TO THE EDITOR:

Factor XI (FXI) is a key element for the amplification of thrombin generation, which participates in the contact pathway. This explains why FXI deficiency has minor physiological relevance but protects against thrombotic events, supporting FXI as an excellent target for antithrombotic treatments.1,2 

FXI deficiency (MIM #612416) has been considered a rare disorder that might reach relatively high prevalence in certain populations. The best example is within the Ashkenazi Jews, demonstrating an incidence of 8% of heterozygous individuals for 2 mutations: p.Glu117Ter and p.Phe283Leu, which account for 98% of alleles. So far, 220 different causative mutations have been identified throughout the FXI gene (F11) (http://www.factorix.org/). Recently, the exome-based data obtained from >60 000 individuals (Exome Aggregation Consortium) have revealed new information regarding genetic variation in F11, showing (a) profound differences...

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