Recurrent inversion breaking intron 1 of the factor VIII gene is a frequent cause of severe hemophilia A

A scan of pleiotropic immune mediated disease genes identifies novel determinants of baseline FVIII inhibitor status in hemophilia A

Hemophilia-A (HA) is the X-linked bleeding disorder caused by heterogeneous factor (F)VIII gene (F8)-mutations and deficiencies in plasma-FVIII-activity that prevent intrinsic-pathway mediated coagulation-amplification. Severe-HA patients (HAPs) require life-long infusions of therapeutic-FVIII-proteins (tFVIIIs) but ~30% develop neutralizing-tFVIII-antibodies called "FVIII-inhibitors (FEIs)". We investigated the genetics underlying the variable risk of FEI-development in 450 North American HAPs (206 and 244 respectively self-reporting black-African- or white-European-ancestry) by analyzing the genotypes of single-nucleotide-variations (SNVs) in candidate immune-mediated-disease (IMD)-genes using a binary linear-mixed model of genetic association with baseline-FEI-status, the dependent variable, while simultaneously accounting for their genetic relationships and heterogeneous-F8-mutations to prevent the statistical problem of non-independence. We a priori selected gene-centric-association-scans of pleiotropic-IMD-genes implicated in the development of either ≥2 autoimmune-/autoinflammatory-disorders (AADs) or FEIs and ≥1 AAD. We found that baseline-FEI-status was significantly associated with NOS2A (rs117382854; p = 3.2 × 10-6) and B3GNT2 (rs10176009; p = 5.1 × 10-6)-pleiotropic-IMD-genes known previously to function in anti-microbial-/-tumoral-immunity but not in the development of FEIs-and confirmed associations with CTLA4 (rs231780; p = 2.2 × 10-5). We also found that baseline-FEI-status has a substantial heritability (~55%) that involves (i) a F8-mutation-specific component of ~8%, (ii) an additive-genetic contribution from SNVs in IMD-genes of ~47%, and (iii) race, which is a significant determinant independent of F8-mutation-types and non-F8-genetics.

Expanded carrier screening for 224 monogenic disease genes in 1,499 Chinese couples: a single-center study

OBJECTIVES

Expanded carrier screening (ECS) is a preventive genetic test that enables couples to know their risk of having a child affected by certain monogenetic diseases. This study aimed to evaluate the carrier frequency for rare monogenic diseases in the general Chinese population and the impacts of ECS on their reproductive decisions and pregnancy outcomes.

METHODS

This single-center study was conducted between September 2022 and April 2023. An ECS panel containing 224 recessive genes was offered to 1,499 Chinese couples from the general population who were at early gestational ages or planned to conceive.

RESULTS

Overall, 55.0 % of the individuals carried for at least one recessive condition. There were 16 autosomal recessive (AR) genes with a carrier frequency of ≥1/100 and 22 AR genes with a carrier frequency of <1/100 to ≥1/200. The most common AR and X-linked diseases were GJB2-related non-syndromic hearing loss, and hemolytic anemia, respectively. Fifty-five couples (3.67 %; 1 in 27.3) were at increased risk of having an affected child with 19 pregnant at the time of testing. Of these, 10 opted for amniocentesis, and four affected pregnancies were identified, with three of them being terminated.

CONCLUSIONS

This study not only provides valuable information about the recessive genetic landscape, but also establishes a solid foundation for couple-based ECS in a real clinical setting.

Genetic Analysis and Reproductive Interventions for Two Rare Families Affected by Severe Haemophilia A

BACKGROUND

Haemophilia A (HA) is a rare bleeding disorder caused by variants in F8. Although traditional mutational analyses have identified numerous pathogenic variants, the aetiology of HA in certain patients remains unclear. Furthermore, female patients with severe HA are rare.

AIM

To investigate the molecular defects underlying severe HA in two patients and provide personalised reproductive interventions for their families.

METHODS

Two patients diagnosed with severe HA without other clinical phenotypes were enrolled in the study. A combination of whole-exome sequencing, real-time quantitative polymerase chain reaction and long-read sequencing (LR-sequencing) was performed to reveal the molecular defects of them, followed by the application of different reproductive intervention strategies.

RESULTS

Proband 1, a 29-year-old man with FVIII activity of 0.8%, did not exhibit common F8 variants, including Inv1 or Inv22, in the coding region. However, he carried a rare maternal novel inversion on ChrX:154148973_154170321, spanning approximately 21.345 Kbp, with breakpoints in introns 13 and 14 of F8. Finally, the couple of Proband 1 opted for assisted reproductive technology using preimplantation genetic testing and successfully conceived. Proband 2, a 20-year-old female with severe HA and FVIII activity of 0.6%, carried inv22 of F8. Further investigation combining whole exome sequencing (WES) and pedigree analysis revealed that she carried a maternal cross-deletion encompassing exons 1-22 of F8, FUNDC2, BRCC3 and CLIC2, along with a de novo missense variant c.5852T>C (p.Leu1951Ser) on her paternal X-chromosome. Chromosome X-inactivation (XCI) analysis demonstrated a highly skewed inactivation of the maternal X chromosome, with a ratio of 98:2. Subsequently, prenatal diagnosis confirmed that the third child in this family did not carry any of the F8 variants present in Proband 2.

CONCLUSION

Our findings provide novel insights into the genetic aetiology of HA and emphasise the importance of a definitive diagnosis in guiding genetic counselling and personalised reproductive interventions for affected individuals and their families.

Inverse Shifting-PCR Modified by Capillary Electrophoresis for Detecting F8 int22h and int1h Inversions in Severe Hemophilia A Patients and Probable Carriers

Globally, intron 22 inversions (Inv22s) of the factor VIII gene (F8) are the most frequent pathogenic variants and account for 45-50% of severe hemophilia A (SHA) cases, while intron 1 inversion (Inv1) explains 1-5% of SHA cases. The detection of both inversions by an inverse shifting-polymerase chain reaction (IS-PCR) is the first choice worldwide for the diagnosis of patients and carriers of SHA. To improve its sensitivity and reproducibility in the visualization of PCR products, we approached the IS-PCR with fluorescent capillary electrophoresis instead of agarose electrophoresis. Based on the original protocol, we modified two primers by 5'-end labeling with FAM™ fluorescent dye for the detection of the PCR products by capillary electrophoresis. Additionally, the "fast enzymes" BclI and T4-Ligase were incorporated for work saving in the genomic digestion and ligation reactions, respectively. Once we accomplished the standardization and verified the reproducibility of the modified IS-PCR method, we applied it for the diagnosis of a cohort of SHA patients and carriers. The modified IS-PCR by fluorescent capillary electrophoresis for PCR product detection is more sensitive than agarose electrophoresis. The method was also improved by using the new rapid enzymes to save time in the whole process.

Detection of hemophilia A genetic variants using third-generation long-read sequencing

BACKGROUND

Hemophilia A (HA) is an X-linked recessive genetic disorder caused by pathogenic variations of the factor VIII -encoding gene, F8 gene. Due to the large size and diverse types of variations in the F8 gene, causative mutations in F8 cannot be simultaneously detected in one step by traditional molecular analysis, and genetic molecular diagnosis and prenatal screening of HA still face significant difficulties and challenges in clinical practice. Therefore, we aimed to develop and validate an efficient, accurate, and time-saving method for the genetic detection of HA.

METHODS

A comprehensive analysis of hemophilia A (CAHEA) method based on long-range PCR and long-read sequencing (LRS) was used to detect F8 gene mutations in 14 clinical HA samples. The LRS results were compared with those of the conventional methods to evaluate the accuracy and sensitivity of the proposed approach.

RESULTS

The CAHEA method successfully identified 14 F8 variants in all probands, including 3 small insertion deletions, 4 single nucleotide variants, and 7 intron 22 inversions in a "one-step" manner, of which 2 small deletions have not been reported previously. Moreover, this method provided an opportunity to analyze the mechanism of rearrangement and the pathogenicity of F8 variants. The LRS results were validated and found to be in 100% agreement with those obtained using the conventional method.

CONCLUSION

Our proposed LRS-based F8 gene detection method is an accurate and reproducible genetic screening and diagnostic method with significant clinical value. It provides efficient, comprehensive, and accurate genetic screening and diagnostic services for individuals at high risk of HA as well as for premarital and prenatal populations.

DNA base editing corrects common hemophilia A mutations and restores factor VIII expression in in vitro and ex vivo models

BACKGROUND

Replacement and nonreplacement therapies effectively control bleeding in hemophilia A (HA) but imply lifelong interventions. Authorized gene addition therapy could provide a cure but still poses questions on durability. FVIIIgene correction would definitively restore factor (F)VIII production, as shown in animal models through nuclease-mediated homologous recombination (HR). However, low efficiency and potential off-target double-strand break still limit HR translatability.

OBJECTIVES

To correct common model single point mutations leading to severe HA through the recently developed double-strand break/HR-independent base editing (BE) and prime editing (PE) approaches.

METHODS

Screening for efficacy of BE/PE systems in HEK293T cells transiently expressing FVIII variants and validation at DNA (sequencing) and protein (enzyme-linked immunosorbent assay; activated partial thromboplastin time) level in stable clones. Evaluation of rescue in engineered blood outgrowth endothelial cells by lentiviral-mediated delivery of BE.

RESULTS

Transient assays identified the best-performing BE/PE systems for each variant, with the highest rescue of FVIII expression (up to 25% of wild-type recombinant FVIII) for the p.R2166∗ and p.R2228Q mutations. In stable clones, we demonstrated that the mutation reversion on DNA (∼24%) was consistent with the rescue of FVIII secretion and activity of 20% to 30%. The lentiviral-mediated delivery of the selected BE systems was attempted in engineered blood outgrowth endothelial cells harboring the p.R2166∗ and p.R2228Q variants, which led to an appreciable and dose-dependent rescue of secreted functional FVIII.

CONCLUSION

Overall data provide the first proof-of-concept for effective BE/PE-mediated correction of HA-causing mutations, which encourage studies in mouse models to develop a personalized cure for large cohorts of patients through a single intervention.

Whole F8 gene sequencing identified pathogenic structural variants in the remaining unsolved patients with severe hemophilia A

BACKGROUND

No F8 genetic abnormality is detected in approximately 1% to 2% of patients with severe hemophilia A (HA) using conventional genetic approaches. In these patients, deep intronic variation or F8 disrupting genomic rearrangement could be causal.

OBJECTIVES

The study aimed to identify the causal variation in families with a history of severe HA for whom genetic investigations failed.

METHODS

We performed whole F8 gene sequencing in 8 propositi. Genomic rearrangements were confirmed by Sanger sequencing of breakpoint junctions and/or quantitative polymerase chain reaction.

RESULTS

A structural variant disrupting F8 was found in each propositus, so that all the 815 families with a history of severe HA registered in our laboratory received a conclusive genetic diagnosis. These structural variants consisted of 3 balanced inversions, 3 large insertions of gained regions, and 1 retrotransposition of a mobile element. The 3 inversions were 105 Mb, 1.97 Mb, and 0.362 Mb in size. Among the insertions of gained regions, one corresponded to the insertion of a 34 kb gained region from chromosome 6q27 in F8 intron 6, another was the insertion of a 447 kb duplicated region from chromosome 9p22.1 in F8 intron 14, and the last one was the insertion of an Xq28 349 kb gained in F8 intron 5.

CONCLUSION

All the genetically unsolved cases of severe HA in this cohort were due to structural variants disrupting F8. This study highlights the effectiveness of whole F8 sequencing to improve the molecular diagnosis of HA when the conventional approach fails.

Mutation detection and inhibitor analysis of 43 children with severe hemophilia A in a single center: three novel mutations

To investigate the risk factors of FVIII inhibitors development in severe hemophilia A (HA) patients who were received on-demand therapy and were infused with plasma cryoprecipitate and multiple FVIII concentrates alternately. We collected clinical information from 43 severe HA children who were treated with plasma cryoprecipitate and multiple FVIII concentrates. The F8 mutation was detected by long-distance PCR for inversion and detected by all exons and their flanking sequencing for other mutations. The inhibitor detection was performed by Nijmegen-modified Bethesda assay. The impact of novel amino substitutions on FVIII protein was predicted by SIFT and PolyPhen-2. The 3D analysis of missense mutations was performed using Swiss-PdbViewer. FVIII inhibitors were detected in nine cases (20.9%). All of the inhibitor positive cases had high risk F8 gene mutations. In most of the positive cases (7/9), inhibitors were developed during the first 10 EDs, which was significantly higher than that in the 10-50 EDs group and 50 EDs group (p = 0.009). Three novel mutations were reported, including c.214G > T (E72X), c.218 T > C (F73S), and c.2690C > G (S840X). For severe HA patients who are treated with multiple products of replacement therapy, it is important to supervise inhibitor during the first 10EDs, especially for those with high risk F8 gene mutations. F8 gene mutation is one of the most important genetic factors for inhibitor development. It is essential to detect F8 gene for all severe HA patients. Three novel mutations were reported to expand the mutation spectrum of the F8 gene.

Comprehensive Analysis of Hemophilia A (CAHEA): Towards Full Characterization of the F8 Gene Variants by Long-Read Sequencing

BACKGROUND

 Hemophilia A (HA) is the most frequently occurring X-linked bleeding disorder caused by heterogeneous variants in the F8 gene, one of the largest genes known. Conventional molecular analysis of F8 requires a combination of assays, usually including long-range polymerase chain reaction (LR-PCR) or inverse-PCR for inversions, Sanger sequencing or next-generation sequencing for single-nucleotide variants (SNVs) and indels, and multiplex ligation-dependent probe amplification for large deletions or duplications.

MATERIALS AND METHODS

 This study aimed to develop a LR-PCR and long-read sequencing-based assay termed comprehensive analysis of hemophilia A (CAHEA) for full characterization of F8 variants. The performance of CAHEA was evaluated in 272 samples from 131 HA pedigrees with a wide spectrum of F8 variants by comparing to conventional molecular assays.

RESULTS

 CAHEA identified F8 variants in all the 131 pedigrees, including 35 intron 22-related gene rearrangements, 3 intron 1 inversion (Inv1), 85 SNVs and indels, 1 large insertion, and 7 large deletions. The accuracy of CAHEA was also confirmed in another set of 14 HA pedigrees. Compared with the conventional methods combined altogether, CAHEA assay demonstrated 100% sensitivity and specificity for identifying various types of F8 variants and had the advantages of directly determining the break regions/points of large inversions, insertions, and deletions, which enabled analyzing the mechanisms of recombination at the junction sites and pathogenicity of the variants.

CONCLUSION

 CAHEA represents a comprehensive assay toward full characterization of F8 variants including intron 22 and intron 1 inversions, SNVs/indels, and large insertions and deletions, greatly improving the genetic screening and diagnosis for HA.

Molecular Diagnosis of Hemophilia A and Pathogenesis of Novel F8 Variants in Shanxi, China

The aim of this study was to perform a molecular diagnosis of hemophilia A (HA) among patients in the Shanxi Province of China. Fifty-two HA patients were tested, including IVS22 (31 samples), IVS1 (3 samples), missense (11 samples), nonsense (3 samples), and 4 cases of frameshift (2 cases of deletion, 1 case of insertion, 1 case of single-base duplication). With the exception of the single-base G duplication variant (p.Ile1213Asnfs*28), this was the hotspot variant reported by research groups at an early stage. The remaining variants were found, for the first time, in the region. The missense variants p.Cys172Ser, p.Tyr404Ser, p.Asp1903Gly, and p.Ser2284Asn, the deletion variant p.Leu2249fs*9, and the insertion variant p.Pro2319fs*97 were novel variants. The application of next-generation sequencing (NGS) molecular diagnosis enriched the variant spectrum of HA, which is greatly significant for individualized genetic counseling, clinical diagnosis, and treatment. NGS and a variety of bioinformatics prediction methods can further analyze the impact of genetic variation on protein structure or function and lay the foundation to reveal the molecular pathogenic mechanism of novel variants.

Four Decades of Carrier Detection and Prenatal Diagnosis in Hemophilia A: Historical Overview, State of the Art and Future Directions

Hemophilia A (HA), a rare recessive X-linked bleeding disorder, is caused by either deficiency or dysfunction of coagulation factor VIII (FVIII) resulting from deleterious mutations in the F8 gene encoding FVIII. Over the last 4 decades, the methods aimed at determining the HA carrier status in female relatives of HA patients have evolved from phenotypic studies based on coagulation tests providing merely probabilistic results, via genetic linkage studies based on polymorphic markers providing more accurate results, to next generation sequencing studies enabling highly precise identification of the causative F8 mutation. In parallel, the options for prenatal diagnosis of HA have progressed from examination of FVIII levels in fetal blood samples at weeks 20-22 of pregnancy to genetic analysis of fetal DNA extracted from chorionic villus tissue at weeks 11-14 of pregnancy. In some countries, in vitro fertilization (IVF) combined with preimplantation genetic diagnosis (PGD) has gradually become the procedure of choice for HA carriers who wish to prevent further transmission of HA without the need to undergo termination of pregnancies diagnosed with affected fetuses. In rare cases, genetic analysis of a HA carrier might be complicated by skewed X chromosome inactivation (XCI) of her non-hemophilic X chromosome, thus leading to the phenotypic manifestation of moderate to severe HA. Such skewed XCI may be associated with deleterious mutations in X-linked genes located on the non-hemophilic X chromosome, which should be considered in the process of genetic counseling and PGD planning for the symptomatic HA carrier. Therefore, whole exome sequencing, combined with X-chromosome targeted bioinformatic analysis, is highly recommended for symptomatic HA carriers diagnosed with skewed XCI in order to identify additional deleterious mutations potentially involved in XCI skewing. Identification of such mutations, which may profoundly impact the reproductive choices of HA carriers with skewed XCI, is extremely important.

Tandem and inverted duplications in haemophilia A: Breakpoint characterisation provides insight into possible rearrangement mechanisms

INTRODUCTION

Approximately half of patients with severe haemophilia A are caused by structural variants in the F8 gene. Unlike inversions or deletions directly impairing the integrity of F8, some duplications do not completely disrupt the open reading frame or even retain an intact F8 copy. Currently, only a few duplication breakpoints were precisely characterized, and the corresponding rearrangement mechanisms and clinical outcomes remain to be further investigated.

AIM

Establishing an effective strategy for breakpoint characterization of duplications and revealing their rearrangement mechanisms.

METHODS

AccuCopy is used for the detection of duplications, long-distance PCR for the characterization of tandem duplications, genome walking technique and whole genome sequencing for the characterization of inverted duplications.

RESULTS

Four F8 duplication rearrangements were successfully characterized at the nucleotide level: one tandem duplication (exons 7-11) and three inverted duplications (exons 7-22, exons 2-26, and exons 15-22). Two shared features of inverted duplication were found after carefully analysing our results and breakpoint information in the literature: 1, an inverted fragment was inserted into the original chromosome via two junctions; 2, one junction is mediated by a pair of inverted repetitive elements, while the other consists of two breakpoints with microhomology.

CONCLUSION

Similar breakpoint features motivated us to propose a DNA replication-based model to explain the formation of duplication rearrangements. Based on our model, we further divide the inverted duplications into three basic types: type I with a DEL-NOR/INV-DUP pattern, type II with a DUP-NOR/INV-DUP pattern and type III with a DUP-TRP/INV-DUP pattern.

A novel F8 variant in a Chinese hemophilia A family and involvement of X-chromosome inactivation: A case report

RATIONALE

Hemophilia A (HA) is an X-linked recessive bleeding disorder, which shows factor VIII (FVIII) deficiency caused by genetic variant in F8 gene.

PATIENT CONCERNS

Males with F8 variants are affected, whereas female carriers with a wide range of FVIII levels are usually asymptomatic, it is possible that different X-chromosome inactivation (XCI) may effect the FVIII activity.

DIAGNOSES

We identified a novel variant F8: c.6193T > G in a Chinese HA proband, it was inherited from the mother and grandmother with different FVIII levels.

INTERVENTIONS

We performed Androgen receptor gene (AR) assays and RT-PCR.

OUTCOMES

AR assays revealed that the X chromosome with the F8 variant was severely skewed inactivated in the grandmother with higher FVIII levels, but not in the mother with lower FVIII levels. Further, RT-PCR of mRNA confirmed that only the wild allele of F8 was expressed in the grandmother, with lower expression in the wild allele of the mother.

LESSONS

Our findings suggest that F8: c.6193T > G could be the cause of HA and that XCI affected the FVIII plasma levels in female carriers.

Haemophilia A: A Review of Clinical Manifestations, Treatment, Mutations, and the Development of Inhibitors

The purpose of this narrative review was to provide an overview that allows readers to improve their understanding of hemophilia A, which is considered a genetic disease with a high impact on the quality of life of people who suffer from it is considered one of the diseases with the highest cost for health systems (In Colombia it is part of the five diseases with the greatest economic impact). After this exhaustive review, we can see that the treatment of hemophilia is on the way to precision medicine, which involves genetic variables specific to each race and ethnicity, pharmacokinetics (PK), as well as environmental factors and lifestyle. Knowing the impact of each of these variables and their relationship with the efficacy of treatment (prophylaxis: regular infusion of the missing clotting factor VIII in order to prevent spontaneous bleeding) will allow for individualizing the medical behavior in a cost-effective way. For this is required to build more strong scientific evidence with statistical power that allows us to infer.

F8 gene inversion and duplication cause no obvious hemophilia A phenotype

Hemophilia A (HA, OMIM#306700) is an X-linked recessive bleeding disorder caused by the defects in the F8 gene, which encodes coagulation factor VIII (FVIII). Intron 22 inversion (Inv22) is found in about 45% of patients with severe hemophilia A. Here, we reported a male without obvious hemophilia A phenotype but bearing an inherited segmental variant duplication encompassing F8 as well as Inv22. The duplication was approximately 0.16 Mb and involved from exon 1 to intron 22 of F8. This partial duplication and Inv22 in F8 was first found in the abortion tissue of his older sister with recurrent miscarriage. The genetic testing of his family revealed that his phenotypically normal older sister and mother also had this heterozygous Inv22 and a 0.16 Mb partial duplication of F8, while his father was genotypically normal. The integrity of the F8 gene transcript was verified by sequencing of the adjacent exons at the inversion breakpoint, which explained why this male had no phenotype for hemophilia A. Interestingly, although he had no significant hemophilia A phenotype, the expression of C1QA in his mother, sister, and the male subject was only about half of that in his father and normal population. Our report broadens the mutation spectrum of F8 inversion and duplication and its pathogenicity in hemophilia A.

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.

Insights into the Molecular Genetic of Hemophilia A and Hemophilia B: The Relevance of Genetic Testing in Routine Clinical Practice

Hemophilia A and hemophilia B are rare congenital, recessive X-linked disorders caused by lack or deficiency of clotting factor VIII (FVIII) or IX (FIX), respectively. The severity of the disease depends on the reduction of coagulation FVIII or FIX activity levels, which is determined by the type of the pathogenic variants in the genes encoding the two factors (F8 and F9, respectively). Molecular genetic analysis is widely applied in inherited bleeding disorders. The outcome of genetic analysis allows genetic counseling of affected families and helps find a link between the genotype and the phenotype. Genetic analysis in hemophilia has tremendously improved in the last decades. Many new techniques and modifications as well as analysis softwares became available, which made the genetic analysis and interpretation of the data faster and more accurate. Advances in genetic variant detection strategies facilitate identification of the causal variants in up to 97% of patients. In this review, we discuss the milestones in genetic analysis of hemophilia and highlight the importance of identification of the causative genetic variants for genetic counseling and particularly for the interpretation of the clinical presentation of hemophilia patients.

Comprehensive analysis of F8 large deletions: Characterization of full breakpoint junctions and description of a possible DNA breakage hotspot in intron 6

BACKGROUND

Large F8 deletions represent 3-5% of the variations found in severe hemophilia A patients, but only a few deletion breakpoints have been characterized precisely.

OBJECTIVES

Resolving at the nucleotide level 24 F8 large deletions to provide new data on the mechanisms involved in these rearrangements.

METHODS

Breakpoint junctions of 24 F8 large deletions were characterized using a combination of long-range polymerase chain reaction, whole F8 NGS sequencing, and Sanger sequencing. Repeat elements, non-B DNA, and secondary structures were analyzed around the breakpoints.

RESULTS

Deletions ranged from 1.667 kb to 0.5 Mb in size. Nine involved F8 neighboring genes. Simple blunt ends and 2-4 bp microhomologies were identified at the breakpoint junctions of 10 (42%) and 8 (33%) deletions, respectively. Five (21%) deletions resulted from homeologous recombination between two Alu elements. The remaining case corresponded to a more complex rearrangement with an insertion of a 19 bp-inverted sequence at the junction. Four different breakpoints were located in a 562-bp region in F8 intron 6. This finding suggested that this region, composed of two Alu elements, is a DNA breakage hotspot. Non-B DNA and secondary structures were identified in the junction regions and may contribute to DNA breakage.

CONCLUSION

Molecular characterization of deletion breakpoints revealed that non-homologous non-replicative DNA repair mechanisms and replication-based mechanisms seemed to be the main causative mechanisms of F8 large deletions. Moreover, we identified a possible F8 DNA breakage hotspot involved in non-recurrent rearrangements.

Skewed X-Chromosome Inactivation and Parental Gonadal Mosaicism Are Implicated in X-Linked Recessive Female Hemophilia Patients

Background: Hemophilia A (HA) and B (HB) are X-linked recessive disorders that mainly affect males born from a mother carrier. Females are rarely affected but a number of mechanisms have been suggested in symptomatic females, such as skewed X-chromosome inactivation (XCI), chromosomal rearrangements, and hermaphrodites. Different methodologies are required to elucidate the underlying causes of such diseases in female patients. Methods: Three families with female hemophilia patients, including two HA and one HB, were enrolled for genetic analyses. Cytogenetics, molecular examinations on F8 and F9 genes, XCI assay, and linkage analysis were performed. Results: All three female patients are demonstrated to be heterozygous for an F8, or F9 mutation: one patient is inherited from her unaffected mother and the other two are sporadic cases. All three patients exhibit skewed XCI. The inherited patient is found to be unmethylated in the maternal X chromosome, which increases the potential for the expression of the mutant allele. The two sporadic cases are hypomethylated or unmethylated in the paternal X chromosome, suggesting that paternal gonadal mosaicism may exist in these families. Conclusions: In addition to screening for coagulation function, different genetic analyses are mandatory to explore the nature of mechanisms responsible for the X-linked recessive disorders in female patients as shown in this study. Our results confirm that skewed XCI is responsible for hemophilia in heterozygous female patients. Likewise, our results implicate that parental gonadal mosaicism, followed by skewed XCI, contributes to hemophilia in “sporadic” female patients.

Therapeutic applications of gene editing in chronic liver diseases: an update

Innovative genome editing techniques developed in recent decades have revolutionized the biomedical research field. Liver is the most favored target organ for genome editing owing to its ability to regenerate. The regenerative capacity of the liver enables ex vivo gene editing in which the mutated gene in hepatocytes isolated from the animal model of genetic disease is repaired. The edited hepatocytes are injected back into the animal to mitigate the disease. Furthermore, the liver is considered as the easiest target organ for gene editing as it absorbs almost all foreign molecules. The mRNA vaccines, which have been developed to manage the COVID-19 pandemic, have provided a novel gene editing strategy using Cas mRNA. A single injection of gene editing components with Cas mRNA is reported to be efficient in the treatment of patients with genetic liver diseases. In this review, we first discuss previously reported gene editing tools and cases managed using them, as well as liver diseases caused by genetic mutations. Next, we summarize the recent successes of ex vivo and in vivo gene editing approaches in ameliorating liver diseases in animals and humans.

Therapeutic applications of gene editing in chronic liver diseases: an update

Innovative genome editing techniques developed in recent decades have revolutionized the biomedical research field. Liver is the most favored target organ for genome editing owing to its ability to regenerate. The regenerative capacity of the liver enables ex vivo gene editing in which the mutated gene in hepatocytes isolated from the animal model of genetic disease is repaired. The edited hepatocytes are injected back into the animal to mitigate the disease. Furthermore, the liver is considered as the easiest target organ for gene editing as it absorbs almost all foreign molecules. The mRNA vaccines, which have been developed to manage the COVID-19 pandemic, have provided a novel gene editing strategy using Cas mRNA. A single injection of gene editing components with Cas mRNA is reported to be efficient in the treatment of patients with genetic liver diseases. In this review, we first discuss previously reported gene editing tools and cases managed using them, as well as liver diseases caused by genetic mutations. Next, we summarize the recent successes of ex vivo and in vivo gene editing approaches in ameliorating liver diseases in animals and humans. [BMB Reports 2022; 55(6): 251-258].

Genetic Characterization of the Factor VIII Gene in a Cohort of Colombian Patients with Severe Hemophilia A with Inhibitors

Hemophilia A is an X-linked bleeding disorder caused by mutations in the FVIII gene. Genetic factors have been shown to be a risk factor for the development of inhibitors. We aimed to identify the specific variations of the FVIII gene of patients with hemophilia A with inhibitors and their association with the inhibitor titer. Methods: Cross-sectional descriptive study. We included 12 Colombian patients from a health care provider, “Integral Solutions SD”, who underwent analysis of genetic material (DNA), which was reported by the Molecular Hemostasis Laboratory in Bonn, Germany. Results: All of these patients were diagnosed with severe hemophilia A with inhibitors; ages ranged between 6 and 48 years, with a median age of 13.5 years. Molecular analysis showed the inversion of intron 22 in six patients (50.0%), a small duplication in two patients (16.7%), the inversion of intron 1 in one patient (8.3%), a large deletion (8.3%), a nonsense mutation (8.3%) and a splice-site (8.3%), findings similar to those of other studies. A total of 58.3% of the patients presented inversion mutations with a high risk of developing inhibitors A total of 83.3% of the evaluated patients presented null mutations; however the presence of high inhibitor titers was 66.7%. The most frequent mutation was the inversion intron 22. Knowing the type of mutation and its association as a risk factor for generating inhibitors invites us to delve into other outcomes such as residual values of coagulation FVIII as well as its impact on the half-life of the exogenous factor applied in prophylaxis.

A founder effect in hemophilia A patients from Russian Ural region with a new p.(His634Arg) variant in F8 gene

Hemophilia A is a clotting disease caused by defects in the F8 gene. A lot of them are described and most are unique or have polyphyletic origin. We here study the origin of a pathogenic variant found in a few patients. We sequenced F8 gene for seven hemophilia A patients from the Ural region, Sverdlovskaya oblast, Russia. We constructed haplotypes for them and for 21 hemophilia A patients with other defects from the same area as a control group using four previously described X-chromosome loci associated with F8 gene. We identified a new missense variant p.(His634Arg) in seven apparently unrelated patients with mild hemophilia A from Sverdlovskaya oblast. The haplotype analysis showed that all patients share the same haplotype, absent in the other patients, suggesting a founder effect. The most recent common ancestor for the p.(His634Arg) patients is estimated to exist around the end of XVII century; however, the 95% confidence interval spans from XII to early XX century. The Ural region did not suffer from the recent bottlenecks or isolation. Therefore, the founder effect could be a natural consequence of population structuring in a relatively stable population. We identified a founder effect mutation in hemophilia A, which is a quite rare event for this disease.

Generation of iPSC line from urine cells of hemophilia A with F8 (p. R814X) mutation

The lack of coagulation factor VIII in patient with nonsense mutation hemophilia A leads to varying degrees of bleeding symptoms, and long-term use of alternative therapies can produce inhibitors that affect the efficacy. In this study, human induced pluripotent stem cells (iPSCs) of hemophilia A were generated by reprogramming of urine cells. Human urine cells (HUCs) were isolated by collecting patients' mid-stream urine, and cultured to good state in urine medium. Then, the HUCs were transfected with PEP4-EO2S-ET2K and pCEP4-M2L, and iPSCs were obtained in the medium without trophoblast cells and the composition was determined. Finally, alkaline phosphatase staining, karyotype analysis, immunofluorescence staining and teratoma were used to verify that we successfully reprogrammed hemophilia A-specific human induced pluripotent stem cells from patients' urine cells, providing a safe and effective cell model for the study of molecular mechanism and related treatment of hemophilia.

Determining common variants in patients with haemophilia A in South Vietnam and screening female carriers in their family members

AIMS

The aim of this study was to determine common variants in F8, including intron 22 inversion (Inv22), intron 1 inversion (Inv1) and point mutations, the transmission of these variants between patients with haemophilia A (HA) and their family members.

METHODS

Genetic analysis was conducted in 71 patients who were clinically diagnosed with HA and 152 related female members in South Vietnam by a combination of inversion PCR (I-PCR), multiplex PCR and direct sequencing.

RESULTS

Variants in F8, including Inv22, point mutations (with 37 genotypes) and two novel variants, occupied 60 patients with HA. Among severe patients, the rate of Inv22 was 44%. Missense was the common point mutation of over 50% in patients with moderate HA and mild HA. Inv1 was absent in all patients. F8 variants were also found in 119 female carriers (FCs) (78.3%) from families related to patients with HA. There were 56 mothers (93.3%) carrying F8 variants and passing the same variants to their sons.

CONCLUSIONS

These findings were the first to provide important information about the presence of Inv22 and point mutation in Vietnamese patients with HA, the mothers and their female family members. It demonstrated that genetic diagnosis and counselling for HA carriers were essential factors for future improvements in comprehensive and equitable healthcare polices for patients with HA and FCs in Vietnam.

Genetic and Bioinformatic Strategies to Improve Diagnosis in Three Inherited Bleeding Disorders in Bogotá, Colombia

Inherited bleeding disorders (IBDs) are the most frequent congenital diseases in the Colombian population; three of them are hemophilia A (HA), hemophilia B (HB), and von Willebrand Disease (VWD). Currently, diagnosis relies on multiple clinical laboratory assays to assign a phenotype. Due to the lack of accessibility to these tests, patients can receive an incomplete diagnosis. In these cases, genetic studies reinforce the clinical diagnosis. The present study characterized the molecular genetic basis of 11 HA, three HB, and five VWD patients by sequencing the F8, F9, or the VWF gene. Twelve variations were found in HA patients, four in HB patients, and 19 in WVD patients. From these variations a total of 25 novel variations were found. Disease-causing variations were used as positive controls for validation of the high-resolution melting (HRM) variant-scanning technique. This approach is a low-cost genetic diagnostic method proposed to be incorporated in developing countries. For the data analysis, we developed an accessible open-source code in Python that improves HRM data analysis with better sensitivity of 95% and without bias when using different HRM equipment and software. Analysis of amplicons with a length greater than 300 bp can be performed by implementing an analysis by denaturation domains.

Risk factors for antibody formation in children with hemophilia: methodological aspects and clinical characteristics of the HEMFIL cohort study

Up to 35% of patients with hemophilia A and 5% with hemophilia B develop neutralizing antibodies which can inhibit the therapeutic activity of factor replacement (inhibitors). Despite the clinical relevance of antifactor VIII and IX neutralizing antibodies, there is still a major gap on the knowledge of risk factors for their development. Furthermore, most of the studies on risk factors for inhibitor development come from Caucasian and Afro-American populations. The HEMFIL is a Brazilian prospective cohort study of previously untreated children with hemophilia, which primary aim is to identify new risk factors related to inhibitor development. This manuscript aims at describing the study design and its methodology. After the diagnosis, children are followed up to 75 exposure days or to inhibitor development. Standardized forms and blood samples are collected to describe clinical characteristics and to perform the measurement of immunological and genetic biomarkers at three time points; Inclusion time (T0), at inhibitor development or at 75 exposure days without inhibitors (T1) and after immune tolerance induction for patients in whom it is indicated and performed (T2). Currently, 120 children have been included, of whom, 95 have completed the follow-up. For severe/moderately severe hemophilia A, the cumulative incidence of inhibitors at 75 exposure days was 35% (95% confidence interval, 26-46%). The inclusion of additional patients and a longer follow-up will allow the analysis of risk factors for inhibitor development.

Complete characterisation of two new large Xq28 duplications involving F8 using whole genome sequencing in patients without haemophilia A

INTRODUCTION

Depending on the location of insertion of the gained region, F8 duplications can have variable clinical impacts from benign impact to severe haemophilia A phenotype.

AIM

To characterize two large Xq28 duplications involving F8 incidentally detected by chromosome microarray analysis (CMA) in two patients presenting severe intellectual disability but no history of bleeding disorder.

METHODS

Whole genome sequencing (WGS) was performed in order to characterize the two large Xq28 duplications at nucleotide level.

RESULTS

In patient 1, a 60-73 kb gained region encompassing the exons 23-26 of F8 and SMIM9 was inserted at the int22h-2 locus following a non-homologous recombination between int22h-1 and int22h-2. We hypothesized that two independent events, micro-homology-mediated break-induced replication (MMBIR) and break-induced replication (BIR), could be involved in this rearrangement. In patient 2, the CMA found duplication from 101 to 116-kb long encompassing the exons 16-26 of F8 and SMIM9. The WGS analysis identified a more complex rearrangement with the presence of three genomic junctions. Due to the multiple micro-homologies observed at breakpoints, a replication-based mechanism such as fork stalling and template switching (FoSTeS) was greatly suspected. In both cases, these complex rearrangements preserved an intact copy of the F8.

CONCLUSION

This study highlights the value of WGS to characterize the genomic junction at the nucleotide level and ultimately better describe the molecular mechanisms involved in Xq28 structural variations. It also emphasizes the importance of specifying the structure of the genomic gain in order to improve genotype-phenotype correlation and genetic counselling.

Dissection of pleiotropic effects of variants in and adjacent to F8 exon 19 and rescue of mRNA splicing and protein function

The pathogenic significance of nucleotide variants commonly relies on nucleotide position within the gene, with exonic changes generally attributed to quantitative or qualitative alteration of protein biosynthesis, secretion, activity, or clearance. However, these changes may exert pleiotropic effects on both protein biology and mRNA splicing due to the overlapping of the amino acid and splicing codes, thus shaping the disease phenotypes. Here, we focused on hemophilia A, in which the definition of F8 variants' causative role and association to bleeding phenotypes is crucial for proper classification, genetic counseling, and management of affected individuals. We extensively characterized a large panel of hemophilia A-causing variants (n = 30) within F8 exon 19 by combining and comparing in silico and recombinant expression analyses. We identified exonic variants with pleiotropic effects and dissected the altered protein features of all missense changes. Importantly, results from multiple prediction algorithms provided qualitative results, while recombinant assays allowed us to correctly infer the likely phenotype severity for 90% of variants. Molecular characterization of pathogenic variants was also instrumental for the development of tailored correction approaches to rescue splicing affecting variants or missense changes impairing protein folding. A single engineered U1snRNA rescued mRNA splicing of nine different variants and the use of a chaperone-like drug resulted in improved factor VIII protein secretion for four missense variants. Overall, dissection of the molecular mechanisms of a large panel of HA variants allowed precise classification of HA-affected individuals and favored the development of personalized therapeutic approaches.

Discovering and genotyping genomic structural variations by yeast genome synthesis and inducible evolution

Genomic structural variations (SVs) promote the evolution of Saccharomyces cerevisiae, and play an important role in phenotypic diversities. Yeast genomic structures can be remodeled by design and bottom-up synthesis. The synthesis of yeast genome creates novel copy number variations (CNVs) and SVs and develops new strategies to discover gene functions. Further, an inducible evolution system SCRaMbLE, consisted of 3,932 loxPsym sites, was incorporated on synthetic yeast genome. SCRaMbLE enables genomic rearrangements at will and rapidly generates chromosomal number variations, and massive SVs under customized conditions. The impacts of genetic variations on phenotypes can be revealed by genome analysis and chromosome restructuring. Yeast genome synthesis and SCRaMbLE provide a new research paradigm to explore the genotypic mechanisms of phenotype diversities, and can be used to improve biological traits and optimize industrial chassis.

The severe spontaneous bleeding phenotype in a novel hemophilia A rat model is rescued by platelet FVIII expression

Previous studies have shown that platelet-specific factor VIII (FVIII) expression (2bF8) restores hemostasis and induces immune tolerance in hemophilia A (HA) mice even with preexisting inhibitors. Here we investigated for the first time whether platelet FVIII expression can prevent severe spontaneous bleeding in rat HA, a model mimicking the frequent spontaneous bleeding in patients with severe HA. A novel FVIII-/- rat model in a Dahl inbred background (Dahl-FVIII-/-) with nearly the entire rat FVIII gene inverted was created by using a CRISPR/Cas9 strategy. There was no detectable FVIII in plasma. Spontaneous bleeding in the soft tissue, muscles, or joints occurred in 100% of FVIII-/- rats. Sixty-one percent developed anti-FVIII inhibitors after ≥2 doses of recombinant human FVIII infusion. However, when 2bF8 transgene was crossed into the FVIII-/- background, none of the resulting 2bF8tg+FVIII-/- rats (with platelet FVIII levels of 28.26 ± 7.69 mU/108 platelets and undetectable plasma FVIII) ever had spontaneous bleeding. When 2bF8tg bone marrow (BM) was transplanted into FVIII-/- rats, only 1 of 7 recipients had a bruise at the early stage of BM reconstitution, but no other spontaneous bleeding was observed during the study period. To confirm that the bleeding diathesis in FVIII-/- rats was ameliorated after platelet FVIII expression, rotational thromboelastometry and whole-blood thrombin generation assay were performed. All parameters in 2bF8tg BM transplantation recipients were significantly improved compared with FVIII-/- control rats. Of note, neither detectable levels of plasma FVIII nor anti-FVIII inhibitors were detected in 2bF8tg BM transplantation recipients. Thus, platelet-specific FVIII expression can efficiently prevent severe spontaneous bleeding in FVIII-/- rats with no anti-FVIII antibody development.

An aberrant F8 intron 1 inversion with concomitant large duplication and deletion in a Chinese severe hemophilia A patient

OBJECTIVES

Hemophilia A (HA, OMIM: 306700) is an X-linked recessive bleeding disorder, caused by defects of the F8 gene which encodes the coagulation factor VIII (FVIII). F8 intron 22 and intron 1 inversion (Inv22 and Inv1) account for ∼45% and 1-5% of severe HA cases, respectively. We herein described an aberrant Inv1 with concomitant large duplication and deletion in a Chinese severe HA patient.

METHODS

Long distance PCR and multiplex PCR were used to detect Inv22 and Inv1. Multiplex ligation-dependent probe amplification (MLPA) was applied to examine exonic duplication and deletion of the F8 gene. Coverage analysis of read depth data from whole-genome sequencing (WGS) was used to analyze the intronic duplication and deletion of the F8 gene.

RESULTS

We have identified an aberrant F8 Inv1 in a 1-year-old Chinese severe HA patient showing inversed int1h-1 and normal int1h-2. Coverage analysis of WGS data further illustrated the aberrant Inv1 with concomitant a duplication of 117 kb and a deletion of 1.8 kb.

CONCLUSION

In conclusion, we reported an aberrant Inv1 with concomitant large duplication and deletion in a severe Chinese HA patient. Moreover, WGS provides rapid genetic diagnosis of hereditary disorders with point mutations, deletions, insertions and CNVs.

CAR- and TRuC-redirected regulatory T cells differ in capacity to control adaptive immunity to FVIII

Regulatory T cells (Tregs) control immune responses in autoimmune disease, transplantation, and enable antigen-specific tolerance induction in protein-replacement therapies. Tregs can exert a broad array of suppressive functions through their T cell receptor (TCR) in a tissue-directed and antigen-specific manner. This capacity can now be harnessed for tolerance induction by "redirecting" polyclonal Tregs to overcome low inherent precursor frequencies and simultaneously augment suppressive functions. With the use of hemophilia A as a model, we sought to engineer antigen-specific Tregs to suppress antibody formation against the soluble therapeutic protein factor (F)VIII in a major histocompatibility complex (MHC)-independent fashion. Surprisingly, high-affinity chimeric antigen receptor (CAR)-Treg engagement induced a robust effector phenotype that was distinct from the activation signature observed for endogenous thymic Tregs, which resulted in the loss of suppressive activity. Targeted mutations in the CD3ζ or CD28 signaling motifs or interleukin (IL)-10 overexpression were not sufficient to restore tolerance. In contrast, complexing TCR-based signaling with single-chain variable fragment (scFv) recognition to generate TCR fusion construct (TRuC)-Tregs delivered controlled antigen-specific signaling via engagement of the entire TCR complex, thereby directing functional suppression of the FVIII-specific antibody response. These data suggest that cellular therapies employing engineered receptor Tregs will require regulation of activation thresholds to maintain optimal suppressive function.

Partial F8 gene duplication (factor VIII Padua) associated with high factor VIII levels and familial thrombophilia

High coagulation factor VIII (FVIII) levels comprise a common risk factor for venous thromboembolism (VTE), but the underlying genetic determinants are largely unknown. We investigated the molecular bases of high FVIII levels in 2 Italian families with severe thrombophilia. The proband of the first family had a history of recurrent VTE before age 50 years, with extremely and persistently elevated FVIII antigen and activity levels (>400%) as the only thrombophilic defects. Genetic analysis revealed a 23.4-kb tandem duplication of the proximal portion of the F8 gene (promoter, exon 1, and a large part of intron 1), which cosegregated with high FVIII levels in the family and was absent in 103 normal controls. Targeted screening of 50 unrelated VTE patients with FVIII levels ≥250% identified a second thrombophilic family with the same F8 rearrangement on the same genetic background, suggesting a founder effect. Carriers of the duplication from both families showed a twofold or greater upregulation of F8 messenger RNA, consistent with the presence of open chromatin signatures and enhancer elements within the duplicated region. Testing of these sequences in a luciferase reporter assay pinpointed a 927-bp region of F8 intron 1 associated with >45-fold increased reporter activity in endothelial cells, potentially mediating the F8 transcriptional enhancement observed in carriers of the duplication. In summary, we report the first thrombophilic defect in the F8 gene (designated FVIII Padua) associated with markedly elevated FVIII levels and severe thrombophilia in 2 Italian families.

The Possible Non-Mutational Causes of FVIII Deficiency: Non-Coding RNAs and Acquired Hemophilia A

Hemophilia type A (HA) is the most common type of blood coagulation disorder. While the vast majority of cases are inherited and caused by mutations in the F8 gene, recent data raises new questions regarding the non-heritability of this disease, as well as how other molecular mechanisms might lead to the development of HA or increase the severity of the disease. Some data suggest that miRNAs may affect the severity of HA, but for some patients, miRNA-based interference might cause HA, in the absence of an F8 mutation. A mechanism in HA installation that is also worth investigating and which could be identified in the future is the epigenetic silencing of the F8 gene that might be only temporarily. Acquired HA is increasingly reported and as more cases are identified, the description of the disease might become challenging, as cases without FVIII autoantibodies might be identified.

The spectrum of FVIII gene variants detected by next generation sequencing in 236 Chinese non-inversion hemophilia A pedigrees

INTRODUCTION

The reported variants of hemophilia A are mainly from European subjects and American subjects of European descent, and limited data are available from more diverse ethnic backgrounds. This study was performed to identify the causative variants in a large HA cohort from Chinese population.

MATERIALS AND METHODS

A total of 236 HA pedigrees were included. Molecular analysis of F8 gene was performed using next-generation sequencing (NGS) and then validated by Sanger sequencing and multiplex ligation probe amplification (MLPA) results. Variants were classified as pathogenic, likely pathogenic, variant of unknown significance, likely benign, and benign according to the American College of Medical Genetics and Genomics guidelines.

RESULTS

A total of 186 F8 variants were identified, with 139 (139/186, 74.73%) point mutations, 44 (44/186, 23.66%) small insertions/deletions (InDels), and 3 (3/186, 1.61%) large deletions, they included 80 pathogenic and 84 likely pathogenic variants. Of these variants, 119 had been reported previously, and 67 were novel. No potentially causative mutations were found in the targeted F8 region in seventeen HA pedigrees.

CONCLUSIONS

The spectrum of F8 variants identified in this study provides additional information about HA and enriches our knowledge of the variant spectrum in a wider range of ethnic backgrounds.

Droplet digital PCR and mile-post analysis for the detection of F8 int1h inversions

BACKGROUND

F8 int1h inversions (Inv1) are detected in 1%-2% of severe hemophilia A (HA) patients. Long-range polymerase chain reaction (PCR) and inverse-shifting PCR have been used to diagnose these inversions.

OBJECTIVES

To design and validate a sensitive and robust assay for detection of F8 Inv1 inversions.

METHODS

Archival DNA samples were investigated using mile-post assays and droplet digital PCR.

RESULTS

Milepost assays for Inv1 showing high specificities and sensitivities were designed and optimized. Analysis of four patients, two carrier mothers, and 40 healthy controls showed concordance with known mutation status with one exception. One patient had a duplication involving exons 2-22 of the F8 gene instead of an Inv1 mutation. DNA mixtures with different proportions of wild-type and Inv1 DNA correlated well with the observed relative linkage for both wild type and Inv1 assays and estimated the limit of detection of these assays to 2% of the rare chromosome.

CONCLUSIONS

The milepost strategy has several inherent control systems. The absolute counting of target molecules by both assays enables determination of template quantity, detection of copy number variants, and rare variants occurring in primer and probe annealing sites and estimation of DNA integrity through the observed linkage. The presented Inv1 milepost analysis offers sensitive and robust detection and quantification of the F8 int1h inversions and other rearrangements involving intron 1 in patients and their mothers.

General concepts on hemophilia A and on women carrying the disease

Hemophilia A affects one in every 5000 live male births. As the disorder follows a hereditary X-linked recessive pattern, women who inherit the mutation become carriers of the disease. The exact prevalence of carriers of hemophilia A or B is unknown. A search of the literature identified only one study that provides an approximation. According to its authors, for every 100 male with hemophilia there are 277 potential carriers. We will review through this supplement carrier condition from reproductive to care giver and individual point of view.

Mutation detection and inhibitor risk in Iranian patients with Hemophilia A: Six novel mutations

This investigation facilitates a better understanding of inhibitor development, the critical treatment morbidity in HA patients. Furthermore, six novel mutations are reported, which would expand the mutation spectrum of the F8 gene.

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.

Mutation analysis in the F8 gene in 485 families with haemophilia A and prenatal diagnosis in China

BACKGROUND

Haemophilia A (HA) is an X-linked bleeding disorder caused by mutations in the coagulation factor Ⅷ (F8) gene. Its incidence in men is estimated to be approximately 1/5000.

OBJECTIVE

This study aimed to characterize the mutation spectrum of the F8 gene in 485 Chinese families, encompassing all HA phenotypic classes. Additionally, we evaluated the accuracy of prenatal diagnosis of foetuses at risk of having HA.

METHODS

Long-Distance PCR (LD-PCR) and Multiplex PCR were used to detect inversions, next-generation sequencing (NGS) was used for point mutations, and multiplex ligation-dependent probe amplification (MLPA) was used for large deletions or duplications.

RESULTS

A mutation spectrum of 478 HA families was produced. Throughout 26 exons and 15 introns, a total of 237 different alterations of mutations were detected, of which 146 are known mutations (64.5%) and 91 are novel mutations (35.5%). Prenatal diagnosis revealed 97 normal males (35.79%), 103 HA males (38.01%), 36 normal females (13.28%), and 38 HA carrier females (14.02%).

CONCLUSION

Using a systematic approach comprised of three steps, 237 pathogenic variants in 478 out of 485 patient samples (98.6%) were detected, including the identification of a heterogeneous mutation spectrum of 91 novel mutations. In addition, prenatal diagnosis of HA in pregnant carriers allowed for accurate determination of the foetal F8 gene state.

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.

X Chromosome inactivation: a modifier of factor VIII and IX plasma levels and bleeding phenotype in Haemophilia carriers

Haemophilia A and B are X-linked hemorrhagic disorders caused by gene variants in the F8 and F9 genes. Due to recessive inheritance, males are affected, while female carriers are usually asymptomatic with a wide range of factor VIII (FVIII) or IX (FIX) levels. Bleeding tendency in female carriers is extremely variable and may be associated with low clotting factor levels. This could be explained by F8 or F9 genetic variations, numerical or structural X chromosomal anomalies, or epigenetic variations such as irregular X chromosome inactivation (XCI). The aim of the study was to determine whether low FVIII or FIX coagulant activity in haemophilia carriers could be related to XCI and bleeding symptoms. HUMARA assay was performed on 73 symptomatic carriers with low clotting activity ≤50 IU/dL. Bleeding Assessment Tool (BAT) from the International Society on Thrombosis and Haemostasis (ISTH) was used to describe symptoms in the cohort of carriers. In 97% of haemophilia carriers, a specific gene variant in heterozygous state was found, which alone could not justify their low FVIII or FIX levels (≤50 IU/dL). A statistical association between XCI pattern and FVIII and FIX levels was observed. Moreover, female carriers with low coagulant activity (≤20 IU/dL) and high degree of XCI ( ≥ 80:20) had a higher ISTH-BAT score than the carriers with the opposite conditions (>20 IU/dL and <80:20). In our cohort of haemophilia carriers, XCI was significantly skewed, which may contribute to the low expression of clotting factor levels and bleeding symptoms.

Intronic regions of the human coagulation factor VIII gene harboring transcription factor binding sites with a strong bias towards the short-interspersed elements

Increasing data show that intronic derived regulatory elements, such as transcription factor binding sites (TFBs), play key roles in gene regulation, and malfunction. Accordingly, characterizing the sequence context of the intronic regions of the human coagulation factor VIII (hFVIII) gene can be important. In this study, the intronic regions of the hFVIII gene were scrutinized based on in-silico methods. The results disclosed that these regions harbor a rich array of functional elements such as repetitive elements (REs), splicing sites, and transcription factor binding sites (TFBs). Among these elements, TFBs and REs showed a significant distribution and correlation to each other. This survey indicated that 31% of TFBs are localized in the intronic regions of the gene. Moreover, TFBs indicate a strong bias in the regions far from splice sites of introns with mapping to different REs. Accordingly, TFBs showed highly bias toward Short Interspersed Elements (SINEs), which in turn they covering about 12% of the total of REs. However, the distribution pattern of TFBs-REs showed different bias in the intronic regions, spatially into the Introns 13 and 25. The rich array of SINE-TFBs and CR1-TFBs were situated within 5′UTR of the gene that may be an important driving force for regulatory innovation of the hFVIII gene. Taken together, these data may lead to revealing intronic regions with the capacity to renewing gene regulatory networks of the hFVIII gene. On the other hand, these correlations might provide the novel idea for a new hypothesis of molecular evolution of the FVIII gene, and treatment of Hemophilia A which should be considered in future studies.

Factor VIII inhibitor development in Egyptian hemophilia patients: does intron 22 inversion mutation play a role?

BACKGROUND

Hemophilia A (HA) is an X-linked recessive bleeding disorder characterized by qualitative and quantitative deficiency of factor VIII (FVIII). The development of inhibitor antibodies against FVIII is the most challenging complication of treatment. Mutations in the FVIII gene is one of the genetic factors that leads to development of FVIII inhibitors especially intron 22 inversion (Inv22).

OBJECTIVES

This study was carried out to assess the frequency of Inv22 of FVIII gene in Egyptian patients with hemophilia A and its role as a risk factor for developing inhibitors.

PATIENTS AND METHODS

Seventy-two patients with severe HA and 48 patients with moderate HA were enrolled in the current study. All patients were treated on demand with either plasma-derived factor VIII or recombinant factor VIII concentrates. Genotyping of FVIII Inv22 was performed by LD-PCR while the presence and magnitude of inhibitor activity in blood was determined by the Bethesda assay.

RESULTS

Around 23% of all hemophilia cases had positive Inv22. Intron 22 inversion mutation was detected in 6 and 33% of patients with moderate and severe HA respectively. Twenty-one cases (18%) of all hemophilic patients developed inhibitors. Thirty-7% of patients with Inv22 had inhibitor in their blood, almost all, but one, had severe HA. The risk of an inhibitor development during replacement therapy was four folds higher among Inv22 positive cases as compared with mutation negative peers (OR 4.3, 95% CI 1.6-11.9, P = 0.003).

CONCLUSIONS

The prevalence of Inv22 of F VIII in Egyptian hemophiliacs is nearly like that of other population. This mutation was more frequently detected among severe hemophilic patients as compared with moderately affected peers. The presence of Inv22 mutation significantly predispose to FVIII inhibitor development.

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.

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.

Aberrant X chromosomal rearrangement through multi-step template switching during sister chromatid formation in a patient with severe hemophilia A

Background

Hemophilia A (HA) is an X‐linked recessive bleeding disorder caused by pathogenic variants of the coagulation factor VIII gene (F8). Half of the patients with severe HA have a recurrent inversion in the X chromosome, that is, F8 intron 22 or intron 1 inversion. Here, we characterized an abnormal F8 due to atypical complex X chromosome rearrangements in a Japanese patient with severe HA.

Methods

Recurrent F8 inversions were tested with inverse shifting‐PCR. The genomic structure was investigated using PCR‐based direct sequencing or quantitative PCR.

Results

The proband's X chromosome had a 119.5 kb insertion, a reverse duplex of an extragenic sequence on the F8 telomere region into the F8 intron 1 with two breakpoints. The telomeric breakpoint was a joining from the F8 intron 1 to the inverted FUNDC2 via a two‐base microhomology, and the centromeric breakpoint was a recombination between F8 intron 1 homologous sequences. The rearrangement mechanism was suggested as a multi‐step rearrangement with template switching such as fork stalling and template switching (FoSTeS)/microhomology‐mediated break‐induced replication (MMBIR) and/or homologous sequence‐associated recombination during a sister chromatid formation.

Conclusion

We identified the aberrant X chromosome with a split F8 due to a multi‐step rearrangement in a patient with severe HA.