Mutation Analysis in F9 Gene of 17 Families with Haemophilia B from Iran

Current therapeutic approaches in the management of hemophilia-a consensus view by the Romanian Society of Hematology

Hemophilia A (HA) and hemophilia B (HB) are rare disorders, being caused by the total lack or under-expression of two factors from the coagulation cascade coded by genes of the X chromosome. Thus, in hemophilic patients, the blood does not clot properly. This results in spontaneous bleeding episodes after an injury or surgical intervention. A patient-centered regimen is considered optimal. Age, pharmacokinetics, bleeding phenotype, joint status, adherence, physical activity, personal goals are all factors that should be considered when individualizing therapy. In the past 10 years, many innovations in the diagnostic and treatment options were presented as being either approved or in development, thus helping clinicians to improve the standard-of-care for patients with hemophilia. Recombinant factors still remain the standard of care in hemophilia, however they pose a challenge to treatment adherence because they have short half-life, which where the extended half-life (EHL) factors come with the solution, increasing the half-life to 96 hours. Gene therapies have a promising future with proven beneficial effects in clinical trials. We present and critically analyze in the current manuscript the pros and cons of all the major discoveries in the diagnosis and treatment of HA and HB, as well as identify key areas of hemophilia research where improvements are needed.

A new in silico approach to investigate molecular aspects of factor IX missense causative mutations and their impact on the hemophilia B severity

Factor IX (encoded by F9) is a protein in the coagulation process, where its lack or deficiency leads to hemophilia B. This condition has been much less studied than hemophilia A, especially in Latin America. We analyzed the structural and functional impact of 54 missense mutations (18 reported by us previously, and 36 other mutations from the Factor IX database) through molecular modeling approaches. To accomplish this task, we examine the electrostatic patterns, hydrophobicity/hydrophilicity, disulfide, and H-bond differences of the Factor IX structures harboring the missense mutations found, correlating them with their clinical effects. The 54 mutated sequences were modeled and their physicochemical features were determined and used as input in clusterization tools. The electrostatic pattern seems to influence in disease severity, especially for mutations investigated in epidermal growth factors 1 and 2 (EGF1/2) domains. The combined use of all physicochemical information improved the clustering of structures associated to similar phenotypes, especially for mutations from GLA and EGF1-2 domains. The effect of mutations in the disease phenotype severity seems to be a complex interplay of molecular features, each one contributing to different impacts. This highlights that previous studies and tools analyzing individually single features for single mutations are missing elements that fulfill the whole picture.

Noninvasive prenatal diagnosis for X-linked disease by maternal plasma sequencing in a family of Hemophilia B

OBJECTIVE

To apply a Hidden Markov Model to test Hemophilia B in a fetus by maternal plasma sequencing only employing proband and maternal haplotypes.

CASE REPORT

A family at risk for Hemophilia B was recruited in this study. We performed genetic diagnosis on the proband using our targeted capture system (containing F9 gene coding region, highly heterozygous SNPs and a 13-kb chromosome Y specific region), and revealed a causative F9 gene mutation (c.190T>C, p.Cys64Arg). Maternal plasma cell-free DNA obtained at 8 weeks of gestation was targeted-captured and sequenced using the customized system. The fetus inherited the F9 (c.190T>C, p.Cys64Arg) mutation according to the Hidden Markov Model. The mother continued the pregnancy.

CONCLUSIONS

This study is the first report of a haplotype-based approach in NIPD of Hemophilia B. With further evaluation, this method might be useful for NIPD of Hemophilia B and for other X-linked single-gene disorders.

Molecular Analysis of Factor VIII and Factor IX Genes in Hemophilia Patients: Identification of Novel Mutations and Molecular Dynamics Studies

Background

Hemophilias A and B are X-linked bleeding disorders caused by mutations in the factor VIII and factor IX genes, respectively. Our objective was to identify the spectrum of mutations of the factor VIII and factor IX genes in Saudi Arabian population and determine the genotype and phenotype correlations by molecular dynamics (MD) simulation.

Methods

For genotyping, blood samples from Saudi Arabian patients were collected, and the genomic DNA was amplified, and then sequenced by Sanger method. For molecular simulations, we have used softwares such as CHARMM (Chemistry at Harvard Macromolecular Mechanics; http://www.charmm-gui.org) and GROMACS. In addition, the secondary structure was determined based on the solvent accessibility for the confirmation of the protein stability at the site of mutation.

Results

Six mutations (three novel and three known) were identified in factor VIII gene, and six mutations (one novel and five known) were identified in factor IX gene. The factor VIII novel mutations identified were c.99G>T, p. (W33C) in exon 1, c.2138 DelA, p. (N713Tfs*9) in eon14, also a novel mutation at splicing acceptor site of exon 23 c.6430 - 1G>A. In factor IX, we found a novel mutation c.855G>C, p. (E285D) in exon 8. These novel mutations were not reported in any factor VIII or factor IX databases previously. The deleterious effects of these novel mutations were confirmed by PolyPhen2 and SIFT programs.

Conclusion

The protein functional and structural studies and the models built in this work would be appropriate for predicting the effects of deleterious amino acid substitutions causing these genetic disorders. These findings are useful for genetic counseling in the case of consanguineous marriages which is more common in the Saudi Arabia.

[Perioperative management of patients with hemophilia]

Hemophilia A and hemophilia B are X chromosome-linked congenital bleeding disorders caused by a deficiency or absence of activity of coagulation factor VIII (hemophilia A) or factor IX (hemophilia B), which are graded in different degrees of severity (mild, moderate, severe). Depending on the severity patients may experience spontaneous bleeding episodes or will develop excessive bleeding in the context of injuries or surgery. Hemophilia should not be a contraindication for an invasive procedure; however, a number of conditions are required to provide successful surgery and an uncomplicated and safe postoperative course. This review provides an overview of hemophilia and the key biochemical laboratory and clinical aspects as well as possible specific and non-specific treatment options and addresses the special needs for the perioperative care of these patients.

Robustness of factor assays following cordocentesis in the prenatal diagnosis of haemophilia and other bleeding disorders

Prenatal diagnosis is the generally accepted option for genetic disorders including haemophilias and other bleeding disorders. Cord blood analysis between 17.4 and 20.6 weeks of gestation was performed in 172 confirmed carriers belonging to families of haemophilia A, haemophilia B, von Willebrand disease (VWD), factor VII and X deficiency; 133 were carriers for haemophilia A, 30 for haemophilia B, six for type 3 VWD, two for FX deficiency and one for FVII deficiency. The approach to the cord was either transabdominal or transamniotic. The volume of blood collected varied between 1 and 2 mL. In case of haemophilias, the diagnosis was offered by factor VIII/IX:C activity and antigen assays wherever required. In case of VWD, the diagnosis was based on von Willebrand factor antigen assays as detected by ELISA along with FVIII:C assay while in cases of FVII and FX deficiency, the diagnosis was based on FVII:C and FX:C respectively. The factor levels were compared with the normal range established in the laboratory for different coagulation factors between 18 and 21 weeks of gestation in women tested for other haematological disorders. Only in two cases, the procedure had to be repeated for reasons of extensive maternal contamination. All the deliveries have been followed up and the diagnoses reconfirmed by repeat clotting factor assays and DNA analysis whenever informative. Simple precautions like collection of fetal blood samples in smaller volumes in separate tubes, assaying multiple coagulation factors in the fetal blood samples helped us to offer diagnoses in all the women analysed. No fetal death or abortion was reported following the procedure. We suggest that accurate fetal blood sampling is a safe technique for the diagnosis of many of the bleeding disorders in places where genetic diagnostic services are not available.

Identification of factor IX mutations in Iranian haemophilia B patients by SSCP and sequencing

Different kinds of mutations, mostly point mutations, in the coagulation factor IX (FIX) gene F9 result in a recessive X-linked bleeding disorder known as haemophilia B. In this study, molecular analysis of 76 unrelated Iranian haemophilia B patients was performed by PCR, single strand conformational polymorphism (SSCP) on important functional regions of the F9 gene followed by sequencing on samples with different migration pattern. Using this approach we found mutation in 52 out of 76 patients. Our data showed that the pathologic mechanisms are heterogeneous as recorded for patients in haemophilia B mutation database and seven of the mutations are previously undescribed.