Characterisation of mutations and molecular studies of type 2 von Willebrand disease

Type 2M/2A von Willebrand disease: a shared phenotype between type 2M and 2A

ABSTRACT

Four variants have been continuously subjected to debate and received different von Willebrand disease (VWD) classifications: p.R1315L, p.R1315C, p.R1374H, and p.R1374C. We chose to comprehensively investigate these variants with full set of VWD tests, protein-modeling predictions and applying structural biology. Patients with p.R1315L, p.R1315C, p.R1374H, and p.R1374C were included. A group with type 2A and 2M was included to better understand similarities and differences. Patients were investigated for phenotypic assays and underlying disease mechanisms. We applied deep protein modeling predictions and structural biology to elucidate the causative effects of variants. Forty-three patients with these variants and 70 with 2A (n = 35) or 2M (n = 35) were studied. Patients with p.R1315L, p.R1374H, or p.R1374C showed a common phenotype between 2M and 2A using von Willebrand factor (VWF):GPIbR/VWF:Ag and VWF:CB/VWF:Ag ratios and VWF multimeric profile, whereas p.R1315C represented a type 2M phenotype. There was an overall reduced VWF synthesis or secretion in 2M and cases with p.R1315L, p.R1374H, and p.R1374C, but not in 2A. Reduced VWF survival was observed in most 2A (77%), 2M (80%), and all 40 cases with p.R1315L, p.R1374H, and p.R1374C. These were the only variants that fall at the interface between the A1-A2 domains. p.R1315L/C mutants induce more compactness and internal mobility, whereas p.R1374H/C display a more extended overall geometry. We propose a new classification of type 2M/2A for p.R1315L, p.R1374H, and p.R1374C because they share a common phenotype with 2M and 2A. Our structural analysis shows the unique location of these variants on the A1-A2 domains and their distinctive effect on VWF.

Frustration analysis of TBK1 missense mutations reported in ALS/FTD and cancer patients

Tank-binding kinase 1 (TBK1) is a multifunctional kinase having essential roles in cellular processes, autophagy/mitophagy, and selective clearance of damaged proteins. More than 90 mutations in the TBK1 gene are linked with multiple cancer types, amyotrophic lateral sclerosis (ALS), and frontotemporal dementia (FTD). Some of these missense mutations disrupt the abilities of TBK1 to dimerize, associate with the mitophagy receptor optineurin (OPTN), autoactivate, or catalyze phosphorylation. Some mutations may cause severe dysregulation of the pathway, while others induce a limited disruption. Here, we have studied those mutations reported in cancer, ALS and FTD, and subsequently investigated the effect of missense mutations on the structure and function of TBK1 for localized residual frustration change. Out of 33 ALS/FTD causing mutations and 28 oncogenic mutations, 10 mutations and 12 oncogenic mutations showed significant change in the residual frustration. The local frustration plays an important role in the conformation of protein structure in active and inactive kinases. Our analysis reports the change in residual frustration state, conformational change and effect on active and inactive TBK1 function due to ALS/FTD causing and oncogenic missense mutations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03240-0.

Type 2A and 2M von Willebrand Disease: Differences in Phenotypic Parameters According to the Affected Domain by Disease-Causing Variants and Assessment of Pathophysiological Mechanisms

Type 2A and 2M von Willebrand disease (VWD) broadly show similar phenotypic parameters, but involve different pathophysiological mechanisms. This report presents the clinical and laboratory profiles of type 2A and type 2M patients genotypically diagnosed at one large center. Higher bleeding score values and a higher incidence of major bleeding episodes were observed in type 2A compared with type 2M, potentially reflective of the absence of large and intermediate von Willebrand factor (VWF) multimers in 2A. In type 2A, most of disease-causing variants (DCVs) appeared to be responsible for increased VWF clearance and DCV clustered in the VWF-A1 domain resulted in more severe clinical profiles. In type 2M, DCV in the VWF-A1 domain showed different laboratory patterns, related to either reduced synthesis or shortened VWF survival, and DCV in the VWF-A2 domain showed patterns related mainly to shortened survival. VWF-type 1 collagen binding/Ag (C1B/Ag) showed different patterns according to DCV location: in type 2A VWD, C1B/Ag was much lower when DCVs were located in the VWF-A2 domain. In type 2M with DCV in the VWF-A1domain, C1B/Ag was normal, but with DCV in the VWF-A2 domain, C1B/Ag was low. The higher frequency of major bleeding in VWD 2M patients with DCV in the VWF-A2 domain than that with DCV in the VWF-A1 domain could be a summative effect of abnormal C1B/Ag, on top of the reduced VWF-GPIb binding. In silico modeling suggests that DCV impairing the VWF-A2 domain somehow modulates collagen binding to the VWF-A3 domain. Concomitant normal FVIII:C/Ag and VWFpp/Ag, mainly in type 2M VWD, suggest that other nonidentified pathophysiological mechanisms, neither related to synthesis/retention nor survival of VWF, would be responsible for the presenting phenotype.

Molecular coevolution of coagulation factor VIII and von Willebrand factor

Ancestral sequence reconstruction provides a unique platform for investigating the molecular evolution of single gene products and recently has shown success in engineering advanced biological therapeutics. To date, the coevolution of proteins within complexes and protein-protein interactions is mostly investigated in silico via proteomics and/or within single-celled systems. Herein, ancestral sequence reconstruction is used to investigate the molecular evolution of 2 proteins linked not only by stabilizing association in circulation but also by their independent roles within the primary and secondary hemostatic systems of mammals. Using sequence analysis and biochemical characterization of recombinant ancestral von Willebrand factor (VWF) and coagulation factor VIII (FVIII), we investigated the evolution of the essential macromolecular FVIII/VWF complex. Our data support the hypothesis that these coagulation proteins coevolved throughout mammalian diversification, maintaining strong binding affinities while modulating independent and distinct hemostatic activities in diverse lineages.

Diagnosis of von Willebrand disease in Western Mexico

INTRODUCTION

Von Willebrand disease (VWD) is the most common inherited bleeding disorder with a prevalence of 0.1%, characterised by quantitative or functional deficiency of von Willebrand factor (VWF). VWD diagnosis is based on symptomology, biochemical and genetic tests, but limited laboratory resources and VWD heterogeneity still generate an important subdiagnosis gap worldwide and in our country.

AIM

To identify the type and subtype of VWD in a cohort of patients with a history of excessive bleeding in Western Mexico.

METHODS

This prospective cohort study from 2012 to 2019 included patients with mucocutaneous bleeding or abnormal laboratory tests. A standardised questionnaire and confirmatory tests were applied: FVIII:C, VWF activity, VWF antigen, and VWF multimeric analysis.

RESULTS

Of the 297 patients recruited, 207 (69.7%) were excluded because their values exceeded 50% in VWF activity and VWF antigen. Of those 90 remaining, 54 (18.2%) had low VWF, and only 36 patients (12.1%) were diagnosed with VWD. Among them, 17 (47.2%) had quantitative deficiencies, of whom 14 were assigned as type 1 and 3 as type 3.The remaining 19 cases were diagnosed as type 2 (52.8%): type 2A and 2B were the most frequent with 6 and 7 cases respectively; 4 cases were possible type 2M and two suggestive of 2N, however, this was not confirmed.

CONCLUSION

This study highlights the challenges of VWD diagnosis using a comprehensive panel of diagnostic tests which should extend to supplemental tests of VWF:CB, VWF:FVIIIB, and sequencing the VWD gene to confirm the results from the panel assays.

Molecular and clinical profile of type 2 von Willebrand disease in Iran: a thirteen-year experience

Type 2 von Willebrand disease (VWD) is the most common congenital bleeding disorder, with variable bleeding tendency and a complex laboratory phenotype. In the current study, we report the clinical and molecular profile of a large number of Iranian patients with type 2 VWD. All exons, intron-exon boundaries, and untranslated regions were sequenced by Sanger sequencing for direct mutation detection. All identified mutations were confirmed in family members and by relevant bioinformatics studies. A total of 136 patients with type 2 VWD were diagnosed, including 42 (30.9%), 32 (23.6%), 38 (27.9%), and 24 (17.6%) patients with type 2A, type 2B, type 2M, and type 2N, respectively. Epistaxis (49%), gum bleeding (30.2%), ecchymosis (23.2%), and menorrhagia (16.3%) were the most common clinical presentations, while miscarriage (2.3%) and umbilical cord bleeding (0.8%) were the rarest. Thirty mutations were identified within the VWF gene, nine (30%) being novel, with p.Arg1379Cys (n = 20), p.Val1316Met (n = 13), p.Arg1597Trp (n = 13), p.Arg1374Cys (n = 10), p.Ser1506Leu (n = 10), and p.Arg1308Cys (n = 9) the most common. Type 2 VWD is a hemorrhagic disorder with variable bleeding tendency and a heterogeneous molecular basis in patients in Iran.

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.

Effects of Pro1266Leu mutation on structure and function of glycoprotein Ib binding domain of von Willebrand factor

Glycoprotein Ibα (GpIbα) binding ability of A1 domain of von Willebrand factor (vWF) facilitates platelet adhesion that plays a crucial role in maintaining hemostasis and thrombosis at the site of vascular damage. There are both "loss as well as gain of function" mutations observed in this domain. Naturally occurring "gain of function" mutations leave self-activating impacts on the A1 domain which turns the normal binding to characteristic constitutive binding with GPIbα. These "gain of function" mutations are associated with the von Willebrand disease type 2B. In recent years, studies focused on understanding the mechanism and conformational patterns attached to these phenomena have been conducted, but the conformational pathways leading to such binding patterns are poorly understood as of now. To obtain a microscopic picture of such events for the better understanding of pathways, we used molecular dynamics (MD) simulations along with principal component analysis and normal mode analysis to study the effects of Pro1266Leu (Pro503Leu in structural context) mutation on the structure and function of A1 domain of vWF. MD simulations have provided atomic-level details of intermolecular motions as a function of time to understand the dynamic behavior of A1 domain of vWF. Comparative analysis of the trajectories obtained from MD simulations of both the wild type and Pro503Leu mutant suggesting appreciable conformational changes in the structure of mutant which might provide a basis for assuming the "gain of function" effects of these mutations on the A1 domain of vWF, resulting in the constitutive binding with GpIbα.

Genetic variants of VWF gene in type 2 von Willebrand disease

INTRODUCTION

von Willebrand disease (VWD) is the most common inherited bleeding disorder. Few studies have explored the molecular basis of type 2 VWD.

AIM

This study aimed to identify variants associated with type 2 VWD.

METHODS

We collected clinical and laboratory data, as well as response to desmopressin and bleeding assessment tool (BAT) score in patients diagnosed with type 2 VWD. We sequenced exons 17, 18, 20 and 28 of the VWF gene.

RESULTS

We identified 19 different variants in 40 unrelated patients (47.5%). Most of the variants (84.2%) were found in exon 28. A total of 10/19 variants (52.6%) were identified as "likely causative" in 17/40 patients (42.5%), according to the ISTH-SSC and EAHAD VWF gene mutations databases. Nine variants were initially identified as potentially benign. However, through analyses in silico, four of these variants were reclassified as "likely pathogenic" (Ile1380Val, Asn1435Ser, Ser1486Leu and Tyr1584Cys). Response to desmopressin was associated with three variants: Met740Ile, Arg1597Gln and Tyr1584Cys. Major bleeding was associated with variants related to VWD subtypes 2B and 2M.

CONCLUSION

In conclusion, we identified 19 variants, of which 14 are "likely pathogenic" and therefore associated with VWD. We suggest a possible association of pathogenic variants with major bleeding, response to desmopressin and BAT score ≥10, although this requires further confirmation.

Functional Prediction of Hypothetical Proteins from Shigella flexneri and Validation of the Predicted Models by Using ROC Curve Analysis

Shigella spp. constitutes some of the key pathogens responsible for the global burden of diarrhoeal disease. With over 164 million reported cases per annum, shigellosis accounts for 1.1 million deaths each year. Majority of these cases occur among the children of the developing nations and the emergence of multi-drug resistance Shigella strains in clinical isolates demands the development of better/new drugs against this pathogen. The genome of Shigella flexneri was extensively analyzed and found 4,362 proteins among which the functions of 674 proteins, termed as hypothetical proteins (HPs) had not been previously elucidated. Amino acid sequences of all these 674 HPs were studied and the functions of a total of 39 HPs have been assigned with high level of confidence. Here we have utilized a combination of the latest versions of databases to assign the precise function of HPs for which no experimental information is available. These HPs were found to belong to various classes of proteins such as enzymes, binding proteins, signal transducers, lipoprotein, transporters, virulence and other proteins. Evaluation of the performance of the various computational tools conducted using receiver operating characteristic curve analysis and a resoundingly high average accuracy of 93.6% were obtained. Our comprehensive analysis will help to gain greater understanding for the development of many novel potential therapeutic interventions to defeat Shigella infection.

Genetic Variation in the von Willebrand Factor Gene in Swedish von Willebrand Disease Patients

von Willebrand factor (VWF) level and function are influenced by genetic variation in VWF and several other genes in von Willebrand disease type 1 (VWD1) patients. This study comprehensively screened for VWF variants and investigated the presence of ABO genotypes and common and rare VWF variants in Swedish VWD1 patients. The VWF gene was resequenced using Ion Torrent and Sanger sequencing in 126 index cases historically diagnosed with VWD. Exon 7 of the ABO gene was resequenced using Sanger sequencing. Multiplex ligation-dependent probe amplification analysis was used to investigate for copy number variants. Genotyping of 98 single nucleotide variants allowed allele frequency comparisons with public databases. Seven VWD2 mutations and 36 candidate VWD1 mutations (5 deletions, 4 nonsense, 21 missense, 1 splice, and 5 synonymous mutations) were identified. Nine mutations were found in more than one family and nine VWD1 index cases carried more than one candidate mutation. The T-allele of rs1063857 (c.2385T > C, p.Y795 = ) and blood group O were both frequent findings and contributed to disease in the Swedish VWD1 population. VWD2 mutations were found in 20 and candidate VWD1 mutations in 51 index cases out of 106 (48%). VWF mutations, a VWF haplotype, and blood group O all contributed to explain disease in Swedish VWD1 patients.

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.

A Laboratory Phenotype/Genotype Correlation of 1167 French Patients From 670 Families With von Willebrand Disease: A New Epidemiologic Picture

von Willebrand disease (VWD) is a genetic bleeding disease due to a defect of von Willebrand factor (VWF), a glycoprotein crucial for platelet adhesion to the subendothelium after vascular injury. VWD include quantitative defects of VWF, either partial (type 1 with VWF levels <50 IU/dL) or virtually total (type 3 with undetectable VWF levels) and also qualitative defects of VWF (type 2 variants with discrepant antigenic and functional VWF levels). The most bleeding forms of VWD usually do not concern type 1 patients with the mildest VWF defects (VWF levels between 30 and 50 IU/dL). The French reference center for VWD performed a laboratory phenotypic and genotypic analysis in 1167 VWD patients (670 families) selected by their basic biologic phenotype: type 3, type 2, and type 1 with VWF levels <30 IU/dL. In these patients indeed, to achieve an accurate diagnosis of VWD type and subtype is crucial for the management (treatment and genetic counseling). A phenotype/genotype correlation was present in 99.3% of cases; 323 distinct VWF sequence variations (58% of novel) were identified (missense 67% versus truncating 33%). The distribution of VWD types was: 25% of type 1, 8% of type 3, 66% of type 2 (2A: 18%, 2B: 17%, 2M: 19%, 2N: 12%), and 1% of undetermined type. Type 1 VWD was related either to a defective synthesis/secretion or to an accelerated clearance of VWF. In type 3 VWD, bi-allelic mutations of VWF were found in almost all patients. In type 2A, the most frequent mechanism was a hyper-proteolysis of VWF. Type 2B showed 85% of patients with deleterious mutations (distinct from type 2B New York). Type 2M was linked to a defective binding of VWF to platelet glycoprotein Ib or to collagen. Type 2N VWD included almost half type 2N/3. This biologic study emphasizes the complex mechanisms for both quantitative and qualitative VWF defects in VWD. In addition, this study provides a new epidemiologic picture of the most bleeding forms of VWD in which qualitative defects are predominant.

Large scale analysis of the mutational landscape in β-glucuronidase: A major player of mucopolysaccharidosis type VII

The lysosomal storage disorders are a group of 50 unique inherited diseases characterized by unseemly lipid storage in lysosomes. These malfunctions arise due to genetic mutations that result in deficiency or reduced activities of the lysosomal enzymes, which are responsible for catabolism of biological macromolecules. Sly syndrome or mucopolysaccharidosis type VII is a lysosomal storage disorder associated with the deficiency of β-glucuronidase (EC 3.2.1.31) that catalyzes the hydrolysis of β-D-glucuronic acid residues from the non-reducing terminal of glycosaminoglycan. The effects of the disease causing mutations on the framework of the sequences and structure of β-glucuronidase (GUSBp) were analyzed utilizing a variety of bioinformatic tools. These analyses showed that 211 mutations may result in alteration of the biological activity of GUSBp, including previously experimentally validated mutations. Finally, we refined 90 disease causing mutations, which presumably cause a significant impact on the structure, function, and stability of GUSBp. Stability analyses showed that mutations p.Phe208Pro, p.Phe539Gly, p.Leu622Gly, p.Ile499Gly and p.Ile586Gly caused the highest impact on GUSBp stability and function because of destabilization of the protein structure. Furthermore, structures of wild type and mutant GUSBp were subjected to molecular dynamics simulation to examine the relative structural behaviors in the explicit conditions of water. In a broader view, the use of in silico approaches provided a useful understanding of the effect of single point mutations on the structure-function relationship of GUSBp.

Identification of functional candidates amongst hypothetical proteins of Treponema pallidum ssp. pallidum

Syphilis is a globally occurring venereal disease, and its infection is propagated through sexual contact. The causative agent of syphilis, Treponema pallidum ssp. pallidum, a Gram-negative sphirochaete, is an obligate human parasite. Genome of T. pallidum ssp. pallidum SS14 strain (RefSeq NC_010741.1) encodes 1,027 proteins, of which 444 proteins are known as hypothetical proteins (HPs), i.e., proteins of unknown functions. Here, we performed functional annotation of HPs of T. pallidum ssp. pallidum using various database, domain architecture predictors, protein function annotators and clustering tools. We have analyzed the sequences of 444 HPs of T. pallidum ssp. pallidum and subsequently predicted the function of 207 HPs with a high level of confidence. However, functions of 237 HPs are predicted with less accuracy. We found various enzymes, transporters, binding proteins in the annotated group of HPs that may be possible molecular targets, facilitating for the survival of pathogen. Our comprehensive analysis helps to understand the mechanism of pathogenesis to provide many novel potential therapeutic interventions.

A variational Bayes discrete mixture test for rare variant association

Recently, many statistical methods have been proposed to test for associations between rare genetic variants and complex traits. Most of these methods test for association by aggregating genetic variations within a predefined region, such as a gene. Although there is evidence that "aggregate" tests are more powerful than the single marker test, these tests generally ignore neutral variants and therefore are unable to identify specific variants driving the association with phenotype. We propose a novel aggregate rare-variant test that explicitly models a fraction of variants as neutral, tests associations at the gene-level, and infers the rare-variants driving the association. Simulations show that in the practical scenario where there are many variants within a given region of the genome with only a fraction causal our approach has greater power compared to other popular tests such as the Sequence Kernel Association Test (SKAT), the Weighted Sum Statistic (WSS), and the collapsing method of Morris and Zeggini (MZ). Our algorithm leverages a fast variational Bayes approximate inference methodology to scale to exome-wide analyses, a significant computational advantage over exact inference model selection methodologies. To demonstrate the efficacy of our methodology we test for associations between von Willebrand Factor (VWF) levels and VWF missense rare-variants imputed from the National Heart, Lung, and Blood Institute's Exome Sequencing project into 2,487 African Americans within the VWF gene. Our method suggests that a relatively small fraction (~10%) of the imputed rare missense variants within VWF are strongly associated with lower VWF levels in African Americans.

Germline de novo mutations and linkage markers vs. DNA sequencing for carrier detection in von Willebrand disease

Linkage analysis in autosomal inherited von Willebrand disease (VWD) is important to diagnose the carriers and reduce the burden of severe type VWD. The study was designed to identify the carriers and estimate the frequency of variable number of tandem repeats (VNTR) instability in VWD families. Carrier detection was performed in eight recessive type 3 VWD (VWD3) families using VNTRs VWF1 and VWF2, RsaI (789Thr/Ala) linkage markers, multimer analysis and DNA sequencing. Moreover, five dominant VWD families were studied through DNA sequencing and multimer analysis. Frequency of VWF VNTR instability was investigated in 20 VWD families. In VWD3 families, a total of 22 (81.5%) carriers were identified using VWF1 and VWF2 markers. However, only 13(48.1%) carriers were identified through RsaI markers. Mutation screening revealed 22(81.5%) carriers in VWD3 and 4 (33.3%) carriers in VWD2 families. In comparison to DNA sequencing, the accuracy of VWF1 and VWF2 markers in VWD3 was 85.7% while RsaI could identify 68.2% carriers accurately. Mutations p.R1205H and p.C1272R were identified as de novo in families. Multimer analysis confirmed the identified carriers in VWD2 families. Three VWD families were found to be carrying VNTR instability for VWF1 and VWF2 locus. VNTRs could be an effective linkage markers for carrier detection in VWD3 families. However, in the event of germline de novo mutations and VNTR instability, it may confound risk of misdiagnosis of carriers. Multimer analysis could be an alternative way of carrier detection in dominant type 2A and type 2B VWD families.

Genetic heterogeneity in a large cohort of Indian type 3 von Willebrand disease patients

Background

Though von Willebrand disease (VWD) is a common coagulation disorder, due to the complexity of the molecular analysis of von Willebrand factor gene (VWF), not many reports are available from this country. Large size of the gene, heterogeneous nature of mutations and presence of a highly homologous pseudogene region are the major impediments in the genetic diagnosis of VWD. The study is aimed at unravelling the molecular pathology in a large series of VWD patients from India using an effective strategy.

Method

We evaluated 85 unrelated Indian type 3 VWD families to identify the molecular defects using a combination of techniques i.e. PCR-RFLP, direct DNA sequencing and multiple ligation probe amplification (MLPA).

Results

Mutations could be characterized in 77 unrelated index cases (ICs). 59 different mutations i.e. nonsense 20 (33.9%), missense 13 (22%), splice site 4 (6.8%), gene conversions 6 (10.2%), insertions 2 (3.4%), duplication 1 (1.7%), small deletions 10 (17%) and large deletions 3 (5.1%) were identified, of which 34 were novel. Two common mutations i.e. p.R1779* and p.L970del were identified in our population with founder effect. Development of alloantibodies to VWF was seen in two patients, one with nonsense mutation (p.R2434*) and the other had a large deletion spanning exons 16–52.

Conclusion

The molecular pathology of a large cohort of Indian VWD patients could be identified using a combination of techniques. A wide heterogeneity was observed in the nature of mutations in Indian VWD patients.

Phenotypic and molecular characterisation of type 3 von Willebrand disease in a cohort of Indian patients

Severe type 3 VWD (VWD3) is characterised by complete absence or presence of trace amounts of non-functional von Willebrand factor (VWF). The study was designed to evaluate the VWF mutations in VWD3 patients and characterise the breakpoints of two identified homozygous novel large deletions. Patients were diagnosed by conventional tests and VWF multimer analysis. Mutation screening was performed in 19 VWD3 patients by direct sequencing of VWF including flanking intronic sequence and multiplex ligation-dependent probe amplification (MLPA) analysis. Breakpoint characterisation of two identified novel large deletions was done using walking primers and long spanning PCR. A total of 21 different mutations including 15 (71.4%) novel ones were identified in 17 (89.5%) patients. Of these mutations, five (23.8%) were nonsense (p.R1659*, p.R1779*, p.R1853*, p.Q2470*, p.Q2520*), one was a putative splice site (p.M814I) and seven (33.3%) were deletions (p.L254fs*48, p.C849fs*60, p.L1871fs*6, p.E2720fs*24) including three novel large deletions of exon 14-15, 80,830bp (-41510_657+7928A*del) and 2,231bp [1534-2072T_c.1692G*del(p.512fs*terminus)] respectively. A patient carried gene conversion comprising of pseudogene harbouring mutations. The missense mutations (p.G19R, p.K355R, p.D437Y, p.C633R, p.M771V, p.G2044D, p.C2491R) appear to play a major role and were identified in seven (36.8%) patients. In conclusion, a high frequency of novel mutations suggests the high propensity of VWF for new mutations. Missense and deletion mutations found to be a common cause of VWD3 in cohort of Indian VWD3 patients. Breakpoints characterisation of two large deletions reveals the double strand break and non-homologous recombination as deletions mechanism.