Antenatal diagnosis of haemophilia B by amplification and electrophoresis of an exon fragment with a short deletion.

Carrier identification and antenatal diagnosis were performed in 2 sisters by electrophoretic separation of the normal and abnormal bands obtained after amplification of a fragment of exon h in the factor IX gene. The mutation in the family had been characterised as an 8-base pair (bp) deletion in exon h. By amplification of a 326 bp fragment containing the site of deletion, the shorter 318 bp band of the haemophilia B gene could be separated by electrophoresis of the fragments. The comprehensive data collection at the Haemophilia Centre is of vital importance in the genetic counselling of haemophilia families, and was a crucial step for the successful diagnoses in these sisters.