A factor XI deficiency associated with a nonsense mutation (Trp501stop) in the catalytic domain

Factor XI gene variants in factor XI-deficient patients of Southern Italy: identification of a novel mutation and genotype-phenotype relationship

Congenital Factor XI (FXI) deficiency shows a high variability in clinical phenotype. To date, many allele variants have been shown to cause this bleeding disorder. However, the genotype–phenotype relationship is difficult to establish. This report provides insights into this bleeding disorder. Sixteen unrelated Italian index cases with congenital FXI deficiency and their relatives were investigated. After the identification of the deficiency, we obtained DNA from each subject and analyzed the FXI gene using direct sequencing. We identified 5 and 11 individuals with severe and moderate deficiency of FXI activity, respectively. Most patients (8/16) carried mutations in the Apple 2 domain and 4 patients showed c.403G>T (p.Glu135*; type II mutation). Four novel compound heterozygosities were identified. Bleeding symptoms were present in two severely deficient subjects carrying the combinations c.901T>C (p.Phe301Leu)/c.1556G>A (p.Trp519*) and c.943G>A (p.Glu315)/c.1556G>A (p.Trp519*), respectively. Bleeding episodes were also observed in the presence of a moderate deficiency in two individuals heterozygous for c.449C>T (p.Thr150Met) and c.1253G>T (p.Gly418Val), respectively. One novel mutation, c.1682C>A (p.Ala561Asp), was identified as potentially deleterious in an asymptomatic individual. We confirm an unclear prediction of phenotype from mutational data. The FXI levels should be coupled with FXI analysis for a more comprehensive prediction of the bleeding phenotype in FXI deficiency.

Coagulation factor XI gene analysis in three factor XI deficient Austrian patients

OBJECTIVES

Hereditary factor XI deficiency is a rare bleeding disorder with worldwide distribution. In Austrian patients only one mutation leading to congenital factor XI deficiency has been reported. In the present study, we identified the molecular basis of factor XI deficiency in three Austrian patients.

METHODS

Patients attended hospital for other reasons than bleeding disorders. Routine laboratory tests revealed prolonged APTTs due to decreased factor XI levels. We performed automated fluorescent sequencing of the promotor region, exons 1-15 and the flanking intronic regions of the factor XI gene. The mutations found were confirmed by restriction enzyme analysis or sequencing of the non-coding strand.

RESULTS

Fluorescent sequencing revealed two novel mutations, the nonsense mutation Gln116X (443C>T) in exon 5 and a deletion of Ile197 and Asp198 (687_692delTCGACA) in exon 7. Furthermore, we detected a heterozygous A>G exchange at the third nucleotide of IVS6 (IVS 6 +3A>G), which had already been reported in a FXI deficient individual of French Basque origin.

CONCLUSION

While the IVS 6 +3A>G decreases the calculated splice consensus score from 0.98 in the wild type to 0.56 in the altered sequence and therefore interferes with the consensus splice sequence, the complete loss of the two amino acids Ile197 and Asp198 is expected to interfere with the steric structure and hence the functions of the third apple domain. The Gln116X leads to a premature termination codon resulting in a lack of the light as well as parts of the heavy chain of the FXI protein, most likely resulting in rapid degradation of the truncated mRNA.

Inhibitors to Factor XI in Patients With Severe Factor XI Deficiency

Factor XI (FXI) deficiency is a rare bleeding disorder that may arise from any of a number of missense, nonsense, splice site, insertion, and deletion mutations within the FXI gene. Severely affected patients are at considerable risk of developing inhibitors to FXI and, although spontaneous bleeding is uncommon in such patients, bleeding after surgery or trauma can be severe. As treatment with fresh frozen plasma (FFP) or FXI concentrates is ineffective in patients with inhibitors, other therapies must be sought. Traditionally, such patients have been treated with various agents and methods, including plasma exchange, cyclophosphamide, intravenous immunoglobulin, and prothrombin complex concentrates. However, emerging data indicate that recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark) may also be effective in FXI deficiency with inhibitors. Further work is required to determine the optimal dosing schedules of the agent in this indication.

Factor XI deficiency database: an interactive web database of mutations, phenotypes, and structural analysis tools

Factor XI (FXI) is the zymogen of a serine protease enzyme in the intrinsic pathway of blood coagulation and is an important factor in the creation of a stable fibrin clot. Deficiency of FXI leads to an injury-related bleeding disorder and is remarkable for the lack of correlation between bleeding symptoms and FXI coagulant activity (FXI:C). The FXI protein is composed of five domains: four tandem repeat domains of approximately 80 residues known as Apple (Ap) domains, and the catalytic serine protease (Sp) domain. A total of 65 mutations throughout the FXI gene (F11) have been reported in FXI deficient patients. An interactive web database of these mutations has been created (www.FactorXI.org) that integrates the phenotypic data with genetic data and structural homology models for the five FXI domains. The database provides a central repository for all reported genetic alterations within F11. With the use of recently developed visualization tools, each mutation can be highlighted on the structural models of the FXI domains together with an appropriate survey of patient data, such as FXI:C levels and FXI antigen levels. The database also enables new F11 mutations to be interpreted. The interactive design of this database will lead to a more comprehensive comparative understanding of the genetic factors that influence bleeding risk.

Severe factor XI deficiency in a Lebanese family

In this study, a Lebanese woman with severe factor XI deficiency as well as several unaffected family members were analysed. The F11 gene was screened by polymerase chain reaction amplification of all 15 exons, including intron-exon junctions followed by single-strand conformational analysis. Variant single-strand conformational analysis profiles were obtained for exon 13; sequencing of these products allowed the identification of a novel missense mutation (Trp501Cys) situated in the catalytic domain, in homozygosity in the proband.

Compound heterozygosity for two novel mutations in a severe factor XI deficiency

We identified two novel mutations in an asymptomatic 25-year-old Japanese patient with severe factor XI deficiency. Direct sequencing analysis of PCR products from his factor XI gene revealed a G to T transversion in exon 12, resulting in the nonsense mutation (Glu447Stop) and a G insertion in five consecutive guanine nucleotides ((501)Trp(TGG)-(502)Gly(GGG)) in exon 13 that is expected to lead to the substitution of the last 105 amino acids ((503)Tyr-(607)Val) with 32 abnormal amino acid residues ((503)Val-(534)Thr) followed by stop codon. We also demonstrated that two mutations are associated with the separate alleles in this patient, indicating compound heterozygosity for these mutations. Both mutations lead to the disruption of the catalytic domain structure of the FXI molecule and thus are responsible for his deficiency of factor XI.

Factor XI deficiency in French Basques is caused predominantly by an ancestral Cys38Arg mutation in the factor XI gene

Inherited factor XI deficiency is an injury-related bleeding disorder that is rare in most populations except for Jews, in whom 2 mutations, a stop mutation in exon 5 (type II) and a missense mutation in exon 9 (type III), predominate. Recently, a cluster of 39 factor XI-deficient patients was described in the Basque population of Southwestern France. In this study, we determined the molecular basis of factor XI deficiency in 16 patients belonging to 12 unrelated families of French Basque origin. In 8 families, a nucleotide 209T>C transition in exon 3 was detected that predicts a Cys38Arg substitution. Four additional novel mutations in the factor XI gene, Cys237Tyr, Tyr493His, codon 285delG, and IVS6 + 3A>G, were identified in 4 families. Expression studies showed that Cys38Arg and Cys237Tyr factor XI were produced in transfected baby hamster kidney cells, but their secretion was impaired. Cells transfected with Tyr493His contained reduced amounts of factor XI and displayed decreased secretion. A survey of 206 French Basque controls for Cys38Arg revealed that the prevalence of the mutant allele was 0.005. Haplotype analysis based on the study of 10 intragenic polymorphisms was consistent with a common ancestry (a founder effect) for the Cys38Arg mutation.