Novel missense mutation in the coagulation factor IX catalytic domain associated with severe haemophilia B--Factor IXDelhi.

Factor IX is a vitamin K-dependent serine protease, which exists as a zymogen in the blood. On activation to factor IXa, by factor XIa or tissue factor-factor VIIa complex, it forms tenase complex with factor VIIIa, in the presence of Ca2+. This tenase complex enzymatically converts factor X to factor Xa, thereby bringing about the coagulation cascade. Mutations in factor IX gene have been shown to cause haemophilia B, which is inherited as an X-linked recessive disorder. Herein we report a novel missense mutation at the nucleotide position 30829-T > A in the exon 8 of factor IX gene. This transversion leads to the substitution of histidine 236 to glutamine. This resulting abnormal protein has been named factor IXDelhi. Molecular modelling was performed to predict the molecular pathology of this mutation. We predict that this change in the catalytic domain may affect the surface loop that accommodates Ca2+, thereby leading to severe bleeding disorder.