Informativeness of linkage analysis for genetic diagnosis of haemophilia A in India

The objective of this study was to assess the frequency of factor VIII (FVIII) gene intron 1 and intron 22 inversions and the informativeness of polymorphic markers for the genetic diagnosis of patients with haemophilia A (HA). Fifty unrelated patients with HA were first assessed for the intron 1 and intron 22 inversion mutations. Inversion-negative families were then screened for the bi-allelic intragenic markers--intron 7 G-->A polymorphism, HindIII site in intron 19 and XbaI site in intron 22 and the multiallelic dinucleotide CA repeat alleles in introns 13 and 22. The extragenic, multiallelic VNTR DXS52 (st14) was also analysed. Intron 22 inversion mutation was found in 38% (n = 19) of all patients and 46% of those with severe HA. Intron 1 inversion was found in one (2%) patient. Of the 30 inversion-negative families, XbaI site polymorphism was the single most informative marker (70%, n = 21/30) followed by HindIII (60%, n = 18/30), intron 13 CA repeats (56.66%, n = 17/30), intron 22 CA repeats (50%, n = 15/30), DXS52 VNTR (23.33%, n = 7/30) and intron 7 G-->A polymorphism (6.66%, n = 2/30). The combined use of these markers was informative in 92% (n = 46/50) of HA families. Based on the informativeness of these markers a comprehensive algorithm has been proposed for genetic diagnosis of HA in India.     

Prenatal diagnosis in haemophilia A: experience of the genetic diagnostic laboratory

The paper describes the experience of the Genetic Diagnostic Laboratory in prenatal testing for haemophilia A, an X‐linked recessive disease caused by mutations in the F8 gene. Knowledge of a familial mutation prior to pregnancy can benefit prenatal diagnosis and decrease wait time for molecular testing during pregnancy. This is a retrospective review of a series of pregnant women who pursued F8 gene testing from December 1997 through May 2012, highlighting three cases, which demonstrate the technical complexities of analysis and the implications of not knowing carrier status prior to pregnancy. Mutations of the F8 gene were detected in affected males, obligate female carriers and suspected female carriers by DNA sequencing, inverse‐PCR, qRT‐PCR, Southern blot and exonic dosage analysis. The same methods were used to analyse prenatal samples from obligate or suspected female carriers upon request. Maternal cell contamination studies were performed for all prenatal samples analysed. Ninety‐nine women pursued F8 testing during pregnancy, either for carrier status alone or carrier status and prenatal diagnosis. Ninety‐one women (91%) requested carrier testing because they did not know their F8 mutation carrier status prior to pregnancy. Eight women requested prenatal diagnosis only, and only 4 of these were aware of their mutation status. Thirty‐seven individuals were found to be mutation carriers. Forty‐two prenatal samples were received for prenatal diagnosis. In total 21 foetuses were identified as mutation carriers. Mutation detection was complex and increased the turnaround time in some cases. Only four of 99 women who submitted samples for F8 testing were aware of their F8 mutation status prior to pregnancy. Knowledge of F8 mutation status prior to pregnancy allows for efficient prenatal diagnosis, when desired. Thus, preconception genetic counselling is required to inform patients of the available options and the complex and time‐consuming nature of F8 testing.     

Ribosomal RNA analysis in the diagnosis of Diamond‐Blackfan Anaemia

Diamond‐Blackfan anaemia (DBA) is an inherited disease characterized by pure erythroid aplasia that has been tagged as a ‘ribosomopathy’. We report a multi‐centre study focused on the analysis of rRNA processing of 53 Italian DBA patients using capillary electrophoresis analysis of rRNA maturation of the 40S and 60S ribosomal subunits. The ratio of 28S/18S rRNA was higher in patients with mutated ribosomal proteins (RPs) of the small ribosomal subunit. In contrast, patients with mutated RPs of the large ribosomal subunit (RPLs) had a lower 28S/18S ratio. The assay reported here would be amenable for development as a diagnostic tool.     

Molecular analysis of F8 in Lebanese haemophilia A patients: novel mutations and phenotype–genotype correlation

Summary.  Haemophilia A (HA) is an X-linked recessive hereditary bleeding disorder affecting one in 5000 men, resulting from mutations in the F8 gene. Our objective was to identify the spectrum of mutations of the F8 gene in Lebanese patients, and to perform genotype/phenotype correlations. A group of 79 HA patients from 55 unrelated families was studied. Patients were screened for intron 22 and intron 1 inversion using PCR. In the absence of mutations in both introns, a dHPLC screening followed by a DNA sequencing of all coding regions was performed. When patients presented novel mutations, 150 control chromosomes were tested to exclude common polymorphisms. Large deletions were confirmed by MLPA technique. The mRNA was specifically studied whenever a splice site mutation was detected. In addition, studies of the putative biochemical function and FVIII 3D structures were conducted. Thirty-four mutations were identified in this study of which 21 were novel: 11 missense, two nonsense, two splice sites, five small deletions and one large deletion. Inhibitor found in three over 75 patients correlated with large deletion, intron 22 inversion, and nonsense mutations. We were able to identify all causative mutations in those HA patients. This knowledge represents a huge step for genetic counselling.     

Diagnosis and management challenges in patients with mild haemophilia A and discrepant FVIII measurements

Thirty per cent of patients with mild haemophilia A (MHA) present markedly different FVIII: C level when assayed by one‐stage clotting and two‐stage chromogenic assays. It is, therefore, a real clinical challenge to predict the individual bleeding risk of these patients. The aim of the present work was to study the relationship between the bleeding tendency of these patients with the results of a panel of phenotypic and genotypic tools. Thirty‐six patients with MHA were included in this multicentre prospective clinical study. The severity of bleeding symptoms was evaluated using the ISTH/SSC score. FVIII:C levels were measured using an activated partial thromboplastin time‐based one‐stage FVIII assay (FVIII: C1) and three commercial chromogenic kits (FVIII:CR). FVIII antigen levels, thrombin generation measurement and FVIII gene mutation analysis were also performed. Our results showed that a one‐stage FVIII: C assay cannot rule out the diagnosis of MHA, a combined use of FVIII:C1 with a FVIII:CR is suitable for detecting MHA. We observed that FVIII:CR results better reflected the clinical bleeding tendency of patients compared to FVIII:C1. We also observed a relationship between thrombin generation (TG) capacity and FVIII:CR of these patients. FVIII gene mutation analysis showed mutations previously reported in MHA patients with discrepant FVIII:C measurements, but with no predictive value of the individual bleeding phenotype of patients. Overall, we observed a relationship between chromogenic FVIII:C results, TG assay and bleeding tendency of patients with discrepant FVIII:C measurements, while FVIII:C1 was not well correlated with clinical bleeding phenotype in this particular population.     

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.     

A haemophilia A and B molecular genetic diagnostic programme in Hungary: a highly informative and cost-effective strategy

Our aim was to set up a protocol in order to provide carrier and prenatal diagnosis to Hungarian haemophilia A (HA) and B (HB) patients and their relatives. For HA, a combination of direct mutation detection and some indirect marker analyses were used: the detection of the inversion mutation and analysis of three polymorphisms, BclI, IVS13 (CA)n and P39(CA)n. In severe cases, direct mutation detection was performed first. In inversion-negative severe cases and in moderate and mild cases, indirect methods were used. For carrier and prenatal diagnosis in HB, four polymorphisms, DdeI, TaqI, XmnI, and HhaI were examined. Our DNA bank contains samples from 50 HA families (34 severe, 15 moderate and one mild) and seven HB families from different parts of the country. In 100% of the HA cases either the gene inversion and/or at least one of the polymorphisms was found to be informative for carrier or prenatal diagnosis. In the HB cases, an informative marker was found in 95% of the cases (19 of 20). We conclude that these strategies are sufficient to make genetic diagnosis available to almost all HA and HB families in the region. This approach is highly informative and cost-effective, so it can be very useful in countries where direct sequencing of genes for factor VIII and IX is not available for routine diagnosis.     

A modified I-PCR to detect the factor VIII Inv22 for genetic diagnosis and prenatal diagnosis in haemophilia A

To explore the effectiveness of modified inversion-polymerase chain reaction (I-PCR) to detect the factor VIII (FVIII) intron 22 inversion (Inv22) for genetic diagnosis and prenatal diagnosis in haemophilia A (HA). Both modified I-PCR and LD-PCR were applied to analyse the FVIII Inv22 for 24 patients with HA. Prenatal diagnosis was performed on six foetuses. Foetal blood samplings were carried out by cordocentesis from 22 to 26 weeks of gestation. Ten patients with FVIII Inv22 in 10 HA families were found, and the remaining 14 patients were found without the Inv22 in 19 HA families. Prenatal diagnosis confirmed that four foetuses were normal and all of them born normally. However, two foetuses had been identified as abnormal and undergone abortion. Compared with LD-PCR, modified I-PCR is more rapid and convenient for detecting the FVIII Inv22 in genetic diagnosis. It is recommended that a patient undergoes both modified I-PCR (to detect the FVIII Inv22) and biochemical assay (to measure the FVIII activity of umbilical cord blood) in prenatal diagnosis. When we have more experience, the DNA samples from chorionic villus or amniotic fluid can be analysed for prenatal diagnosis using the modified I-PCR alone.     

Feasibility of prenatal diagnosis and carrier detection in South African haemophilia A patients

The feasibility of DNA diagnosis for haemophilia A was tested in South African patients and families by screening for the common inversion mutation in the factor VIII gene and for the intragenic microsatellite markers in introns 13 and 22. The allele frequencies at the two microsatellite loci were significantly different, with informativity being higher in the Negroid (100%) than the Caucasoid group (67%). In severely affected haemophiliacs the inversion was found in 43% (6/14) of Negroids but in only 32% (13/41) of Caucasoids. Presence of a second common unidentified mutation may account for the low frequency in the latter. Haplotype analysis shows a disproportionately high frequency of an (AC)₂₀ intron 13–(AC)₂₆ intron 22 inversion negative Caucasoid haemophilia chromosome, supporting a founder effect.     

Usefulness of an in vitro cellular expression model for haemophilia A carrier diagnosis: illustration with five novel mutations in the F8 gene in women with isolated factor VIII:C deficiency

This study aims to determine the way to predict the haemophilia A (HA) carrier status and the potential severity in six females with low FVIII:C levels (<0.50 IU mL^?1), F8 gene variations and without family history of HA. Except p.Ser577Tyr, F8 gene variations that we reported have never been described (p.Leu107His, p.Pro521Leu, p.Val682Leu, p.Leu2032Pro, p.Ala315dup). Prediction of their potential causal impact was studied by two strategies: bioinformatics approaches and site‐directed mutagenesis followed by FVIII cellular expression into COS‐1 cell. FVIII clotting assay (FVIII:C) and antigen (FVIII:Ag) were assayed in vitro. In silico analysis showed the probably damaging effect of all substitutions and the full conservation of the residues across mammalian species, except for p.Leu2032Pro. The in vitro variant expression model showed abnormal intra and/or extracellular FVIII:C and FVIII:Ag levels for five mutations, which suggest their causality in HA and provide informations about the involved mechanism. We suspect a defect in synthesis and secretion for p.Leu107His, p.Ala315dup and p.Pro521Leu. The mutation p.Val682Leu only affects the FVIII function while p.Ser577Tyr alters function and synthesis. The variant p.Leu2032Pro is probably a polymorphism because no alteration of the FVIII protein expression was observed in vitro. In vitro results suggest that mutations p.Ser577Tyr and p.Ala315dup could led to a severe HA in men. This study demonstrates the ability of this in vitro cellular expression model to contribute to the diagnosis strategy for female suspected of being HA carrier, without HA family history and with a novel F8 gene variation and to provide new criteria for the genetic counselling.     

Prenatal diagnosis of recessive congenital methaemoglobinaemia type II: novel mutation in the NADH-cytochrome b5 reductase gene leading to stop codon read-through

A case of type II recessive congenital methaemoglobinaemia (RCM) observed in a Lebanese subject with a novel mutation in NADH-cytochrome b5 reductase gene is described. A homozygous mutation CAC to AA identified at Thr 295 with an out-of-frame 1-bp deletion leads to a frameshift with translational read-through of the natural stop codon. The molecular mechanism is demonstrated by an in vitro translation study. The model of mutated cytochrome b5 reductase protein possessing 46 additional amino acids was obtained by homology modelling. The mutation causes an alteration of hydrophobicity in the carboxyl-terminal portion, resulting in the conformation being drastically disturbed by the presence of 46 supplementary amino acids. The identical mutation was found in the heterozygous state in the patient's parents and sister. Identification of this new mutation enabled us to perform the molecular prenatal diagnosis of type II RCM at the DNA level.     

Factor (F)VIII/VIIa enhances global haemostatic function in the co‐presence of bypassing agents and FVIII among patients with haemophilia A with inhibitor

Bypassing therapy is essential for the haemostatic management of patients with haemophilia A with inhibitor (PWHA‐inh), but the therapeutic effects are inconsistent. We previously reported that activated prothrombin complex concentrates (aPCC) activated factor (F)VIIIin vitro, and was mediated mainly by the activated FVII (FVIIa) contained in aPCC. We have extended those studies to assess global coagulation in whole blood from 18 PWHA‐inh in the co‐presence of aPCC and FVIII using Ca²⁺‐triggered rotational thromboelastometry. The clot times (CTs) in the presence of both aPCC (0·05 iu/ml) and recombinant (r)FVIII (1 iu/ml) ex vivo were shortened compared to the aPCC alone (P < 0·01). These enhancing effects of rFVIII were observed, irrespective of recognizing inhibitor epitopes; however, the clot formation time and ‘α’‐angle were not significantly different. In samples from 7 PWHA‐inh post‐infusion of aPCC (70‐80 iu/kg), only the CTs were shortened in the presence of rFVIIIex vivo compared to its absence (P < 0·05), indicating that the enhanced activity centred on the initiation phase of coagulation. Furthermore, experiments in the co‐presence of rFVIIa and rFVIII demonstrated that FVIII accelerated only the CTs. We concluded that FVIII/FVIIa‐related coagulation mechanism enhanced global haemostatic function by the co‐presence of bypassing agents and FVIII in PWHA‐inh.     

Mutation spectrum and inhibitor risk in 100 Korean patients with severe haemophilia A

Haemophilia A (HA) is an X‐linked recessive bleeding disorder caused by defects in the F8 gene encoding the coagulation factor VIII. Mutation analysis in HA is important to confirm the diagnosis, genotype‐phenotype correlations and for genetic counselling and family study. The aim of this study was to detect causative mutations of F8 in severe HA patients in Korea and to correlate the mutation type with the risk of inhibitor development. A total of 100 unrelated Korean patients with severe HA were enrolled for this study. The Nijeman modification of the Bethesda assay was used to determine the presence of inhibitor. Molecular analysis of F8 was performed using a combination of molecular techniques, including long‐distance polymerase chain reaction, direct sequencing and multiplex ligation‐dependent probe amplification (MLPA). We identified causative mutations in 98% of severe HA patients (98/100). Inv22 and Inv1 mutations were detected in 30 patients and one patient, respectively. A total of 59 unique mutations were identified in 69 non‐inversion patients, including 24 novel mutations. The overall prevalence of inhibitor was 26%. Inhibitor risk was highest in patients with large deletion mutations identified using MLPA (100%). Among those with point mutations, the prevalence of inhibitor was highest when the mutation occurred in the A3 and C2 domains (60% and 50%, respectively). The molecular diagnostic strategy involving multiplex PCR, sequencing and dosage analyses identified causative mutations in most cases of severe HA. The high inhibitor risk was associated with large deletion mutations and point mutations in A3 and C2 domains.     

Genetic analysis in FXI deficiency: six novel mutations and the use of a polymerase chain reaction-based test to define a whole gene deletion

The genetic basis of factor XI (FXI) deficiency was investigated in 30 patients from 13 different families of non-Jewish origin. Twelve different mutations were detected (including six novel changes), seven missense mutations and three mutations leading to null alleles. Haplotype analysis suggested a large gene deletion in one family. We confirmed the presence of a recently reported Alu-mediated FXI gene deletion. An unrelated patient with severe deficiency was shown to be compound heterozygous for A412V and this whole gene deletion. We suggest that this recurrent gene deletion should be included in the genetic analysis of FXI deficiency.     

Characterization of F8 defects in haemophilia A in Pakistan: investigation of correlation between mutation type and the in vitro thrombin generation assay

Hereditary haemophilia A is an X‐linked bleeding disorder caused by mutations in the coagulation factor VIII gene (FVIII abbreviates protein, gene symbol F8). The mutation spectrum has been reported in various populations but not in Pakistan. The aims of this study were to (i) characterize F8 mutations in a large haemophilia A cohort from Pakistan and to (ii) investigate whether in vitro thrombin generation (TG) differs according to mutation type (null compared with missense) in severe haemophilia A. One hundred individuals diagnosed with haemophilia A and 100 healthy controls were recruited in Pakistan. Phenotypic measurements were re‐evaulated in Cardiff; the essential regions of F8 were screened for the causative defect. A diagnosis of haemophilia A was confirmed for 92 individuals, 7 were found to have haemophilia B and 1 did not have haemophilia. The F8 defects were characterized for 80 of the 92 haemophilia A individuals and comprised point mutations, inversions (intron 22 and intron 1) and frameshifts. Point mutations (41%) were the most frequent, followed by the intron 22 inversion (20%). Thirty novel variants were identified. Comparison of in vitro TG parameters [velocity index (VI) and peak] was made between severe individuals who had a null mutation (no FVIII) and those with a missense change (dysfunctional FVIII), no significant difference was observed. The spectrum of F8 defects in Pakistan is heterogenous; VI and peak in severe haemophilia A are not influenced by whether the underlying mutation gives rise to dysfunctional FVIII or no coagulation factor at all.