Genotype-phenotype correlation in a cohort of Portuguese patients comprising the entire spectrum of VWD types: impact of NGS

Genetic variations of type 2 and type 3 von Willebrand diseases in Thailand

AIMS

Von Willebrand disease (VWD) is an inherited haemostatic disorder with a wide range of bleeding phenotypes based on von Willebrand factor (VWF) levels. Multiple assays including VWF gene analysis are employed to correctly diagnose VWD and its subtypes. However, data on VWF mutations among Southeast Asian populations are lacking. We, therefore, aimed to explore genetic variations in Thai patients with type 2 and type 3 VWD by whole exome sequencing (WES).

METHODS

In this multicentre study, Thai patients with type 2 and type 3 VWD, according to the definitions and VWF levels recommended by the international guidelines, were recruited. WES was performed using DNA extracted from peripheral blood in all cases. The novel variants were verified by Sanger sequencing.

RESULTS

Fifteen patients (73% females; median age at diagnosis 3.0 years) with type 2 (n=12) and type 3 VWD (n=3) from 14 families were enrolled. All patients harboured at least one VWF variant. Six missense (p.Arg1374Cys, p.Arg1374His, p.Arg1399Cys, p.Arg1597Trp, p.Ser1613Pro, p.Pro1648Arg) and one splice-site (c.3379+1G>A) variants in the VWF gene were formerly described. Notably, six VWF variants, including three missense (p.Met814Ile, p.Trp856Cys, p.Pro2032Leu), one deletion (c.2251delG) and two splice-site (c.7729+4A>C, c.8115+2delT) mutations were novelly identified. Compound heterozygosity contributed to type 2 and type 3 VWD phenotypes in two and one patients, respectively.

CONCLUSIONS

Type 2 and type 3 VWD in Thailand demonstrate the mutational variations among VWF exons/introns with several unique variants. The WES-based approach potentially provides helpful information to verify VWD diagnosis and facilitate genetic counselling in clinical practice.

Application of genetic testing for the diagnosis of von Willebrand disease

von Willebrand disease (VWD) is the most frequent inherited bleeding disorder, with an estimated symptomatic prevalence of 1 per 1000 in the general population. VWD is characterized by defects in the quantity, quality, or multimeric structure of von Willebrand factor (VWF), a glycoprotein being hemostatically essential in circulation. VWD is classified into 3 principal types: low VWF/type 1 with partial quantitative deficiency of VWF, type 3 with virtual absence of VWF, and type 2 with functional abnormalities of VWF, being classified as 2A, 2B, 2M, and 2N. A new VWD type has been officially recognized by the ISTH SSC on von Willebrand factor which has also been discussed by the joint ASH/ISTH/NHF/WFH 2021 guidelines (ie, type 1C), indicating patients with quantitative deficiency due to an enhanced VWF clearance. With the advent of next-generation sequencing technologies, the process of genetic diagnosis has substantially changed and improved accuracy. Therefore, nowadays, patients with type 3 and severe type 1 VWD can benefit from genetic testing as much as type 2 VWD. Specifically, genetic testing can be used to confirm or differentiate a VWD diagnosis, as well as to provide genetic counseling. The focus of this manuscript is to discuss the current knowledge on VWD molecular pathophysiology and the application of genetic testing for VWD diagnosis.

A comparative study in patients with type 2 von Willebrand disease using 4 different platelet-dependent von Willebrand factor assays

Background

Several assays are now available to evaluate platelet-dependent von Willebrand factor (VWF) activity.

Objective

To report the results obtained using 4 different assays in patients with von Willebrand disease (VWD) carrying variants mainly in the A1 domain, which is critical for VWF binding to glycoprotein Ib (GPIb) and ristocetin.

Methods

We evaluated 4 different assays, 2 gain-of-function mutant GPIb binding (VWF:GPIbM) and 2 ristocetin cofactor (VWF:RCo) assays, in 76 patients with type 2 VWD. Patients and healthy controls were tested using VWF:GPIbM enzyme-linked immunosorbent assay (ELISA), VWF:GPIbM automated, VWF:RCo aggregometric, and VWF:RCo automated assays.

Results

There was a good correlation (Pearson's r>0.82) and agreement (Bland-Altman plots assessment) between the 4 assays, although several outliers existed among the type 2B without high-molecular-weight multimers (HMWM). The VWF activity/VWF:antigen ratios, calculated for each assay, were used to establish the percentage of a correct diagnosis of type 2 (ratio<0.60) in these patients: VWF:RCo aggregometric, 2A(100%), 2M(78%), 2M/2A(100%), 2B(68%); VWF:RCo automated, 2A(88%), 2M(89%), 2M/2A(100%), 2B(63%); VWF:GPIbM ELISA, 2A(96%), 2M(67%), 2M/2A(67%), 2B(0%); VWF:GPIbM automated, 2A(73%), 2M(44%), 2M/2A(75%), 2B(84%). In type 2B patients with HMWM, all assays gave a ratio ≥0.60.

Conclusion

The VWF:GPIbM-automated assay is the most effective to diagnose as type 2 the 2B variants, whereas the VWF:RCo assays are the most effective in detecting 2M and 2M/2A variants. The VWF:GPIbM ELISA greatly overestimates the activity of the type 2B patients lacking HMWM. In this study, the use of a VWF activity/VWF:antigen ratio cut-off of 0.70 halved the number of misdiagnosed patients.

Type 2N VWD: Conclusions from the Spanish PCM-EVW-ES project

INTRODUCTION

Type 2N von Willebrand disease (VWD) is characterized by a decreased affinity of von Willebrand factor (VWF) for factor VIII (FVIII). Abnormal binding of FVIII to VWF (VWF:FVIIIB), results in low FVIII plasma levels, which can lead to a misdiagnosis of mild haemophilia A. Accurate diagnosis of type 2N VWD is essential for appropriate genetic counselling and therapy. This disease can be distinguished from haemophilia A by in vitro assays (measurement VWF:FVIIIB activity) and/or genetic analysis.

AIM

To identify the current challenges in the diagnosis and treatment of this type of VWD and provide an in-depth description of the phenotypes and mutations identified.

RESULTS

Twenty-eight patients had at least one type 2N mutation, and 13 of these had a type 2N mutation combined with other variations. Three type 2N mutations were detected: p.Arg816Trp, p.Arg854Gln, and p.Arg763Ser. Two of these are the most frequently described mutations worldwide. This mutational spectrum differs from the broad spectrum seen in neighbouring France, where at least eight distinct 2N mutations have been found. In the PCM-EVW-ES cohort, 11 asymptomatic type 2N carriers with borderline FVIII plasma levels would probably have been excluded if the evaluation had been based on clinical and laboratory data only. Likewise, three patients with a severe phenotype would have been classified as homozygous for a 2N mutation if only the phenotype study had been performed.

CONCLUSION

The high detection yield and affordability of next-generation sequencing support the use of this technology as a first-line diagnostic tool in this setting.

Genotypes of European and Iranian patients with type 3 von Willebrand disease enrolled in 3WINTERS-IPS

Type 3 von Willebrand disease (VWD3) is a rare and severe bleeding disorder characterized by often undetectable von Willebrand factor (VWF) plasma levels, a recessive inheritance pattern, and heterogeneous genotype. The objective of this study was to identify the VWF defects in 265 European and Iranian patients with VWD3 enrolled in 3WINTERS-IPS (Type 3 Von Willebrand International Registries Inhibitor Prospective Study). All analyses were performed in centralized laboratories. The VWF genotype was studied in 231 patients with available DNA (121 [115 families] from Europe [EU], and 110 [91 families] from Iran [IR]). Among 206 unrelated patients, 134 were homozygous (EU/IR = 57/77) and 50 were compound heterozygous (EU/IR = 43/7) for VWF variants. In 22 patients, no or only one variant was found. A total of 154 different VWF variants (EU/IR = 101/58 [5 shared]) were identified among the 379 affected alleles (EU/IR = 210/169), of which 48 (EU/IR = 18/30) were novel. The variants p.Arg1659*, p.Arg1853*, p.Arg2535*, p.Cys275Ser, and delEx1_Ex5 were found in both European and Iranian VWD3 patients. Sixty variants were identified only in a single allele (EU/IR = 50/10), whereas 18 were recurrent (≥3 patients) within 144 affected alleles. Nine large deletions and one large insertion were found. Although most variants predicted null alleles, 21% of patients carried at least 1 missense variant. VWD3 genotype was more heterogeneous in the European population than in the Iranian population, with nearly twice as many different variants. A higher number of novel variants were found in the Iranian VWD3 patients.

Two cases of von Willebrand disease type 3 in consanguineous Chinese families

BACKGROUND

von Willebrand disease (VWD) is the most common inherited bleeding disorder caused by defective or deficient von Willebrand factor (VWF). VWD type 3 is inherited in autosomal recessive manner. We described clinical and molecular features of VWD type 3 in two consanguineous marriage families.

METHODS

Peripheral blood was collected, PT, APTT, FVIII:C, VWF:RCo, VWF:Ag were measured. A targeted next-generation sequencing panel covering F8, F9, and VWF genes was applied followed by Sanger sequencing.

RESULTS

Both families had a baby die in their first year due to bleeding disorders. A 23-year-old female patient from family A suffered menorrhagia, and another 30-year-old male patient from family B was characterized with hematoma in the lower extremity. Both patients showed severely decreased FVIII:C, VWF:Ag. Recurrent homozygous VWF c.4696C>T (p.Arg1566Ter) nonsense mutation was identified in the female patient, and novel homozygous VWF c.6450C>A (p.Cys2150Ter) nonsense mutation was identified the male patient. Heterozygotes in family members showed mild/moderate decrease in VWF:Ag or VWF:RCo.

CONCLUSIONS

We identified VWD type 3 in two consanguineous marriage families, and our work further strengthen the risk of delivering disorders inherited in AR manner in populations with frequent consanguineous partnerships.

Updated overview on von Willebrand disease: focus on the interest of genotyping

Introduction: Von Willebrand disease (VWD) is the most common inherited bleeding disorder, characterized by a quantitative or qualitative defect of von Willebrand factor (VWF), a multimeric glycoprotein crucial for primary hemostasis and coagulation. VWD pathophysiology is heterogeneous as it includes several types and subtypes which therapeutic management is different. The mainstays of VWD treatment are desmopressin and replacement therapy based on both plasma-derived concentrates and a recently developed recombinant VWF. VWD definitive diagnosis is achieved by a battery of phenotypic biologic assays and genotyping is currently performed mostly for research.Areas covered: This narrative review will firstly present a general overview on VWD epidemiology, pathophysiology, classification, clinics, phenotypic biologic diagnosis, and treatment. Secondly, a focus on VWD genotyping will be presented with specific emphasis on the evolution of its technical aspects, its applications for research dedicated to a better understanding of VWD pathophysiology and epidemiology and its interest in both a faster diagnosis and an optimal treatment of VWD.Expert opinion: Based on analysis of the literature, it can be concluded that the fast evolution of genetic techniques together with the development of innovating treatments may significantly change diagnostic flow charts for VWD and their use for specific and personalized treatment.

Unraveling the effect of silent, intronic and missense mutations on VWF splicing: contribution of next generation sequencing in the study of mRNA

Large studies in von Willebrand disease patients, including Spanish and Portuguese registries, led to the identification of >250 different mutations. It is a challenge to determine the pathogenic effect of potential splice site mutations on VWF mRNA. This study aimed to elucidate the true effects of 18 mutations on VWF mRNA processing, investigate the contribution of next-generation sequencing to in vivo mRNA study in von Willebrand disease, and compare the findings with in silico prediction. RNA extracted from patient platelets and leukocytes was amplified by RT-PCR and sequenced using Sanger and next generation sequencing techniques. Eight mutations affected VWF splicing: c.1533+1G>A, c.5664+2T>C and c.546G>A (p.=) prompted exon skipping; c.3223-7_3236dup and c.7082-2A>G resulted in activation of cryptic sites; c.3379+1G>A and c.7437G>A) demonstrated both molecular pathogenic mechanisms simultaneously; and the p.Cys370Tyr missense mutation generated two aberrant transcripts. Of note, the complete effect of three mutations was provided by next generation sequencing alone because of low expression of the aberrant transcripts. In the remaining 10 mutations, no effect was elucidated in the experiments. However, the differential findings obtained in platelets and leukocytes provided substantial evidence that four of these would have an effect on VWF levels. In this first report using next generation sequencing technology to unravel the effects of VWF mutations on splicing, the technique yielded valuable information. Our data bring to light the importance of studying the effect of synonymous and missense mutations on VWF splicing to improve the current knowledge of the molecular mechanisms behind von Willebrand disease. clinicaltrials.gov identifier:02869074.

Molecular and clinical profile of von Willebrand disease in Spain (PCM-EVW-ES): comprehensive genetic analysis by next-generation sequencing of 480 patients

Molecular diagnosis of patients with von Willebrand disease is pending in most populations due to the complexity and high cost of conventional molecular analyses. The need for molecular and clinical characterization of von Willebrand disease in Spain prompted the creation of a multicenter project (PCM-EVW-ES) that resulted in the largest prospective cohort study of patients with all types of von Willebrand disease. Molecular analysis of relevant regions of the VWF, including intronic and promoter regions, was achieved in the 556 individuals recruited via the development of a simple, innovative, relatively low-cost protocol based on microfluidic technology and next-generation sequencing. A total of 704 variants (237 different) were identified along VWF, 155 of which had not been previously recorded in the international mutation database. The potential pathogenic effect of these variants was assessed by in silico analysis. Furthermore, four short tandem repeats were analyzed in order to evaluate the ancestral origin of recurrent mutations. The outcome of genetic analysis allowed for the reclassification of 110 patients, identification of 37 asymptomatic carriers (important for genetic counseling) and re-inclusion of 43 patients previously excluded by phenotyping results. In total, 480 patients were definitively diagnosed. Candidate mutations were identified in all patients except 13 type 1 von Willebrand disease, yielding a high genotype-phenotype correlation. Our data reinforce the capital importance and usefulness of genetics in von Willebrand disease diagnostics. The progressive implementation of molecular study as the first-line test for routine diagnosis of this condition will lead to increasingly more personalized and effective care for this patient population.

Molecular and clinical profile of VWD in a large cohort of Chinese population: application of next generation sequencing and CNVplex® technique

Von Willebrand disease (VWD), the most common inherited bleeding disorder, is characterised by a variable bleeding tendency, heterogeneous laboratory phenotype and race specific distribution of mutations. The present study aimed to determine the correlation of genotype and phenotype in 200 Chinese individuals from 90 unrelated families with VWD. Next generation sequencing (NGS) of the whole coding VWF, copy number analysis of VWF by CNVplex^® technique as well as a comprehensive phenotypic assessment were carried out in all index patients (IPs). We identified putative mutations in all IPs except five mild type 1 (85/90, 94.4 %). In total, 98 different mutations were detected, 62 (63.3 %) of which were reported for the first time (23 missense mutations, 1 regulatory mutation, 12 splice site mutations and 26 null mutations). Mutations p.Ser1506Leu and p.Arg1374His/Cys/Ser were the most frequent mutations in 2A (33 % of cases) and 2M VWD (67 % of cases), respectively. In addition, mutation p.Arg816Trp was detected repeatedly in type 2N patients, while mutation p.Arg854Gln, extremely common in Caucasians, was not found in our cohort. Thirty-three patients had two or more putative mutations. Unlike most cases of type 1 and type 2 VWD, which were transmitted dominantly, we presented seven severe type 1, two type 2A and one type 2M with autosomal recessive inheritance. Here the phenotypic data of patients with novel mutations will certainly contribute to the better understanding of the molecular genetics of VWF-related phenotypes.

Combined study of ADAMTS13 and complement genes in the diagnosis of thrombotic microangiopathies using next-generation sequencing

BACKGROUND

The 2 main forms of thrombotic microangiopathy (TMA) are thrombotic thrombocytopenic purpura (TTP) and atypical hemolytic uremic syndrome (aHUS). Deficiency of ADAMTS13 and dysregulation of the complement pathway result in TTP and aHUS, respectively; however, overlap of their clinical characteristics makes differential diagnosis challenging.

OBJECTIVES AND METHODS

We aimed to develop a TMA diagnosis workflow based on ADAMTS13 activity and screening of ADAMTS13 and complement genes using a custom next-generation sequencing (NGS) gene panel.

PATIENTS

For this, from a cohort of 154 Portuguese patients with acute TMA, the genotype-phenotype correlations were analyzed in 7 hereditary TTP (ADAMTS13 activity <10%, no inhibitor), 36 acquired TTP (ADAMTS13 activity <10%, presence of an inhibitor), and in 34 presumable aHUS.

RESULTS

In total, 37 different rare variants, 8 of which novel (in ADAMTS13,CFH, and CD46), were identified across 7 genes. Thirteen TTP patients were homozygous (n=6), compound heterozygous (n=2), and heterozygous (n=5) for 11 ADAMTS13 variants (6 pathogenic mutations). Among the 34 aHUS patients, 17 were heterozygous for 23 variants in the different complement genes with distinct consequences, ranging from single pathogenic mutations associated with complete disease penetrance to benign variants that cause aHUS only when combined with other variants and/or CFH and CD46 risk haplotypes or CFHR1-3 deletion.

CONCLUSIONS

Our study provides evidence of the usefulness of the NGS panel as an excellent technology that enables more rapid diagnosis of TMA, and is a valuable asset in clinical practice to discriminate between TTP and aHUS.

Molecular diagnosis of von Willebrand disease

The role of molecular characterization in the diagnosis of von Willebrand disease (VWD) is not essential if the patients have been extensively investigated using phenotypic analysis. On the other hand, if some of these phenotype assays are not available, the identification of the mutation causing the disease could be crucial for an accurate diagnosis. Nevertheless, there are several reasons for performing molecular analysis in patients phenotypically well characterized, e.g. to identify the mutation causing VWD can be useful for patients and their family members when prenatal diagnosis is required (type 3 or severe type 2). In this manuscript, we report the techniques used for the molecular characterization of suspected VWD patients. We describe the use of online von Willebrand factor database and online single nucleotide variation databases, the former to verify whether a candidate mutation has been previously identified in other VWD patients and the latter to ascertain whether a putative mutation has been reported earlier in healthy individuals. We listed the available in silico analysis tools, to determine the predicted pathogenicity of a sequence variant and to establish its possible negative effect on the normal splicing process. We also report the strategy that can be used to identify VWD type 2 patients' mutations in subjects who have been fully characterized using the phenotype assays.