Some factor VIII exon 14 frameshift mutations cause moderately severe haemophilia A

Variant spectrum of F8 and F9 in hemophilia patients from southern China and 26 novel variants

Hemophilia, an X-linked recessive disorder, is characterized by spontaneous or trauma-induced prolonged bleeding. It is classified as hemophilia A when caused by variants in the F8 gene, and hemophilia B when caused by F9 variants. Few studies have described hemophilia variants in the Chinese population. This study aimed to investigate the clinical and genetic profiles of 193 hemophilia patients from southern China. Utilizing Sanger sequencing, multiplex ligation-dependent probe amplification, gap detection, long-range PCR, and multiplex PCR, we identified both F8 and F9 gene variants. Pregnant women with a history of hemophilia A offspring underwent amniocentesis or villus sampling for the variant detection. Variants in F8 and F9 were pinpointed in 183 patients, with 26 being novel discoveries. Notably, genetic testing was absent in the initial evaluation of 133 out of 161 patients, leading to a protracted average definitive diagnosis timeline of 2 years. Remarkably, two hemophilia A cases with anticipated severe phenotypes due to protein-truncating variants presented with only moderate or mild clinical manifestations. Among the 40 fetuses tested, 34 were males, with 17 exhibiting hemizygous variants in the F8 gene. Our results contribute to the broader understanding of F8 and F9 variant spectrum and highlight the underuse of genetic analyses in southern China.

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.

Mutational Profiles of F8 and F9 in a Cohort of Haemophilia A and Haemophilia B Patients in the Multi-ethnic Malaysian Population

Background

Haemophilia A (HA) and Haemophilia B (HB) are X-linked blood disorders that are caused by various mutations in the factor VIII (F8) and factor IX (F9) genes respectively. Identification of mutations is essential as some of the mutations are associated with the development of inhibitors. This study is the first comprehensive study of the F8 mutational profile in Malaysia.

Materials and methods

We analysed 100 unrelated HA and 15 unrelated HB patients for genetic alterations in the F8 and F9 genes by using the long-range PCR, DNA sequencing, and the multiplex-ligation-dependent probe amplification assays. The prediction software was used to confirm the effects of these mutations on factor VIII and IX proteins.

Results

44 (53%) of the severe HA patients were positive for F8 intron 22 inversion, and three (3.6%) were positive for intron one inversion. There were 22 novel mutations in F8, including missense (8), frameshift (9), splice site (3), large deletion (1) and nonsense (1) mutations. In HB patients, four novel mutations were identified including the splice site (1), small deletion (1), large deletion (1) and missense (1) mutation.

Discussion

The mutational spectrum of F8 in Malaysian patients is heterogeneous, with a slightly higher frequency of intron 22 inversion in these severe HA patients when compared to other Asian populations. Identification of these mutational profiles in F8 and F9 genes among Malaysian patients will provide a useful reference for the early detection and diagnosis of HA and HB in the Malaysian population.

Spectrum of Molecular Defects in 216 Chinese Families With Hemophilia A: Identification of Noninversion Mutation Hot Spots and 42 Novel Mutations

Hemophilia A (HA) is an X-linked bleeding disorder caused by heterogeneous mutations in the factor VIII gene ( F8). Our aim is to identify the causative mutations in a large HA cohort from China. We studied 216 unrelated HA families. Molecular analyses of F8 were performed using a combination of molecular techniques, including polymerase chain reaction, direct sequencing, and multiplex ligation-dependent probe amplification. The deleterious consequences of the unreported missense mutations were evaluated using various bioinformatics approaches. Causative mutations in F8 were identified in 209 families, intron 22 inversion (Inv22) was identified in 89 severe families, and intron 1 inversion (Inv1) was positive in 5 severe families; 95 mutations were detected among 115 noninversion families, of which 42 were novel, including 29 null variations and 13 missense mutations for which causality was demonstrated via bioinformatics. Among the 53 previously reported mutations, more nonsense (5 of 9) and missense (10 of 26) mutation sites were found to occur at Arginine (Arg) sites and multiple small deletions/insertions (5 of 10) located within the poly-A runs of the B domain. The majority of these sequence variants frequently recurred in the database. The odds ratios for the likelihood of developing inhibitors significantly increased in the presence of nonsense mutation. Our F8 defect spectrum was heterogeneous. Small deletions/insertions in the poly-A runs of the B domain and nonsense and missense mutations at Arg sites were identified as mutation hot spots. Nonsense mutation increased the risk of developing inhibitors.

First report of molecular diagnosis of Tunisian hemophiliacs A: identification of 8 novel causative mutations

Introduction

Hemophilia A is an X linked recessive hemorrhagic disorder caused by mutations in the F8 gene that lead to qualitative and/or quantitative deficiencies of coagulation factor VIII (FVIII). Molecular diagnosis of hemophilia A is challenging because of the high number of different causative mutations that are distributed throughout the large F8 gene. Molecular studies of these mutations are essential in order to reinforce our understanding of their pathogenic effect responsible for the disorder.

Aim

In this study we have performed molecular analysis of 28 Tunisian hemophilia A patients and analyzed the F8 mutation spectrum.

Methods

We screened the presence of intron 22 and intron 1 inversion in severe hemophilia A patients by southern blotting and polymerase chain reaction (PCR). Detection of point mutations was performed by dHPLC/sequencing of the coding F8 gene region. We predict the potential functional consequences of novel missense mutations with bioinformatics approaches and mapping of their spatial positions on the available FVIII 3D structure.

Results

We identified 23 different mutations in 28 Tunisian hemophilia A patients belonging to 22 unrelated families. The identified mutations included 5 intron 22 inversions, 7 insertions, 4 deletions and 7 substitutions. In total 18 point mutations were identified, of which 9 are located in exon 14, the most mutated exonic sequence in the F8 gene. Among the 23 mutations, 8 are novel and not deposited in the HAMSTeRS database nor described in recently published articles.

Conclusion

The mutation spectrum of Tunisian hemophilia A patients is heterogeneous with the presence of some characteristic features.

Virtual slides

The virtual slide(s) for this article can be found here:

http://www.diagnosticpathology.diagnomx.eu/vs/1693269827490715

F8 gene mutation type and inhibitor development in patients with severe hemophilia A: systematic review and meta-analysis

This systematic review was designed to provide more precise effect estimates of inhibitor development for the various types of F8 gene mutations in patients with severe hemophilia A. The primary outcome was inhibitor development and the secondary outcome was high-titer-inhibitor development. A systematic literature search was performed to include cohort studies published in peer-reviewed journals with data on inhibitor incidences in the various F8 gene mutation types and a mutation detection rate of at least 80%. Pooled odds ratios (ORs) of inhibitor development for different types of F8 gene mutations were calculated with intron 22 inversion as the reference. Data were included from 30 studies on 5383 patients, including 1029 inhibitor patients. The inhibitor risk in large deletions and nonsense mutations was higher than in intron 22 inversions (pooled OR = 3.6, 95% confidence interval [95% CI], 2.3-5.7 and OR = 1.4, 95% CI, 1.1-1.8, respectively), the risk in intron 1 inversions and splice-site mutations was equal (pooled OR = 0.9; 95% CI, 0.6-1.5 and OR = 1.0; 95% CI, 0.6-1.5), and the risk in small deletions/insertions and missense mutations was lower (pooled OR = 0.5; 95% CI, 0.4-0.6 and OR = 0.3; 95% CI, 0.2-0.4, respectively). The relative risks for developing high titer inhibitors were similar.

Factor VIII gene mutations profile in 148 Chinese hemophilia A subjects

BACKGROUND

Hemophilia A (HA) is a common X-linked recessive bleeding disease caused by mutations in FVIII gene. The identification of mutation in HA subjects can lead to more accurate diagnosis and contribute to the genetic counseling/prenatal diagnosis.

OBJECTIVES

Our objective is to identify the FVIII defects in 148 unrelated Chinese HA subjects and to analyze the potential consequence of novel mutations.

METHODS

FVIII: C was assayed using one-stage method, and FVIII inhibitor was tested using Bethesda method. Intron 22 and 1 inversions were identified by PCR technique. Non-inversion mutations of FVIII gene were identified by direct sequencing. Novel mutations were further analyzed based on a B-domain deleted FVIII crystallographic structure and bioinformatics tools.

RESULTS

The intron 22 and 1 inversions affected 57 and three severe subjects, respectively. Sixty-seven different mutations were identified in non-inversion subjects including 35 novel mutations that were not reported previously. Novel mutations include five nonsense mutations, 15 missense mutations, three insertions, eight small deletions, two splice site mutations and two partial gene deletions. The potential deleterious effects of these novel missense mutations include disruption of the protein core, impairment of inter-domain interaction and FVIII binding with other proteins.

CONCLUSION

Similar to other races, intron 22 and one inversions are also recurrent mutation in severe HA subjects monitored in our centre. Sixty-seven mutations (52% novel reported) among 88 non-inversion subjects represent the high degree of heterogeneity of FVIII gene mutations causing HA. Characteristic of HA FVIII gene mutations extend our insight into structure-function relationship of the FVIII molecule.

Mosaicism and haemophilia

Mosaicism may affect the haemophilia phenotype. Well-known instances include chromosomal mosaicism due to aneuploidy and pseudo-mosaicism due to varying patterns of X-chromosome inactivation. Chromosomal mosaicism in a chimera is a potential source of phenotypic variation. Gene mosaicism is commonplace. Its pattern and effect depend on the stage of development at which a mutation occurs. Proven or possible genetic mosaicism is an important consideration when predicting the likelihood of transmission of haemophilia to a future generation.

Six years' experience performing RHD genotyping to confirm D- red blood cell units in Germany for preventing anti-D immunizations

BACKGROUND

Red blood cell (RBC) units of D+ donors are falsely labeled D- if regular serologic typing fails to detect low D antigen expression or chimerism. The limitations of serology can be overcome by molecular typing.

STUDY DESIGN AND METHODS

In January 2002, we introduced a polymerase chain reaction (PCR)-based assay for RHD as a routine test for first-time donors who typed D- by serologic methods including the indirect antiglobulin test. Samples were tested in pools of 20 for the RHD-specific polymorphism in Intron 4. RHD alleles were identified by PCR and nucleotide sequencing.

RESULTS

Within 6 years, 46,133 serologically D- first-time donors were screened for the RHD gene. The prevalence of RHD gene carriers detected by this method was 0.21 percent. Twenty-three RHD alleles were found of which 15 were new. Approximately one-half of the RHD gene carriers harbored alleles expressing a DEL phenotype resulting in a prevalence of 0.1 percent.

CONCLUSION

The integration of RHD genotyping into the routine screening program was practical. We report 6 years' experience of this donor testing policy, which is not performed in most transfusion services worldwide. RBC units of donors with DEL phenotype have been reported to anti-D immunize D- recipients. We transferred those donors to the D+ donor pool with the rationale of preventing anti-D immunizations, especially dreaded in pregnancies. For each population, it will be necessary to adapt the RHD genotyping strategy to the spectrum of prevalent alleles.

F8 gene mutation profile and ITT response in a cohort of Italian haemophilia A patients with inhibitors

Anti factor VIII (FVIII) antibodies represent the main complication of replacement therapy in severe cases of haemophilia and most patients with inhibitor have gross gene rearrangements or point mutations that hamper the production of normal circulating FVIII. In this study we have investigated 82 haemophilia A patients with inhibitors. Seventy six were severe, three were moderate and three were mild. We screened the patients for the causative mutations using long range PCR for the recurrent intron 22 inversion (invint22), multiplex PCR for intron 1 inversion (invint1) and conformation sensitive gel electrophoresis followed by DNA sequencing for all other mutation types in the F8 gene. Diverse genetic defects were detected in the severe cases (with a predominance of severe molecular defects): F8 gene inversions, large deletions and non-sense mutations account for 71% of the mutations. Only missense and splicing mutations were identified in the non-severe patients and we confirmed that the presence of inhibitors correlates well with the presence of severe mutations, but a proportion of severe patients develops inhibitors despite the presence of diverse less severe mutations. When we have analysed the subgroup of patients who underwent immunetolerance, we have found that F8 gene large deletions are likely to be a high risk factor also for immunetolerance therapy unresponsiveness, while no clear evidence has been demonstrated for other mutation types.

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.

Spectrum of mutations in Albanian patients with haemophilia A: identification of ten novel mutations in the factor VIII gene

Genetic analysis was carried out in 37 Albanian patients with haemophilia A. The factor VIII intron 22 inversion was detected only in 2/19 (10.5%) apparently unrelated patients with severe haemophilia A, while the intron 1 inversion was absent. A total of 19 different gene mutations were identified. Ten mutations were novel: four null mutations in severe haemophilia A patients (Gln1090X, Cys1832X, 2374delT, 5676insT) and six missense mutations (five in severe haemophilia A) (Ile76Thr, Leu299Pro, Asp525Glu, Cys692Tyr, His1755Leu and Trp1835Cys). None of these novel mutations occurred at CpG hotspots. These results further emphasize the extreme heterogeneity of the molecular basis of haemophilia A. The low prevalence of intron 22 inversion in Albanian patients with severe haemophilia A should be addressed by further studies.

Spectrum of molecular defects and mutation detection rate in patients with mild and moderate hemophilia A

The amount of residual F8 (FVIII:C) determines the clinical severity of hemophilia A. Recently, we showed that the mutation detection rate in severely affected male patients (FVIII:C<1% of normal) is virtually 100% when testing for the common intron 22-/intron 1- inversions and big deletions, followed by genomic sequencing of the F8 gene. Here we report on the spectrum of mutations and their distribution throughout the F8 gene sequence in 135 patients with moderate (n=23) or mild (n=112) hemophilia A. In contrast to the severe form of the disorder, analysis on the genomic level failed to detect the molecular defect in approximately 4% of the moderately and in approximately 12% of the mildly affected patients. A total of 36 of the mutations identified in this study are novel. The vast majority of the detected changes were missense. The newly detected amino acid substitutions were scored for potential distant or local conformational changes and influence on molecular stability for every single F8 domain with available structures, using homology modeling. Two molecular changes in the promoter region of the factor VIII gene (c.-112G>A and -219C>T), affecting the core segment (minimal promoter) were detected in two patients with mild hemophilia A. To our knowledge this is the first report on promoter mutations in the F8 gene.

Female hemophilia A heterozygous for a de novo frameshift and a novel missense mutation of factor VIII

BACKGROUND

Hemophilia A (HA) is an X-chromosome-linked recessive disorder.

AIM

We report the case of a female HA patient with a moderate decrease of factor (F) VIII activity and antigen (FVIII:C 3.4%, FVIII:Ag 4.2%) and severe bleeding symptoms.

METHODS

The patient's father had mild FVIII deficiency (FVIII:C 6.9%, FVIII:Ag 7.4%), and her mother had normal FVIII activity. The von Willebrand disease antigen and von Willebrand factor ristocetin cofactor activity were normal in all family members. The genomic DNA was extracted from the peripheral blood lymphocytes of the patient and her family members. Long-distance polymerase chain reaction (PCR) was employed to screen for the intron 22 inversion of the FVIII coding gene (F8). The F8 coding sequence was amplified with PCR and sequenced with an automatic sequencer.

RESULTS

Two heterozygous mutations were identified in the patient: one a substitution of nucleotide 5981T by C that leads to a missense mutation Leu1975Pro, and the other an insertion of an 'A' between nucleotides 3,637 and 3,638 (3637_3638insA) that shifts the reading frame and predicts a premature stop codon downward. The mutation Leu1975Pro was identified in the father's F8; however, 3637_3638insA was a de novo mutation that occurred in the patient's maternal-derived F8. Real-time PCR was applied to analyze the level of ectopically F8 gene transcripts in the peripheral lymphocytes of family members. The ectopic transcripts of F8 of the patient were less abundant than the normal control (patient:normal control ratio 0.67), whereas her parents showed no significant difference from the normal control.

CONCLUSION

The FVIII deficiency of the HA patient resulted from a de novo occurrence of a frameshift 3637_3638insA in her maternal-derived F8 and a novel missense mutation Leu1975Pro inherited from her father.

Mutation analysis in 51 patients with haemophilia A: report of 10 novel mutations and correlations between genotype and clinical phenotype

We report the results of genetic analysis on a series of 51 patients attending this Haemophilia Comprehensive Care Centre. The most common cause of severe haemophilia A--the factor VIII intron 22 inversion was detected in eight families and the factor VIII intron 1 inversion in three families. Mutation analysis was carried out on the remaining patients by nucleotide sequencing of genomic DNA after screening with conformation-sensitive gel electrophoresis (CSGE) or denaturing high-performance liquid chromatography (dHPLC). A total of 27 different FVIII non-inversion mutations were detected. Severe haemophilia was associated with 12 null mutations (six nonsense, six frameshift) and four missense mutations. A further 11 different missense mutations were associated with moderate or mild disease. To our knowledge, six null mutations [1950del 4(tttg), 3270-75insA, 4416del 10, 6735-38delA, W1029X, Y1792X] and four missense mutations (E1682K, M1947V, P2048L, P2143L) have not been previously published. Each novel missense mutation occurred at a highly conserved residue, no other candidate mutation was detected on screening the entire coding region of the FVIII gene and they were not detected in a screen of individuals without haemophilia A. The genotype-phenotype correlations of the FVIII mutations detected will be discussed.

Small FVIII gene rearrangements in 18 hemophilia A patients: five novel mutations

Hemophilia A (HA) is a disorder caused by mutations of the FVIII gene, which is located on the tip of the long arm of the X chromosome. In a cohort of 18 unrelated Italian patients affected with HA of varying severity, we performed mutational screening of the gene by denaturing high-performance liquid chromatography (DHPLC) and direct sequencing of abnormal peaks. We identified five novel mutations and 9 previously reported DNA alterations. Two of the 9 previously reported alterations were each common to 3 unrelated patients. Six different mutations were characterized as missense alterations, while 8 were non-missense mutations. Among the new gene alterations, one created a stop codon, one consisted of an out-of frame deletion, and one was a splice-site mutation. The last two were missense alterations. In an attempt to better understand the causative effect of the mutations and the clinical variability of the patients, we investigated the consequences of each missense mutation and visualized the effect of the amino acid change on structural FVIII models.