Detection of 95 novel mutations in coagulation factor VIII gene F8 responsible for hemophilia A: results from a single institution

Spectrum of Causative Mutations in Patients with Hemophilia A in Russia

Hemophilia A (HA) is one of the most widespread, X-linked, inherited bleeding disorders, which results from defects in the F8 gene. Nowadays, more than 3500 different pathogenic variants leading to HA have been described. Mutation analysis in HA is essential for accurate genetic counseling of patients and their relatives. We analyzed patients from 273 unrelated families with different forms of HA. The analysis consisted of testing for intron inversion (inv22 and inv1), and then sequencing all functionally important F8 gene fragments. We identified 101 different pathogenic variants in 267 patients, among which 35 variants had never been previously reported in international databases. We found inv22 in 136 cases and inv1 in 12 patients. Large deletions (1-8 exons) were found in 5 patients, and we identified a large insertion in 1 patient. The remaining 113 patients carried point variants involving either single nucleotide or several consecutive nucleotides. We report herein the largest genetic analysis of HA patients issued in Russia.

Spectrum of F8 Genotype and Genetic Impact on Inhibitor Development in Patients with Hemophilia A from Multicenter Cohort Studies (J-HIS) in Japan

Some genetic and treatment-related factors are risk factors for inhibitor development in patients with hemophilia A (PwHA). However, the genotype distribution of the factor VIII gene (F8) and genetic impact on inhibitor development in Japanese PwHA remain unknown. In 2007, the Japan Hemophilia Inhibitor Study 2 (J-HIS2) was organized to establish a nationwide registry system for hemophiliacs and to elucidate risk factors for inhibitor development, designed for prospective investigation following a retrospective study (J-HIS1) which had already finished. Patients, newly diagnosed after January 2007, were enrolled in J-HIS2 and followed up for inhibitor development and clinical environments since 2008 onward. In the present study, F8 genotypes of PwHA were investigated in the patients recruited from the J-HIS2 cohort as well as those with inhibitor from the J-HIS1 cohort. F8 variants identified in 59 PwHA with inhibitor in J-HIS1 were: 20 intron-22 inversions, 5 intron-1 inversions, 9 large deletions, 4 nonsense, 8 missense, 11 small in/del, and 2 splice-site variants. F8 variants identified in 267 (67 with inhibitor) PwHA in J-HIS2 were: 76(28) intron-22 inversions, 3(2) intron-1 inversion, 1(0) duplication, 8(5) large deletions, 21(7) nonsense, 109(7) missense, 40(11) small in/del, and 9(7) splice-site variants. Forty variants were novel. The cumulative inhibitor incidence rate in the severe group with null changes was 42.4% (95% confidence interval [CI]: 33.7-50.8), higher than that with nonnull changes (15.6% [95%CI: 6.8-27.8]), in J-HIS2. Relative risk for inhibitor development of null changes was 2.89. The spectrum of F8 genotype and genetic impact on inhibitor development in Japanese PwHA were consistent with the previous reports.

Impact of variation in reagent combinations for one-stage clotting assay on assay discrepancy in nonsevere haemophilia A

INTRODUCTION

Factor VIII activity (FVIII:C) is measured by one-stage clotting assay (OSA) or chromogenic substrate assay (CSA). Significant differences in FVIII:C between OSA (FVIII:C_1st ) and CSA (FVIII:C_Chr ) are described as assay discrepancy in nonsevere haemophilia A (HA). A large number of reagent combinations (APTT reagent and FVIII-deficient plasma) are used for OSA, but the impact of variations in reagent combinations on assay discrepancy has not been fully characterized.

AIM

To clarify the variations in FVIII:C_1st /FVIII:C_Chr ratios according to OSA reagent combination in HA subjects with/without assay discrepancy.

METHODS

Thirty-nine patients previously diagnosed with nonsevere HA were enrolled, and their FVIII genes were investigated and FVIII:C levels were assessed by a single CSA reagent and 11 OSA reagent combinations. Receiver operating characteristic (ROC) curve analysis was used to predict possible cut-off values of the FVIII:C_1st /FVIII:C_Chr ratio to define FVIII assay discrepancy for each reagent combination.

RESULTS

Patients were categorized into nondiscrepant (n = 25), discrepant (n = 5) and unclassified (n = 9) groups according to their genotypes and information in the database. The FVIII:C_1st /FVIII:C_Chr ratio in nondiscrepant HA varied widely, depending on the APTT reagents and FVIII-deficient plasma used. The ratio in discrepant HA patients differed with respect to their genotype and the reagent combination used. ROC curve analyses revealed that cut-off values to distinguish the assay discrepancy differed depending on the reagents used, but revealed two novel genotype variants, p.Cys573Gly and p.Gly582Arg, associated with FVIII assay discrepancy.

CONCLUSION

Our findings showed that the FVIII:C_1st /FVIII:C_Chr ratio is dependent on the reagent combination used for OSA.

Identification of the Intron 22 and Intron 1 Inversions of the Factor VIII Gene in Iraqi Kurdish Patients With Hemophilia A

Hemophilia A (HA) is a severe coagulation disorder affecting 1 in 5000 to 10 000 male births. In severe cases, the most deleterious large DNA rearrangements are inversions of intron 22 (Inv22) and intron 1 (Inv1) of the factor VIII (FVIII) gene. These account for 40% to 50% and 1% to 5% of all causative mutations, respectively. Nevertheless, no genetic analysis to identify the actual causative mutation of FVIII, particularly Inv22 and Inv1, among Iraqi Kurdish hemophiliacs has been performed. In this study, we aimed to genotype Inv22 and Inv1 of the FVIII gene in our patients with HA and reveal the genotype/phenotype correlation with the inversion mutations and their role as a risk factor for the development of inhibitors. Analyses of the Inv22 and Inv1 mutations in 80 Iraqi Kurdish patients with HA (60 severe, 18 moderate, and 2 mild) were performed using the inverse shifting–polymerase chain reaction (IS-PCR) method. In severe cases, 46.7% (28/60) had Inv22 and 3.3% (2/60) had Inv1. The genotype/phenotype relation of Inv22 and Inv1 illustrated a statistically significant association (P = .012) between disease severity and inversion mutations. Slightly more patients with Inv22 (39%) developed inhibitors than those without Inv22 (28%; odds ratio = 1.65, 95% confidence interval = 0.56-4.87, P = .361). Inv22 is a major cause of severe HA in Iraqi Kurdish patients, and IS-PCR is a rapid, robust, and effective method that can be applied for carrier detection and prenatal diagnosis of HA in developing countries.

Molecular Mechanisms and Determinants of Innovative Correction Approaches in Coagulation Factor Deficiencies

Molecular strategies tailored to promote/correct the expression and/or processing of defective coagulation factors would represent innovative therapeutic approaches beyond standard substitutive therapy. Here, we focus on the molecular mechanisms and determinants underlying innovative approaches acting at DNA, mRNA and protein levels in inherited coagulation factor deficiencies, and in particular on: (i) gene editing approaches, which have permitted intervention at the DNA level through the specific recognition, cleavage, repair/correction or activation of target sequences, even in mutated gene contexts; (ii) the rescue of altered pre-mRNA processing through the engineering of key spliceosome components able to promote correct exon recognition and, in turn, the synthesis and secretion of functional factors, as well as the effects on the splicing of missense changes affecting exonic splicing elements; this section includes antisense oligonucleotide- or siRNA-mediated approaches to down-regulate target genes; (iii) the rescue of protein synthesis/function through the induction of ribosome readthrough targeting nonsense variants or the correction of folding defects caused by amino acid substitutions. Overall, these approaches have shown the ability to rescue the expression and/or function of potentially therapeutic levels of coagulation factors in different disease models, thus supporting further studies in the future aimed at evaluating the clinical translatability of these new strategies.

Case Report: Development of Factor VIII Inhibitor in a Patient with an Uncommon de novo Mutation in the Factor VIII Gene

The development of factor VIII inhibitors remains a significant clinical challenge in the management of hemophilia A. We present a patient of mixed ethnicity with severe hemophilia A who was found to have a F8 gene hemizygous c.5815G>T mutation resulting in an Ala1939Ser substitution (Ala1920Ser in legacy nomenclature) and possible splice site change that has been reported in only 1 patient previously. He developed an inhibitor shortly after starting replacement recombinant factor VIII (Advate®; Baxalta, Bannockburn, IL, USA) and was successfully treated with immune tolerance therapy. Our report describes the second patient reported to have severe hemophilia due to this mutation and the only case of a factor VIII inhibitor associated with this mutation.

Effect of F8 B domain gene variants on synthesis, secretion, activity and stability of factor VIII protein

The B domain of the coagulation factor (F)VIII comprises some unique characteristics. Though the B domain is important for processing, intracellular transport and secretion of FVIII protein, its role in the coagulation still remains unclear. This study aims to investigate the influence of 19 reported B domain variants on quantity and quality of expressed FVIII protein. F8 variants were transiently expressed in HEK293T cells. Media and cell lysates were collected after 72 hours. FVIII synthesis, relative secretion, activity and thermostability were analysed in comparison to FVIII wild-type. Eleven of 19 analysed B domain variants showed normal FVIII activity (FVIII:C), and antigen values (40–150 %). Eight variants exhibited a decreased FVIII:C, corresponding to a mild phenotype most likely due to impaired expression and secretion mechanism, reduced thermostability or combined mechanisms. One variant, p.His1066Tyr, showed markedly reduced FVIII antigen in cell lysate. The variants p.Asp845Glu, p.His998Gln, and p.Ala1610Ser revealed a significantly decreased relative secretion. Additionally, six B domain variants significantly reduced stability of FVIII. In conclusion, none of the analysed missense mutations was causative for a severe haemophilia A (HA) phenotype. Nevertheless, the mutations p.Asp845Glu, p.Pro947Arg, p.Glu1057Lys, p.His1066Tyr, p.Arg1126Trp, p.Arg1329His, p.Leu1481Pro, and p.Ala1610Ser resulted in decreased FVIII:C values that may explain mild HA phenotypes.

Preimplantation genetic diagnosis of hemophilia A

Preimplantation genetic diagnosis (PGD) is a powerful tool to tackle the transmission of monogenic inherited disorders in families carrying the diseases from generation to generation. It currently remains a challenging task, despite PGD having been developed over 25 years ago. The major difficulty is it does not have an easy and general formula for all mutations. Different gene locus needs individualized, customized design to make the diagnosis accurate enough to be applied on PGD, in which the quantity of DNA is scanty, whereas timely laboratory diagnosis is mandatory if fresh embryo transfer is desired occasionally. Indicators for outcome assessment of a successful PGD program include the successful diagnosis rate on blastomeres (Day 3 cleavage-stage embryo biopsy) or trophectoderm cells (Day 5/6 blastocyst biopsy), the implantation rate per embryo transferred, and the livebirth rate per oocyte retrieval cycle. Hemophilia A (HA) is an X-linked recessive bleeding disorder caused by various types of pathological defects in the factor VIII gene (F8). The mutation spectrum of the F8 is complex, according to our previous report, including large segmental intra-gene inversions, large segmental deletions spanning a few exons, point mutations, and total deletion caused by chromosomal structural rearrangements. In this review, the molecular methodologies used to tackle different mutants of the F8 in the PGD of HA are to be explained, and the experiences of successful use of amplification refractory mutation system-quantitative polymerase chain reaction (ARMS-qPCR) and linkage analysis for PGD of HA in our laboratory are also provided.

Co-inheritance of mild hemophilia A and heterozygosity for type 2N von Willebrand disease: a diagnostic and therapeutic challenge

Hemophilia A and von Willebrand disease are the two most common inherited bleeding disorders. Despite their frequency, however, there are very few reports of co-inheritance of the two disorders. We present the first report of a patient with mild hemophilia A and heterozygosity for type 2N von Willebrand disease (VWD). We discuss the patient's phenotype and highlight the diagnostic and therapeutic challenges caused by this co-inheritance.

Two novel missense mutations associated with hemophilia A in a family of Boxers, and a German Shepherd dog

BACKGROUND

Hemophilia A is an X-linked disorder caused by a deficiency in coagulation factor VIII. Over 2300 unique mutations in the gene-encoding factor VIII have been documented in people, but limited information is known in dogs. An 11-week-old male Boxer and a 5-year-old male German Shepherd were diagnosed with hemophilia A based on diminished factor VIII activity.

OBJECTIVE

The purpose of the study was to identify genetic mutations associated with hemophilia A in both dogs.

METHODS

Genomic DNA was isolated from EDTA blood samples from the affected German Shepherd and Boxer, the Boxer's dam, 3 female siblings, and one asymptomatic male sibling. Primers were designed in noncoding regions to amplify the 26 exons of the factor VIII gene via PCR.

RESULTS

The affected Boxer sequence revealed a single nucleotide change, cytosine to guanine, at nucleotide position 1412 (1412C>G) in exon 10. The change is predicted to result in the substitution of arginine for proline at amino acid 471 (P471R) in the A2 domain of factor VIII. The dam and female siblings were carriers, the male sibling did not have the mutation. The German Shepherd dog had a single nucleotide change of a guanine to adenine at position 1643 (1643G>A) in exon 11, predicting the substitution of tyrosine for cysteine at amino acid 548 (C548Y) in the A2 domain.

CONCLUSIONS

Here we document 2 mutations associated with canine hemophilia A associated with < 1% factor VIII activity, similar to that in people. Another related Boxer with the P471R mutation was later identified.

A gene-specific method for predicting hemophilia-causing point mutations

A fundamental goal of medical genetics is the accurate prediction of genotype-phenotype correlations. As an approach to develop more accurate in silico tools for prediction of disease-causing mutations of structural proteins, we present a gene- and disease-specific prediction tool based on a large systematic analysis of missense mutations from hemophilia A (HA) patients. Our HA-specific prediction tool, HApredictor, showed disease prediction accuracy comparable to other publicly available prediction software. In contrast to those methods, its performance is not limited to non-synonymous mutations. Given the role of synonymous mutations in disease and drug codon optimization, we propose that utilizing a gene- and disease-specific method can be highly useful to make functional predictions possible even for synonymous mutations. Incorporating computational metrics at both nucleotide and amino acid levels along with multiple protein sequence/structure alignment significantly improved the predictive performance of our tool. HApredictor is freely available for download at http://www.ncbi.nlm.nih.gov/CBBresearch/Przytycka/HA_Predict/index.htm.

Chemical chaperones improve protein secretion and rescue mutant factor VIII in mice with hemophilia A

Inefficient intracellular protein trafficking is a critical issue in the pathogenesis of a variety of diseases and in recombinant protein production. Here we investigated the trafficking of factor VIII (FVIII), which is affected in the coagulation disorder hemophilia A. We hypothesized that chemical chaperones may be useful to enhance folding and processing of FVIII in recombinant protein production, and as a therapeutic approach in patients with impaired FVIII secretion. A tagged B-domain-deleted version of human FVIII was expressed in cultured Chinese Hamster Ovary cells to mimic the industrial production of this important protein. Of several chemical chaperones tested, the addition of betaine resulted in increased secretion of FVIII, by increasing solubility of intracellular FVIII aggregates and improving transport from endoplasmic reticulum to Golgi. Similar results were obtained in experiments monitoring recombinant full-length FVIII. Oral betaine administration also increased FVIII and factor IX (FIX) plasma levels in FVIII or FIX knockout mice following gene transfer. Moreover, in vitro and in vivo applications of betaine were also able to rescue a trafficking-defective FVIII mutant (FVIIIQ305P). We conclude that chemical chaperones such as betaine might represent a useful treatment concept for hemophilia and other diseases caused by deficient intracellular protein trafficking.

Molecular diagnosis of haemophilia A at Centro Hospitalar de Coimbra in Portugal: study of 103 families--15 new mutations

Haemophilia A (HA), the most commonly inherited bleeding disorder, has well known phenotype heterogeneity, influenced by the type of mutation, modulating factors and development of inhibitors. Nowadays, new technologies in association with bioinformatics tools allow a better genotype/phenotype correlation. With the main objective of identifying familial carrier women and to offer prenatal diagnosis, 141 HA patients belonging to 103 families, followed or referred to the Haemophilia Centre of CHC, E.P.E., were studied. Molecular diagnosis strategy was based on HA severity: IVS22 and IVS1 inversions, direct sequencing and MLPA technique. New missense and splicing mutations were further analyzed using molecular modelling. Genotype/phenotype correlation was assessed taking into account the known modulating factors. During this study, mutations were detected in 102/103 families, carrier status was determined in 83 women and 14 prenatal diagnoses were performed. In a total of 46 different mutations identified, 15 have not been reported previously by the HAMSTeRS and HGMD. Genotype/phenotype correlation revealed two cases with a clinical picture less severe than expected by the type of mutation identified. Six patients developed inhibitors: five severe (IVS22, IVS1, large deletion) and one mild (p. Gln2265Lys). The adopted strategy allowed the identification of 99% of the molecular alterations underlying the HA phenotype (98% detection rate for severe and 100% for moderate and mild). Evaluation of genotype-phenotype correlation was complemented with structural protein modelling of newly identified missense mutations, contributing to better understanding of the disease-causing mechanisms and to deepening knowledge on protein structure-function.

Characterization of duplication breakpoints in the factor VIII gene

BACKGROUND

Hemophilia A is caused by a wide spectrum of different mutations in the factor (F)VIII gene (F8), leading to deficiencies in coagulation FVIII activity and thus resulting in an inefficient blood clotting cascade. Large duplications comprising whole exons of F8 have been published for only a few cases so far.

RESULTS

In the current study, we characterized the exact breakpoints for a total of 10 exon-spanning duplications of F8, including six novel duplications in seven unrelated patients. Seven breakpoints were located within long interspersed nuclear elements (LINEs), whereas short interspersed nuclear elements (SINEs) of the Alu-repeat type were observed at both breakpoint sites in four of the 10 duplications. At three breakpoints, microhomologies of 2 bp and 3 bp each could be identified.

CONCLUSIONS

Duplication breakpoints in F8 were shown to be located in repetitive elements, especially SINEs or LINEs, but also in unique sequences. In addition, microhomologies, particular genomic features or sequence motifs, contribute to the duplication formation mechanisms.

Introns 1 and 22 inversions and factor VIII inhibitors in patients with severe haemophilia A in southern Brazil

A total of 107 unrelated severe haemophilia A patients living in the southern Brazilian state of Rio Grande do Sul were studied in relation to the prevalence of inversions present in introns 22 and 1 and a subsample of them (95) tested for the presence of Factor VIII inhibitors. These data were then incorporated with those from 15 other countries and 3871 patients. The frequencies of these two inversions show a remarkable homogeneity in series collected in different continents, from people with diverse ethnic extraction. The prevalence of inhibitors among patients with inversion 22, on the other hand, varies widely (5-51%; seven countries, 1482 patients), the value observed by us being the highest. The importance of obtaining data from patients throughout the world to clarify the aetiology of this important complicating factor in the therapeutics of the disease is emphasized.

Identification of 31 novel mutations in the F8 gene in Spanish hemophilia A patients: structural analysis of 20 missense mutations suggests new intermolecular binding sites

Hemophilia A (HA) is an X-linked bleeding disorder caused by a wide variety of mutations in the factor 8 (F8) gene, leading to absent or deficient factor VIII (FVIII). We analyzed the F8 gene of 267 unrelated Spanish patients with HA. After excluding patients with the common intron-1 and intron-22 inversions and large deletions, we detected 137 individuals with small mutations, 31 of which had not been reported previously. Eleven of these were nonsense, frameshift, and splicing mutations, whereas 20 were missense changes. We assessed the impact of the 20 substitutions based on currently available information about FV and FVIII structure and function relationship, including previously reported results of replacements at these and topologically equivalent positions. Although most changes are likely to cause gross structural perturbations and concomitant cofactor instability, p.Ala375Ser is predicted to affect cofactor activation. Finally, 3 further mutations (p.Pro64Arg, p.Gly494Val, and p.Asp2267Gly) appear to affect cofactor interactions with its carrier protein, von Willebrand factor, with the scavenger receptor low-density lipoprotein receptor-related protein (LRP), and/or with the substrate of the FVIIIapi*FIXa (Xase) complex, factor X. Characterization of these novel mutations is important for adequate genetic counseling in HA families, but also contributes to a better understanding of FVIII structure-function relationship.

Factor VIII (FVIII) gene mutations in 120 patients with hemophilia A: detection of 26 novel mutations and correlation with FVIII inhibitor development

BACKGROUND

As the publication of the sequence of the factor VIII gene (FVIII) in 1984, a large number of mutations that cause hemophilia A (HA) have been identified. Thanks to the advances in the detection of mutations, it is now possible to identify a putative FVIII sequence alteration in the vast majority of patients with HA.

OBJECTIVES

Our main objective was to report on the spectrum of FVIII mutations and their distribution throughout the gene in 120 patients with HA.

METHODS

Screening of FVIII mutations was performed using direct sequencing. Newly described missense mutations were further studied by molecular modeling.

RESULTS

A total of 47 different HA causative FVIII mutations have been identified, 26 of which are described for the first time. These novel mutations include 14 missense and six nonsense mutations, two small deletions, one large deletion and three splice-site mutations. We further investigated the development of FVIII-specific inhibitors in all patients with HA. We found that four novel mutations (Ser882X, Tyr1786Ser, Ala2218Thr and a splice-site defect in intron 22) were associated with inhibitor development.

CONCLUSION

These data extend our insight into the mechanisms by which novel amino acid substitutions may lead to HA, and how HA patient genotypes influence the risk of FVIII inhibitor development.