Genetic sequence analysis of inherited bleeding diseases

Rare bleeding disorders: Real-world data from a Spanish tertiary hospital

INTRODUCTION

Due to their low prevalence, rare bleeding disorders (RBDs) remain poorly characterized.

AIM

To gain insight of RBDs through our clinical practice.

METHODS

Retrospective study of the medical records of RBD patients followed up at the Central University Hospital of Asturias between January 2019 and December 2022.

RESULTS

A total of 149 patients were included. Factor (F) VII (44 %) and FXI (40 %) deficiencies were the most common diagnosed coagulopathies. Most of the patients were asymptomatic (60.4 %) and the most frequent type of bleeding were mucocutaneous and after surgery. All replacement treatments were administered on demand and no patient was on a prophylaxis regimen. Currently available products were safe; allergic reactions after administration of plasma were the most frequent complication. Genetic analysis, carried out on 55 patients (37 %), showed that the most frequent mutations in RBDs are of missense type (71.9 %). We identified 11 different novel genetic alterations in affected genes. The c.802C > T (p.Arg268Cys) variant, previously described, was identified in 71 % (15 of 21) of the patients with FXI deficiency genotyped and none were related (probable founder effect).

CONCLUSION

Our study on an unusual large single center cohort of RBD patients portrays location-dependent distinct genetic drives and clinical practice particularities.

Gastrointestinal Bleeding in Congenital Bleeding Disorders

Gastrointestinal bleeding (GIB) is serious, intractable, and potentially life-threatening condition. There is considerable heterogeneity in GIB phenotypes among congenital bleeding disorders (CBDs), making GIB difficult to manage. Although GIB is rarely encountered in CBDs, its severity in some patients makes the need for a comprehensive and precise assessment of underlying factors and management approaches imperative. Initial evaluation of GIB begins with assessment of hematological status; GIB should be ruled out in patients with chronic anemia, and in presentations that include hematemesis, hematochezia, or melena. High-risk patients with recurrent GIB require urgent interventions such as replacement therapy for treatment of coagulation factor deficiency (CFD). However, the best management strategy for CFD-related bleeding remains controversial. While several investigations have identified CBDs as potential risk factors for GIB, research has focused on assessing the risks for individual factor deficiencies and other CBDs. This review highlights recent findings on the prevalence, management strategies, and alternative therapies of GIB related to CFDs, and platelet disorders.

Rare Coagulation Factor Deficiencies (Factors VII, X, V, and II)

Although rare clotting factor deficiencies primarily referred to as rare bleeding disorders (RBD), including factors II, V, VII, and X, make up ∼5% of all inherited bleeding disorders worldwide, each of these clotting factors play a critical role in the coagulation cascade. Incomplete bleeding evaluation or misinterpretation of laboratory studies can result in delayed diagnoses that ultimately affect patient outcomes. Bleeding manifestations can range from mild to severe, but the most common are mucocutaneous bleeding. The ideal treatment in RBD is dedicated single-factor concentrates that can be used for acute bleeding events, surgical management, and prophylaxis.

Case Report: Identification of a de novo Missense Mutation in the F8 Gene, p.(Phe690Leu)/c.2070C > A, Causing Hemophilia A: A Case Report

Hemophilia A is an X-linked recessive bleeding disorder caused by various types of pathological defects in the factor VIII gene (F8/FVIII). Preimplantation genetic testing for monogenic disease (PGT-M) is a powerful tool to tackle the transmission of monogenic inherited disorders from generation to generation. In our case, a mutation in F8 had passed through female carriers in a hemophilia A family and resulted in two male patients with hemophilia A. To identify the etiological genetic variants of F8, next-generation sequencing (NGS) was used for chromosome copy number variation detection, Sanger sequencing to verify mutation sites, single nucleotide polymorphism (SNP) for site amplification, and sequencing to validate the genetic linkage. Finally, a novel missense mutation, p. (Phe690Leu)/c.2070C > A, occurring in exon 13 of F8, was screened out as a pathogenic mutation. Following this, an F8 normal euploid blastocyst was transferred. At the 18th week, the pregnant mother underwent amniocentesis, NGS, Sanger sequencing, and SNP typing that further confirmed that the fetus had a healthy genotype. After delivery, a neonatal blood sample was sent for FVIII concentration detection, and the result established that the FVIII protein was rescued to a nearly average level. We first identified a new type of pathogenic mutation in F8, which has not been previously reported, selected a genetically healthy progeny for an affected family, and provided valuable knowledge of the diagnosis and treatment of hemophilia A.

Gene Therapy for Inherited Bleeding Disorders

Decades of preclinical and clinical studies developing gene therapy for hemophilia are poised to bear fruit with current promising pivotal studies likely to lead to regulatory approval. However, this recent success should not obscure the multiple challenges that were overcome to reach this destination. Gene therapy for hemophilia A and B benefited from advancements in the general gene therapy field, such as the development of adeno-associated viral vectors, as well as disease-specific breakthroughs, like the identification of B-domain deleted factor VIII and hyperactive factor IX Padua. The gene therapy field has also benefited from hemophilia B clinical studies, which revealed for the first time critical safety concerns related to immune responses to the vector capsid not anticipated in preclinical models. Preclinical studies have also investigated gene transfer approaches for other rare inherited bleeding disorders, including factor VII deficiency, von Willebrand disease, and Glanzmann thrombasthenia. Here we review the successful gene therapy journey for hemophilia and pose some unanswered questions. We then discuss the current state of gene therapy for these other rare inherited bleeding disorders and how the lessons of hemophilia gene therapy may guide clinical development.

The challenge of genetically unresolved haemophilia A patients: Interest of the combination of whole F8 gene sequencing and functional assays

BACKGROUND

The causative variant remains unidentified in 2%-5% of haemophilia A (HA) patients despite an exhaustive sequencing of the full F8 coding sequence, splice consensus sequences, 5'/3' untranslated regions and copy number variant (CNV) analysis. Next-generation sequencing (NGS) has provided significant improvements for a complete F8 analysis.

AIM

The aim of this study was to identify and characterize pathogenic non-coding variants in F8 of 15 French and Canadian HA patients genetically unresolved, through the use of NGS, mRNA sequencing and functional confirmation of aberrant splicing.

METHODS

We sequenced the entire F8 gene using an NGS capture method. We analysed F8 mRNA in order to detect aberrant transcripts. The pathogenic effect of candidate intronic variants was further confirmed using a minigene assay.

RESULTS

After bioinformatic analysis, 11 deep intronic variants were identified in 13 patients (8 new variants and 3 previously reported). Three variants were confirmed to be likely pathogenic with the presence of an aberrant transcript during mRNA analysis and minigene assay. We also found a small intronic deletion in 6 patients, recently described as causing mild HA.

CONCLUSION

With this comprehensive work combining NGS and functional assays, we report new deep intronic variants that cause HA through splicing alteration mechanism. Functional analyses are critical to confirm the pathogenic effect of these variants and will be invaluable in the future to study the large number of variants of uncertain significance that may affect splicing that will be found in the human genome.

Genetic Basis of Human Congenital Heart Disease

Congenital heart disease (CHD) is the most common major congenital anomaly with an incidence of ∼1% of live births and is a significant cause of birth defect-related mortality. The genetic mechanisms underlying the development of CHD are complex and remain incompletely understood. Known genetic causes include all classes of genetic variation including chromosomal aneuploidies, copy number variants, and rare and common single-nucleotide variants, which can be either de novo or inherited. Among patients with CHD, ∼8%-12% have a chromosomal abnormality or aneuploidy, between 3% and 25% have a copy number variation, and 3%-5% have a single-gene defect in an established CHD gene with higher likelihood of identifying a genetic cause in patients with nonisolated CHD. These genetic variants disrupt or alter genes that play an important role in normal cardiac development and in some cases have pleiotropic effects on other organs. This work reviews some of the most common genetic causes of CHD as well as what is currently known about the underlying mechanisms.

A novel splicing mutation in F8 causes various aberrant transcripts in a hemophilia A patient and identifies a new transcript from healthy individuals

: Hemophilia A is an X-linked hemorrhagic disorder caused by deficiency or dysfunction of the coagulation factor VIII (FVIII), and a great variety of mutations in the factor VIII gene (F8) are identified. We aimed to identify the genetic defects of the F8 gene in a Chinese patient with moderate hemophilia A. We have identified a novel intronic variant in the hemophilia A patient by DNA sequence analysis, cDNA sequencing, and TA clone sequencing. An intronic variant, c.5816-1G>A, was identified and the cDNA sequencing confirmed the pathogenicity of the transition. TA clone sequencing showed that the splicing mutation produced two aberrant premRNA skipping exons (18 and exon 18 + 19, respectively). These aberrant mRNA forms maintain the reading frame and are predicted to code for deleted FVIII isoforms and the shorter abnormal transcript accounted for one-eighth of the total mRNA. There was a new unreported transcript with E22 spliced out in healthy individuals and our patient, whose specific functions need to be determined in further studies. Our study widens the mutation spectrum of the F8 gene. In addition, the study findings could provide the opportunity to reveal alternative splicing patterns.

Deep intronic F8 c.5999-27A>G variant causes exon 19 skipping and leads to moderate hemophilia A

: Hemophilia A, an X-linked recessive bleeding disorder, is caused by mutations of F8 gene. In about 2% hemophilia A patients, no exonic mutation of F8 gene was found. We aimed to identify deep intronic mutations of F8 gene. We reanalyzed the next-generation sequencing data of six hemophilia A patients with negative F8 variant in either coding region or splice site. Deep intronic F8 c.5999-27A>G variant (NM_000132.3) was found in two unrelated moderate hemophilia A patients from different region, and one patient's mother was mild hemophilia A patient. Splice site prediction algorithms showed no impact of this variant on F8 mRNA splicing of exon 19, including Human Splicing Finder 3.1, NNSPLICE 0.9, NetGene2, and Transcript-inferred Pathogenicity score. Exonic splicing enhancer was predicted by ESEfinder, and no difference was found between the wild type and mutant sequence. The branch point predicted by SVM-BPfinder suggested that F8 c.5999-27A>G variant may disrupt the branch point in intron 18 and affect the acceptor site splicing of F8 exon 19. Sanger sequencing of F8 cDNA from peripheral blood mononuclear cells confirmed that F8 c.5999-27A>G variant caused F8 exon 19 skipping in proband and his mother. Skewed X chromosome inactivation was found in another X chromosome of this mother, combined with F8 c.5999-27A>G variant in trans. In conclusion, our study suggests that deep intronic F8 c.5999-27A>G variant may be responsible for F8 exon 19 skipping and lead to moderate hemophilia A. Systematic reanalysis of next-generation sequencing data could promote the diagnostic yields.

A Closed-Tube Nested Quantitative PCR Assay for Rapid Detection of Intron 22 Inversions in the Factor VIII Gene

BACKGROUND

An inversion of intron 22 in the Factor VIII gene (Inv22) is the causative mutation for 45% of severe hemophilia A cases. Available methods for molecular diagnosis of Inv22 are generally tedious and not ideal for routine clinical use.

METHODS

We report here a new method using a single closed-tube nested quantitative PCR (CN-qPCR) for rapid detection of Inv22. This method combines a 12-cycle long-distance PCR (LD-PCR) amplifying the int22h regions, followed by a duplex qPCR targeting two specific regions close to the int22h regions. All reagents were added to a single PCR mixture for the closed-tube assay. Sequential LD-PCR and qPCR was achieved by designing primers at substantially different melting temperatures and optimizing PCR conditions.

RESULTS

Seventy-nine male hemophilia A patients of different disease severity were tested by both the CN-qPCR assay and the standard LD-PCR assay. CN-qPCR successfully made calls for all samples, whereas LD-PCR failed in eight samples. For the 71 samples where both methods made calls, the concordance was 100%. Inv22 was detected in 17 out of the 79 samples. Additionally, CN-qPCR achieved clear separation for 10 female carriers and 10 non-Inv22 females, suggesting the assay may also be useful for molecular diagnosis of female carriers.

CONCLUSIONS

This new CN-qPCR method may provide a convenient and accurate F8 Inv22 test suitable for clinical use.

Elevated thrombin generation in patients with congenital disorder of glycosylation and combined coagulation factor deficiencies

BACKGROUND

Congenital disorders of glycosylation are rare inherited diseases affecting many different proteins. The lack of glycosylation notably affects the hemostatic system and leads to deficiencies of both procoagulant and anticoagulant factors.

OBJECTIVE

To assess the hemostatic balance in patients with multiple coagulation disorders by using a thrombin generation assay.

METHOD

We performed conventional coagulation assays and a thrombin generation assay on samples from patients with congenital disorder of glycosylation. The thrombin generation assay was performed before and after activation of the protein C system by the addition of soluble thrombomodulin.

RESULTS

A total of 35 patients were included: 71% and 57% had low antithrombin and factor XI levels, respectively. Protein C and protein S levels were abnormally low in 29% and 26% of the patients, respectively, whereas only 11% displayed low factor IX levels. Under baseline conditions, the thrombin generation assay revealed a significantly higher endogenous thrombin potential and thrombin peak in patients, relative to controls. After spiking with thrombomodulin, we observed impaired involvement of the protein C system. Hence, 54% of patients displayed a hypercoagulant phenotype in vitro. All the patients with a history of stroke-like episodes or thrombosis displayed this hypercoagulant phenotype.

CONCLUSION

A thrombin generation assay revealed a hypercoagulant in vitro phenotype under baseline condition; this was accentuated by impaired involvement of the protein C system. This procoagulant phenotype may thus reflect the risk of severe vascular complications. Further research will have to determine whether the thrombin generation assay is predictive of vascular events.

Clinical and laboratory diagnosis of rare coagulation disorders (RCDs)

Rare coagulation disorders (RCDs) are a group of diseases due to coagulation factors deficiency leading to life-long bleeding diathesis. The diagnosis of RCDs is challenging due to the limited knowledge of these disorders and the large heterogeneity of their bleeding patterns. The clinical symptoms of RCDs are extremely diverse in terms of bleeding type, site, severity, age at onset, and duration. The strength of the association between clotting factor activity level in plasma and clinical symptoms is also variable within each RCD. The clinical evaluation of RCDs starts with a detailed collection of clinical history and has been facilitated by bleeding assessment tools, however their effectiveness in diagnosing RCDs requires further investigation. The following laboratory diagnosis of RCDs involves coagulation screening tests, including activated partial thromboplastin time, prothrombin time, and thrombin time. After ruling out the presence of an inhibitor by mixing studies, in case of abnormal results, the specific deficiency is identified by performing one-stage clotting assays using the specific factor-depleted plasmas as substrate. In fibrinogen and FXIII deficiencies coagulation screening tests are not informative, therefore additional tests are needed. Global assays have been developed and are thought to aid in patient management, however, they are not well standardized yet. In addition to outlining the principles of clinical and laboratory diagnosis, this review explores molecular basis of RCDs and laboratory techniques for genetic analysis, and discusses the importance and effectiveness of quality control programs to ensure standardized laboratory results.

Management of rare coagulation disorders in 2018

Rare bleeding disorders (RBDs) comprise inherited deficiencies of factors I (fibrinogen), II (prothrombin), V, VII, X, XI, and XIII as well as combined factor V + VIII and vitamin K-dependent factors. They represent 3-5% of all congenital bleeding disorders and are usually transmitted as autosomal recessive traits. These disorders often manifest during childhood and have varied clinical presentations from mucocutaneous bleeding to life-threatening symptoms such as central nervous system and gastrointestinal bleeding. Bleeding manifestations generally vary within the same RBD and may also vary from 1 RBD to the other. Laboratory diagnosis is based on coagulation screening tests and specific factor assays, with molecular techniques providing diagnostic accuracy and enabling prenatal counseling. The approach to treatment of bleeding episodes and invasive procedures needs to be individualized and depends on the severity, frequency and procedure-related risk of bleeding. The first line of treatment of RBDs is replacement of the deficient factor, using specific plasma-derived or recombinant products and using fresh frozen plasma or cryoprecipitate when specific products are not available or in resource-limited countries. Prophylaxis may be considered in individuals with recurrent serious bleeding and especially after life-threatening bleeding episodes. Novel no-replacement strategies promoting hemostasis by through different mechanisms need to be studied in RBDs as alternative therapeutic options.

Identification of a novel mutation in the factor VIII gene causing severe haemophilia A

Background

Deficiency in coagulation factor VIII encoded by F8 results in the X-linked recessive bleeding disorder haemophilia A (HEMA). Here we describe the identification of a novel variant in the factor VIII gene, F8, in an adult male patient with severe haemophilia A.

Case presentation

The patient was diagnosed in early childhood and subsequently co-infected with Hepatitis C and HIV acquired during early blood transfusion for haemophilia in the 1980ies. The identified F8 deletion, c.5411_5413delTCT, p.F1804del lies within a conserved part of the molecule, is predicted by bioinformatic software to be deleterious by the loss of Phenylalanine, and has not been previously described in any database.

Conclusion

This novel F8 deletion as a cause of haemophilia A did not result in generation of inhibitory antibodies to Factor VIII treatment and may have impact on (prenatal) diagnosis, genetic counselling, and treatment decisions in the affected family as well as in other families diagnosed with this F8 mutation. Finally, this novel mutation should be included in the panel of known genetic variants in F8 when searching for the genetic etiology in patients suspected of HEMA.

Electronic supplementary material

The online version of this article (10.1186/s12878-018-0113-4) contains supplementary material, which is available to authorized users.

TC21/RRas2 regulates glycoprotein VI-FcRγ-mediated platelet activation and thrombus stability

Essentials RAS proteins are expressed in platelets but their functions are largely uncharacterized. TC21/RRas2 is required for glycoprotein VI-induced platelet responses and for thrombus stability in vivo. TC21 regulates platelet aggregation by control of αIIb β3 integrin activation, via crosstalk with Rap1b. This is the first indication of functional importance of a proto-oncogenic RAS protein in platelets.

SUMMARY

Background Many RAS family small GTPases are expressed in platelets, including RAC, RHOA, RAP, and HRAS/NRAS/RRAS1, but most of their signaling and cellular functions remain poorly understood. Like RRAS1, TC21/RRAS2 reverses HRAS-induced suppression of integrin activation in CHO cells. However, a role for TC21 in platelets has not been explored. Objectives To determine TC21 expression in platelets, TC21 activation in response to platelet agonists, and roles of TC21 in platelet function in in vitro and in vivo thrombosis. Results We demonstrate that TC21 is expressed in human and murine platelets, and is activated in response to agonists for the glycoprotein (GP) VI-FcRγ immunoreceptor tyrosine-based activation motif (ITAM)-containing collagen receptor, in an Src-dependent manner. GPVI-induced platelet aggregation, integrin αIIb β3 activation, and α-granule and dense granule secretion, as well as phosphorylation of Syk, phospholipase Cγ2, AKT, and extracellular signal-regulated kinase, were inhibited in TC21-deficient platelets ex vivo. In contrast, these responses were normal in TC21-deficient platelets following stimulation with P2Y, protease-activated receptor 4 and C-type lectin receptor 2 receptor agonists, indicating that the function of TC21 in platelets is GPVI-FcRγ-ITAM-specific. TC21 was required for GPVI-induced activation of Rap1b. TC21-deficient mice did not show a significant delay in injury-induced thrombosis as compared with wild-type controls; however, thrombi were unstable. Hemostatic responses showed similar effects. Conclusions TC21 is essential for GPVI-FcRγ-mediated platelet activation and for thrombus stability in vivo via control of Rap1b and integrins.

Evolving Complexity in Hemophilia Management

Rapid expansion of therapeutic options have increased the complexity of hemophilia care. Previously, on-demand therapy aimed to reduce morbidity and early mortality; however, now aggressive prophylaxis, particularly in children, encourages an active lifestyle. Accurate diagnosis, recognition of early threats to musculoskeletal health, and optimization of therapy are critical for both males and females affected by hemophilia. The diversity of emerging hemophilia therapies, from modified factor protein concentrates, to gene therapy, to nonfactor hemostatic strategies, provide an exciting opportunity to target unmet needs in the bleeding disorder community.

Clustered F8 missense mutations cause hemophilia A by combined alteration of splicing and protein biosynthesis and activity

Dissection of pleiotropic effects of missense mutations, rarely investigated in inherited diseases, is fundamental to understanding genotype-phenotype relationships. Missense mutations might impair mRNA processing in addition to protein properties. As a model for hemophilia A, we investigated the highly prevalent F8 c.6046c>t/p.R2016W (exon 19) mutation. In expression studies exploiting lentiviral vectors, we demonstrated that the amino acid change impairs both Factor VIII (FVIII) secretion (antigen 11.0±0.4% of wild-type) and activity (6.0±2.9%). Investigations in patients' ectopic F8 mRNA and with minigenes showed that the corresponding nucleotide change also decreases correct splicing to 70±5%, which is predicted to lower further FVIII activity (4.2±2%), consistently with patients' levels (<1-5%). Masking the mutated exon 19 region by antisense U7snRNA supported the presence of a splicing regulatory element, potentially affected by several missense mutations causing hemophilia A. Among these, the c.6037g>a (p.G2013R) reduced exon inclusion to 41±3% and the c.6053a>g (p.E2018G) to 28±2%, similarly to a variant affecting the 5' splice site (c.6113a>g, p.N2038S, 26±2%), which displayed normal protein features upon recombinant expression. The p.G2013R reduced both antigen (7.0±0.9%) and activity (8.4±0.8%), while the p.E2018G produced a dysfunctional molecule (antigen: 69.0±18.1%; activity: 19.4±2.3%). In conclusion, differentially altered mRNA and protein patterns produce a gradient of residual activity, and clarify genotype-phenotype relationships. Data detail pathogenic mechanisms that, only in combination, account for moderate/severe disease forms, which in turn determine the mutation profile. Taken together we provide a clear example of interplay between mRNA and protein mechanisms of disease that operate in shaping many other inherited disorders.

Rare bleeding disorders-old diseases in the era of novel options for therapy

Rare diseases are defined as life-threatening or chronically debilitating diseases with a prevalence of less than one per 2000 according to the European Union or one per 1250 according to the USA. Congenital rare bleeding disorders RBD are reported in most populations, with incidence varying from 1 in 5000 (Hemophilia A), 1:30,000 (Hemophilia B) to much rarer (1:500,000 for FVII deficiency, 1-3 million for Prothrombin or FXIII deficiency). Acquired Hemophilia A is also a rare bleeding disorder with estimated frequency of 1 in million. Most RBDs are inherited as autosomal recessive (AR); however, heterozygous carriers with varying degrees of corresponding factor deficiency may render an unpredictable propensity for bleeding. In patients with bleeding symptoms, laboratory assessment and especially molecular techniques currently enable accurate diagnosis and may provide tools for prenatal and family counseling. Currently hemostasis control is mainly based upon replacement of the missing coagulation factors (unless presence of inhibitors renders it impossible), however future gene therapy and disruptive, non-replacement alternatives may be promising for patients with RBD.

Treatment of rare factor deficiencies in 2016

Rare bleeding disorders (RBDs) are a heterogeneous group of coagulation disorders characterized by fibrinogen, prothrombin, factors V, VII, X, XI, or XIII (FV, FVII, FX, FXI, or FXIII, respectively), and the combined factor V + VIII and vitamin K-dependent proteins deficiencies, representing roughly 5% of all bleeding disorders. They are usually transmitted as autosomal, recessive disorders, and the prevalence of the severe forms could range from 1 case in 500 000 for FVII up to 1 in 2-3 million for FXIII in the general population. Patients affected with RBDs may present a wide range of clinical symptoms, varying from mucocutaneous bleeding, common to all types of RBDs to the most life-threatening symptoms such as central nervous system and gastrointestinal bleeding. Treatment of these disorders is mainly based on the replacement of the deficient factor, using specific plasma-derived or recombinant products. In countries where these facilities are not available, bleedings could be managed using cryoprecipitate, fresh frozen plasma (FFP), or virus-inactivated plasma. Minor bleedings could be managed using antifibrinolytic agents. Recently, 2 novel drugs, recombinant FXIIIA and a plasma-derived FX, have been added to the list of available specific hemostatic factors; only prothrombin and FV deficiencies still remain without a specific product. Novel no-replacement therapies, such as monoclonal antibody anti-tissue factor pathway inhibitor, RNA interference, and a bispecific antibody that is an FVIIIa mimetic, enhancing thrombin generation through different mechanisms, were developed for patients with hemophilia and may in the future be a good therapeutic option also in RBDs.

Combined variants in factor VIII and prostaglandin synthase-1 amplify hemorrhage severity across three generations of descendants

Essentials Co-existent damaging variants are likely to cause more severe bleeding and may go undiagnosed. We determined pathogenic variants in a three-generational pedigree with excessive bleeding. Bleeding occurred with concurrent variants in prostaglandin synthase-1 (PTGS-1) and factor VIII. The PTGS-1 variant was associated with functional defects in the arachidonic acid pathway.

SUMMARY

Background Inherited human variants that concurrently cause disorders of primary hemostasis and coagulation are uncommon. Nevertheless, rare cases of co-existent damaging variants are likely to cause more severe bleeding and may go undiagnosed. Objective We prospectively sought to determine pathogenic variants in a three-generational pedigree with excessive bleeding. Patients/methods Platelet number, size and light transmission aggregometry to multiple agonists were evaluated in pedigree members. Transmission electron microscopy determined platelet morphology and granule content. Thromboxane release studies and light transmission aggregometry in the presence or absence of prostaglandin G2 assessed specific functional defects in the arachidonic acid pathway. Whole exome sequencing (WES) and targeted nucleotide sequence analysis identified potentially deleterious variants. Results Pedigree members with excessive bleeding had impaired platelet aggregation with arachidonic acid, epinephrine and low-dose ADP, as well as reduced platelet thromboxane B2 release. Impaired platelet aggregation in response to 2MesADP was rescued with prostaglandin G2 , a prostaglandin intermediate downstream of prostaglandin synthase-1 (PTGS-1) that aids in the production of thromboxane. WES identified a non-synonymous variant in the signal peptide of PTGS-1 (rs3842787; c.50C>T; p.Pro17Leu) that completely co-segregated with disease phenotype. A variant in the F8 gene causing hemophilia A (rs28935203; c.5096A>T; p.Y1699F) was also identified. Individuals with both variants had more severe bleeding manifestations than characteristic of mild hemophilia A alone. Conclusion We provide the first report of co-existing variants in both F8 and PTGS-1 genes in a three-generation pedigree. The PTGS-1 variant was associated with specific functional defects in the arachidonic acid pathway and more severe hemorrhage.

The past and future of haemophilia: diagnosis, treatments, and its complications

Haemophilia A and B are hereditary haemorrhagic disorders characterised by deficiency or dysfunction of coagulation protein factors VIII and IX, respectively. Recurrent joint and muscle bleeds lead to severe and progressive musculoskeletal damage. Existing treatment relies on replacement therapy with clotting factors, either at the time of bleeding (ie, on demand) or as part of a prophylactic schedule. The major complication of such therapy is the development of neutralising antibodies (ie, inhibitors), which is most frequent in haemophilia A. Treatment might improve considerably with the availability of new modified drugs, which might overcome existing prophylaxis limitations by reducing dosing frequency and thereby rendering therapy less distressing for the patient. Subcutaneous administration of some new therapies would also simplify prophylaxis in children with poor venous access. Gene therapy has the potential for a definitive cure, and important results have been obtained in haemophilia B. Despite improvements in haemophilia care, the availability of clotting factor concentrates for all affected individuals worldwide remains the biggest challenge.

Misfolding of vWF to pathologically disordered conformations impacts the severity of von Willebrand disease

The primary hemostatic von Willebrand factor (vWF) functions to sequester platelets from rheological blood flow and mediates their adhesion to damaged subendothelium at sites of vascular injury. We have surveyed the effect of 16 disease-causing mutations identified in patients diagnosed with the bleeding diathesis disorder, von Willebrand disease (vWD), on the structure and rheology of vWF A1 domain adhesiveness to the platelet GPIbα receptor. These mutations have a dynamic phenotypical range of bleeding from lack of platelet adhesion to severe thrombocytopenia. Using new rheological tools in combination with classical thermodynamic, biophysical, and spectroscopic metrics, we establish a high propensity of the A1 domain to misfold to pathological molten globule conformations that differentially alter the strength of platelet adhesion under shear flow. Rheodynamic analysis establishes a quantitative rank order between shear-rate-dependent platelet-translocation pause times that linearly correlate with clinically reported measures of patient platelet counts and the severity of thrombocytopenia. These results suggest that specific secondary structure elements remaining in these pathological conformations of the A1 domain regulate GPIbα binding and the strength of vWF-platelet interactions, which affects the vWD functional phenotype and the severity of thrombocytopenia.

Rare bleeding disorders: diagnosis and treatment

Despite the worldwide prevalence of rare bleeding disorders (RBDs), knowledge of these conditions and their management is suboptimal; health care professionals often have little diagnostic and treatment experience with variable access to diagnostic modalities required for accurate identification. Therefore, patients often experience morbidity and mortality due to delayed diagnosis. As RBDs represent a small potential commercial market, few, if any, specific therapies exist for these conditions. As a result, affected individuals commonly face delayed diagnosis, incomplete laboratory evaluation, and limited treatment options. Standardization and customization of coagulation assays, full genome sequencing, and global clotting assays will significantly improve diagnosis of patients with RBDs. In addition, new therapeutic modalities, both recombinant and plasma derived, are emerging, at least in developed countries. Registries and clinical trials have demonstrated decreased bleeding and improved outcomes when patients are appropriately diagnosed and properly treated. Expansion and harmonization of international registries has been initiated to correlate genotype, laboratory, and clinical phenotypes including bleeding severity to improve the diagnosis and therapeutic approach. This review focuses on the latest advances in our understanding, diagnosis, and treatment of RBDs.