Genotyping of intron 22-related rearrangements of F8 by inverse-shifting PCR in Egyptian hemophilia A patients

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.

Genomic alterations in the F8 gene correlating with severe hemophilia A in Egyptian patients

Background

Hemophilia A (HA) is an inherited X‐linked recessive coagulation disorder caused by factor VIII (F8) deficiency. F8 rearrangements involving intron 22 (int22) and intron 1 (int1) account for almost half of severe HA phenotype also a hotspot exon 14 provides numerous mutational patterns. This study aims to identify F8 gene mutations among Egyptian HA patients.

Methods

DNA samples from 60 HA patients were screened for int22 and int1 rearrangements using simplified inverse shifting PCR (IS‐PCR) followed by exon 14 sequencing. Also, four uncharacterized patients were studied by targeted exome sequencing.

Results

In 33.3% of the studied patients, we identified three int22 rearrangements, three exon 14 mutations (two frameshift; one novel (NM_000132.3:c.2734_2735delAA, p.(N912Ffs*6)), a second reported mutation (NM_000132.3:c.3091_3094delAGAA, p.(K1031Lfs*9)), and one nonsense mutation (NM_000132.3:c.2440C>T, p.(R814*)). All identified mutations were detected in patients with severe HA phenotype. Targeted exome sequencing could not detect any known pathogenic variants.

Conclusion

Intron 22 rearrangement and exon 14 mutations correlate with most severe hemophilia A Egyptian patients.

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.

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.

Detection of F8 int22h inversions using digital droplet PCR and mile-post assays

BACKGROUND

Inversions involving intron 22 (Inv22) of F8 are detected in approximately 45% of all severe hemophilia A patients. Diagnosis is complicated by the large size of the ~9.5 kb int22h repeated sequence, which generates the inversions. Methods such as long-range polymerase chain reaction (PCR) and inverse-shifting PCR are currently used diagnostically, but suffer from low PCR efficiencies and are difficult to standardize.

OBJECTIVES

To design and validate a sensitive and robust assay for the detection of F8 int22h inversions.

METHODS

Digital droplet PCR using mile-post assays was used to investigate archival DNA samples.

RESULTS

The detection of linkage as a function of physical distance between loci was investigated using an anchor locus and mile-post loci at 1, 6, 12 and 15 kb distances from the anchor locus. The proportion of linked molecules decreased with increasing distance between loci and showed 30% to 40% linked molecules for loci 12 to15 kb apart. Mile-post assays specific for wild type and Inv22 type 1 and 2 chromosomes were then designed and optimized. All three assays showed high specificities and sensitivities, with coefficients of variation <5% for all assays. Analysis of 106 patients and 20 carrier mothers showed complete concordance with previously known mutation status. The analysis demonstrated the robustness of the assays versus input DNA concentration (6 ng and higher) and level of fragmentation.

CONCLUSIONS

Digital droplet PCR and mile-post assays can be used to detect F8 int22h inversions. The assay systems are technically simple to perform, highly efficient, and robust.

Direct and indirect gene diagnosis of hemophilia A pedigrees in the Chinese population

Hemophilia A (HA) is an X‑linked recessive hereditary disorder caused by defects in the coagulation factor VIII (FVIII) gene. In order to diagnose patients with presymptomatic HA and carriers, the present study conducted direct gene diagnosis for the common abnormalities in FVIII and subsequently performed indirect gene diagnosis for the other abnormalities in FVIII for Chinese HA pedigrees. Direct gene diagnosis was performed in 10 HA pedigrees using inverse shifting‑polymerase chain reaction to detect intron 22 inversion (inv22), intron 22 deletion, intron 22 duplication and inv1 of FVIII. Pedigrees with no detected mutations were further analyzed using indirect genetic diagnosis (haplotype linkage analysis), where the genetic markers of FVIII included one variable number of tandem repeat, seven short tandem repeats and three restriction fragment length polymorphisms. The results of three pedigrees were taken as examples. Pedigree 1 underwent direct gene diagnosis, which demonstrated that the proband was inv22 distal pattern hemophiliac and the mother was an inv22 distal pattern carrier. The other two pedigrees were subjected to indirect gene diagnosis. In pedigree 2, the detection of DXS52, 13(CA) n, DXS9901(GT) n, intron (int)18, int19 and int22 confirmed the proband's baby brother was normal, the proband's maternal aunt was a carrier and her baby son was normal. Detection of DXS9901(GT)n, int18, int19 and int22 in pedigree 3 demonstrated that the proband's maternal grandmother was not a carrier. As the maternal grandfather was not affected by the disease, it was deduced that a mutation of FVIII occurred in the proband's mother. The combination of direct and indirect gene diagnoses provides reliable evidence for the use of genetic counseling in HA pedigrees, particularly for screening presymptomatic males and female carriers with normal offspring.

Molecular cytogenetic characterization of five F8 complex rearrangements: utility for haemophilia A genetic counselling

BACKGROUND

Genomic inversions are usually balanced, but unusual patterns have been described in haemophilia A (HA) patients for intron 22 (Inv22) and intron 1 (Inv1) inversions leading to the hypothesis of more complex rearrangements involving deletions or duplications.

AIM

To characterize five abnormal patterns either in Southern blot and long-range PCR for Inv22 or in PCR for Inv1.

MATERIALS AND METHODS

All patients were studied using cytogenetic microarray analysis (CMA).

RESULTS

In all cases, CMA analysis found that each inversion was associated with complex Xq28 rearrangement. In three patients, CMA analysis showed large duplication ranging from 230 to 1302 kb and encompassing a various number of contiguous genes among which RAB39B. RAB39B duplication is a strong candidate gene for X-linked intellectual disability (XLID). Surprisingly, none of the severe HA patients with RAB39B duplication reported in this study or in the literature exhibited XLID. We hypothesise that F8 complex rearrangement down regulated RAB39B expression. In the two remaining patients, CMA analysis found Xq28 large deletion (from 285 to 522 kb). Moyamoya syndrome was strongly suspected in one of them who carried BRCC3 deletion.

CONCLUSION

Because several F8 neighbouring genes are associated with other pathologies such as XLID and cardiovascular disease, all HA patients where complex Xq28 rearrangement was suspected should be referred to a geneticist for possible utility of a pangenomic study. Such investigation should be carefully considered in genetic counselling in female carriers to assess the risk of transmitting severe HA with a "contiguous gene syndrome".

Genotyping of Intron Inversions and Point Mutations in Exon 14 of the FVIII Gene in Iranian Azeri Turkish Families with Hemophilia A

Hemophilia A (HA) is an inherited X-linked bleeding disorder caused by a variety of mutations that are distributed throughout the large FVIII gene (F8). The most common mutations in studied populations with severe HA are introns 22 and 1 inversions, gross exon deletions and point mutations in exon 14. The aim of this study was to define the frequency of these common mutations in Iranian population of Azeri Turkish in North West of Iran. Fifty patients with severe HA and forty-three female potential carriers were genotyped by inverse shifting polymerase chain reaction (IS-PCR), long-range PCR, multiplex PCR, and sequencing methods for the detection of Intron 22 and 1 inversions, gross exon deletions, and exon 14 point mutations, respectively. F8 intron 22 inversion was detected in 22 (44 %) out of 50 patients. Moreover, we detected one intron 1 inversion (2 %), and one point mutation in exon 14 (2 %). In this population, 52 % of the patients with hemophilia A did not show to carry a mutation in the analyzed regions by three mentioned methods. F8 intron 22 inversion was the major causative mutation in nearly 50 % of severe HA cases in an Azerbaijani Turkish population, which is similar to the incidence of other populations. IS-PCR is a robust, rapid, efficient, and cost-effective method for the genetic analysis of patients with severe HA and for HA carrier detection, especially in developing countries.

F8 intron 22 inversions and SNP rs73563631 in unrelated families with severe haemophilia A: clinical features and gene testing implications

Supplementary Material to this article is available online at www.thrombosis-online.com.

Validation and genotyping of multiple human polymorphic inversions mediated by inverted repeats reveals a high degree of recurrence

In recent years different types of structural variants (SVs) have been discovered in the human genome and their functional impact has become increasingly clear. Inversions, however, are poorly characterized and more difficult to study, especially those mediated by inverted repeats or segmental duplications. Here, we describe the results of a simple and fast inverse PCR (iPCR) protocol for high-throughput genotyping of a wide variety of inversions using a small amount of DNA. In particular, we analyzed 22 inversions predicted in humans ranging from 5.1 kb to 226 kb and mediated by inverted repeat sequences of 1.6-24 kb. First, we validated 17 of the 22 inversions in a panel of nine HapMap individuals from different populations, and we genotyped them in 68 additional individuals of European origin, with correct genetic transmission in ∼ 12 mother-father-child trios. Global inversion minor allele frequency varied between 1% and 49% and inversion genotypes were consistent with Hardy-Weinberg equilibrium. By analyzing the nucleotide variation and the haplotypes in these regions, we found that only four inversions have linked tag-SNPs and that in many cases there are multiple shared SNPs between standard and inverted chromosomes, suggesting an unexpected high degree of inversion recurrence during human evolution. iPCR was also used to check 16 of these inversions in four chimpanzees and two gorillas, and 10 showed both orientations either within or between species, providing additional support for their multiple origin. Finally, we have identified several inversions that include genes in the inverted or breakpoint regions, and at least one disrupts a potential coding gene. Thus, these results represent a significant advance in our understanding of inversion polymorphism in human populations and challenge the common view of a single origin of inversions, with important implications for inversion analysis in SNP-based studies.

First molecular analysis of F8 gene in algeria: identification of two novel mutations

The aim of this study was to detect the genetic alterations in the Factor 8 gene in 26 patients from Western Algeria. We detected the presence of "intron 22 inversion" with long-range polymerase chain reaction (PCR). Negative patients for this inversion were analyzed for "intron 1 inversion" using multiplex PCR. Patients who were negative for both inversions were analyzed using a direct sequencing. Deleterious effects of novel mutations on protein were assayed with bioinformatics tools. Causing mutations were identified in 85.71% of the families, including 11 "intron 22 inversion," 1 "intron 1 inversion," and 6 different point mutations (2 nonsense, 1 splice site, and 3 missense mutations). Among these mutations, c.2189G > A (p.Cys711Tyr) and c.5219+1G>T are novel. This is the first study that reports spectrum of mutations in the Factor 8 gene in the Western Algerian population. Knowledge of these mutations is important for genetic counseling and medical care of affected families.

Study of intron 22 inversion mutation in north India with review

The present study assessed the frequency of intron 22 inversion mutation (Inv 22) in north Indian population with a cost analysis of different methods used for Inv 22 detection. We assessed the frequency of intron 22 inversion mutation in a series of 181 cases with hemophilia A and also compared methods used for detection of the mutation including the long-distance PCR, Southern blot analysis, and inverse PCR in terms of cost, infrastructure, and technical input as well as turnaround time. The study group comprised 102 severe cases and 79 moderate cases of hemophilia A from a north Indian population of which 77 cases tested positive for Inv 22. The observed frequency of Inv22 mutation was 42.5%. Inv 22 resulted in a more severe phenotype and lower FVIII bioassay levels as compared to Inv 22 negative cases. Inv 22 positive cases also frequently presented with bleeding episodes at birth and the mean age for commencement of bleeding was lower (19 months) as compared to Inv-negative cases (50 months). The mean frequency of Inv 22 in cases with hemophilia A in a worldwide review is 44.25% of hemophilia A. Inv 22 can be conveniently detected by using the inverse PCR method. This technique is easy to standardize and lowest in cost.

A possible mechanism for Inv22-related F8 large deletions in severe hemophilia A patients with high responding factor VIII inhibitors

BACKGROUND

Intron 22 inversion (Inv22) of the coagulation factor (F)VIII gene (F8) is a frequent cause of severe hemophilia A. In addition to Inv22, a variety of F8 mutations (1492 unique mutations) causing hemophilia A have been reported, of which 171 involve deletions of over 50 bp (HAMSTeRs database; http://hadb.org.uk/). However, only 10% of these large deletions have been fully characterized at the nucleotide level.

PATIENTS AND METHODS

We investigated gene abnormalities in three unrelated severe hemophilia A patients with high titer FVIII inhibitors. They had previously been shown to carry large deletions of the F8, but the precise gene abnormalities remain to be elucidated.

RESULTS

Inverse shifting-PCR (IS-PCR) Inv22 diagnostic tests revealed that these patients carried either type I or II Inv22. However, they showed a wild-type (WT) pattern in the IS-PCR Inv22 complementary tests. We further analyzed their X chromosomes to account for the puzzling results, and found that they had different centromeric breakpoints in the Inv22 X chromosomes, adjacent to the palindromic regions containing int22h-2 or -3, and their spacer region, respectively. The connections appeared to be shifted towards the telomere of the WT F8 Xq28, resulting in a new telomere with an additional intact int22h copy.

CONCLUSIONS

These gene rearrangements might result from double-strand breaks in the most distal regions of the long arms of the Inv22 X chromosomes, followed by DNA restorations using the WT F8 Xq28 by non-homologous end joining or break-induced replication; thus leading to large F8 deletions in severe hemophilia A patients.

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

Eighteen years of molecular genotyping the hemophilia inversion hotspot: from southern blot to inverse shifting-PCR

The factor VIII gene (F8) intron 22 inversion (Inv22) is a paradigmatic duplicon-mediated rearrangement, found in about one half of patients with severe hemophilia A worldwide. The identification of this prevalent cause of hemophilia was delayed for nine years after the F8 characterization in 1984. The aim of this review is to present the wide diversity of practical approaches that have been developed for genotyping the Inv22 (and related int22h rearrangements) since discovery in 1993. The sequence- Southern blot, long distance-PCR and inverse shifting-PCR-for Inv22 genotyping is an interesting example of scientific ingenuity and evolution in order to resolve challenging molecular diagnostic problems.