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

Lentiviral gene therapy reverts GPIX expression and phenotype in Bernard-Soulier syndrome type C

Bernard-Soulier syndrome (BSS) is a rare congenital disease characterized by macrothrombocytopenia and frequent bleeding. It is caused by pathogenic variants in three genes (GP1BA, GP1BB, or GP9) that encode for the GPIbα, GPIbβ, and GPIX subunits of the GPIb-V-IX complex, the main platelet surface receptor for von Willebrand factor, being essential for platelet adhesion and aggregation. According to the affected gene, we distinguish BSS type A1 (GP1BA), type B (GP1BB), or type C (GP9). Pathogenic variants in these genes cause absent, incomplete, or dysfunctional GPIb-V-IX receptor and, consequently, a hemorrhagic phenotype. Using gene-editing tools, we generated knockout (KO) human cellular models that helped us to better understand GPIb-V-IX complex assembly. Furthermore, we developed novel lentiviral vectors capable of correcting GPIX expression, localization, and functionality in human GP9-KO megakaryoblastic cell lines. Generated GP9-KO induced pluripotent stem cells produced platelets that recapitulated the BSS phenotype: absence of GPIX on the membrane surface and large size. Importantly, gene therapy tools reverted both characteristics. Finally, hematopoietic stem cells from two unrelated BSS type C patients were transduced with the gene therapy vectors and differentiated to produce GPIX-expressing megakaryocytes and platelets with a reduced size. These results demonstrate the potential of lentiviral-based gene therapy to rescue BSS type C.

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.

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 GP1BB Reveals the Role of the Cytoplasmic Domain of GPIbβ in the Pathophysiology of Bernard-Soulier Syndrome and GPIb-IX Complex Assembly

Bernard-Soulier syndrome (BSS) is an autosomal-recessive bleeding disorder caused by biallelic variants in the GP1BA, GP1BB, and GP9 genes encoding the subunits GPIbα, GPIbβ, and GPIX of the GPIb-IX complex. Pathogenic variants usually affect the extracellular or transmembrane domains of the receptor subunits. We investigated a family with BSS caused by the homozygous c.528_550del (p.Arg177Serfs*124) variant in GP1BB, which is the first mutation ever identified that affects the cytoplasmic domain of GPIbβ. The loss of the intracytoplasmic tail of GPIbβ results in a mild form of BSS, characterized by only a moderate reduction of the GPIb-IX complex expression and mild or absent bleeding tendency. The variant induces a decrease of the total platelet expression of GPIbβ; however, all of the mutant subunit expressed in platelets is correctly assembled into the GPIb-IX complex in the plasma membrane, indicating that the cytoplasmic domain of GPIbβ is not involved in assembly and trafficking of the GPIb-IX receptor. Finally, the c.528_550del mutation exerts a dominant effect and causes mild macrothrombocytopenia in heterozygous individuals, as also demonstrated by the investigation of a second unrelated pedigree. The study of this novel GP1BB variant provides new information on pathophysiology of BSS and the assembly mechanisms of the GPIb-IX receptor.

Bernard-Soulier syndrome (BSS) with uncontrollable menorrhagia

Menorrhagia is a common problem in women of reproductive age group and 5% of women between 30 and 49 years of age group consult their general practitioner for this problem. Menorrhagia occurring in adolescent age group and perimenopausal age group is chiefly due to anovulatory cycles. In perimenopausal age group, local pathology like leiomyomas can also contribute to menorrhagia. Recently, bleeding disorders like von Willebrand Disease, single coagulation factor deficiencies particularly factor XI, VIII, Factor V and platelet function disorders have been found to be prevalent in patients presenting with menorrhagia. Bernerd soulier syndrome is extremely rare haemostatic disorder due deficiency in GP IB/IX/V receptor complex present on platelet membrane which is necessary for platelet aggregation. As a result of the defect patients have prolonged bleeding time, which might vary in symptoms ranging from spontaneous self- limiting epistaxis to life threatening haemorrhage. Here we report a case of 31-year-old woman known case of Bernard soulier syndrome with severe menorrhagia treated with mirena insertion and course of complication and its management.

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.

In the line-up: deleted genes associated with DiGeorge/22q11.2 deletion syndrome: are they all suspects?

BACKGROUND

22q11.2 deletion syndrome (22q11DS), a copy number variation (CNV) disorder, occurs in approximately 1:4000 live births due to a heterozygous microdeletion at position 11.2 (proximal) on the q arm of human chromosome 22 (hChr22) (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011). This disorder was known as DiGeorge syndrome, Velo-cardio-facial syndrome (VCFS) or conotruncal anomaly face syndrome (CTAF) based upon diagnostic cardiovascular, pharyngeal, and craniofacial anomalies (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011; Burn et al., J Med Genet 30:822-4, 1993) before this phenotypic spectrum was associated with 22q11.2 CNVs. Subsequently, 22q11.2 deletion emerged as a major genomic lesion associated with vulnerability for several clinically defined behavioral deficits common to a number of neurodevelopmental disorders (Fernandez et al., Principles of Developmental Genetics, 2015; Robin and Shprintzen, J Pediatr 147:90-6, 2005; Schneider et al., Am J Psychiatry 171:627-39, 2014).

RESULTS

The mechanistic relationships between heterozygously deleted 22q11.2 genes and 22q11DS phenotypes are still unknown. We assembled a comprehensive "line-up" of the 36 protein coding loci in the 1.5 Mb minimal critical deleted region on hChr22q11.2, plus 20 protein coding loci in the distal 1.5 Mb that defines the 3 Mb typical 22q11DS deletion. We categorized candidates based upon apparent primary cell biological functions. We analyzed 41 of these genes that encode known proteins to determine whether haploinsufficiency of any single 22q11.2 gene-a one gene to one phenotype correspondence due to heterozygous deletion restricted to that locus-versus complex multigenic interactions can account for single or multiple 22q11DS phenotypes.

CONCLUSIONS

Our 22q11.2 functional genomic assessment does not support current theories of single gene haploinsufficiency for one or all 22q11DS phenotypes. Shared molecular functions, convergence on fundamental cell biological processes, and related consequences of individual 22q11.2 genes point to a matrix of multigenic interactions due to diminished 22q11.2 gene dosage. These interactions target fundamental cellular mechanisms essential for development, maturation, or homeostasis at subsets of 22q11DS phenotypic sites.

Bernard Soulier Syndrome: 10 years' experience at a tertiary care hospital

Objective:

To determine clinical manifestations and laboratory findings in patients with BSS diagnosed through platelet aggregometry followed in a tertiary care hospital in Lahore, Pakistan.

Methods:

The retrospective study comprised patients who presented in Hematology and Transfusion Medicine Department of The Children Hospital & Institute of Child Health, Lahore with the relevant diagnosis from 2006 to 2013. The result of all the patients were collected on a predesigned proforma. Medical data was scrutinized to collect age, gender, clinical findings along with results of complete blood count, bleeding time and platelet aggregation studies for the diagnosis of Bernard Soulier Syndrome.

Results:

Among 49 patients, 26 patients were females and 23 males. The mean age of the patients was 5±2.5 years. 81% had a family history of consanguinity. The most common presenting symptom included epistaxis seen in 73.4% patients. Complete blood count demonstrated decreased platelets in 85.7% of patients ranging from 20 X 10⁹/L to 130 X 10⁹/L. Anemia was seen in 67.3% and 93.8% had prolonged bleeding time. Peripheral blood smears demonstrated giant platelets in all patients. The majority of patients 65.3% had mild bleeding episodes. Platelet aggregation studies showed normal aggregation with ADP, Collagen and Epinephrine in 100% of our patients whereas all showed no response of aggregation with Ristocetin.

Conclusion:

Our data is consistent with other reports regarding clinical presentation of BSS, but we report large number of BSS patients from our area, emphasizing significance to provide diagnostic services in Pakistan to find out exact magnitude of disease.

Angeborene Thrombozytenfunktionsstörungen

Angeborene Thrombozytopathien können zu Blutungssymptomen unterschiedlichen Schweregrades führen, da die Thrombozyten nicht mehr ihre Funktion nach einer Gefäß-verletzung erfüllen können. In manchen Fällen sind Thrombozytopathien schwierig zu diagnostizieren und können Probleme in der Therapie und im Management verursachen. Dieser Review beschreibt den klinischen und molekulargenetischen Phänotyp der verschiedenen angeborenen Thrombozytopathien. Die angeborenen Thrombozytopathien werden entsprechend des Thrombozytendefekts eingeteilt: Rezeptordefekte (Adhäsion oder Aggregation), Sekretionsdefekte und Zytoskelettdefekte.

Die am besten charakterisierten thrombozytären Rezeptordefekte sind die Glanzmann Thrombasthenie (Defekt des Integrins [uni03B1]IIb[uni03B2]3) und das Bernard-Soulier Syndrom (Defekt des GPIb/IX/V Rezeptors). Umfassende Fall-berichte über die Blutungsdiathese sowie die Untersuchung der Thrombozytenaggregation bzw. -agglutination und Rezeptorexpression von Patienten, die an der Glanzmann Thrombasthenie (GT) oder am Bernard-Soulier Syndrom (BSS) leiden, sollen diesen Review ergänzen. Darüber hinaus wird das HermanskyPudlak Syndrom (HPS) als eine bedeutende Störung der [uni03B4]-Granula Sekretion zusammen mit einer Fallbeschreibung eines Patienten, der an HPS Typ 1 leidet, beschrieben.

Molecular pathology of rare bleeding disorders (RBDs) in India: a systematic review

Background

Though rare in occurrence, patients with rare bleeding disorders (RBDs) are highly heterogeneous and may manifest with severe bleeding diathesis. Due to the high rate of consanguinity in many caste groups, these autosomal recessive bleeding disorders which are of rare occurrence in populations across the world, may not be as rare in India.

Objectives

To comprehensively analyze the frequency and nature of mutations in Indian patients with RBDs.

Methods

Pubmed search was used (www.pubmed.com) to explore the published literature from India on RBDs using the key words “rare bleeding disorders”, “mutations”, “India”, “fibrinogen”, “afibrinogenemia”, “factor II deficiency”, “prothrombin” “factor VII deficiency”, “factor V deficiency”, “factor X deficiency”, “factor XI deficiency”, “combined factor V and VIII deficiency”, “factor XIII deficiency”, “Bernard Soulier syndrome” and “Glanzmanns thrombasthenia” in different combinations. A total of 60 relevant articles could be retrieved. The distribution of mutations from India was compared with that of the world literature by referring to the Human Gene Mutation Database (HGMD) (www.hgmd.org).

Results

Taken together, 181 mutations in 270 patients with different RBDs have been reported from India. Though the types of mutations reported from India and their percentage distribution with respect to the world data are largely similar, yet much higher percentage of small deletions, duplication mutations, insertions, indels were observed in this analysis. Besides the identification of novel mutations and polymorphisms, several common mutations have also been reported, which will allow to develop a strategy for mutation screening in Indian patients with RBDs.

Conclusion

There is a need for a consortium of Institutions working on the molecular pathology of RBDs in India. This will facilitate a quicker and cheaper diagnosis of RBDs besides its utility in first trimester prenatal diagnosis of the affected families.

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.

Endodontic management of a patient with Bernard-Soulier syndrome

Bernard-Soulier syndrome is a rare inherited disorder with giant platelets, thrombocytopenia and a prolonged bleeding time. These abnormalities are caused by genetic defects of the glycoprotein Ib/IX/V complex that constitutes the von Willebrand factor receptor on the platelet surface. We are documenting a 30-year-old female patient reported with a chief complaint of swelling in relation to right maxillary canine for 5 days. The primary treatment remains platelet transfusion. Root canal treatment was performed following platelet rich plasma transfusion. As the tooth was necrotic and had a periapical pathology post-operative bleeding was absent. The root canal treatment was uneventful and the patient was asymptomatic. Optimum oral hygiene practices were emphasized to avoid dental diseases.

The organizing principle of the platelet glycoprotein Ib-IX-V complex

The glycoprotein (GP)Ib-IX-V complex is the platelet receptor for von Willebrand factor and many other molecules that are critically involved in hemostasis and thrombosis. The lack of functional GPIb-IX-V complexes on the platelet surface is the cause of Bernard-Soulier syndrome, a rare hereditary bleeding disorder that is also associated with macrothrombocytopenia. GPIb-IX-V contains GPIbα, GPIbβ, GPIX and GPV subunits, all of which are type I transmembrane proteins containing leucine-rich repeat domains. Although all of the subunits were identified decades ago, not until recently did the mechanism of complex assembly begin to emerge from a systematic characterization of inter-subunit interactions. This review summarizes the forces driving the assembly of GPIb-IX-V, discusses their implications for the pathogenesis of Bernard-Soulier syndrome, and identifies questions that remain about the structure and organization of GPIb-IX-V.