Characterisation of five factor XI mutations.

A large scale factor XI (FXI) mutation screening program identified a number of novel candidate mutations and previously reported mutations and polymorphisms. Five potential missense mutations were selected for further study; these included two novel missense mutations - Met-18Ile (p.Met1Ile) and Met102Thr (p.Met120Thr), two previously reported missense mutations - Tyr133Ser (Tyr151Ser) and Thr575Met (Thr593Met), and one amino acid substitution previously reported as a polymorphism - Arg378Cys (Arg396Cys). The substitutions were recreated by the site-directed mutagenesis of a FXI cDNA and stably expressed in a BHK-570 cell line. Subsequent analysis of both the conditioned media and cell lysates showed that three of the substitutions, Met-18Ile, Met102Thr andTyr133Ser, prevented secretion of the mutated protein from the transfected cell line, resulting in a cross-reactive material negative (CRM-) phenotype. The remaining two mutants, Thr575Met and Arg378Cys, secreted significant levels of FXI into the conditioned media; however, these mutant FXIs were shown to have negligible factor IX activation activity in an APTTbased assay. These results confirmed all five of the missense mutations as being causative of factor XI deficiency, despite one having been previously reported as a polymorphism (Arg378Cys) and one (Tyr133Ser) as a mild mutation - FXI:C 38 U/dl in a homozygous patient.

Spectrum of factor XI (F11) mutations in the UK population--116 index cases and 140 mutations.

Factor XI deficiency is an autosomal bleeding disorder of variable severity. It is particularly common in the Ashkenazi Jewish population, the result of two founder mutations - E117X and F283L. Recent studies have shown the causative mutations of Factor XI deficiency, outside the Ashkenazi Jewish population, to be highly heterogeneous. We have studied 116 index cases, mostly from an ethnically diverse UK population, in order to better understand the spectrum of mutations responsible for factor XI deficiency. A total of 140 causative mutations of the F11 gene were identified in 109 patients. Fifty-five (39.3%) of the mutations were one of three common mutations--E117X (Type II), F283L (Type III), or C128X. The remaining 85 (60.7%) mutations comprised at least 57 variants including 31 novel mutations and whole gene deletions. This large study reconfirms that, despite the presence of founder mutations in discrete populations, factor XI deficiency remains a highly heterogeneous disease at the molecular level. .

An Alu-mediated 31.5-kb deletion as the cause of factor XI deficiency in 2 unrelated patients.

Factor XI deficiency (MIM 264900) is an autosomal bleeding disorder of variable severity. Inheritance is not completely recessive as heterozygotes may display a distinct, if mild, bleeding tendency. Recent studies have shown the causative mutations of factor XI deficiency, outside the Ashkenazi Jewish population, to be highly heterogeneous. We studied 39 consecutively referred patients with factor XI deficiency to identify the molecular defect. Conventional mutation screening failed to identify a causative mutation in 4 of the 39 patients. Epstein-Barr virus (EBV)-transformed cells from these 4 patients were converted from a diploid to haploid chromosome complement. Subsequent analysis showed that 2 of the patients had a large deletion, which was masked in the heterozygous state by the presence of a normal allele. We report here the first confirmed whole gene deletion as the causative mutation of factor XI deficiency, the result of unequal homologous recombination between flanking Alu repeat sequences.

Eighteen unrelated patients with factor XI deficiency, four novel mutations and a 100% detection rate by denaturing high-performance liquid chromatography.

Factor XI (FXI) deficiency is an autosomal bleeding disorder of variable severity. Inheritance is not completely recessive as heterozygotes may display a distinct, if mild, bleeding tendency. Eighteen unrelated FXI-deficient patients were screened blind by fluorescent single-stranded conformation polymorphism (F-SSCP) analysis and denaturing high-performance liquid chromatography (dHPLC). Mutations were detected in 14 of the 18 patients ( approximately 78%) by F-SSCP and in all 18 patients by dHPLC. Dideoxy sequencing confirmed the mutations in all 18 patients: eight of the mutations being novel (four of which were in previously reported patients). This showed dHPLC to be a highly sensitive, reliable technique for mutation screening in heterogeneous disorders.