A Novel Case of Hemophilia B Due to a Partial Duplication of the Factor 9 Gene

Abstract 4423

Hemophilia B is an X-linked recessive coagulation disorder. The disease is caused by a deficiency of procoagulant Factor IX and is characterised by easy bruising and prolonged bleeding and oozing after injury or surgery. The severity of the disease and the frequency of bleeding events vary, depending on the FIX clotting activity, and in severe cases males suffer from spontaneous joint and muscle bleeds which significantly impact on their health and quality of life. Hemophilia B is less common than Hemophilia A, with a frequency of approximately 1 in 25000 males worldwide. The F9 gene is located on the long arm of the × chromosome at Xq27. The gene comprises 8 exons, spanning approximately 33.5 kb DNA. The molecular basis of Hemophilia B is heterogeneous and to date over a 1000 different mutations have been reported, including missense and nonsense mutations, splicing mutations and large deletions. Here we report the identification of a previously uncharacterised duplication spanning a large part of the F9 gene in a patient with severe Hemophilia B. The patient, a 6 year old male of mixed Iranian and UK origin, was referred to the centre with severe Hemophilia B. He had a FIX level of less than 1iu/dL. No family history of bleeding diathesis could be confirmed due to loss of maternal family members in an earthquake. Mutation analysis of all exons including immediate flanking regions to allow detection of splice site mutations, and the 5’ and 3’ untranslated regions was performed by direct sequencing but no changes from the normal sequence were identified. There have been several reports of Hemophilia B being associated with partial duplications of the F9 gene so we analysed gene copy number using multiplex ligation-dependant probe amplification (MLPA). A large duplication, involving exons 2 to 6 was identified in the affected male. Subsequent analyses of maternal samples were normal, indicating that the mutation arose de novo.