Severe factor XI (FXI) deficiency is a bleeding disorder generally inherited as an autosomal recessive trait and characterized by haemorrhagic symptoms mainly associated with injury or surgery. So far, more than 150 causative molecular defects have been identified throughout the F11 gene. In the present study, we investigated the molecular basis of FXI deficiency in two Italian patients. Mutational screening of the F11 gene disclosed a novel missense substitution (Arg184Gly) in exon 7 and two splicing mutations: a novel G>A transition affecting the last nucleotide of exon 4 (325G>A), and the already known IVS6+3A>G. RT-PCR assays were performed on total RNA extracted from platelets and lymphocytes of each patient. Sequencing of RT-PCR products demonstrated that both 325G>A and IVS6+3A>G mutations abolish the corresponding donor splice site, causing the skipping of the affected exon; this in turn results in a frameshift introducing a premature termination codon. Expression of recombinant FXI-Arg184Gly revealed a 70% reduction in FXI activity, suggesting that the Arg184Gly mutation might cause a cross-reactive material positive (CRM+) deficiency. In conclusion, the functional consequences of two splicing mutations leading to FXI deficiency have been elucidated. Moreover, we report a novel missense mutation in the FIX-binding region of the FXI A3 domain leading to a CRM+ deficiency.

Prothrombin 19911 A > G polymorphism was independently associated with a 1.5-fold increased risk of VTE and increased 2-fold the risk of VTE associated with FV Leiden, both increases statistically significant. No effect was observed in carriers of prothrombin 20210 GA, perhaps because this polymorphism has a stronger influence on plasma prothrombin levels than the prothrombin 19911 polymorphism.

Genetic analysis was carried out in 37 Albanian patients with haemophilia A. The factor VIII intron 22 inversion was detected only in 2/19 (10.5%) apparently unrelated patients with severe haemophilia A, while the intron 1 inversion was absent. A total of 19 different gene mutations were identified. Ten mutations were novel: four null mutations in severe haemophilia A patients (Gln1090X, Cys1832X, 2374delT, 5676insT) and six missense mutations (five in severe haemophilia A) (Ile76Thr, Leu299Pro, Asp525Glu, Cys692Tyr, His1755Leu and Trp1835Cys). None of these novel mutations occurred at CpG hotspots. These results further emphasize the extreme heterogeneity of the molecular basis of haemophilia A. The low prevalence of intron 22 inversion in Albanian patients with severe haemophilia A should be addressed by further studies.

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