Molecular insights into the mechanism of large F8-deletions causing severe haemophilia A in two families: full breakpoint characterization by non-conventional approaches and bioinformatic analysis of implicated DNA elements

WAISMAN K; RADIC CP; ZIEGLER B; ROSSETTI LC; ABELLEYRO MM; MARCHIONE VD; DE BRASI CD

Kuala Lumpur

Congreso; World Federation of Hemophilia (WFH) 2020 World Congress; 2020

World Federetion of Haemophilia

Structural variants (SV) resulting in large deletions of the F8 cause 8-15% of cases with severe-haemophilia A (HA) and predispose to develop FVIII inhibitors, the major complication in HA treatment. Despite the involvement of high-throughput massive parallel sequencing approaches to identify genomic variation in the clinical practice, detection and characterization of breakpoints of large deletions and, consequently, the analysis of the mechanisms leading to its origin in the human genome still remains a challenge. Several molecular mechanisms have been associated with the origin of different aberrant genomic rearrangements. These models include non-allelic homologous recombination (NAHR) and non-homologous end joining (NHEJ), microhomology-mediated end joining (MMEJ) associated with repair of DNA breaks, and microhomology-mediated break-induced replication (MMBIR) and fork stalling and template switching (FoSTeS) associated with DNA synthesis. Different sequence motifs have been reported to stimulate events of localised double strand breaks (DSB) and leading to recombination. Some molecular rearrangements in the F8 have been associated with long interspersed nuclear elements (LINEs) and short interspersed nuclear elements (SINEs), such as Alu repeat sequences. Therefore, the full sequence characterization of SVs is crucial to elucidate the possible molecular mechanism involved. For this purpose, our objectives were to develop alternative approaches to diagnose and characterise large F8-deletions in hemizygous and heterozygous state and to estimate large F8-deletions mechanisms by looking at their breakpoints.