Thromb Haemost 2014; 112(03): 459-465
DOI: 10.1160/TH13-12-1060
Blood Coagulation, Fibrinolysis and Cellular Haemostasis
Schattauer GmbH

Characterisation of large F9 deletions in seven unrelated patients with severe haemophilia B

Xi Wu#
1   State Key Laboratory of Medical Genomics, Shanghai Institute of Hematology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
,
Yeling Lu#
2   Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
,
Qiulan Ding
2   Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
,
Guoling You
1   State Key Laboratory of Medical Genomics, Shanghai Institute of Hematology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
,
Jing Dai
2   Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
,
Xiaodong Xi
1   State Key Laboratory of Medical Genomics, Shanghai Institute of Hematology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
,
Hongli Wang
1   State Key Laboratory of Medical Genomics, Shanghai Institute of Hematology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
,
Xuefeng Wang
2   Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
› Author Affiliations
Financial support: This study was supported by the National Basic Research Program of China (2013CB96680), the Youth Program of National Natural Science Foundation of China 81000206 and the General Program of National Natural Science Foundation of China (81170480).
Further Information

Publication History

Received: 26 December 2013

Accepted after major revision: 25 March 2014

Publication Date:
20 November 2017 (online)

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Summary

Large deletions in the F9 gene are detected in approximately 5% of patients with severe haemophilia B, but only a few deletion breakpoints have been characterised precisely until now. In this study we identified a total of seven large F9 deletions in the index patients and nine female carriers by the AccuCopy technique. We also successfully characterised the exact breakpoints for each large deletion including four deletions encompassing the entire F9 gene by the genome walking method combined with primer walking strategy. The extents of deletion regions ranged from 11.1 to 884 kb. Microhomologies ranged from 2 to 6 bp were identified in the breakpoint junctions of six deletions. The other deletion occurred between two highly homologous sequences of the same long interspersed nuclear element 1 (LINE/L1). Non-homologous end joining (NHEJ) and microhomology-mediated break-induced replication (MMBIR) may be the main causative mechanisms for the six large deletions with microhomologies. Non-allelic homologous recombination (NAHR) may mediate the deletion occurred between the two tandem LINEs in the other large deletion. Repetitive elements and non-B DNA forming motifs identified in the junction regions may contribute to DNA breakage leading to large deletions.

# These authors contributed equally to this work.