F11 mutation screen

Factor XI deficiency can not definitively be regarded as either autosomal recessive or dominant. Although homozygotes or compound heterozygotes will have lower plasma factor XI levels than heterozygotes, this does not correlate well with bleeding tendency, unlike haemophilia A or B. Some severely affected individuals (FXI <1 U/dL) remain asymptomatic, whilst some heterozygotes may show a bleeding tendency. Dominant-Negative mutations have also been reported in F11.
Bleeding symptoms, when present, tend to be in the milder range, with no spontaneous joint bleeds etc.
The prevalence of factor XI deficiency is generally quoted as 1:1,000,000 but may be as high as 1:10,000 as it is significantly under-reported due to the absent/mild bleeding diathesis. It is very much more common in the Askhenazi Jewish population at 1:450 and an allele frequency of ~8-13.4%, due mainly to two common founder mutations - p.Glu135* (Type II) and p.Phe301Leu (Type III). Founder mutations have also been identified in the Basque population (p.Cys58Arg), southern France (p.Gln106*) and the north-west of England (p.Cys146*).