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Background: Von Willebrand disease (VWD), the most prevalent hereditary bleeding disorder, results from deficiency of von Willebrand factor (VWF)., Objectives: This large cohort study aims to offer a comprehensive exploration of mutation spectra and laboratory features in quantitative VWF deficiencies, shedding light on genetic underpinnings and genotype-phenotype associations., Methods: Our cohort consisted of 221 Caucasian index patients with quantitative VWD, along with 47 individuals whose plasma VWF levels fell within the lower normal boundaries (50-70 IU/dL). We conducted comprehensive VWF assays and genetic analyses, encompassing VWF gene sequencing, copy number variation investigations, and bioinformatic assessments., Results: Following International Society on Thrombosis and Haemostasis-Scientific and Standardization Committee VWF guidelines, 77 index patients were characterized as having type 1 VWD (VWF antigen [VWF:Ag] < 30 IU/dL), 111 as having type 1 VWD (VWF:Ag, 30-50 IU/dL), and 33 as having type 3 VWD. Mutation detection rates were 88%, 65%, and 92%, respectively. Notably, blood group O overrepresentation was evident in type 1 with VWF:Ag of 30 to 50 IU/dL, particularly among mutation-negative patients, suggesting a potential causal role of blood group O. A total of 223 VWF variants, comprising 147 distinct variations, were identified in quantitative VWD patients, of which 57 were novel variants (39%). Additionally, approximately 70% of individuals with VWF levels within the lower normal boundaries (50-70 IU/dL) displayed VWF variants., Conclusion: Our data advance our understanding of the molecular mechanisms underlying quantitative VWD, offering valuable insights for future research and clinical management. Distinct mutation patterns were observed among subgroups, particularly the contrast between type 1 VWD (VWF:Ag < 30 IU/dL) and type 1 VWD (VWF:Ag, 30-50 IU/dL), an area with limited prior investigation., Competing Interests: Declaration of competing interests The authors declare that they have no conflicts of interest and do not have anything to disclose., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Vitamin K dependent coagulation factor deficiency type 1 (VKCFD1) is a rare hereditary bleeding disorder caused by mutations in γ-Glutamyl carboxylase ( GGCX ) gene. The GGCX enzyme catalyzes the γ-carboxylation of 15 different vitamin K dependent (VKD) proteins, which have function in blood coagulation, calcification, and cell signaling. Therefore, in addition to bleedings, some VKCFD1 patients develop diverse non-hemorrhagic phenotypes such as skin hyper-laxity, skeletal dysmorphologies, and/or cardiac defects. Recent studies showed that GGCX mutations differentially effect γ-carboxylation of VKD proteins, where clotting factors are sufficiently γ-carboxylated, but not certain non-hemostatic VKD proteins. This could be one reason for the development of diverse phenotypes. The major manifestation of non-hemorrhagic phenotypes in VKCFD1 patients are mineralization defects. Therefore, the mechanism of regulation of calcification by specific VKD proteins as matrix Gla protein (MGP) and Gla-rich protein (GRP) in physiological and pathological conditions is of high interest. This will also help to understand the patho-mechanism of VKCFD1 phenotypes and to deduce new treatment strategies. In the present review article, we have summarized the recent findings on the function of GRP and MGP and how these proteins influence the development of non-hemorrhagic phenotypes in VKCFD1 patients.

Inactivation of thrombin by the endogenous inhibitor antithrombin (AT) is a central mechanism in the regulation of hemostasis. This makes hereditary AT deficiency, which is caused by SERPINC1 gene mutations, a major thrombophilic risk factor. Aim of this study was to assess to what extent AT mutations impair thrombin inhibition kinetics. The study population included 36 thrombophilic patients with 19 different mutations and mean AT levels of 65% in a thrombin-based functional assay, and 26 healthy controls. To assess thrombin inhibition kinetics, thrombin (3.94 mU/mL final concentration) was added to citrated plasma. Subsequently, endogenous thrombin inhibition was stopped by addition of the reversible thrombin inhibitor argatroban and the amount of argatroban-complexed thrombin quantified using an oligonucleotide-based enzyme capture assay. The plasma half-life of human thrombin was significantly longer in patients with AT mutations than in the controls (119.9 versus 55.9 s). Moreover, it was disproportionately prolonged when compared with preparations of wild type AT in plasma, in whom a comparable thrombin half-life of 120.8 s was reached at a distinctly lower AT level of 20%. These findings may help to better understand the increased thrombotic risk of SERPINC1 mutations with near normal AT plasma levels in functional assays.

Background: Hemophilia A (HA) is associated with mutations in the F8 gene that expresses factor VIII (FVIII). Unexpectedly, HA also manifests in a small subset of individuals with no mutations (exonic or intronic) in their F8 gene. MicroRNAs (miRNAs) cause translational interference, affecting protein quality and stoichiometry. Here, by analyzing miRNAs of two patients from this subset, we evaluated miRNA-based FVIII suppression as a testable hypothesis to explain FVIII deficiency in patients with HA with no F8 gene mutations., Study Design and Methods: To test the hypothesis, miRNA sequencing from two patients with mild and moderate HA with no mutations in their F8 gene, followed by experimental verification, was used to identify a group of upregulated miRNAs in patients with HA compared to normal controls; with binding sites in the 3' untranslated region (UTR) of F8 messenger RNA (mRNA), a prerequisite for miRNA-based gene regulation. From this pool, miR-374b-5p and miR-30c-5p, known to be expressed in human liver, where FVIII is expressed, were subjected to extensive characterization., Results: In two cell lines that constitutively express FVIII, we demonstrated that overexpression of miR-374b or miR-30c decreased FVIII expression, while an miR-30c inhibitor partially restored FVIII expression., Conclusion: These data support a role for microRNAs in fine-tuning F8 gene regulation. Based on our findings, our current model suggests that in HA cases where the F8 gene is normal and is predicted to express normal levels of FVIII, F8 mRNA 3' UTR targeting miRNAs may be responsible for a FVIII-deficiency phenotype clinically manifesting as HA., (© 2019 AABB.)

Introduction: Type 3 von Willebrand disease (VWD), a severe autosomal recessive hereditary bleeding disorder, is described by the virtual absence of von Willebrand factor (VWF). In consanguineous populations, for example Pakistan, the disease is reported with a higher incidence rate than the worldwide prevalence., Aims: This study aims to characterize molecular pathology and clinical profile of type 3 VWD cohort of Pakistani origin., Methods: In total, 48 patients were enrolled in the current study. Initially, the index patients (IPs) were evaluated by a standardized questionnaire for recording bleeding manifestations and by performing conventional coagulation tests. The diagnosis of VWD type 3 was confirmed by VWF antigens less than 5 IU/dL. Direct sequencing of VWF gene (VWF) was carried out to identify causative gene variations. We evaluated the potential consequence of novel splice site and missense variations by predictive computational programs and in silico structural analysis., Results: VWF mutations were detected in 46 out of 48 IPs (95.8%), predominantly as homozygous variants. In total, twenty-nine different gene defects were characterized in this cohort from which 10 (34.5%) are novel. The majority of the mutations were null alleles (66%; including gene conversions, nonsense, splice site variations, small deletions and insertions), and 34% of them were missense substitutions., Conclusion: Herein, we reported for the first time, the pattern of gene defects in Pakistani type 3 VWD cohort. We identified a wide heterogeneous mutation spectrum along with variability in the type of bleeding episodes., (© 2019 John Wiley & Sons Ltd.)

One of the most common and unwanted side effects during oral anticoagulant therapy (OAT) is bleeding complications. In rare cases, vitamin K antagonist (VKA)-related bleeding events are associated with mutations affecting the F9 propeptide at amino acid position 37 due to a substitution of alanine to either valine or threonine. Based on our actual cohort of 18 patients, we update the knowledge on this rare phenotype and its origin. A founder mutation for both variants was reconfirmed by haplotype analysis of intronic and extragenic short tandem repeat (STR) polymorphisms with a higher prevalence in Switzerland than in other regions of Europe. Screening of healthy individuals for the presence of these F9 gene mutations did not identify any of these variants, thus proving the rare occurrence of this genotype. Furthermore, both variants were expressed in vitro and warfarin dose responses were studied. Our warfarin dose response analysis confirmed higher sensitivity of both variants to warfarin with the effect being more apparent for Ala37Thr. Thus, although F9 propeptide mutation-associated hypersensitivity to VKA is a rare phenomenon, awareness towards this bleeding phenotype is important to identify patients at risk.

Introduction: Congenital factor XIII (FXIII) deficiency is a rare, autosomal recessive bleeding disorder usually caused by mutations in the F13A1 gene that produce a severe quantitative (type I) deficiency of the FXIII-A subunit., Aim: To determine the genotypes of patients with severe FXIII-A deficiency treated with recombinant FXIII-A subunit (rFXIII-A 2 ) participating in three international efficacy and safety trials., Methods: We determined the genotypes of 73 patients in total; 32 had already undergone genotype analysis and were known to carry F13A1 mutations that have been previously reported in the literature. Mutation screening was performed in 41 patients with unknown genetic status using direct sequencing., Results: In total, 51 distinct mutations in 73 patients were identified. Two patients showed a phenotype of severe FXIII-A deficiency, despite having heterozygous missense mutations. Two siblings carried a missense mutation in the F13A1 gene (p.Ser296Arg) in combination with a novel, probably polymorphic variant of the F13B gene (p.Ser654Phe). Molecular modelling of five F13A1 novel missense mutations (p.Leu171Phe, p.Glu204Lys, p.Leu276Phe, p.Asp405His and p.Gly411Cys) predicted a damaging effect of these mutations on protein structure. Although five patients treated with rFXIII-A 2 had transient, low-titre, non-neutralizing anti-rFXIII antibodies, no patients developed FXIII-neutralizing antibodies (inhibitors)., Conclusion: The identified mutations are causally implicated in severe FXIII deficiency; however, they do not appear to increase the risk of neutralizing antibody development against rFXIII-A 2 ., (© 2017 John Wiley & Sons Ltd.)

Current screening methods for factor VIII gene (F8) mutations can reveal the causative alteration in the vast majority of haemophilia A patients. Yet, standard diagnostic methods fail in about 2% of cases. This study aimed at analysing the entire intronic sequences of the F8 gene in 15 haemophilia A patients by next generation sequencing. All patients had a mild to moderate phenotype and no mutation in the coding sequence and splice sites of the F8 gene could be diagnosed so far. Next generation sequencing data revealed 23 deep intronic candidate variants in several F8 introns, including six recurrent variants and three variants that have been described before. One patient additionally showed a deletion of 9.2 kb in intron 1, mediated by Alu-type repeats. Several bioinformatic tools were used to score the variants in comparison to known pathogenic F8 mutations in order to predict their deleteriousness. Pedigree analyses showed a correct segregation pattern for three of the presumptive mutations. In each of the 15 patients analysed, at least one deep intronic variant in the F8 gene was identified and predicted to alter F8 mRNA splicing. Reduced F8 mRNA levels and/or stability would be well compatible with the patients' mild to moderate haemophilia A phenotypes. The next generation sequencing approach used proved an efficient method to screen the complete F8 gene and could be applied as a one-stop sequencing method for molecular diagnostics of haemophilia A.

Glanzmann thrombasthenia (GT) is an autosomal recessive bleeding disorder characterised by quantitative and/or qualitative defects of the platelet glycoprotein (GP) IIb/IIIa complex, also called integrin αIIbβ3. αIIbβ3 is well known as a platelet fibrinogen receptor and mediates platelet aggregation, firm adhesion, and spreading. This study describes the molecular genetic analyses of 19 patients with GT who were diagnosed on the basis of clinical parameters and platelet analyses. The patients' bleeding signs include epistaxis, mucocutaneous bleeding, haematomas, petechiae, gastrointestinal bleeding, and menorrhagia. Homozygous or compound heterozygous mutations in ITGA2B or ITGB3 were identified as causing GT by sequencing of genomic DNA. All exons including exon/intron boundaries of both genes were analysed. In a patient with an intronic mutation, splicing of mRNA was analysed using reverse transcriptase (RT)-PCR of platelet-derived RNA. In short, 16 of 19 patients revealed 27 different mutations (ITGA2B: n=17, ITGB3: n=10). Seventeen of these mutations have not been published to date. Mutations in ITGA2B or ITGB3 were identified as causing GT in 16 patients. We detected a total of 27 mutations in ITGA2B and ITGB3 including 17 novel missense, nonsense, frameshift and splice site mutations. In addition, three patients revealed no molecular genetic anomalies in ITGA2B or ITGB3 that could explain the suspected diagnosis of GT. We assume that these patients may harbour defects in a regulatory element affecting the transcription of these genes, or other proteins may exist that are important for activating the αIIbβ3 complex that may be affected.

Functional limitations for the vitamin K cycle, caused either by mutations in gamma-glutamyl carboxylase or vitamin K epoxide reductase genes, result in hereditary deficiency of vitamin K-dependent coagulation factors (VKCFD1 and VKCFD2, respectively). Patients suffering from VKCFD often share several other anatomical irregularities which are not related to haemostasis. Here we report on nine patients, eight of them previously unreported, who presented with VKCFD1. All were examined with special attention to vitamin K-dependent coagulation factors as well as to bone and heart development and to other anatomical signs of embryonal vitamin K deficiency. In total, we detected ten mutations in the gamma-glutamyl carboxylase gene of which seven have not been previously reported. Most interestingly, additional non-bleeding phenotypes were observed in all patients including midfacial hypoplasia, premature osteoporosis, cochlear hearing loss, heart valve defects, pulmonary stenosis, or pseudoxanthoma elasticum-like phenotype. Undercarboxylated matrix Gla protein, osteocalcin, and periostin appear to be responsible for these defects which are also observed in cases of fetal warfarin syndrome., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

About 10% of mutations in haemophilia A cases generate a premature termination codon in the factor VIII gene (F8). Upon therapeutic FVIII substitution, it was noted that the risk of developing inhibitors is higher when the nonsense mutation is located in the light chain (LC) of the factor VIII (FVIII) protein than in the heavy chain (HC). We analysed the impact of six different nonsense mutations distributed over the six FVIII domains on recombinant FVIII expression to elucidate the process of inhibitor formation in haemophilic patients. Full-length F8 mRNA was transcribed from all constructs despite the presence of nonsense mutations. Polyclonal antigen assays revealed high antigen levels in transfection experiments with constructs truncated in LC whereas low antigen was detected from constructs truncated in HC. Those results were supported by FVIII localization experiments. These findings suggest that F8 transcription occurs in a usual way despite nonsense mutations, whereas translation appears to be interrupted by the premature stop codon. We hypothesize that the inclusion of the B domain enables proteins truncated in LC to accumulate in the ER. Proteins truncated in HC are mainly degraded or may pass through the ER and be secreted into the blood circulation, thus presumably preventing inhibitor formation after therapeutic FVIII substitution. The LC is known to have higher immunogenicity than the HC. Moreover, translation of the F8B gene comprising F8 exons 23-26 may be dependent on the position of the premature stop codon and thus contributes to the immune response of truncated FVIII proteins., (© 2014 John Wiley & Sons Ltd.)

Background: In a small group of typical hemophilia A (HA) patients no mutations in the F8 coding sequence (cDNA) could be found. In the current study, we performed a systematic screening of genetic and non-genetic parameters associated with reduced FVIII:C levels in a group of mostly mild HA (only one moderate) patients with no detectable mutations in F8 cDNA., Methods: We determined FVIII and VWF activity and antigen levels and performed VWF-FVIII binding (VWF:FVIIIB) and VWF-collagen binding assays (VWF:CB) as well as VWF multimer analysis. VWF was completely sequenced to exclude mutations. The F8 locus, including the introns, was sequenced using overlapping long-range PCRs (LR-PCRs) combined with a next generation sequencing (NGS) approach. Moreover, the F8 mRNA was analyzed quantitatively and qualitatively by real-time PCR (qRT) and overlapping reverse transcription (RT) PCRs, respectively., Results: All VWF tests were normal. The LR-PCRs demonstrated the integrity of the F8 locus. Eight unique polymorphisms were found in the patients, with two being recurrent. Furthermore, RT-PCRs analysis confirmed that two of the unique variants create detectable new cryptic splice sites in the patients that result in the introduction of intronic DNA sequences into the mRNA and create premature stop codons., Conclusion: By systematically excluding all possible causes of HA, we could with great certainty conclude that deep intronic mutations in F8, although rare, cause abnormal mRNA splicing, leading to mild HA., (© 2013 International Society on Thrombosis and Haemostasis.)

Mutation screenings in haemophilia A (HA) patients identified a great variety of mutations in the factor VIII gene (F8): intron 22 or intron 1 inversions, missense mutations, nonsense mutations, small or large deletions, insertions, duplications and splice site mutations. Mutations which do not result in amino acid substitutions (silent mutations) and intronic variants located outside the splice site consensus sequences cannot be easily classified as causative for HA. In these cases, special prediction software algorithms are applied to estimate their impact on splicing. Here, we present mRNA analysis of novel F8 mutations with possible impact on splicing in four HA patients with silent mutations and seven patients with intronic variants close to or within splice site consensus sequences. Seven of eleven mutations examined in vitro could be shown to have an effect on F8 mRNA splicing and the results were compared to in silico predictions. In addition, to validate the splice site prediction software Alamut v2.0 (Interactive Biosoftware), we compared published F8 mRNA analyses with the results of the in silico prediction. In general, the results of the splice site prediction tools of Alamut were in good accordance with the experimental F8 mRNA analyses, but a fundamental discrepancy between in silico and in vitro analyses was obtained in some cases. In conclusion, this study shows that the functional classification of potential splicing mutations should not only rely on prediction software, but be rather based on mRNA analysis experiments., (© 2012 Blackwell Publishing Ltd.)

Von Willebrand disease (VWD) is the most common inherited bleeding disorder caused by quantitative or qualitative defects of the von Willebrand factor (VWF). VWD is classified into three types--type 1 (partial quantitative deficiencies), type 2 (qualitative defects) and type 3 (complete deficiency of VWF). In this study we explored genotype and phenotype characteristics of patients with VWD with the aim of dissecting the distribution of mutations in different types of VWD. One hundred fourteen patients belonging to 78 families diagnosed to have VWD were studied. Mutation analysis was performed by direct sequencing of the VWF . Large deletions were investigated by multiplex ligation-dependent probe amplification (MLPA) analysis. The impact of novel candidate missense mutations and potential splice site mutations was predicted by in silico assessments. We identified mutations in 66 index patients (IPs) (84.6%). Mutation detection rate was 68%, 94% and 94% for VWD type 1, 2 and 3, respectively. In total, 68 different putative mutations were detected comprising 37 missense mutations (54.4%), 10 small deletions (14.7%), two small insertions (2.9%), seven nonsense mutations (10.3%), five splice-site mutations (7.4%), six large deletions (8.8%) and one silent mutation (1.5%). Twenty-six of these mutations were novel. Furthermore, in type 1 and type 2 VWD, the majority of identified mutations (74% vs. 88.1%) were missense substitutions while mutations in type 3 VWD mostly caused null alleles (82%). Genotyping in VWD is a helpful tool to further elucidate the pathogenesis of VWD and to establish the relationship between genotype and phenotype.

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.

Mutational reports over the past two decades have accumulated an immense amount of literature for inherited Factor XIII deficiency. However, the genotype and phenotype correlations for inherited Factor XIII deficiency are complicated. While many studies clearly prove a cause and effect relationship for the reported mutations, others are lacking in this regard. The F13B gene remains an elusive component as far as inherited Factor XIII deficiencies are concerned. Also, an in-depth analysis into the heterozygous state of this deficiency is also lacking. In this review we have tried to analyze and present an exhaustive amount of mutational data from the past three decades. The source of our mutational data is our website dedicated to Factor XIII deficiencies (www.F13-database.de) as well as literature search done on the Pubmed (www.ncbi.nlm.nih.gov/pubmed)., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Antithrombin (AT) is the most important physiological inhibitor of coagulation proteases. It is activated by glycosaminoglycans such as heparin. Hereditary antithrombin deficiency is a rare disease that is mainly associated with venous thromboembolism. So far, more than 200 different mutations in the antithrombin gene (SERPINC1) have been described. The aim of our study was to characterise the molecular background in a large cohort of patients with AT deficiency. Mutation analysis was performed by direct sequencing of SERPINC1 in 272 AT-deficient patients. Large deletions were identified by multiplex PCR coupled with liquid chromatography or multiplex ligation-dependent probe amplification (MLPA) analysis. To predict the effect of SERPINC1 sequence variations on the pathogenesis of AT deficiency, in silico assessments, multiple sequence alignment, and molecular graphic imaging were performed. The mutation profile consisted of 59% missense, 10% nonsense, 8% splice site mutations, 15% small deletions/insertions/duplications, and 8% large deletions. Altogether 87 different mutations, including 42 novel mutations (22 missense and 20 null mutations), were identified. Of the novel missense mutations, nine are suspected to impair the conformational changes that are needed for AT activation, two to affect the central reactive loop or the heparin binding site, and six to impair the structural integrity of the molecule. Despite the heterogeneous background of AT deficiency, 10 AT variants occurred in multiple index patients. Characterisation of the SERPINC1 mutation profile in large cohorts of patients may help to further elucidate the pathogenesis of AT deficiency and to establish genotype-phenotype associations.

Female carriers of haemophilia might suffer from increased bleeding tendency therefore the assessment of the bleeding risk is very important for improving care. This single-centre study documents the occurrence of bleedings in 46 carriers of haemophilia A including bleeding after tooth extraction (77%), easy bruising (67%), postsurgical bleeding (61%), menorrhagia (50%) or prolonged postpartum bleeding (43%). The F8 gene mutation of all 46 carriers (median age: 36.5 years, 15-80 years; mean FVIII:C activity: 59 ± 24.45%; normal range: 64-167%) was determined, and family history of haemophilia was recorded. For analysis, the bleeding tendency of the carriers was differentiated by severity into three groups. There was no statistically significant difference of FVIII:C between these groups. However, a correlation was found between the severity of bleeding tendency and the type of F8 gene mutation (P < 0.05) as well as the severity of haemophilia in affected male relatives (P < 0.0005). Results show that even carriers with a FVIII:C activity as high as 50-60% are at increased risk of bleeding. Incidence and intensity of bleeding symptoms of haemophilia A carriers are high and correlated with the phenotype of the male haemophilic relative and the underlying F8 gene mutation., (© 2010 Blackwell Publishing Ltd.)

Severe factor XIII (FXIII) deficiency is a rare autosomal recessive coagulation disorder affecting one in two million individuals. The aim of the present study was to screen for and analyse F13B gene defects in the German population. A total of 150 patients presenting with suspected FXIII deficiency and one patient with severe (homozygous) FXIII deficiency were screened for mutations in F13A and F13B genes. Twenty-five individuals presented with detectable heterozygous mutations, 12 of them in the F13A gene and 13 of them in the F13B gene. We report on the genotype-phenotype correlations of the individuals showing defects in the F13B gene. Direct sequencing revealed 12 unique mutations including seven missense mutations (Cys5Arg, Ile81Asn, Leu116Phe, Val217Ile, Cys316Phe, Val401Glu, Pro428Ser), two splice site mutations (IVS2-1G>C, IVS3-1G>C), two insertions (c.1155&#95;1158dupACTT, c.1959insT) and one in-frame deletion (c.471-473delATT). Two of the missense mutations (Cys5Arg, Cys316Phe) eliminated disulphide bonds (Cys5-Cys56, Cys316-Cys358). Another three missense mutations, (Leu116Phe, Val401Glu, Pro428Ser) were located proximal to other cysteine disulphide bonds, therefore indicating that the region in and around these disulphide bonds is prone to functionally relevant mutations in the FXIII-B subunit. The present study reports on a fairly common prevalence of F13B gene defects in the German population. The regions in and around the cysteine disulphide bonds in the FXIII-B protein may be regions prone to frequent mutations.

Background: Severe hereditary coagulation factor XIII deficiency is a rare homozygous bleeding disorder affecting one person in every two million individuals. In contrast, heterozygous factor XIII deficiency is more common, but usually not associated with severe hemorrhage such as intracranial bleeding or hemarthrosis. In most cases, the disease is caused by F13A gene mutations. Causative mutations associated with the F13B gene are rarer., Design and Methods: We analyzed ten index patients and three relatives for factor XIII activity using a photometric assay and sequenced their F13A and F13B genes. Additionally, structural analysis of the wild-type protein structure from a previously reported X-ray crystallographic model identified potential structural and functional effects of the missense mutations., Results: All individuals except one were heterozygous for factor XIIIA mutations (average factor XIII activity 51%), while the remaining homozygous individual was found to have severe factor XIII deficiency (<5% of normal factor XIII activity). Eight of the 12 heterozygous patients exhibited a bleeding tendency upon provocation., Conclusions: The identified missense (Pro289Arg, Arg611His, Asp668Gly) and nonsense (Gly390X, Trp664X) mutations are causative for factor XIII deficiency. A Gly592Ser variant identified in three unrelated index patients, as well as in 200 healthy controls (minor allele frequency 0.005), and two further Tyr167Cys and Arg540Gln variants, represent possible candidates for rare F13A gene polymorphisms since they apparently do not have a significant influence on the structure of the factor XIIIA protein. Future in vitro expression studies of the factor XIII mutations are required to confirm their pathological mechanisms.

Human coagulation factor V (FV), a non-enzymatic cofactor of the prothrombinase complex, is required for the rapid generation of thrombin. FV deficiency is a rare autosomal recessive bleeding disorder. We describe two novel mutations, Tyr91Asn and Asp2098Tyr, found in two probands with a residual FV activity of 51% and 4%, respectively. Modelling and structural analysis of these mutations were performed following short-duration molecular dynamics (MD) simulation. Asp2098Tyr lead to abolishment of the highly conserved salt bridge Asp2098-Arg2171 presumably required for structural integrity of the C2 domain. MD studies suggest that additional conformational changes resulting from this mutation involve local rearrangements at Tyr2063 and Tyr2064 and so affect the phospholipid-membrane binding. MD modelling of the Try91Asn mutant revealed a conformational change nearby the Cu(2+) binding site that could affect overall stabilization of the heavy and light chains. These findings suggest that both mutations influence the structural integrity of FV protein. Transient expression data of wild-type and mutant FV variants in 293T human embryonic kidney cells showed FV-specific activity reduced to 26% for Asp2098Tyr and 56% for Tyr91Asn compared to that of wild-type. Thus, both the data from the short duration molecular dynamic simulation and from expression analysis indicate alterations of the FV protein variants that explain the clinical phenotype.

Question Under Study: In most countries hypersensitivity to vitamin K antagonists (VKA) is considered to be a rare congenital bleeding diathesis. It occurs in patients with FIX propeptide mutations at locus -10. We present a Swiss family with two patients who suffered major bleedings under oral anticoagulant treatment in the presence of therapeutic or subtherapeutic INR levels and abnormally prolonged aPTT. In both patients a mutation in the propeptide of FIX at locus -10 with substitution of alanine by threonine (Ala-10Thr) was found. In one patient FIX clotting activity was found to be severely reduced (2%). The observed bleeding tendency is related to this--compared to the other vitamin K dependent factors (FII, FVII, FX)--excessively and disproportionately low level of FIX. Three generations of this family were tested for propeptide mutations, which are transmitted in an X-chromosomal recessive mode of inheritance. Apart from the two symptomatic male patients we found another male with the mutation who has not been exposed to VKA, six female carriers and four potential male carriers in the fourth generation who have not been tested. A founder effect for this mutation has been previously described for cases in Switzerland and Germany., Conclusion: FIX propeptide mutation-associated hypersensitivity to VKA is a rare occurrence in Switzerland. The severity of associated bleeding complications and the reversible nature of the bleeding diathesis may nonetheless warrant increased awareness on the part of primary care physicians in Switzerland.

Hereditary angioedema (HAE) is an autosomal dominant disease that manifests as intermittent acute swellings of the skin and mucosal surfaces, which, in the gastrointestinal tract and larynx, may even be fatal. HAE results from functional deficiency of the C1 inhibitor (C1INH) protein, which plays a key role in the classical pathway of complement activation. C1INH is the sole inhibitor of the activated proteases C1r and C1s, and is the major regulator of activated coagulation Factor XII and plasma kallikrein, which limits the generation of the vasoactive peptide bradykinin. In this paper, we report on the genetic analysis of 173 families (including 326 members) with a clinical diagnosis of HAE. Direct sequencing, Southern blotting and quantitative PCR by the MLPA method were used to screen for mutations in C1INH (SERPING1). In 142 families (82.1%), a causative C1INH gene mutation could be identified. A total of 80 novel point mutations of C1INH not published previously were detected in 96 pedigrees (including 172 members). Our results corroborate C1INH (SERPING1) deficiency as a disease of extreme allelic heterogeneity with almost each individual family carrying their own mutation. Routine molecular genetic analysis is an effective way of confirming the clinical diagnosis and identifying mutation carriers early on before any clinical manifestation becomes apparent. It is, therefore, a valuable tool in prevention and adequate treatment of acute and life-threatening oedema., (Copyright 2008 S. Karger AG, Basel.)

Factor XIII (FXIII) deficiency is a very rare (1:2 000 000) severe autosomal recessive bleeding disorder, mostly due to mutations in the coagulation FXIII A-subunit gene. We have studied the molecular basis of FXIII deficiency in five unrelated Italian families. The coding region, intron-exon boundaries and 5'- and 3'-untranslated regions of the FXIII gene encoding the A subunit were amplified and directly sequenced. Candidate mutations were identified in all the patients. Three novel mutations occurred in three patients. These include a novel homozygous deletion of two base pairs (bp) in exon 14 (c.2002-2003 DelCT). This deletion causes a frameshift from Leu667 and the formation of a stop codon at amino acid position 681. The second patient presents a novel homozygous (c.2126 G>A) transition in exon 15, predicting a Ser708Asn in Barrel 2 domain. The third patient is compound heterozygote for two missense mutations, a previously reported Arg260His substitution, and a novel transition in exon 4 (c.560 C>T) predicting a Pro186Leu in the core domain. The remaining two patients have two previously reported mutations: a 4-bp homozygous deletion in exon 11 (c.1392-1395 Del AATT), previously reported to occur in the Vicenza Area, and a homozygous nonsense mutation in exon 8 (c.979 C>T) predicting an Arg326X in the core domain. The novel mutations occurred at amino acid residues highly conserved among different species (pig, monkey, mouse and dog) and were not detected in 110 normal alleles. Structural analysis shows that Pro186Leu mutation leads to the replacement of the rigid proline pyrrolidine ring by the larger and more flexible leucine side chain and Ser708Asn may probably disrupt the hydrogen bond with Ala291.

For decades coumarins have been the most commonly prescribed drugs for therapy and prophylaxis of thromboembolic conditions. Despite the limitation of their narrow therapeutic dosage window, the broad variation of intra- and inter-individual drug requirement, and the relatively high incidence of bleeding complications, prescriptions for coumarins are increasing due to the aging populations in industrialised countries. The identification of the molecular target of coumarins, VKORC1, has greatly improved the understanding of coumarin treatment and illuminated new perspectives for a safer and more individualized oral anticoagulation therapy. Mutations and SNPs within the translated and non-translated regions of the VKORC1 gene have been shown to cause coumarin resistance and sensitivity, respectively. Besides the known CYP2C9 variants that affect coumarin metabolism, the haplotype VKORC1*2 representing a frequent SNP within the VKORC1 promoter has been identified as a major determinant of coumarin sensitivity, reducing VKORC1 enzyme activity to 50% of wild type. Homozygous carriers of the VKORC1*2 allele are strongly predisposed to coumarin sensitivity. Using individualized dose adaptation, a significant reduction of bleeding complications can be expected, especially in the initial drug saturation phase. Furthermore, concomitant application of low dose vitamin K may significantly reduce intra-individual coumarin dose variation and, thus, may stabilize oral anticoagulation therapy. The use of new pharmacogenetics-based dosing schemes and the concomitant application of low-dose vitamin K with coumarins will decidedly influence the current practice of oral anticoagulation and greatly improve coumarin drug safety.

Inherited factor XIII (FXIII) deficiency is known as one of the most rare blood coagulation disorder in humans. In the present study, phenotype and genotype of eight FXIII deficient Polish patients from five unrelated families were compared. The patients presented with a severe phenotype demonstrated by a high incidence of intracerebral haemorrhages (seven of eight patients), haemarthrosis (six patients) and bleeding due to trauma (five patients). Introduction of regular substitution with FXIII concentrate prevented spontaneous bleeding in seven patients. In all patients, mutations within the F13A gene have been identified revealing four missense mutations (Arg77Cys, Arg260Cys, Ala378Pro, Gly420Ser), one nonsense mutation (Arg661X), one splice site mutation (IVS5-1 G>A) and one small deletion (c.499-512del). One homozygous large deletion involving exon 15 was detected by failure of PCR product. The corresponding mutations resulted in severely reduced FXIII activity and FXIII A-subunit antigen concentration, while FXIII B-subunit antigen remained normal or mildly decreased. Structural analysis demonstrated that the novel Ala378Pro mutation may cause a disruption of the FXIII catalytic triad leading to a non-functional protein which presumably undergoes premature degradation. In conclusion, the severe phenotype with high incidence of intracranial bleeding and haemarthrosis was in accordance with laboratory findings on FXIII and with severe molecular defects of the F13A gene.

Acquired imatinib resistance in advanced Philadelphia-positive acute lymphoblastic leukemia (Ph(+) ALL) has been associated with mutations in the kinase domain (KD) of BCR-ABL. We examined the prevalence of KD mutations in newly diagnosed and imatinib-naive Ph(+) ALL patients and assessed their clinical relevance in the setting of uniform frontline therapy with imatinib in combination with chemotherapy. Patients enrolled in the German Multicenter Study Group for Adult Acute Lymphoblastic Leukemia (GMALL) trial ADE10 for newly diagnosed elderly Ph(+) ALL were retrospectively examined for the presence of BCR-ABL KD mutations by denaturing high-performance liquid chromatography (D-HPLC), cDNA sequencing, and allele-specific polymerase chain reaction (PCR). A KD mutation was detected in a minor subpopulation of leukemic cells in 40% of newly diagnosed and imatinib-naive patients. At relapse, the dominant cell clone harbored an identical mutation in 90% of cases, the overall prevalence of mutations at relapse was 80%. P-loop mutations predominated and were not associated with an inferior hematologic or molecular remission rate or shorter remission duration compared with unmutated BCR-ABL. BCR-ABL mutations conferring high-level imatinib resistance are present in a substantial proportion of patients with de novo Ph(+) ALL and eventually give rise to relapse. This provides a rationale for the frontline use of kinase inhibitors active against these BCR-ABL mutants.

FXIII deficiency is known as one of the rarest blood coagulation disorders. In this study, the phenotypic and in part genotypic data of 104 FXIII-deficient patients recorded from 1993 - 2005 are presented. The most common bleeding symptoms were subcutaneous bleeding (57%) followed by delayed umbilical cord bleeding (56%), muscle hematoma (49%), hemorrhage after surgery (40%), hemarthrosis (36%), and intracerebral bleeding (34%). Prophylactic treatment was initiated in about 70% of all patients. FXIII-B subunit-deficient patients had a milder phenotype than patients with FXIII-A subunit deficiency. The most frequent mutation affecting the F13A gene was a splice site mutation in intron 5 (IVS5-1G>A). This mutation was found in eight (17%) of 46 analyzed families. The haplotype analysis of patients carrying the IVS5-1A allele was consistent with a founder effect. The international registry (http://www.f13-database.de) will provide clinicians and scientists working on FXIII deficiency with a helpful tool to improve patient care and direct future studies towards better understanding and treatment of the disease.

Background: The null phenotype of the Lutheran blood group system, Lu(null) or Lu(a-b-), is characterized by the lack of all Lutheran system antigens. It can arise from three genetic backgrounds: recessive, dominant, or X-linked. Lu(null) of the recessive type appears to result from homozygosity for an inactive LU gene., Study Design and Methods: Three unrelated recessive Lu(null) individuals were assessed by standard serologic tests. All exons of the LU gene were directly sequenced from amplified genomic DNA. The validity of the observed mutations within the LU gene was confirmed by the use of either restriction enzymes or allele-specific primers., Results: All three individuals had the serologic characteristics of recessive Lu(null). One individual was doubly heterozygous for a nonsense mutation 691C>T in exon 6 (Arg231STOP) and a deletion of LU exons 3 and 4. The other two samples showed homozygous nonsense mutations: one had 711C>A in exon 6 (Cys237STOP) and the other 361C>T in exon 3 (Arg121STOP)., Conclusions: The results revealed four unique genetic backgrounds from three examples of the rare recessive Lu(null) phenotype, each encoding Lutheran glycoproteins with a disrupted structure.

The formation of alloantibodies against factor VIII (FVIII) or factor IX (FIX) is the most severe complication of replacement therapy in patients with haemophilia. In the last decade, genetic factors have been shown to constitute a decisive risk determinant for the development of inhibitors. In severe haemophilia A and B, mutations that result in an absent or truncated FVIII/FIX protein are associated with a 20-80% risk of inhibitor formation. In mild to moderate haemophilia, missense mutations represent the main mutation type, with an inhibitor prevalence of 5%. These patients synthesize some endogenous, although non-functional protein that is sufficient to induce immune tolerance. However, in patients with missense mutations clustered in the A2 and C2 domains (C1/C2 junction), the risk of inhibitor formation is fourfold greater than in patients with mutations outside this region, indicating that inhibitor prevalence in missense mutations is also dependent on localization of the mutation. Recently, a significant association between inhibitor formation and polymorphisms in genes coding for cytokines (IL-10) and other immunoregulatory factors (TNF-alpha) has been shown. These genetic factors constitute the individual genetic risk profile of a haemophilic patient. This risk is imprinted and fixed; however, environmental factors such as treatment schedule may increase or decrease the inhibitor risk in an individual patient. Improved understanding of these complex interactions may lead to the development of preventive measures to minimize inhibitor formation.

An imprinting disorder has been believed to underlie the etiology of familial biparental hydatidiform moles (HMs) based on the abnormal methylation or expression of imprinted genes in molar tissues. However, the extent of the epigenetic defect in these tissues and the developmental stage at which the disorder begins have been poorly defined. In this study, we assessed the extent of abnormal DNA methylation in two HMs caused by mutations in the recently identified 19q13.4 gene, NALP7. We demonstrate normal postzygotic DNA methylation patterns at major repetitive and long interspersed nuclear elements (LINEs), genes on the inactive X-chromosome, three-cancer related genes, and CpG rich regions surrounding the PEG3 differentially methylated region (DMR). Our data provide a comprehensive assessment of DNA methylation in familial molar tissues and indicate that abnormal DNA methylation in these tissues is restricted to imprinted DMRs. The known role of NALP7 in apoptosis and inflammation pinpoints previously unrecognized pathways that could directly or indirectly underlie the abnormal methylation of imprinted genes in molar tissues.

The most common cause for severe cases of hemophilia A is the homologous recombination involving intron 22 and related sequences outside the F8 gene. F8 coding regions of the gene including the exon/intron junctions were sequenced in 10 Turkish hemophilia A patients all of whom have been typed negative for intron 22 inversion and who did not have a detectable change by DGGE analysis. Pathological changes including two novel deletions (c. 205del CT and c. 3699del ACAT), one novel missense mutation (9546A) and two recurrent missense mutations were observed in five patients. The c. 2110C > T is another novel pathological change affecting exonic splicing enhancer site in two patients. One of the remaining three patients had a recurrent vWD type 2N mutation in the F8 binding site of the vWF (C788R). The S1269S polymorphism (c. 3864A > C) detected phenotype. Conclusively, sequencing of the promoter and the coding regions of 10 hemophilia A patients contributes four novel pathological mutations to the F8 mutations list and reveals a rediagnosis of hemophilia A but is still not sufficient to confirm hemophilia A phenotype in two patients.

Hemophilia A (HA) is caused by partial or total deficiency of F8 protein activity. In a small group, about 1.8% of patients with HA, no mutation is found in the F8 gene. Among this group, we report here on one patient with severe HA in whom no mRNA of the F8 gene was detected. Using 2 common polymorphisms in F8 exon 14, we were able to show that the same allele shared by the patient, his mother, and his sister was not detected by reverse transcription-polymerase chain reaction (RT-PCR) from total blood mRNA. Skewed X-chromosome inactivation in both the mother and the sister was excluded by studying the methylation profile of the androgen receptor gene (HUMARA locus). These findings strongly suggest that the cause of HA in this patient is either absence or rapid degradation of the F8 mRNA, which points to a novel mechanism leading to HA.

Anticoagulant compounds, i.e., derivatives of either 4-hydroxycoumarin (e.g., warfarin, bromadiolone) or indane-1,3-dione (e.g., diphacinone, chlorophacinone), have been in worldwide use as rodenticides for >50 years. These compounds inhibit blood coagulation by repression of the vitamin K reductase reaction (VKOR). Anticoagulant-resistant rodent populations have been reported from many countries and pose a considerable problem for pest control. Resistance is transmitted as an autosomal dominant trait although, until recently, the basic genetic mutation was unknown. Here, we report on the identification of eight different mutations in the VKORC1 gene in resistant laboratory strains of brown rats and house mice and in wild-caught brown rats from various locations in Europe with five of these mutations affecting only two amino acids (Tyr139Cys, Tyr139Ser, Tyr139Phe and Leu128Gln, Leu128Ser). By recombinant expression of VKORC1 constructs in HEK293 cells we demonstrate that mutations at Tyr139 confer resistance to warfarin at variable degrees while the other mutations, in addition, dramatically reduce VKOR activity. Our data strongly argue for at least seven independent mutation events in brown rats and two in mice. They suggest that mutations in VKORC1 are the genetic basis of anticoagulant resistance in wild populations of rodents, although the mutations alone do not explain all aspects of resistance that have been reported. We hypothesize that these mutations, apart from generating structural changes in the VKORC1 protein, may induce compensatory mechanisms to maintain blood clotting. Our findings provide the basis for a DNA-based field monitoring of anticoagulant resistance in rodents.

Background and Objectives: The strongest risk factor identified for inhibitor development in people with severe hemophilia A is the type of factor VIII gene mutation. The objective of this study was to evaluate the mutation type dependent concordance rate of inhibitor formation in siblings., Design and Methods: The gene defect, treatment and inhibitor history were evaluated in 113 families in which two or more siblings had severe hemophilia A., Results: Seventy-nine of the families (69.9%) were concordant in that either all or none of the siblings had a history of inhibitors. The concordance in 59 families with inhibitors was 42.4%. The corresponding figures for the 74 families with intron 22 inversion were 63.5% and 40.0%, respectively, and the overall concordance within 14 families with nonsense mutations was 78.6%. The siblings in two families with large gene deletions had no inhibitor history. A small proportion of the families with missense mutations, small deletions/insertions and splice site mutations developed inhibitors, but in four of the families two or more siblings developed high-responding inhibitors. In 18 of the 25 concordant families (72.0%) with inhibitors, the inhibitor was also of the same type (high-responding)., Interpretation and Conclusions: This is the first study of the association between inhibitor formation and the causative factor VIII gene mutation in siblings. The data show that the type of mutation provides, to some extent, the basis for this relationship, but the mutation itself is not enough to predict the risk for therapy-induced inhibitor formation.

Haemophilia is caused by hundreds of different mutations and manifests itself in clinical conditions of varying severity. Despite being inherited in monogenic form, the clinical features of haemophilia can be influenced by other genetic factors, thereby confounding the boundary between monogenic and multifactorial disease. Unlike sufferers of other genetic diseases, haemophiliacs can be treated successfully by intravenous substitution of coagulation factors. Haemophilia is also the most attractive model for developing gene-therapy protocols, as the normal life expectancy of haemophiliacs allows the side effects of gene therapy, as well as its efficiency, to be monitored over long periods.

Background: haemophilia A (HA) is characterized by partial or total deficiency of factor VIII (FVIII) protein activity. It is caused by a broad spectrum of mutations in the FVIII gene. Despite tremendous improvements in mutation screening methods, in about 2% of HA patients no DNA change could be found, even after sequencing the whole coding part of the FVIII gene including the flanking splice sites, as well as the promotor and the 3' UTR regions., Objectives, Patients and Methods: In the present study we performed a detailed RNA analysis of three groups of patients. The first included control patients with known splicing defects, the second included two patients with already identified nucleotide changes close to splicing sites, that could potentially alter the normal splicing process, and a third group of 11 unrelated patients whose genomic DNA have already been screened for mutations by DHPLC and direct sequencing with no mutation being identified., Results: Both candidate splice site mutations were shown to result in either skipping or alternative splicing of at least one exon, therefore these DNA changes must be considered as causal for the patients' HA phenotype. In contrast, no abnormalities on the RNA level were observed in any of 11 unrelated patients without mutations in the FVIII gene., Conclusions: These findings exclude mutations that could be located deep in the introns and affecting either normal splicing or lead to mechanisms causing some unknown rearrangements of the FVIII gene. In fact, our results point to the presence of still unknown factor(s) causing HA, which might be either allelic or in the close proximity of the FVIII gene or non-allelic associated with other genetic loci that are involved in the processing of the FVIII protein.

Hereditary combined deficiency of the vitamin K-dependent coagulation factors II, VII, IX, X, protein C, S and protein Z (VKCFD) is a very rare autosomal recessive inherited bleeding disorder. The phenotype may result from functional deficiency of either the gamma-glutamyl carboxylase (GGCX) or the vitamin K epoxide reductase (VKOR) complex. We report on the third case of VKCFD1 with mutations in the gamma-glutamyl carboxylase gene, which is remarkable because of compound heterozygosity. Two mutations were identified: a splice site mutation of exon 3 and a point mutation in exon 11, resulting in the replacement of arginine 485 by proline. Screening of 100 unrelated normal chromosomes by restriction fragment length polymorphism and denaturing high-performance liquid chromatography analysis excluded either mutation as a frequent polymorphism. Substitution of vitamin K could only partially normalize the levels of coagulation factors. It is suggested that the missense mutation affects either the propeptide binding site or the vitamin K binding site of GGCX.

Von Willebrand disease type Normandy (VWD 2N) is caused by mutations at the factor VIII (FVIII) binding site of VWF, located at the amino-terminus of mature VWF. It is inherited in a recessive fashion and both homozygous and compound heterozygous mutations have been identified. Homozygous mutations are correlated with a clinical phenotype indistinguishable from mild hemophilia A by conventional laboratory tests, whereas compound heterozygosity with a quantitative defect may appear as VWD type 1 (VWD1). We have now identified and expressed a novel heterozygous mutation (Y795C) which is responsible for both, a defective FVIII-binding and aberrant multimers in a female patient with mild FVIII deficiency. Additionally we expressed another mutation (E787K), previously identified by us in a male patient with a severe 'pseudohemophilic' phenotype. Analysis of the FVIII binding and the multimer structure of the respective recombinant VWF mutants reproduced the observed phenotype: the FVIII binding defect in addition to the aberrant multimer structure of the patient with Y795C and the FVIII binding defect only, in the patient with E787K. Our results demonstrate the causative nature of the two mutations and emphasize the impact of 'cysteine mutations' on the multimer structure of VWF.

The Committee of Haemophilia of the GTH has established a central registry for all German centers treating patients with haemophilia. The intention was to establish a suitable system for collecting and analyzing epidemiological data relevant to bleeding disorders. The registry provides the database within the scope of the German Human-Genome-Project. The set goal is the complete molecular characterization of the genetic mutations on chromosome X of haemophilia A patients in Germany and subsequent correlation with the phenotype. An electronic network is applied for communication. A Java-application was developed for online electronic data acquirement by the participating centers. Offline data entry and sending encrypted data carriers is possible, too. A high level of security is assured by personalized access. Data are anonymized and scrambled by secure encoding. The concept was confirmed by the official data security offices. A considerable improvement for the epidemiological sciences and a better basis on therapy for patients with bleeding disorders is expected. Furthermore the registry is available for other scientific projects.

Haemophilia A is caused by a genetic defect of the factor VIII gene resulting in complete or considerable functional loss of factor VIII molecule within blood. The high bleeding risk of patients can be prevented by intravenous injections of factor VIII protein. However, 25% of patients affected with severe haemophilia, develop factor VIII antibodies against the concentrate substituted. Within this study we try to comprise the phenotypic parameters (e. g. detailed documentation of disease course, basic laboratory values) and the therapy-associated data (e. g. applicated type and amount of factor VIII, number of substitutions, factor VIII recovery, inhibitor development and inhibitor elimination). We hope to identify differences of variable therapeutic treatments on course of disease as already identified for the factor VIII gene defects. At least we expect that certain mutations and mutation types, respectively, can be referred to typical phenotypes and similar course of treatment protocols.

Haemophilia A represents the most frequent hereditary bleeding disorder in humans. The disease is caused by mutations within the factor VIII gene leading to decreased or absent factor VIII activities with a bleeding tendency depending on the degree of factor VIII deficiency. Nowadays, the causative mutations can be routinely detected and have substantially improved diagnostic and understanding of the pathophysiology of haemophilia A. Identification of the gene defects in haemophilic families have enabled fast and save carrier diagnosis. The correlation of the genetic defects with the clinical course revealed that the type of mutation represents the most important genetic predisposing factor for inhibitor formation, the most severe complication of treatment with factor VIII concentrates. Mitigated clinical courses of haemophilia A were shown to be due to special types of mutations or the presence of concomitant thrombophilic mutations. Molecular models of the factor VIII protein allowed to investigate the effects of specific mutations thus giving new insights in the structure/function relationship of the factor VIII molecule. These findings might promote the development of novel recombinant factor VIII concentrates with higher efficacy, longer half life and reduced immunogenicity.

Alloantibodies (inhibitors) against factor VIII (FVIII) develop in 20-30% of patients with severe haemophilia A and render classical FVIII substitution therapy ineffective. Several studies have shown that genetic factors, the type of FVIII gene mutation and immune response genes (e.g. the Major Histocompatibility Complexes), influence the risk of inhibitor formation. In particular, the type of FVIII gene mutation has proven to be a decisive risk factor. Patients with severe molecular gene defects (e.g. large deletions, nonsense mutations, intron-22 inversion) and no endogenous FVIII synthesis have a 7-10 times higher inhibitor prevalence than patients with milder molecular gene defects (e.g. missense mutations, small deletions, splice site mutations). To date, at least 10 distinct classes of mutations have been shown which have differing risks of associated inhibitor formation. A challenging observation in inhibitor patients is the heterogeneity of the antibody epitopes with respect to their number and their specificity. At least five epitopes in the FVIII molecule have been identified that constitute the targets for antibodies in most inhibitor patients. These epitopes are located in the ar3 region and the A2, A3, C1, C2 domains which correspond to the functional binding sites of the ligands of the FVIII protein. At present, the determinants of the characteristics of these epitopes and the subsequent inhibitor titre are unknown. A relationship of the mutation site and the epitope localization has been shown for some individual patients with mild haemophilia A. However, in severely affected haemophilia A patients, the influence of patient genetics on inhibitor titre and epitope specificity has yet to be elucidated.

Mutations in the large gene of clotting factor VIII (FVIII) are the most common events leading to severe human bleeding disorder. The high proportion of de novo mutations observed in this gene raises the possibility that a significant proportion of such mutations does not derive from a single germ cell but instead should be attributed to a germline or somatic mosaic originating from a mutation during early embryogenesis. The present study explores this hypothesis by using allele-specific PCR to analyze 61 families that included members who had sporadic severe hemophilia A and known FVIII gene defects. The presence of somatic mosaicisms of varying degrees (0.2%-25%) could be shown in 8 (13%) of the 61 families and has been confirmed by a mutation-enrichment procedure. All mosaics were found in families with point mutations (8 [25%] of 32 families). In the subgroup of 8 families with CpG transitions, the percentage with mosaicism increased to 50% (4 of 8 families). In contrast, no mosaics were observed in 13 families with small deletions/insertions or in 16 families with intron 22 inversions. Our data suggest that mosaicism may represent a fairly common event in hemophilia A. As a consequence, risk assessment in genetic counseling should include consideration of the possibility of somatic mosaicism in families with apparently de novo mutations, especially families with the subtype of point mutations.