A Pericentric Inversion Of Chromosome X Disrupting F8 And Resulting In Severe Haemophilia

Background and PurposeHaemophilia A(HA)is the most common X-linked recessive bleeding disorder and is caused by mutations in the F8 gene,resulting in a quantitative and qualitative abnormality of coagulation factor VIII.There is a wide spectrum of mutation in the F8 gene causing HA,including missense and nonsense mutations(59.83%),splice site mutations(6.72%),small deletions and insertions(del/ins)(22.46%),large deletions(9.18%),gross insertion/duplication(1.12%),complex rearrangements(0.52%)and regulatory abnormality(0.17%).Apart from these,inversion of intron 22(Inv22)is responsible for approximately 45% of severe HA cases,and inversion of intron 1(Inv1)for approximately 2-5% of severe HA cases,both of which disrupt the F8 coding sequence and cause severe HA.So far,pericentric inversions of X chromosome disrupting F8 gene have rarely been reported.In this report,we characterized the pericentric inversion of X chromosome associated with severe HA in a sporadic pedigree.MethodsPCR primer walking and genome walking strategies were applied to identify exact breakpoints of the inversion.Copy number variation(CNVs)of F8 and the whole chromosome were detected by Accu Copy and Affymetrix Cyto Scan HD assays.Karyotype analysis was performed by cytogenetic G banding technique.We applied a multiplex fluorescent PCR to detect somatic mosaic analysis of causative mutation in the maternal grandfather.ResultsWe identified a previously undescribed type of pericentric inversion inv(X)(p11.21q28)in the proband.One breakpoint was located inside intron 7,102 bp distance to exon 8 of the F8 on Xq28 of the X chromosome,which disrupted the transcription of F8 gene and was consistent with sever HA(FVIII:C <1%).The other breakpoint was located in the upstream of PFKFB1,3538 bp distance to exon 1 of the PFKFB1 gene on Xp11.21 of the X chromosome.The inversion segment was approximately 64.4% of the total X chromosomal length.G banded karyotype analysis of the X chromosome had confirmed the existing of pericentric inverted X chromosome in the proband and his mother.Haplotype analysis showed that the inversion was originated from his maternal grandfather,who was not a somatic mosaic of the inversion.This finding indicated that the causative mutation may originate from germ cells as a reason of a unique meiotic event(de novo mutation)or a rare possibility of a germ cell mosaicism involved partially the maternal grandfather's gonad.ConclusionIn Conclusions,the characteristic of pericentric inversion involving F8 extended the molecular mechanisms of HA.The pericentric inversion rearrangement could be explained by the mechanism of non-homologous end joining(NHEJ).