Unbalanced X-chromosome inactivation with a novel FVIII gene mutation resulting in severe hemophilia A in a female

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

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

A Novel Deletion Mutation of the F8 Gene for Hemophilia A

Background: Hemophilia A (HA) is an X-linked recessive blood coagulation disorder caused by a variety of abnormalities in F8 gene, resulting in the absence of impaired molecule production of factor VIII (FVIII) in the plasma. The genetic testing of the F8 gene encoding FVIII is used for confirmation of HA diagnosis, which significantly reduced serious complications of this disease and, ultimately, increased life expectancy. Methods: Sanger sequencing was performed in F8 gene exons of the suspected patients with blood coagulation-related indicators. Results: A novel F8 indel variant c.6343delC, p.Leu2115SerfsTer28 in exon 22 of the F8 gene was identified in the suspected families. The infant with this novel variant appeared the symptom of minor bleeding and oral cavity bleeding, and decreased activity of FVIII, which is consistent with that of F8 deleterious variants. The 3'D protein structural analysis of the novel variant shows a change in FVIII protein stability, which may be responsible for the pathogenesis of HA. Conclusions: A novel deleterious variant was identified in our case, which expands the F8 variants spectrum. Our result is helpful for HA diagnosis and benefits carrier detection and prenatal diagnosis. Our study also reveals that mutation screening of the F8 gene should be necessary for HA suspected patients.

Three-Decade Successive Establishment of Care for Women/Girls from Families with Haemophilia

Objective

The study aimed to report a 3-decade successive establishment of care for women/girls from families with haemophilia.

Methods

A retrospective analysis was conducted on 462 women/girls from 243 families from 1987 to 2021.

Results

Combining phenotypic analysis of coagulation factor and genotypic analysis of either linkage analysis or mutation detection confirmed the status of all obligate haemophilia carriers (A118, B19). For potential carrier, 159 proven carriers (A130, B29) and 146 noncarrier status (A126, B20) were diagnosed except 20 potential carriers (A16, B4). Only 54 prenatal diagnoses were requested resulting in normal males (n = 21), males with haemophilia A (n = 12) and females with either normal or carrier status (n = 21). Additionally, 40 women/girls with haemophilia carrier received a diagnosis of severe haemophilia A with Turner’s syndrome (n = 2) and mild haemophilia (A31, B7). The skewed X-chromosome inactivation of the nonmutant factor VIII/IX carrying X-chromosome of 8% (2/25) was found in mild haemophilia. Factor concentrate and desmopressin are prescribed for these affected women/girls. The response of women/girls with either haemophilia carrier or haemophilia was amazement with their religious beliefs and cultural acceptance.

Conclusion

Appropriate care for women/girls from families with haemophilia concerning diagnosis and management of haemophilia and carrier has been successively established.

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

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

Molecular Mechanisms of Skewed X-Chromosome Inactivation in Female Hemophilia Patients-Lessons from Wide Genome Analyses

Introduction: Hemophilia A (HA) is an X-linked bleeding disorder caused by factor VIII (FVIII) deficiency or dysfunction due to F8 gene mutations. HA carriers are usually asymptomatic because their FVIII levels correspond to approximately half of the concentration found in healthy individuals. However, in rare cases, a carrier may exhibit symptoms of moderate to severe HA primarily due to skewed inactivation of her non-hemophilic X chromosome. Aim: The aim of the study was to investigate X-chromosome inactivation (XCI) patterns in HA carriers, with special emphasis on three karyotypically normal HA carriers presenting with moderate to severe HA phenotype due to skewed XCI, in an attempt to elucidate the molecular mechanism underlying skewed XCI in these symptomatic HA carriers. The study was based on the hypothesis that the presence of a pathogenic mutation on the non-hemophilic X chromosome is the cause of extreme inactivation of that X chromosome. Methods: XCI patterns were studied by PCR analysis of the CAG repeat region in the HUMARA gene. HA carriers that demonstrated skewed XCI were further studied by whole-exome sequencing (WES) followed by X chromosome-targeted bioinformatic analysis. Results: All three HA carriers presenting with the moderate to severe HA phenotype due to skewed XCI were found to carry pathogenic mutations on their non-hemophilic X chromosomes. Patient 1 was diagnosed with a frameshift mutation in the PGK1 gene that was associated with familial XCI skewing in three generations. Patient 2 was diagnosed with a missense mutation in the SYTL4 gene that was associated with familial XCI skewing in two generations. Patient 3 was diagnosed with a nonsense mutation in the NKAP gene that was associated with familial XCI skewing in two generations. Conclusion: Our results indicate that the main reason for skewed XCI in our female HA patients was negative selection against cells with a disadvantage caused by an additional deleterious mutation on the silenced X chromosome, thus complicating the phenotype of a monogenic X-linked disease. Based on our study, we are currently offering the X inactivation test to symptomatic hemophilia carriers and plan to expand this approach to symptomatic carriers of other X-linked diseases, which can be further used in pregnancy planning.

Genetic causes of haemophilia in women and girls

Women and girls reported as "haemophilic females" may have complex genetic causes for their haemophilia phenotype. In addition, women and girls may have excessive bleeding requiring treatment simply because they are heterozygous for haemophilia alleles. While severe and moderate haemophilia are rare in females, 16% of patients with mild haemophilia A and almost one-quarter of those with mild haemophilia B seen in U.S. haemophilia treatment centres are women and girls. A phenotypic female with a low level of factor VIII or factor IX may be classified into one of the following categories of causality: homozygosity (two identical haemophilia alleles), compound heterozygosity (two different haemophilia alleles), hemizygosity (one haemophilia allele and no normal allele), heterozygosity (one haemophilia allele and one normal allele), genetic causes other than haemophilia and non-genetic causes. Studies required for classification may include coagulation parameters, F8 or F9 sequencing, F8 inversion testing, multiplex ligation-dependent probe amplification, karyotyping and X chromosome inactivation studies performed on the patient and parents. Women and girls who are homozygous, compound heterozygous or hemizygous clearly have haemophilia, as they do not have a normal allele. Heterozygous women and girls with factor levels below the haemostatic range also meet the definitions used for haemophilia treatment.

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

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

Demonstration of a novel Xp22.2 microdeletion as the cause of familial extreme skewing of X-inactivation utilizing case-parent trio SNP microarray analysis

Background

We report a kindred referred for molecular investigation of severe hemophilia A in a young female in which extremely skewed X‐inactivation was observed in both the proband and her clinically normal mother.

Methods

Bidirectional Sanger sequencing of all F8 gene coding regions and exon/intron boundaries was undertaken. Methylation‐sensitive restriction enzymes were utilized to investigate skewed X‐inactivation using both a classical human androgen receptor (HUMARA) assay, and a novel method targeting differential methylation patterns in multiple informative X‐chromosome SNPs. Illumina Whole‐Genome Infinium microarray analysis was performed in the case‐parent trio (proband and both parents), and the proband's maternal grandmother.

Results

The proband was a cytogenetically normal female with severe hemophilia A resulting from a heterozygous F8 pathogenic variant inherited from her similarly affected father. No F8 mutation was identified in the proband's mother, however, both the proband and her mother both demonstrated completely skewed X‐chromosome inactivation (100%) in association with a previously unreported 2.3 Mb deletion at Xp22.2. At least three disease‐associated genes (FANCB,AP1S2, and PIGA) were contained within the deleted region.

Conclusions

We hypothesize that true “extreme” skewing of X‐inactivation (≥95%) is a rare occurrence, but when defined correctly there is a high probability of finding an X‐chromosome disease‐causing variant or larger deletion resulting in X‐inactivation through a survival disadvantage or cell lethal mechanism. We postulate that the 2.3 Mb Xp22.2 deletion identified in our kindred arose de novo in the proband's mother (on the grandfather's homolog), and produced extreme skewing of X‐inactivation via a “cell lethal” mechanism. We introduce a novel multitarget approach for X‐inactivation analysis using multiple informative differentially methylated SNPs, as an alternative to the classical single locus (HUMARA) method. We propose that for females with unexplained severe phenotypic expression of an X‐linked recessive disorder trio‐SNP microarray should be undertaken in combination with X‐inactivation analysis.

Phenotype-genotype correlations in hemophilia A carriers are consistent with the binary role of the phase between F8 and X-chromosome inactivation

BACKGROUND

The recessive X-linked disorder hemophilia A (HA) is rarely expressed in female carriers, most of whom express about half of normal factor VIII activity (

FVIII

C).

OBJECTIVE

To propose an integrative assessment model for the binary role of the phase between the mutated F8 and the active X-chromosome (Xa) in

FVIII

C in HA carriers.

METHODS

We studied 67 females at risk of severe HA, comprising five symptomatic females (

FVIII

C < 1.5 IU dL(-1) ) and 14 controls. A correlation study between

FVIII

C (observed vs. expected) and X-chromosome inactivation (XCI) patterns (XIPs; androgen receptor gene [AR] system) in blood leukocyte DNA was performed in carriers, by comparison of a model correlating

FVIII

C and XIP with arbitrary models devoid of biological significance, and with

FVIII

C levels in non-carriers (mean model) as a proxy from background data dispersion not influenced by XIP.

RESULTS

We provide proof-of-concept example from a family presenting with extremely skewed XIPs in which the severe HA phenotype appeared in a heterozygous carrier of a crossover between AR and F8 loci that phased the mutated F8 with the maternally inherited Xa. Furthermore, four cases of severe HA affected women who had a combination of a heterozygous F8 mutation and extremely skewed XIPs in leukocytes or oral mucosa are presented. Correlation analyses between

FVIII

C levels and XIPs in carriers (n = 38) but not in non-carriers (n = 20) showed highly significant differences between the proposed correlation model and models without biological significance. The data support a binary influence of XCI, either increasing or decreasing the

FVIII

C, subject to the underlying phase set between the F8 mutation and XCI.

CONCLUSIONS

Our evidence suggests that the phase between XCI and mutated F8 acts as a molecular switch conditioning

FVIII

C levels and HA expression in carriers.

Identification of novel informative loci for DNA-based X-inactivation analysis

The HUMARA assay, the most common method for evaluation of X-inactivation skewing in blood cells, has been reported to be usable in only about 80% of females, emphasizing the need for alternative methods for testing of HUMARA-uninformative individuals. We conducted an in silico search for potentially polymorphic tri-to-hexanucleotide repeats in the proximity of CpG islands located in 5' regions of X-chromosome genes to design five candidate assays (numbered I, II, III, IV, and V) combining methylation-specific restriction digest with PCR amplification in a manner similar to the HUMARA assay. The results obtained by these assays in 100 healthy females were compared to X-inactivation skewing measured by the AR-MSP method which is based on methylation-specific PCR amplification of the first exon of the AR gene. On the basis of statistical evidence, three of the novel assays (II, IV, and V), which were informative in 18%, 61%, and 55% of females in the cohort, respectively, may be used as alternatives or conjointly with the HUMARA assay to improve its reliability. The three new assays were combined with the HUMARA assay into a novel X-inactivation test leading to the increase of informative females in the cohort from 67% to 96%.

Severe and moderate haemophilia A and B in US females

Haemophilia A and B are rare X-lined hemorrhagic disorders that typically affect men. Women are usually asymptomatic carriers, but may be symptomatic and, rarely, also express severe (factor VIII (FVIII) or factor IX (FIX) <0.01 U mL(-1)) or moderately severe (FVIII/FIX 0.01-0.05 U mL(-1)) phenotypes. However, data on clinical manifestations, genotype and the psychosocial ramifications of illness in severely affected females remain anecdotal. A national multi-centre retrospective study was conducted to collect a comprehensive data set on affected US girls and women, and to compare clinical observations to previously published information on haemophilic males of comparable severity and mildly affected haemophilic females. Twenty-two severe/moderate haemophilia A/B subjects were characterized with respect to clinical manifestations and disease complications; genetic determinants of phenotypic severity; and health-related quality of life (HR-QoL). Clinical data were compared as previously indicated. Female patients were older than male patients at diagnosis, but similarly experienced joint haemorrhage, disease- and treatment-related complications and access to treatment. Gynaecological and obstetrical bleeding was unexpectedly infrequent. F8 or F9 mutations, accompanied by extremely skewed X-chromosome inactivation pattern (XIP), were primary determinants of severity. HR-QoL was diminished by arthropathy and viral infection. Using systematic case verification of participants in a national surveillance registry, this study elucidated the genetics, clinical phenotype and quality of life issues in female patients with severe/moderate haemophilia. An ongoing international case-controlled study will further evaluate these observations. Novel mechanistic questions are raised about the relationship between XIP and both age and tissue-specific FVIII and FIX expression.

Compound heterozygous hemophilia A in a female patient and the identification of a novel missense mutation, p.Met1093Ile

Hemophilia A (HA) in females is rare. Female HA cases are often misdiagnosed as acquired HA (AHA) or as von Willebrand disease type 2N (vWD-2N). Here, we report the case of a 37-year-old female HA patient with a moderate factor VIII (FVIII) deficiency. The patient had no personal or family history of bleeding disorders, but presented with heavy uterine bleeding following surgery to remove an intrauterine device. IgG inhibitory antibodies against FVIII were undetected. A compound heterozygote mutation of the FVIII gene (F8) was found in this patient. The p.Val502Asp mutation, which has been reported previously, affects A2 domain function. A novel missense point mutation, p.Met1093Ile, was identified in the B domain. The compound heterozygote mutations in F8, p.Val502Asp and p.Met1093Ile, caused HA in this female patient, with a moderate phenotype.

F8 gene dosage defects in atypical patients with severe haemophilia A

We performed molecular analysis of the factor 8 gene (F8) in 272 unrelated Spanish patients with haemophilia A (HA) and detected a mutation by routine analysis in 267 of them (98.1%). No mutation was detected in the remaining five patients despite clinical and laboratory confirmation of HA. The aim is to describe the molecular alterations in F8 discovered by gene dosage methodologies in three of these patients. For methodology, F8 sequencing, intragenic marker analysis, multiplex ligation-dependent probe amplification and quantitative real time-PCR were followed. One patient had Klinefelter syndrome (47,XXY) and a large deletion spanning exons 1-12 masked by the other F8 allele; the second patient showed a large duplication spanning exons 2-10 and the third patient revealed a non-contiguous double duplication of exons 14 and 23-25. The remaining two patients had mild HA and dosage results were normal. The application of gene dosage methods is useful to define haemophilic patients in whom mutations are not detected using other routine methods. Nevertheless, in a small percentage of patients (<1%), no molecular pathology can be identified after testing several genetic methodologies.

ConteXt of change--X inactivation and disease

Epigenetic regulation is important for stable maintenance of cell identity. For continued function of organs and tissues, illegitimate changes in cell identity must be avoided. Failure to do so can trigger tumour development and disease. How epigenetic patterns are established during cell differentiation has been explored by studying model systems such as X inactivation. Mammals balance the X-linked gene dosage between the sexes by silencing of one of the two X chromosomes in females. This is initiated by expression of the non-coding X-inactive specific transcript (Xist) RNA and depends on specific cellular contexts, in which essential silencing factors are expressed. Normally X inactivation is initiated in early embryogenesis, but recent reports identified instances where Xist is expressed and can initiate gene repression. Here we describe the features that characterize the cellular permissivity to initiation of X inactivation and note that these can also occur in cancer cells and in specific haematopoietic progenitors. We propose that embryonic pathways for epigenetic regulation are re-established in adult progenitor cells and tumour cells. Understanding their reactivation will deepen our understanding of tumourigenesis and may be exploited for cancer therapy.

Mosaicism and haemophilia

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

Determinants of factor VIII plasma levels in carriers of haemophilia A and in control women

Factor VIII (FVIII) levels show a considerable variability in female carriers of haemophilia A. Presently, the reasons for this are poorly understood. The aim of the study was to elucidate the influence of genetic and non-genetic parameters on FVIII plasma levels in carriers (n = 42). Results were compared with age-matched healthy women without carriership of haemophilia A (n = 42). Each carrier was tested for the family-specific mutation, ABO blood group, FVIII level, von Willebrand factor (VWF) antigen and activity and C-reactive protein (CRP). FVIII levels were lower in carriers compared to non-carriers [74% (51-103) vs. 142% (109-169), P < 0.001]. No statistically significant differences were observed between the two groups with respect to VWF activity, prothrombin-time, hs-CRP, fibrinogen, body mass index (BMI), age and smoking status as well as the distribution of ABO blood groups. In non-carriers, FVIII was statistically significantly correlated with BMI, activated partial thromboplastin time (APTT), VWF antigen, hs-CRP and fibrinogen. In carriers, significant correlations between FVIII and APTT, VWF antigen and activity were found, whereas BMI, hs-CRP or fibrinogen did not correlate with FVIII. In non-carriers, the association of FVIII with ABO blood groups was statistically significant (P = 0.006), but not in carriers of haemophilia A (P = 0.234). The type of FVIII gene mutation did not influence FVIII levels. Carrier status is the major determinant of a carrier;s FVIII plasma level. Factors known to influence FVIII levels in the general population do not significantly affect FVIII activity in carriers, neither does the type of mutation influence FVIII levels.

Molecular mechanisms underlying hemophilia A phenotype in seven females

BACKGROUND

Hemophilia A (HA) in females is a rare observation. Here we describe various genetic mechanisms that result in phenotypic expression of HA in seven females.

METHODS

The F8 gene was examined in all patients and relatives by direct sequencing. Multiplex ligation-dependent probe amplification (MLPA) was performed for large deletion screening. X chromosome inactivation was studied by PCR analysis of a polymorphic CAG repeat in the first exon of the human androgen receptor (HUMARA) gene.

RESULTS

In two females sequencing of the F8 gene revealed homozygous missense mutations (Arg593Cys and Tyr1680Phe) as a consequence of consanguineous marriage. The third case was due to compound heterozygosity comprising the missense mutation Leu412Phe inherited from the carrier mother, together with a de novo large deletion spanning exon 9-22, probably originating from the germ cells of the healthy father. Three further cases shared a common mechanism representing heterozygous mutations in the F8 gene (Arg1781His, Arg327His, small deletion in exon 10) combined with non-random inactivation of the X chromosome. The final case describes a coincidental inheritance of HA and Coffin-Lowry syndrome in the same family. The HA phenotype results from a heterozygous small deletion affecting the F8 gene (c.6872 del CT leading to Thr2272fs) and a complete inactivation of the maternal X chromosome, which segregates with Coffin-Lowry syndrome in the two brothers of the proposita.

CONCLUSIONS

In conclusion, molecular genetic analysis represents an essentially valuable tool in elucidating the nature of the molecular mechanisms underlying the HA phenotype in females.

Mosaics and haemophilia

Some mosaic conditions may affect the haemophilia phenotype. Well-known instances include chromosomal mosaicism because of aneuploidy and pseudo-mosaicism because of varying patterns of X-chromosome inactivation. Chromosomal mosaicism in a chimera is a potential source of phenotypic variation. Gene mosaicism is commonplace. Its pattern and effect depend on the stage of development at which a mutation occurs. Proven or possible genetic mosaicism is an important consideration when predicting the likelihood of transmission of haemophilia to a future generation. A mosaic is an individual who has two or more cell lines, genetically different with regard to chromosomes or genes. As techniques improve and studies accumulate, mosaics are being found to be more common than hitherto believed. Some mosaic conditions may affect the phenotype of haemophilia in males and of the carrier state in females. Cells may be mosaic with regard to chromosomes, as in some instances of aneuploidy, and in chimeras, and in females owing to the pattern of X-chromosome inactivation. Cells may be mosaic with regard to new gene mutations. The pattern of mosaicism depends upon the stage in embryogenesis or in germ-cell formation in which the mutation arose.

Female monozygotic twins discordant for hemophilia A due to nonrandom X-chromosome inactivation

We describe monozygotic female twins discordant for hemophilia A, born to a carrier mother and normal father. Affected twin A presented at age 1 year with excessive bruising and factor VIII procoagulant activity (FVIII:C) of less than 1% of normal. Twin B is an asymptomatic carrier with FVIII:C level of 42%. Peripheral blood DNA was tested for X-chromosome inactivation (methylation) patterns of the X-linked human androgen receptor gene, comparing the twins' patterns to parental. Twin A showed nonrandom inactivation skewed toward the paternal X, whereas twin B showed random X-inactivation. This is the first reported case of discordance for hemophilia A between female monozygotic twins.

Severe haemophilia A in a female resulting from an inherited gross deletion and a de novo codon deletion in the F8 gene

Haemophillia A (HA) is an X-linked bleeding disorder caused by mutations in the F8 gene. While the disease affects 1 in 5000 males, phenotypic expression of haemophilia A is rare in females, similar to other X-linked recessive disorders. We describe a 5-year-old female with severe haemophilia A. We determined the underlying molecular defect in the F8 genes of the proband and her closest family members by direct DNA sequencing, marker analysis and quantitative real-time polymerase chain reaction. The patient showed two different mutations in the F8 gene: the paternal copy of the F8 gene had a de novo p.Phe652/653 deletion in exon 13 while the maternally inherited gene showed a large deletion encompassing exons 1 to 22. The structural analysis of residues Phe652/Phe653 based on a three-dimensional model of activated factor VIII provides evidence of the impact of the mutant factor VIII protein in the clinical manifestations of the patient. This unusual finding highlights the need to perform a thorough molecular analysis including sequencing, marker and quantitative analyses to identify compound heterozygous females with HA.

Mutation spectrum of 122 hemophilia A families from Taiwanese population by LD-PCR, DHPLC, multiplex PCR and evaluating the clinical application of HRM

Background

Hemophilia A represents the most common and severe inherited hemorrhagic disorder. It is caused by mutations in the F8 gene, which leads to a deficiency or dysfunctional factor VIII protein, an essential cofactor in the factor X activation complex.

Methods

We used long-distance polymerase chain reaction and denaturing high performance liquid chromatography for mutation scanning of the F8 gene. We designed the competitive multiplex PCR to identify the carrier with exonal deletions. In order to facilitate throughput and minimize the cost of mutation scanning, we also evaluated a new mutation scanning technique, high resolution melting analysis (HRM), as an alternative screening method.

Results

We presented the results of detailed screening of 122 Taiwanese families with hemophilia A and reported twenty-nine novel mutations. There was one family identified with whole exons deletion, and the carriers were successfully recognized by multiplex PCR. By HRM, the different melting curve patterns were easily identified in 25 out of 28 cases (89%) and 15 out of 15 (100%) carriers. The sensitivity was 93 % (40/43). The overall mutation detection rate of hemophilia A was 100% in this study.

Conclusion

We proposed a diagnostic strategy for hemophilia A genetic diagnosis. We consider HRM as a powerful screening tool that would provide us with a more cost-effective protocol for hemophilia A mutation identification.

Haemophilia A: molecular insights

Haemophilia A is the most common inherited bleeding disorder caused by defects in the

Clin Chem Lab Med 2007;45:450–61.

Thirteen novel mutations in the factor VIII gene in the Nijmegen haemophilia A patient population

The development of neutralising antibodies to factor VIII (FVIII) is a major complication of haemophilia A (HA) therapy. We aimed to construct an individual risk profile for the development of inhibitors in HA and started by screening for the causative mutation in our HA patient population. A total of 109 patients and 28 carriers were screened. The analysis revealed 38 different mutations in the FVIII gene, of which 13 have not been described on the Haemophilia A Mutation, Search, Test and Resource Site (HAMSTeRS). Twenty-five mutations have been reported previously and all except two had a similar phenotype to what has been described. Three novel mutations were associated with severe HA: one non-missense mutation, a small insertion in the A2 domain, and two missense mutations, a H256R mutation in the A1 domain and a L2025P substitution in the C1 domain. One novel mutation, Y156C, was associated with moderate HA. Nine novel mutations caused mild HA. The P130R, D167E and V278M mutations are located in the A1 domain. R439C, Y511H, A544G and Q645H in the A2 domain, L1758F in the A3 domain and a S2157R mutation in the C1 domain. In conclusion, the genotypic profile of our HA population was not different from others described and is suitable to study inhibitor formation.

Familial nonrandom inactivation linked to the X inactivation centre in heterozygotes manifesting haemophilia A

A basic tenet of the Lyon hypothesis is that X inactivation occurs randomly with respect to parental origin of the X chromosome. Yet, nonrandom patterns of X inactivation are common - often ascertained in women who manifest recessive X-linked disorders despite being heterozygous for the mutation. Usually, the cause of skewing is cell selection disfavouring one of the cell lineages created by random X inactivation. We have identified a three generation kindred, with three females who have haemophilia A because of extreme skewing of X inactivation. Although they have both normal and mutant factor VIII (FVIII) alleles, only the mutant one is transcribed; and, they share an XIST allele that is never transcribed. The skewing in this case seems to result from an abnormality in the initial choice process, which prevents the chromosome bearing the mutant FVIII allele from being an inactive X.

Management of pregnancy in a patient with severe haemophilia A

Haemophilia A is a bleeding disorder that has a spectrum of manifestations ranging from persistent bleeding after minor trauma to spontaneous haemorrhage. As an X-linked disease, it has a rare occurrence in females. We report a case of a pregnant patient with severe haemophilia A, who received epidural analgesia during labour. The prepartum, intrapartum and postpartum care of a patient with such a bleeding diathesis is discussed.

Skewed X-chromosome inactivation in monochorionic diamniotic twin sisters results in severe and mild hemophilia A

This study describes the genetic mechanisms responsible for the de novo occurrence of severe and mild hemophilia A in monozygotic twin females. Both twins were found to carry a previously known factor VIII mutation (Tyr16Cys) in the heterozygous state which most probably arose in the paternal germ line. Both twins showed concordant skewing of X inactivation toward the maternally derived normal X chromosome, the most severely affected twin exhibiting a higher percentage of inactivation of the normal X chromosome. The degree of skewing of X inactivation closely correlated with both the coagulation parameters and the clinical phenotype of the twins. Since these twins were monochorionic, such results suggest that the twinning event in this case has occurred after the onset of the X-inactivation period.

Anderson-Fabry disease: clinical manifestations of disease in female heterozygotes

Anderson-Fabry disease is a rare, X-chromosomal lipid storage disorder caused by a deficiency of lysosomal alpha-galactosidase A. Clinical manifestations of Anderson-Fabry disease include excruciating pain in the extremities (acroparaesthesia), skin vessel ectasia (angiokeratoma), corneal and lenticular opacity, cardiovascular disease, stroke and renal failure, only renal failure being a frequent cause of death. Heterozygote female carriers have often been reported as being asymptomatic or having an attenuated form of the disease. To evaluate the spectrum of clinical signs in heterozygotes, a comprehensive clinical examination was performed on 20 carriers of Anderson-Fabry disease. This revealed that, in addition to the skin manifestation, various other clinical manifestations of the disease are present, including acroparaesthesia, kidney dysfunction, cerebrovascular disease, and gastrointestinal and heart problems. It therefore appears that Anderson-Fabry disease affects both hemizygotes and heterozyotes and therefore should be considered to be an X-linked dominant disease.