FXI deficiency is a rare bleeding disorder, occurring at a frequency of one in a million in the general population. The condition is more common among defined populations such as French Basques and Jewish communities, with Ashkenazi Jewish populations having the highest prevalence of approximately 10%.
FXI deficiency in Jewish populations has been well-studied with four causative mutations identified. These mutations are referred to as Jewish mutations Types I-IV. This nomenclature should not be confused with phenotypic classification of Type I (low activity and antigen) and Type II (low a ctivity and normal antigen). All four Jewish mutations are in fact Type I.
An increasing number of mutations are being reported in non-Jewish patients. Most of these mutations are missense point mutations and occur throughout the FXI gene clustering in the Ap4 and SP domains.