MOLECULAR FEATURES OF A LARGE DELETION IN THE FACTOR VIII GENE (F8) SUGGEST THE INVOLVEMENT OF THE RETROPOSITION MACHINERY.

ROSSETTI LC, RADIC P, LARRIPA IB, DE BRASI CD

Vancouver, Canadá.

Congreso; XXVII International Congress of the Word Federation of Hemophilia (WFH).; 2006

Word Federation of Hemophilia (WFH).

Large deletions in F8 account for about 10-15% of severe (se) hemophilia A (HA). Although large gene rearrangements cause an important number of genome-wide inherited disorders, the molecular mechanism involved remains poorly understood. This abstract details characterization of an interesting non-homologous mediated rearrangement of the F8. Case report: a sporadic seHA patient without detectable inhibitors demonstrated a consistent absence of PCR-amplification of exon-10 and exon-11 (delE10_E11). Long-distance (LD) PCR amplification from uninvolved vicinal regions permitted carrier detection in the family and the isolation of the deletion breakpoints. Molecular analysis: DNA sequencing and bioinformatics studies indicate that the molecular rearrangement is notably complex as it involved the ectopic complementary insertion of at least two separated intronic sequences (IVS9+2358_+2287 and IVS10+73_+147), two intronic deletion breakpoints (F8-5’: IVS10+72 and F8-3’: IVS11+492), and one 13 bp-deletion affecting exon-10/IVS10 boundary (TACCAAAAGgtaa). To explain the molecular event it was drawn a hypothesis which includes a putative insertion of relevant segments from the F8 primary transcript via retroposition followed by DNA repair; supported by the L1-retroposition theory (internal priming, retroposition-associated large and short deletions of the element and the target) and the finding in the rearranged sequences of retrotrancriptase-endonuclease recognition motive (aaaatt), and microhomologies at or close points of rupture-rejoining. This work points the utility of LD-PCR to study large deletions as it enabled detection of the F8 defect in heterozygous females, and permits the isolation of the molecular event for further analysis. Additionally, it suggests that the retroposition machinery may be involved in large non-homologous rearrangements.