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    Oral Communication

    Diagnostics and OMICs

    High Throughput Methods for Improved Understanding of Coagulation and Bleeding

    OC 57.4 - Deciphering novel complex structural variations in severe hemophilia A patients by optical genome mapping

    Tuesday, June 27, 2023
    11:30 – 11:45 ET
    Room: 518
    Session Available As: On-Demand

      Presenting Author(s)

    • sf

      somayyeh fahiminiya, PhD (she/her/hers)

      Clinical molecular geneticist and Assistant professor
      Division of Hematology-Oncology, Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada.
      Halifax, Nova Scotia, Canada

      • Co-Author(s)

    • SO

      Spyros Oikonomopoulos

      Research Associate
      McGill Genome Centre, Department of Human Genetics, McGill University, Montreal, Québec, Canada.
      Montreal, Quebec, Canada

    • GR

      Georges-Etienne Rivard

      Medical Director, Hemophilia Center, CHU Sainte-Justine
      Division of Hematology-Oncology, Department of Pediatrics, Université de Montréal, CHU Sainte-Justine, Montréal, Quebec, Canada
      Montreal, Quebec, Canada

    • MG

      Mira Gandhi

      Research Assistant
      Pacific Northwest Research Institute (PNRI), Seattle, Washington, USA.
      Seattle, Washington, United States

    • PS

      Patrick Scott

      Clinical Molecular Geneticist
      Molecular Diagnostic Laboratory, CHU Sainte-Justine, Montréal, Québec, Canada.
      Montreal, Quebec, Canada

    • AM

      Alexandre Montpetit

      Scientific Director
      Centre d'expertise et de services Génome Québec, Montréal, Québec, Canada.
      Montreal, Quebec, Canada

    • SC

      Shu-Huang Chen

      Research Assistant
      McGill Genome Centre, Department of Human Genetics, McGill University, Montreal, Québec, Canada.
      Montreal, Quebec, Canada

    • Kp

      KyungHee park

      Research Assistant
      Pacific Northwest Research Institute (PNRI), Seattle, Washington, USA
      Seattle, Washington, United States

    • CV

      Catherine Vezina

      Pediatric Hematologist-Oncologist
      Montréal Children's Hospital, McGill University Health Center, Montréal, Québec, Canada.
      Montreal, Quebec, Canada

    • JS

      Jean St-Louis

      Pediatric Hematologist-Oncologist
      Division of Hematology-Oncology, Department of Pediatrics, Université de Montréal, CHU Sainte-Justine, Montréal, Quebec, Canada.
      Montreal, Quebec, Canada

    • JR

      Jiannis Ragoussis

      Head of Genome Sciences at the McGill University
      McGill Genome Centre, Department of Human Genetics, McGill University, Montreal, Québec, Canada.
      Montreal, Quebec, Canada

    • CC

      Claudia M. B. Carvalho

      Assistant Professor
      Pacific Northwest Research Institute (PNRI), Seattle, Washington, USA.
      Seattle, Washington, United States

    • GM

      Grant A. Mitchell

      Clinical Geneticist
      Division of Medical Genetics, Department of Pediatrics, CHU Sainte-Justine and Université de Montréal, Montreal, Québec, Canada
      Montreal, Quebec, Canada

    • JS

      Jean-Francois Soucy

      Clinical Geneticist
      Division of Medical Genetics, Department of Pediatrics, CHU Sainte-Justine and Université de Montréal, Montreal, Québec, Canada.
      Montreal, Quebec, Canada

    • JG

      Julie Gauthier

      Clinical Molecular Geneticist
      Molecular Diagnostic Laboratory, CHU Sainte-Justine, Montréal, Québec, Canada.
      Montreal, Quebec, Canada

    Background: Around 50% of severe hemophilia A (HA) is caused by recurrent inversions (inv1 or inv22) disrupting the F8 gene. The underlying genetic cause cannot be precisely determined in ~5% of patients using routine diagnostic (Dx) assays. In these cases, deep intronic variants or more complex structural variations (SVs) can be causal.

    Aims: To investigate the molecular basis of unusual results obtained with Dx assays in severe HA families.

    Methods: Dx assays do not detect aberrations outside F8. Optical Genome Mapping (OGM) is a newly developed technology that applies enzymes to fluorescently tag high molecular weight DNA at specific sequence motifs without nicking the DNA. This property enables phasing multiple breakpoint junctions due to the presence of SVs in the same long molecules. We evaluated the Dx capability of OGM in severe HA after obtaining informed consent from families.

    Results: OGM characterized the exact position and orientation of SVs in two HA families: Family 1) a 141.5 kb balanced inversion disrupting intron 1 of F8 (inv1). Family 2) a novel inv22 (~567 kb) concomitant with an extragenic duplication of ~193 kb upstream of F8. A critical gene in the region was RAB39B, a candidate gene for intellectual disabilities (ID) in the Xq28 duplication syndrome mediated by the int22h-related repeats. OGM showed the inversion breakpoint bisected one copy of RAB39B, and another copy was left untouched, which explains the lack of ID in the proband.

    Conclusion(s): OGM has the potential to become a next-generation Dx tool to characterize the molecular basis of severe HA as it can detect known recurrent (inv1, inv22, Del22, and Dup22) as well as more complex SVs affecting F8. Analysis of ultra-long DNA molecules allows resolution and visualization of SVs invisible to other Dx methods.

    Learning Objectives:

    • Explain how Optical Genome Mapping Technology (OGM) works and its application for diagnosing severe hemophilia A.
    • Tackle unsolved severe hemophilia A cases using OGM as a next-generation diagnostic tool.
    • Visualize examples of recurrent or novel complex genomic rearrangements deciphered by OGM.