Heritable FXI deficiency is a rare bleeding disorder resulting
from low functional levels of coagulation factor XI. Inheritance is
autosomal. The estimated prevalence of major FXI deficiency (FXI:C
≤15 IU/dL) in most populations is about 1:1,000,000, however in
Ashkenazi Jews it occurs in about 1:450 individuals.
Most bleeding in FXI deficiency is related to injury, although
bleeding risk is unpredictable and not related to genotype. Some
patients with major FXI deficiency do not bleed, others with
partial FXI deficiency (FXI:C 16 to 60 IU/dL) may bleed.
Heritable FXI deficiency is caused by mutations in the factor XI
gene (F11). Major FXI deficiency is generally associated with
homozygosity or compound heterozygosity for F11 mutations. Partial
FXI deficiency is usually associated with heterozygosity for
mutations in F11. Genetic diagnosis has applications in family
studies in FXI deficiency.