FactorVIII Gene Modifications Observed in Acquired Hemophilia.

Abstract 4450

Acquired hemophilia is a rare bleeding disorder caused by autoantibodies directed against the coagulation factor VIII (FVIII). Usually acquired hemophilia is found in the elderly person, autoimmune disorder or women in the postpartum. Incontrast to alloantibody inhibitors of hereditary hemophilia, acquired inhibitor is presumably due to a spontaneous autoimmune disorder in which patients with previously normal hemostasis develop autoantibodies against FVIII. However, the precise cause of the antibody formation remains obscure and the possibility of abnormal FVIII protein derived from the FVIII gene mutation might have caused the antibody formation was investigated by direct FVIII gene sequencing method. Blood samples were obtained from a 72 year old male who initially presented with a large hematoma in the Rt. Shoulder, and had a prolonged aPTT (46 sec), FVIII level of 14%, and VIII inhibitor titer 2∼5 BU/ml. Direct sequencing of FVIII was performed via amplification for all 26 exons, including the 5′-UTR and 3′-UTR region, using the 35 synthesized primers. Sequencing was conducted using BigDye Terminator cycle sequencing kit on an ABI 3730XL DNA analyzer (Applied Biosystems, Foster City, CA). Sequence variations were analyzed with CLC main workbench program (CLC, Aarhus. Denmark). Firstly, we analyzed translational region of FVIII gene. But we couldn't find any sequence variation. Then we analyzed the sequence of untranslationed region, 5′-UTR and 3′-UTR. As a result, we identified gene variation of substitution to c.8889G>A in the 3′-UTR. We speculate that this variation may have affected the RNA processing or mRNA stability. Thus we need to study about the relationship between this sequence variation and FVIII function. Also, we will investigate whether this gene variation is functional mutation. The cause of acquired hemophilia remains obscure. Variations in FVIII molecules including in untranslatable 5′- or 3′-region should be studied further to delineate the cause of antibodies in acquired HA. We expect that the accumulation of sequence variation can help to understand the cause of acquired hemophilia through this study.