PB0083 - Investigating genotype-phenotype relationships in thrombosis patients with PROC, PROS1 or SERPINC1 variants

Sunday, June 23, 2024

13:45 – 14:45 ICT

Room: Exhibition Hall

Presenting Author(s)

CV

Christine Van Laer, PharmD

Clinical Biologist
Department of Cardiovascular Sciences, Centre for Molecular and Vascular Biology, University of Leuven, Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium

Co-Author(s)

MV

Marthe Vanrenterghem

PharmD, Trainee Clinical biologist
Department of Laboratory Medicine, University Hospitals Leuven, Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium
MJ

Marc Jacquemin

Prof. Dr.
Department of Cardiovascular Sciences, Centre for Molecular and Vascular Biology, University of Leuven, Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium
SB

Sarissa Baert

Scientist
Center for Human Genetics, University Hospitals Leuven, Leuven, Belgium
3000, Vlaams-Brabant, Belgium
KM

Kruijt Mirjam

PhD
Department of Clinical Chemistry and Laboratory Medicine, Leiden University Medical Center, Leiden
Leiden, Zuid-Holland, Netherlands
LR

L. Renee Ruhaak

PhD, Associate professor
Department of Clinical Chemistry and Laboratory Medicine, Leiden University Medical Center, Leiden
Leiden, Zuid-Holland, Netherlands
Veerle Labarque

Professor
Department of Pediatric Hematology and Oncology, University Hospital Leuven Gasthuisberg, Leuven
ฺฺBrussels, Brussels Hoofdstedelijk Gewest, Belgium
Peter Verhamme, MD PhD

Professor
Department of Cardiovascular Diseases, University Hospitals Leuven, Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium
Thomas Vanassche

Professor
Department of Cardiovascular Diseases, University Hospitals Leuven, Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium
Kathleen Freson

Professor
Department of Cardiovascular Sciences, Centre for Molecular and Vascular Biology, University of Leuven, Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium

Background: Laboratory thrombophilia screening includes plasma level determination of protein C, protein S and antithrombin. Since 2019, a multigene panel test is used for clinical diagnosis of inherited thrombophilia, including genes coding for protein C (PROC), protein S (PROS1) and antithrombin (SERPINC1). We observed several patients without matching genotype-phenotype correlations.

Aims: We extended classic laboratory assays for patients with PROC, PROS1 and SERPINC1 variants with additional non-conventional assays to improve variant classification.

Methods: Additional laboratory assays were performed for protein C or S in 32 patients with (likely)pathogenic ((L)PV) variants or variants of unknown significance (VUS) in PROC1 or PROS1 and for 5 patients with VUS in SERPINC1. We used different clotting-based assays for protein C/S on ACL-TOP. Antithrombin protein evaluation was performed by mass spectrometry [Kruijt M., Res Pract Thromb Haemost 2023].

Results: The laboratory results for patients with PROS1 and PROC variants are shown in Figure 1. For protein C, 3 unrelated patients with LPV Arg42His had normal protein C levels with chromogenic test, while decreased to low-normal levels using clotting-based assay. Without genetics and only using the classic functional assay, these patients would remain undiagnosed. Patients carrying LPV PROS1 Heerlen variant showed variable levels using both assays and only genetics allows reliable detection. Performing extra assays for VUS didn’t support variant reclassification. LC-MRM-MS analysis of antithrombin was performed for 5 unrelated patients with VUS in SERPINC1 (Val30Glu/Ala296Pro). Interestingly, though these patients had normal antithrombin levels using the classic assay, LC-MRM-MS analysis showed decreased levels for each variant, allowing variant reclassification to LPV.

Conclusion(s): A two-step approach using different functional assays could be useful for patients with variants in PROC, PROS1 and SERPINC1 when the classic assays are normal to support genetic findings or reclassify VUS. In general, genetic testing seems more sensitive to detect alterations in natural anticoagulant system than functional assays.