Identification of a third rearrangement at Xq28 that causes severe hemophilia A as a result of homologous recombination between inverted repeats

Abstract

To cite this article: Pezeshkpoor B, Rost S, Oldenburg J, El-Maarri O. Identification of a third rearrangement at Xq28 that causes severe hemophilia A as a result of homologous recombination between inverted repeats. J Thromb Haemost 2012; 10: 1600-8.Summary. Background: Intrachromosomal homologous recombination between inverted repeats on the X chromosome account for about half of severe hemophilia A cases. Repeats in F8 intron 1 and intron 22 can recombine with homologous inverted repeats located about 200 kb upstream and 500 kb downstream of F8, respectively, resulting in partial sequence inversion of the F8 open reading frame and, subsequently, no functional protein production. Objectives: In the present study, we characterize a third novel homologous recombination at Xq28 consistent with absence of F8 transcription that we previously reported for the affected chromosome of the index patient as well as his mother and sister. Results: The rearrangement occurs between a repeat in F8 intron 1 (Int1R-1) and an inverted identical repeat (Int1R-2d) in intron 2 of a duplicated copy of IKBKG located about 386 kb upstream of F8. The rearrangement was confirmed by Southern blot and inverse PCR and results in failure of PCR amplification across Int1R-1. Conclusion: We developed a PCR-based diagnostic method that can be used to screen for this genetic rearrangement in cases of severe hemophilia A for which mutations cannot be identified.

Aberrant F8 gene intron 1 inversion with concomitant duplication and deletion in a severe hemophilia A patient from Southern Italy

“…1A). Aberrant diagnostic patterns for inv1 have been occasionally described in severe HA, suggesting the possible existence of extra copies of the int1h region, as shown in int22h‐related inversions [6–8]. In order to detect possible quantitative genomic changes, as copy number variations (CNVs), responsible of the unusual results, we applied different technical approaches, such as multiplex ligation‐dependent probe amplification (MLPA), array comparative genomic hybridization (aCGH) and quantitative‐PCR (qPCR) (details available upon request).…”

Historical Review on Genetic Analysis in Hemophilia A

“…Several gross complex rearrangements in F8, in addition to the well-known intron 22/1 inversions, have been reported. One of the first complex rearrangements in F8 because of slipped mispairing during replication and intragenic recombination was reported by Tavassoli et al 55 Furthermore, nonhomologous end-joining 56 and unequal homologous Alu-mediated recombination, 57,58 large deletions (20.7 kb) within the F8 gene involving long interspersed nuclear element-1 (LINE-1), 59 complex rearrangements consisting two deletion/insertion events at Xq28, 60 and a third inversion due to homologous recombination of inverted repeats within intron 1 61 have been described. The high frequency of micro/macro homologies and repetitive sequences predispose to pathological genomic rearrangements at Xq28.…”

“…48,70 It could be speculated that in severe HA case where no mutation can be identified with the conventional methods, the cause for the disease might be related to breakpoints, large alterations, and rearrangements within the big intronic regions of F8. 61 Through these methods, novel intronic variations can be detected, which are localized in regions of F8 gene, which might explain the HA phenotype. Fig.…”

Molecular Basis of Hemophilia A

“…In this case, the matching repeat sequence is situated 386 kb upstream of F8 in the IKBKG gene. The frequency of this rearrangement as a cause for hemophilia A is unknown [19].…”