A factor IX mutation, verified by direct genomic sequencing, causes haemophilia B by a novel mechanism
Tsang, T.C.; Bentley, D.R.; Mibashan, R.S.; Giannelli, F.
EMBO Journal 7(10): 3009-3015
1988
ISSN/ISBN: 0261-4189 PMID: 3181127 Document Number: 307845
A novel factor IX gene mutation (factor IXLondon 2) has been characterized. This causes severe crm+ haemophilia B as the patient's plasma shows normal factor IX antigen level and <1% clotting activity. Sequence analysis of the entire cloned coding and promoter regions revealed a single point mutation: a G .fwdarw. A transition at position 31 119. This region of patient's DNA was amplified in vitro by the polymerase chain reaction and the nucleotide change was confirmed by direct sequencing of the amplified products. The mutation results in the substitution of the arginine at position 333 by glutamine. This arginine residue is absolutely conserved in the catalytic domain of normal human and bovine factor IX, X and prothrombin. The substitution by glutamine causes the loss of a positive charge from the surface of the factor IXLondon2 protein. This mutation pinpoints a previously unknown, fucntionally critical feature of factor IX which may be involved in substrate or co-factor binding.