Bernard-Soulier syndrome due to the homozygous Asn-45Ser mutation in GPIX: an unexpected, frequent finding in Germany

Bernard Soulier syndrome: A case report from Pakistan

Bernard Soulier Syndrome should be suspected in patients with bleeding disorder symptoms and significant family history, where consanguineous marriages are common. Diagnosis can be confirmed using a ristocetin test and a peripheral blood smear.

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.

My patient is thrombocytopenic! Is (s)he? Why? And what shall I do?

Solving the riddle of a thrombocytopenic patient is a difficult and fascinating task. The spectrum of possible aetiologies is wide, ranging from an in vitro artefact to severe treatment-resistant thrombocytopenic bleeding conditions, or even life-threatening prothrombotic states. Moreover, thrombocytopenia by itself does not protect from thrombosis and sometimes a patient with a low platelet count requires concomitant antithrombotic treatment as well. In order to identify and treat the cause and the effects of the thrombocytopenia, you have to put together several pieces of information, solving a unique jig-jaw puzzle.

The present work is not a textbook article about thrombocytopenia, rather a collection of differential diagnostic thoughts, treatment concepts, and some basic knowledge, that you can retrieve when facing your next thrombocytopenic patient. Enjoy reading it, but most importantly enjoy taking care of patients with a low platelet count. I bet the present work will assist you in this challenging and rewarding clinical task.

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.

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.

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.

Molecular basis of Bernard-Soulier syndrome in 27 patients from India

BACKGROUND

Bernard-Soulier syndrome (BSS) is an extremely rare (1:1 million) bleeding disorder of platelet adhesion, caused by defects in the glycoprotein (GP)Ib/IX/V complex.

PATIENTS AND METHODS

The diagnosis in 27 patients was based on low platelet count, presence of giant platelets and aggregometry studies. Flow cytometry to assess the surface GPIb/IX/V complex showed reduced (7.7-57%) expression. gDNA was screened for mutations in the GPIBA, GPIBB, GP9 genes using PCR-conformation sensitive gel electrophoresis (CSGE).

RESULTS

Thirteen different disease-causing mutations, including missense (54%), frameshifts (38%) and nonsense (8%) mutations, were identified in 27 patients. Eleven of them were novel including five novel frameshifts (GPIbα: p.Gln97_98fsX113, p.Pro402_403fsX52; GPIbβ: p.Arg17fsX14; GPIX: p.Gly24fsX43, p. Pro130fs, a nonsense mutation (GPIX, p.94, Gln>X) and five novel missense mutations (GPIbα: p.492, Tyr>His; GPIbβ: p.65, Pro>Arg, p.129, Gln>His, p.132, Leu>Pro; GPIX: p.55, Phe>Cys). Interestingly, four common mutations, Cys8Arg (n = 6) and Phe55Ser (n = 2), Phe55Cys (n = 2) in GPIX and a novel 22-bp deletion in the GPIBB gene predicting p.Arg17fsX 14 (n = 10) were seen in 20 patients.

CONCLUSION

The molecular data presented here is the largest series of BSS patients to be reported so far, adding significantly to the mutation database of this condition and also useful for its genetic diagnosis in India.

Novel Mutation in Bernard-Soulier Syndrome

BACKGROUND: Bernard-Soulier syndrome (BSS) is a severe congenital bleeding disorder characterized by thrombocytopenia, thrombocytopathy and decreased platelet adhesion. BSS results from genetic alterations of the glycoprotein (GP) Ib/IX/V complex. METHODS: We report on a patient demonstrating typical BSS phenotype (thrombocytopenia with giant platelets, bleeding symptoms). However, BSS was not diagnosed until he reached the age of 39 years. RESULTS: Flow cytometry of the patient's platelets revealed absence of GPIb/IX/V receptor surface expression. In addition, immunofluorescence analysis of patient's platelets demonstrated very faint staining of GPIX. A novel homozygous deletion comprising 11 nucleotides starting at position 1644 of the GPIX gene was identified using molecular genetic analysis. CONCLUSIONS: The novel 11-nucleotide deletion (g.1644_1654del11) was identified as causing the bleeding disorder in the BSS patient. This homozygous deletion includes the last 4 nucleotides of the Kozak sequence as well as the start codon and the following 4 nucleotides of the coding sequence. The Kozak sequence is a region indispensable for the initiation of the protein translation process, thus preventing synthesis of functional GPIX protein in the case of deletion.

Phosphatidylserine exposure and other apoptotic-like events in Bernard-Soulier syndrome platelets

In the Bernard-Soulier syndrome (BSS), the giant platelets are said to have increased phosphatidylserine (PS) surface exposure in the resting state and shortened survival in the circulation. When normal platelets are activated, they undergo many biochemical and morphological changes, some of which are apoptotic. Herein, we investigated apoptotic-like events in BSS platelets upon activation, specifically, PS exposure, microparticle (MP) formation, cell shrinkage, and loss of mitochondrial inner membrane potential (DeltaPsi(m)). Platelets from two unrelated BSS patients were examined in whole blood; agonists used were collagen, thrombin, PAR1- or PAR4-activating peptides (APs), or combinations of collagen with thrombin, and the PAR-APs. Flow cytometry was used to measure PS exposure (annexin A5 binding), platelet-derived MPs (forward scatter; events <0.75 microm size), and DeltaPsi(m) (TMRM fluorescence). PS exposure was increased on resting and activated BSS platelets, and this was independent of the platelet size. MP formation by BSS platelets was generally enhanced. Cell shrinkage occurred on activation to form smaller, PS-exposing platelets in BSS and controls. A proportion of PS-exposing BSS and control platelets exhibited DeltaPsi(m) loss, but unlike controls, there was also loss of DeltaPsi(m) in the BSS platelets not exposing PS. Thus, BSS platelets undergo apoptotic-like events upon activation, with PS exposure and MP formation being enhanced. These events may play a role in the shortened survival in BSS, as well as affecting thrombin generation.

An inherited macrothrombocytopenic disorder with abnormal large granules

Inherited giant platelet syndromes are a heterogeneous group of rare bleeding disorders. In the current study, a patient was reported with prolonged bleeding time, thrombocytopenia and giant platelets. Both the patient's red and white cell counts were normal without morphological abnormalities. The electron microscopy of platelets showed abnormal large electron-dense granules in the cytoplasm with exocytosis being easily observed. Her fathers platelets had the same abnormalities. The expression of glycoprotein (GP)Ib, GPIIb and GPIIIa on the surface of the patient's platelets was normal, and her platelet aggregation in response to ADP and ristocetin was also normal. Immunogold probes combined to monoclonal antibodies against GPIIIa, P-selectin or CD63 could not identify any relationship between the aberrant structures and alpha granules or lysosomes of platelet. Serotonin level was normal in the platelets of the patient, indicating the electron opaque granules are not dense bodies. The morphological abnormalities of the platelets from the patient are clearly distinguishable from other hereditary giant platelet disorders. We propose that the abnormal large granules from the patient's platelets probably represent a novel inherited thrombocytopenic disorder.

Genetic characterization of patients with Bernard-Soulier syndrome and their relatives from Southern Iran

Bernard-Soulier syndrome (BSS) is a rare recessively inherited bleeding disorder caused by the deficiency of the platelet glycoprotein (Gp) complex Ib/IX/V that is the von Willebrand factor receptor on platelets. In patients suffering from BSS platelet adhesion is typically impaired, while platelet aggregation is normal; macrothrombocytopenia is a common feature. In this study three different families from Southern Iran were investigated. GpIb/IX/V platelet expression as detected by flow cytometry was less than 2% of normal in six cases and 12% in the remaining one. Platelet count was 35,000 platelets/microliter and iron deficiency anemia was common. All patients suffered from mucocutaneous bleeding at presentation and were born from consanguineous marriages. Genetic analysis demonstrated the presence of the same GpIX Phe55Ser missense mutation in two families and of a single base insertion (GP1BA C3221 ins), a never described mutation causing a frameshift in the GpIbalpha gene, in the third family. Among the family members studied several heterozygotes were identified. None of them, with one exception, had macrothrombocytopenia. In one family a slight reduction of GpIb/IX/V expression was observed.

Trp207Gly in platelet glycoprotein Ibalpha is a novel mutation that disrupts the connection between the leucine-rich repeat domain and the disulfide loop structure and causes Bernard-Soulier syndrome

BACKGROUND

Bernard-Soulier syndrome (BSS) is a severe inherited bleeding disorder that is caused by a defect in glycoprotein (GP)Ib-IX-V complex, the platelet membrane receptor for von Willebrand factor.

PATIENTS

The diagnosis of BSS was made in two members of a Bukharian Jewish family who had life-long thrombocytopenia associated with mucocutaneous bleeding manifestations.

METHODS AND RESULTS

Flow cytometry and Western blot analyses showed only trace amounts of GPIb and GPIX on the patients' platelets. Sequence analysis of the GPIbalpha gene revealed a homozygous T > G transversion at nucleotide 709 predicting Trp207Gly substitution in the mature protein. Introduction of the mutation into a mammalian expression construct abolished the surface expression of GPIbalpha in transfected baby hamster kidney cells. The crystal structure of the N-terminus of GPIbalpha (PDB: 1SQ0) indicates that Trp207 is completely buried and located in a disulfide loop structure that interacts with the leucine-rich repeat (LRR) domain.

CONCLUSION

A novel mutation, Trp207Gly, causes BSS and predicts disruption of the interaction between a disulfide loop and the LRR domain that is essential for the integrity of GPIbalpha structure.

Bernard-Soulier syndrome (hemorrhagiparous thrombocytic dystrophy)

Bernard-Soulier syndrome (BSS), also known as Hemorrhagiparous thrombocytic dystrophy, is a hereditary bleeding disorder affecting the megakaryocyte/platelet lineage and characterized by bleeding tendency, giant blood platelets and low platelet counts. This syndrome is extremely rare as only approximately 100 cases have been reported in the literature. Clinical manifestations usually include purpura, epistaxis, menorrhagia, gingival and gastrointestinal bleeding. The syndrome is transmitted as an autosomal recessive trait. The underlying defect is a deficiency or dysfunction of the glycoprotein GPIb-V-IX complex, a platelet-restricted multisubunit receptor required for normal primary hemostasis. The GPIb-V-IX complex binds von Willebrand factor, allowing platelet adhesion and platelet plug formation at sites of vascular injury. Genes coding for the four subunits of the receptor, GPIBA, GPIBB, GP5 and GP9, map to chromosomes 17p12, 22q11.2, 3q29, and 3q21, respectively. Defects have been identified in GPIBA, GPIBB, and GP9 but not in GP5. Diagnosis is based on a prolonged skin bleeding time, the presence of a small number of very large platelets (macrothrombocytopenia), defective ristocetin-induced platelet agglutination and low or absent expression of the GPIb-V-IX complex. Prothrombin consumption is markedly reduced. The prognosis is usually good with adequate supportive care but severe bleeding episodes can occur with menses, trauma and surgical procedures. Treatment of bleeding or prophylaxis during surgical procedures usually requires platelet transfusion.

Congenital macrothrombocytopenias

Congenital macrothrombocytopenias comprise a heterogeneous group of rare disorders, characterized by abnormal giant platelets, thrombocytopenia and bleeding tendency with variable severity. Many of these disorders share common clinical and laboratory features, making accurate diagnosis difficult and patients are often misdiagnosed with and treated for idiopathic thrombocytopenic purpura. Recent progress in the elucidation of underlying defects and further developments of specific diagnostic techniques for several congenital macrothrombocytopenias have renewed our approach to the classification and the diagnosis of the disease. This review summarizes the current knowledge on the clinical and laboratory features of common congenital macrothrombocytopenias and discusses how that knowledge aids in making a proper diagnosis.