A-793 G to A transition in the factor IX gene promoter is polymorphic in the Caucasian population

We report the incidence of a prevalent polymorphism at position -703 in the promoter region of the factor IX gene in caucasian individuals. This DNA change was originally reported as one of two changes in the factor IX gene of a severely affected haemophilia B patient from Japan. We confirm the neutral nature of this change and demonstrate that, despite showing linkage disequilibrium with the previously reported Msel RFLP < 100 bp distant, the use of these two loci together in a carrier screening strategy significantly increases the level of informativity over the achieved using either polymorphism alone.