PB0256 - A novel complex gene rearrangement between F8 and chr10 causes moderate hemophilia A with a family history of inhibitor development

Sunday, June 23, 2024

13:45 – 14:45 ICT

Room: Exhibition Hall

Co-Author(s)

YM

Yinqi Mao

Ruijin Hospital, No. 197 Ruijin Second Road, Huangpu District, Shanghai
Shanghai Jiaotong University School of Medicine
Shanghai, Shanghai, China (People's Republic)

Co-Author(s)

HZ

Huayang Zhang

Ruijin Hospital, No. 197 Ruijin Second Road, Huangpu District, Shanghai
Shanghai Jiaotong University School of Meddicine
Shanghai, Shanghai, China (People's Republic)
GC

Guangming Chen

Graduate student
Shanghai Jiaotong Unicersity School of Medicine
Shanghai, Shanghai, China (People's Republic)
QD

Qiulan Ding

Professor
Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
Shanghai, Shanghai, China (People's Republic)
Runhui Wu, PhD, MD

Professor
Department of Hematology, Beijing Children’s Hospital, Capital Medical University, National Center for Children’s Health, Beijing, 100045, China
Beijing, Beijing, China (People's Republic)

Presenting Author(s)

Liyang Zhou, PhD student in medicine

Graduate student
Department of Laboratory Medicine, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
Shanghai, Shanghai, China (People's Republic)

Background: The development of inhibitors during replacement therapy is one of the major challenges in the management of hemophilia A (HA). While the F8 variant type is the most important risk factor for inhibitor development, the development of inhibitors with family history is still not clear.

Aims: To analyze the pathogenic variant in a moderate HA pedigree with variant negative through conventional genetic diagnosis and discuss the potential high-risk factors for their familiar inhibitor development (Figure 1).

Methods: The candidate complex rearrangement of F8 was detected by whole genome sequencing (WGS) combined with optical genome mapping (OGM). The effect of the variant on F8 transcription was analyzed by reverse transcription-PCR (RT-PCR). Potential immune-related genetic risk factors for inhibitor development were analyzed by whole exome sequencing (WES) using blood samples from 4 moderate HA patients in this pedigree.

Results: WGS with OGM first found a complex gene rearrangement between F8 and chr10, an inverted 76.6-kb fragment from chr10 inserted between 2 tandem duplications of F8 intron 6 in this pedigree. RT-PCR found that the variant could produce residual full-length normal F8 mRNA with the giant intron 6 caused by the variant (Figure 2). Analysis of immune-related genetic risk factors by WGS found that 4 patients all carried HLA-DRB1*09:01 and DQB1*03:03 alleles, and TRIM77 c.644A>G heterozygous variant.

Conclusion(s): We found a novel complex gene rearrangement causing moderate HA with residual normal F8 mRNA, which could be explained by recursive splicing and consistent with the phenotype. We speculated that trace expression of normal FVIII could not induce stable immune tolerance, resulting in the high risk of inhibitor development in this pedigree. HLA-DRB1*09:01, DQB1*03:03 and variants on TRIM77 could further increase the risk of inhibitor development.