Characterisation and use of an intragenic polymorphic marker for detection of carriers of haemophilia B (factor IX deficiency).

DNA from 33 healthy White subjects was analysed with a 2 X 5 kilobase subgenomic DNA probe derived from the gene for coagulation factor IX, containing the exon "d" region of that gene. Intragenic Taq I restriction-fragment length polymorphism was revealed, with allelic frequencies estimated at 0 X 65 and 0 X 35 (SE = 0 X 06), also detectable by a cDNA probe. The genomic DNA probe is technically superior to the cDNA probe and has been used in three families with haemophilia B (factor IX deficiency). The polymorphic marker segregates with the deleterious mutation, allowing the identification or exclusion of carriers. The allelic frequencies of the Taq I polymorphism are virtually ideal. Therefore, such a polymorphism should be helpful both in genetic counselling of approximately 40% of affected families and in prenatal diagnosis.