DS. Absence of functional GPIb-IX-V causes Bernard-Soulier syndrome, which is a severe bleeding disorder characterized by macrothrombocytopenia. Patients with 22q11DS are often obligate hemizygotes for GPIBB, and those with only a pathogenically disrupted copy of GPIBB present with Bernard-Soulier syndrome. The objective of this study was to determine how GPIBB hemizygosity and sequence variation relate to macrothrombocytopenia and bleeding in patients with 22q11DS who do not have Bernard-Soulier syndrome. Patients/methods We thoroughly characterized bleeding severity, mean platelet volume, platelet count and GPIBB copy number and sequence in patients with 22q11DS. Results and conclusions Macrothrombocytopenia and mild bleeding were observed in incompletely overlapping subsets of patients, and GPIBB copy number and sequence variation did not correlate with either macrothrombocytopenia or bleeding in patients with 22q11DS. These findings indicate that GPIBB hemizygosity does not result in either macrothrombocytopenia or bleeding in these patients. Alternative genetic causes of macrothrombocytopenia, potential causes of acquired thrombocytopenia and bleeding and ways in which platelet size, platelet count and GPIBB sequence information can be used to aid in the diagnosis and management of patients with 22q11DS are discussed.

Whole exome sequencing in the diagnostic workup of patients with a bleeding diathesis

INTRODUCTION

Bleeding assessment tools and laboratory phenotyping often remain inconclusive in patients with a haemorrhagic diathesis.

AIM

To describe the phenotype and genetic profile of patients with a bleeding tendency.

METHODS

Whole exome sequencing (WES) was incorporated in the routine diagnostic pathway of patients with thrombocytopenia (n = 17), platelet function disorders (n = 19) and an unexplained bleeding tendency (n = 51). The analysis of a panel of 126 OMIM (Online Mendelian Inheritance in Man) genes involved in thrombosis and haemostasis was conducted, and if negative, further exome-wide analysis was performed if informed consent given.

RESULTS

Eighteen variants were detected in 15 patients from a total of 87 patients (17%). Causative variants were observed in MYH9 (two cases), SLFN14, P2RY12 and GP9. In addition, one case was considered solved due to combined carriership of F7 and F13A1 variants and one with combined carriership of F2, F8 and VWF, all variants related to secondary haemostasis protein aberrations. Two variants of uncertain significance (VUS) were found in two primary haemostasis genes: GFI1B and VWF. Eight patients were carriers of autosomal recessive disorders. Exome-wide analysis was performed in 54 cases and identified three variants in candidate genes.

CONCLUSION

Based on our findings, we conclude that performing WES at the end of the diagnostic trajectory can be of additive value to explain the complete bleeding phenotype in patients without a definite diagnosis after conventional laboratory tests. Discovery of combinations of (novel) genes that predispose to bleeding will increase the diagnostic yield in patients with an unexplained bleeding diathesis.

Inherited Macrothrombocytopenia: Correlating Morphology, Epidemiology, Molecular Pathology and Clinical Features

Inherited macrothrombocytopenia is increasingly being recognized as a relatively common condition. This descriptive review aims at focusing on the different areas of advancement that have taken place with this condition with particular reference to India. A pubmed search of articles between January 1990 and October 2017 with the key words-macrothrombocytopenia, asymptomatic macrothrombocytopenia, macrothrombocytopenia India, syndromic macrothrombocytopenia, molecular pathology, megakaryopoiesis and platelet formation were searched. The shortlisted articles were then read. Review articles provided additional references and the articles thus obtained were also read. Special interest and research conducted by the authors provided further sources of information. A total of 487 articles were found of which 68 articles were related to our subject of review. Review articles were read and additional articles from the reference quoted. Forty-four percent of nonsyndromic Inherited macrothrombocytopenia showed mutations of MYH9, GP1BB, GP1Ba, GPIX, ABCG5 and 8, ACTN, FLI, TUBB and RUNX1 frequently in heterozygous state. All types of inheritance pattern namely autosomal dominant, recessive and sex linked patterns have been described. Syndromic causes of this phenomenon are well known and have been described. Many asymptomatic patients do have mild or moderate bleeding history. Clinical algorithms to differentiate chronic ITP associated macrothrombocytopenia from inherited variety have been explored. Inherited macrothrombocytopenia is an emerging area of interest in platelet biology with its implication in diagnosis, prognosis, genetic counseling, management and in transfusion medicine.

Congenital Disorders of Platelet Function and Number

Mucocutaneous bleeding symptoms and/or persistent thrombocytopenia occur in individuals with congenital disorders of platelet function and number. Apart from bleeding, these disorders are often associated with additional hematologic and clinical manifestations, including auditory, immunologic, and oncologic disease. Autosomal recessive, dominant, and X-linked inheritance patterns have been demonstrated. Precise delineation of the molecular cause of the platelet disorder can aid the pediatrician in the detection and prevention of specific disorder-associated manifestations and guide appropriate treatment and anticipatory care for the patient and family.

Genetics of inherited platelet disorders

The current review describes inherited platelet disorders, illustrates their clinical phenotype and molecular genetic defects. Platelets are the key molecules mediating haemostasis via adhesion, activation and clot formation at the site of injury. The inherited platelet disorders can be classified according to their platelet defects: receptor/cytoskeleton defects, secretion disorder, and signal transduction defect.

Patients with inherited thrombocytopathia present with mucous membrane bleedings (epistaxis, gingival bleeding) and may present with serious life threatening bleedings following surgery or trauma. Therefore, biochemical and molecular genetic characterization of inherited platelet disorders is important to understand these disorders and to support an efficient therapy.

Challenges on the diagnostic approach of inherited platelet function disorders: Is a paradigm change necessary?

Inherited platelet function disorders (IPFD) have been assessed for more than 50 years by aggregation- and secretion-based tests. Several decision trees are available intending to standardize the investigation of IPFD. A large variability of approaches is still in use among the laboratories across the world. In spite of costly and lengthy laboratory evaluation, the results have been found inconclusive or negative in a significant part of patients having bleeding manifestations. Molecular investigation of newly identified IPFD has recently contributed to a better understanding of the complexity of platelet function. Once considered "classic" IPFDs, Glanzmann thrombasthenia and Bernard-Soulier syndrome have each had their pathophysiology reassessed and their diagnosis made more precise and informative. Megakaryopoiesis, platelet formation, and function have been found tightly interlinked, with several genes being involved in both inherited thrombocytopenias and impaired platelet function. Moreover, genetic approaches have moved from being used as confirmatory diagnostic tests to being tools for identification of genetic variants associated with bleeding disorders, even in the absence of a clear phenotype in functional testing. In this study, we aim to address some limits of the conventional tests used for the diagnosis of IPFD, and to highlight the potential contribution of recent molecular tools and opportunities to rethink the way we should approach the investigation of IPFD.

The 22q11.2 deletion syndrome: Cancer predisposition, platelet abnormalities and cytopenias

The 22q11.2 deletion syndrome (DS) is associated with variable phenotypic expression as findings range from severely affected individuals with the classical triad of DiGeorge and velocardiofacial syndromes, including congenital heart disease, immunodeficiency, hypocalcemia, and palatal abnormalities, to subtly affected adults who only come to attention following the diagnosis of a more severely affected child. The multiple manifestations can affect all organ systems, including the hematologic system resulting in baseline lower platelet counts for individuals with 22q11.2DS and increased platelet size. In addition, there may be an associated increased risk of bleeding. Individuals with 22q11.2DS are also at increased risk of autoimmune cytopenias that can complicate the evaluation or management of other manifestations. Finally, there may be an increased risk of malignancy, although the mechanism for this risk is not fully understood. This review summarizes the currently available data on hematologic/oncologic manifestations of 22q11.2DS and reports on our findings within a large cohort of individuals with the deletion.

A Brazilian case of Bernard-Soulier syndrome with two distinct founder mutations

Bernard-Soulier syndrome (BSS) is a rare bleeding disorder of autosomal recessive inheritance characterized by macrothrombocytopenia. We report the case of a 14-year-old girl diagnosed with BSS who is a fourth-generation Brazilian of Japanese descent and has a compound heterozygote mutation as the responsible gene. The compound heterozygosity would have occurred from the global and long-term racial migration that brought about an accidental encounter of two rare mutant alleles of different origins.

Inherited platelet function disorders. Diagnostic approach and management

Inherited platelet function disorders (IPFDs) make up a significant proportion of congenital bleeding diatheses, but they remain poorly understood and often difficult to diagnose. Therefore, a rational diagnostic approach, based on a standardized sequence of laboratory tests, with consecutive steps of increasing level of complexity, plays a crucial role in the diagnosis of most IPFDs. In this review we discuss a diagnostic approach through platelet phenotyping and genotyping and we give an overview of the options for the management of bleeding in these disorders and an account of the few systematic studies on the bleeding risk associated with invasive procedures and its treatment.

[Diagnosis of inherited thrombocytopenia]

Inherited thrombocytopenias are rare, heterogenous and probably under-diagnosed because often classified as autoimmune thrombocytopenia. About 20 genes were described responsible for these thrombocytopenias. Precise diagnosis is necessary because the prognosis is different and some of them can evolve into hemopathies. First of all, it is important to gather a body of evidence to orientate towards an inherited cause: presence of the thrombocytopenia since childhood and of other family cases is a strong argument. Secondly, it is difficult to target the genetic investigations that settle the precise diagnosis. Genetic variants responsible for inherited thrombocytopenias affect different stage during megakaryocytopoiesis and cause thrombocytopenias with distinct characteristics. Presence of extra-hematological features, platelets' size measurement and evaluation of bone marrow megakaryocyte morphology when it is possible allow a primary orientation. We propose a diagnostic approach considering extra-hematological features, mode of inheritance, morphology, molecular and functional platelets' studies and bone marrow megakaryocyte morphology in order to better target genetic study. Nevertheless, despite this approach, some inherited thrombocytopenias remain still unexplained and could benefit from new methods of new generation sequencing in the future.

A Novel Homozygous c.800C>G Substitution in GP1BA Exon 2 in a Kuwaiti Family with Bernard-Soulier Syndrome

BACKGROUND

Bernard-Soulier syndrome (BSS) is a congenital bleeding disorder characterised by thrombocytopenia, giant platelets and decreased platelet adhesion resulting from genetic alterations of the glycoprotein (GP) Ib/IX/V complex.

OBJECTIVES

Three sisters with a lifelong bleeding history and a provisional diagnosis of BSS were referred for further characterisation of their bleeding diathesis. The siblings' symptoms varied in severity from skin and gum bleeding to menorrhagia associated with iron-deficiency anaemia requiring regular transfusion of red cells and platelets. The parents were consanguineous but did not demonstrate any bleeding disorder.

METHODS

The family were investigated using standard haematological techniques, platelet aggregometry, platelet membrane GP analysis and DNA sequencing of the genes encoding the GPIb/IX complex.

RESULTS

All 3 sisters had thrombocytopenia and giant platelets. Platelet aggregation and flow cytometry studies confirmed the lack of aggregation with ristocetin and a markedly reduced GPIb/IX surface expression. Molecular analysis demonstrated a novel homozygous c.800C>G substitution in GP1BA exon 2 leading to a serine 267 Ter stop codon in all 3 siblings.

CONCLUSIONS

A novel, nonsense mutation was identified as the cause of the bleeding disorder in this family. This is the first reported BSS mutation identified in a family from Kuwait.

Clinical phenotype in heterozygote and biallelic Bernard-Soulier syndrome--a case control study

Bernard-Soulier syndrome (BSS) is a rare severe autosomal recessive bleeding disorder. To date heterozygous carriers of BSS mutations have not been shown to have bleeding symptoms. We assessed bleeding using a semi-quantitative questionnaire, platelet parameters, PFA-100 closure times, ristocetin response, GP Ib/IX expression and VWF antigen in 14 BSS patients, 30 heterozygote carriers for related mutations and 29 controls. Eight mutations in GP1BA, GP1BB or GP9 were identified including four previously unknown pathogenic mutations. Subjects with BSS reported markedly more mucocutaneous bleeding than controls. Increased bleeding was also observed in heterozygotes. Compared to controls, patients with BSS had lower optical platelet counts (P < 0.001), CD61-platelet counts (P < 0.001) and higher mean platelet volume (17.7 vs. 7.8 fL, P < 0.001) and ristocetin response and closure times were unmeasurable. Heterozygotes had higher MPV (9.7 fL, P < 0.001) and lower platelet counts (P < 0.001) than controls but response to ristocetin and closure times were normal. The VWF was elevated in both BSS and in heterozygotes (P = 0.005). We conclude that heterozygotes for BSS mutations have lower platelet counts than controls and show a bleeding phenotype albeit much milder than in BSS. Both patients with BSS and heterozygote carriers of pathogenic mutations have raised VWF.

Macrothrombocytopenia in north India: role of automated platelet data in the detection of an under diagnosed entity

Congenital macrothrombocytopenia is being increasingly recognised because of the increasing availability of automated platelet counts during routine complete blood count. If not recognised, these patients may be unnecessarily investigated or treated. The study was done to assess the occurrence of macrothrombocytopenia in the North Indian population and the role of automated platelet parameters in its detection. This prospective study was done on patients whose blood samples were sent for CBC to the hematology laboratory of a tertiary care hospital. Samples were run on Advia-120, a 5-part differential automated analyzer. Routine blood parameters including platelet count, mean platelet volume (MPV), platelet cytogram pattern and platelet flagging was studied along with peripheral blood smear examination. ANOVA was used to compare difference in mean MPV in patients with macrothrombocytopenia, and those with secondary thrombocytopenia and ITP. Seventy five (0.6 %) patients with CBC evaluation were detected to have macrothrombocytopenia, majority (96 %) of North Indian origin. The MPV (fl) in the 75 patients ranged from 10.9 to 23.3 (mean 15.1 ± 3.1 fl) with a dispersed cytogram pattern distinct from that seen in patients with normal platelet count, raised platelet count or low platelets due to secondary thrombocytopenia (MPV-10.9 ± 2.6) or ITP (10.8 ± 3.5). The difference in mean MPV in these patients was statistically significant (p < 0.00001). Macrothrombocytopenia is an under diagnosed condition and may be initially suspected on automated blood counts. Along with a blood smear examination, automated data (MPV and platelet cytogram pattern) aids the diagnosis and can avoid unnecessary investigations and interventions for these patients.

Functional and molecular characterization of inherited platelet disorders in the Iberian Peninsula: results from a collaborative study

Background

The diagnostic evaluation of inherited platelet disorders (IPDs) is complicated and time-consuming, resulting in a relevant number of undiagnosed and incorrectly classified patients. In order to evaluate the spectrum of IPDs in individuals with clinical suspicion of these disorders, and to provide a diagnostic tool to centers not having access to specific platelets studies, we established the project “Functional and Molecular Characterization of Patients with Inherited Platelet Disorders” under the scientific sponsorship of the Spanish Society of Thrombosis and Haemostasis.

Patients/methods

Subjects were patients from a prospective cohort of individuals referred for clinical suspicion of IPDs as well as healthy controls. Functional studies included light transmission aggregation, flow cytometry, and when indicated, Western-blot analysis of platelet glycoproteins, and clot retraction analysis. Genetic analysis was mainly performed by sequencing of coding regions and proximal regulatory regions of the genes of interest.

Results

Of the 70 cases referred for study, we functionally and molecularly characterized 12 patients with Glanzmann Thrombasthenia, 8 patients with Bernard Soulier syndrome, and 8 with other forms of IPDs. Twelve novel mutations were identified among these patients. The systematic study of patients revealed that almost one-third of patients had been previously misdiagnosed.

Conclusions

Our study provides a global picture of the current limitations and access to the diagnosis of IPDs, identifies and confirms new genetic variants that cause these disorders, and emphasizes the need of creating reference centers that can help health care providers in the recognition of these defects.

Spectrum of the mutations in Bernard-Soulier syndrome

Bernard-Soulier syndrome (BSS) is a rare autosomal recessive bleeding disorder characterized by defects of the GPIb-IX-V complex, a platelet receptor for von Willebrand factor (VWF). Most of the mutations identified in the genes encoding for the GP1BA (GPIbα), GP1BB (GPIbβ), and GP9 (GPIX) subunits prevent expression of the complex at the platelet membrane or more rarely its interaction with VWF. As a consequence, platelets are unable to adhere to the vascular subendothelium and agglutinate in response to ristocetin. In order to collect information on BSS patients, we established an International Consortium for the study of BSS, allowing us to enrol and genotype 132 families (56 previously unreported). With 79 additional families for which molecular data were gleaned from the literature, the 211 families characterized so far have mutations in the GP1BA (28%), GP1BB (28%), or GP9 (44%) genes. There is a wide spectrum of mutations with 112 different variants, including 22 novel alterations. Consistent with the rarity of the disease, 85% of the probands carry homozygous mutations with evidence of founder effects in some geographical areas. This overview provides the first global picture of the molecular basis of BSS and will lead to improve patient diagnosis and management.

Congenital thrombocytopenia: clinical manifestations, laboratory abnormalities, and molecular defects of a heterogeneous group of conditions

Once considered exceptionally rare, congenital thrombocytopenias are increasingly recognized as a heterogeneous group of disorders characterized by a reduction in platelet number and a bleeding tendency that may range from very mild to life threatening. Although some of these disorders affect only megakaryocytes and platelets, others involve different cell types and may result in characteristic phenotypic abnormalities. This review elaborates the clinical presentation and laboratory manifestations of common congenital thrombocytopenias in addition to exploring our understanding of the molecular basis of these disorders and therapeutic interventions available.

Inherited thrombocytopenias frequently diagnosed in adults

The diagnosis of inherited thrombocytopenias is difficult, for many reasons. First, as they are all rare diseases, they are little known by clinicians, who therefore tend to suspect the most common forms. Second, making a definite diagnosis often requires complex laboratory techniques that are available in only a few centers. Finally, half of the patients have forms that have not yet been described. As a consequence, many patients with inherited thrombocytopenias are misdiagnosed with immune thrombocytopenia, and are at risk of receiving futile treatments. Misdiagnosis is particularly frequent in patients whose low platelet count is discovered in adult life, because, in these cases, even the inherited origin of thrombocytopenia may be missed. Making the correct diagnosis promptly is important, as we recently learned that some forms of inherited thrombocytopenia predispose to other illnesses, such as leukemia or kidney failure, and affected subjects therefore require close surveillance and, if necessary, prompt treatments. Moreover, medical treatment can increase platelet counts in specific disorders, and affected subjects can therefore receive drugs instead of platelet transfusions when selective surgery is required. In this review, we will discuss how to suspect, diagnose and manage inherited thrombocytopenias, with particular attention to the forms that frequently present in adults. Moreover, we describe four recently identified disorders that belong to this group of disorders that are often diagnosed in adults: MYH9-related disease, monoallelic Bernard-Soulier syndrome, ANKRD26-related thrombocytopenia, and familial platelet disorder with predisposition to acute leukemia.

Myocardial infarction in two cousins heterozygous for ASN41HIS autosomal dominant variant of Bernard-Soulier syndrome

Bernard-Soulier Syndrome is characterized by thrombocytopenia with large platelets and defective aggregation to ristocetin. The bleeding tendency is variable but may be severe. The syndrome is due to genetic defects of the GPIb-V-IX complex and it has been maintained to be protective from thrombotic events. Here we present the first two cases of documented M.I. in two cousins, heterozygous for the Arg41His mutation which is responsible for a dominant form of Bernard-Soulier Syndrome. In one of the two patients an aneurysm of the aorta was also present. The patients had a mild bleeding tendency which was severely aggravated by treatment with antiplatelet drugs. These clinical observations are in contrast with experimental studies which demonstrate that Bernard-Soulier-like strains of mice show a decreased thrombus generation in several experimental settings.

Platelet morphology analysis

Platelets are very small blood cells (1.5-3 μm), which play a major role in primary haemostasis and in coagulation mechanisms. Platelet characterization requires their counting (see Chapter 15 ) associated with accurate morphology analysis. We describe the major steps in order to correctly obtain stained blood films, which can be analyzed by optical microscope. Platelet morphology abnormalities are found in acquired malignant hematological diseases such myeloproliferative or myelodysplastic syndromes and acute megakaryoblastic leukemia. A careful analysis of the platelet size and morphology, by detecting either normal platelets with or without excessive anisocytosis, microplatelets, or large/giant platelets, will contribute to inherited thrombocytopenia diagnosis and gather substantial data when looking for an acquired platelet disorders.

Inherited thrombocytopenias: the evolving spectrum

The chapter of inherited thrombocytopenias has expanded greatly over the last decade and many "new" forms deriving from mutations in "new" genes have been identified. Nevertheless, nearly half of patients remain without a definite diagnosis because their illnesses have not yet been described. The diagnostic approach to these diseases can still take advantage of the algorithm proposed by the Italian Platelet Study Group in 2003, although an update is required to include the recently described disorders. So far, transfusions of platelet concentrates have represented the main tool for preventing or treating bleedings, while haematopoietic stem cell transplantation has been reserved for patients with very severe forms. However, recent disclosure that an oral thrombopoietin mimetic is effective in increasing platelet count in patients with MYH9-related thrombocytopenia opened new therapeutic perspectives. This review summarizes the general aspects of inherited thrombocytopenias and describes in more detail MYH9-related diseases (encompassing four thrombocytopenias previously recognized as separate diseases) and the recently described ANKRD26-related thrombocytopenia, which are among the most frequent forms of inherited thrombocytopenia.

Alteration of liver enzymes is a feature of the MYH9-related disease syndrome

Background

MYH9-related disease (MYH9-RD) is a rare autosomal dominant genetic syndrome characterized by congenital thrombocytopenia associated with the risk of developing progressive nephropathy, sensorineural deafness, and presenile cataract. During the collection of a large case-series of patients with MYH9-RD we noticed several cases with unexplained elevation of liver enzymes. Our aim was to evaluate if the alteration of liver tests is a feature of the MYH9-RD and to define its clinical significance.

Methods and Findings

Data concerning liver tests, prospectively recorded in the Italian Registry for MYH9-RD, were collected and compared with those of three control populations: patients with autoimmune thrombocytopenia, patients with inherited thrombocytopenias other than MYH9-RD, and the participants to a large epidemiologic survey in an Italian geographic isolate. Thirty-eight of 75 evaluable MYH9-RD patients (50.7%) showed an elevation of ALT and/or AST, and 17 of 63 (27.0%) an increase of GGT. The increases ranged from 1.9±0.7 to 2.7±1.6 fold the upper normal limit. The prevalence of liver test alterations was significantly higher in MYH9-RD patients than in each of the control populations, with odds ratios ranging from 8.2 (95% CIs 2.2–44.8) to 24.7 (14.8–40.8). Clinical follow-up and more detailed liver studies of a subset of patients, including ultrasound liver scan, liver elastography and liver biopsy in one case, did not show any significant structural damage or evolution towards liver insufficiency.

Conclusions

Elevation of liver enzymes is a frequent and previously unrecognized feature of the MYH9-RD syndrome; however, this defect does not appear to have poor prognostic value.

What To Do When You Suspect an Inherited Platelet Disorder

Inherited platelet disorders (IPDs) comprise a heterogenous group of diseases that include defects in platelet function and disordered megakaryopoiesis. Some IPDs overlap as both defects in function and thrombopoiesis, resulting in both altered aggregation and/or secretion and thrombocytopenia. This review examines the key features of the presentation of IPDs in children and adults and presents a diagnostic algorithm for the evaluation of these patients. In addition, recent advances in our understanding of the pathophysiology of platelet disorders are addressed, with attention given to some of the novel genetic associations. Finally, treatment options and future therapies are briefly discussed.