**5.6. FXI deficiency**

FXI is a 80 kDa protein with a plasma concentration of 30 nM, encoded by a 23 kb gene present on chromosome 4 [81–83]. Mutations in the coding region are the major causes for FXI deficiency and the prevalence of FXI deficiency is 1 in 1000,000 [83, 84]. The common symptoms of FXI deficiency are oral and post-operative bleeding. FXI deficient women are prone to menorrhagia. Fresh frozen plasma, FXI concentrate and antifibrinolytic agents are used to treat FXI deficiency [84].
