Diagnosis of two related carriers of severe haemophilia B with no family history

Haemophilia B is an X-linked disease affecting 1 in 30 000 males. Carrier d iagnosis is usually carried out only in female relatives of haemophilic mal es, and the likelihood of discovering a carrier without a haemophilic male is very low. In this report we present the cases of two related women witho ut a family history of haemophilia who were diagnosed as haemophilia B carr iers. Following a minor haemorrhage in the proband, she and her mother were thought to be haemophilia B carriers because of a low factor IX level (16 and 23 IU dL(-1), respectively; normal values >50 IU dL(-1)). The nonsense mutation C31118T, which is associated with severe haemophila B, was detecte d in both women. This allowed us to diagnose them as being definite carrier s of severe haemophilia B and give appropriate genetic counselling.