Recurrent inversion with concomitant deletion and insertion events in the coagulation factor VIII gene suggests a new mechanism for X-chromosomal rearrangements causing hemophilia A

Abstract

Recurrent int22h-related inversions in the coagulation factor VIII gene (F8) are the most common cause of severe hemophilia A. Such inversions have repeatedly been hypothesized to be associated with concomitant deletions that are responsible for an increased risk of immune responses against therapeutic exogenous factor VIII. However, exact DNA breakpoints have not yet been reported. In a patient with persistent factor VIII-inactivating antibodies, molecular analysis of F8 including Southern Blot, long-range PCR and primer walking techniques revealed a combination of an int22h2-related inversion, deletion of exons 16-22 and insertion of a duplicated part of the X-chromosomal MPP1 gene. This novel genomic rearrangement was also detectable in the patient's mother, but absent in both maternal grandparents. The genetic defect most likely originated from a complex Xchromosomal recombination event during spermatogenesis due to the formation of a DNA loop stabilized by Alu and LINE repeat elements. Elucidation of such combined mutations may allow early identification of patients at high risk of developing factor VIII-neutralizing antibodies and will help to understand the mechanisms behind gross chromosomal rearrangements causing hemophilia A and other diseases.

X-Linked TEX11 Mutations, Meiotic Arrest, and Azoospermia in Infertile Men

“…The molecular structure of the deletion junction fragments suggests a complex mechanism involving an initial inversion of the region, leading to X-chromosome deletions, duplications, or both 29,30,33 (Fig. S2 in the Supplementary Appendix).…”

“…Therefore, we hypothesize that the TEX11 inversion recurs in asymptomatic female carriers, as was shown in the case of exon 22 of F8 (encoding coagulation factor VIII) and multiple exonic inversions in the Duchenne's muscular dystrophy gene that encodes the protein dystrophin. 29,30,34,35 This suggests that TEX11 -associated male infertility is underestimated because of a potential, undetected high-carrier frequency of inversions in the female population and a high risk of new inversion formation in germ cells of fathers of advanced age. 36,37 …”

A possible mechanism for Inv22‐related F8 large deletions in severe hemophilia A patients with high responding factor VIII inhibitors

“…Several independent reports using Southern blot and long PCR analyzes have shown unusual patterns with both int22h ‐related inversion and deletion of F8 causing severe HA (‘rare inversion type’) [8,23,24], and we identified three such cases in our study. So far, we identified three such large deletions in 63 severe HA patients tested for Inv22 in our laboratory, these deletions could be missed using any of the standard Southern blot or PCR approaches to analyze the Inv22.…”

DNA repair systems

“…SINEs and LINEs may move around the genome, usually by a 'copy and paste' mechanism and are classed as retrotransposons (class II transposons). The index pa ent carrying the F8 gene dele on is usually the first case in the family, born to a carrier mother [1546,1547]. Homologous recombina on between repeats producing dele ons or inversions in the Factor IX (F9) gene have been found to be the most common muta on causing Haemophilia B as well.…”