Thromb Haemost 2021; 121(12): 1588-1598
DOI: 10.1055/a-1450-8568
Coagulation and Fibrinolysis

Molecular Characterization of Two Homozygous Factor VII Variants Associated with Intracranial Bleeding

1  Department of Hematology, Oslo University Hospital, Oslo, Norway
2  Research Institute of Internal Medicine, Oslo University Hospital, Oslo, Norway
,
Maria Eugenia Chollet*
1  Department of Hematology, Oslo University Hospital, Oslo, Norway
2  Research Institute of Internal Medicine, Oslo University Hospital, Oslo, Norway
,
Marit Sletten
3  Department of Medical Genetics, Oslo University Hospital, Oslo, Norway
,
Benedicte Stavik
1  Department of Hematology, Oslo University Hospital, Oslo, Norway
2  Research Institute of Internal Medicine, Oslo University Hospital, Oslo, Norway
,
Ellen Skarpen
4  Core Facility for Advanced Light Microscopy, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
,
Paul Hoff Backe
5  Department of Microbiology, Oslo University Hospital, Oslo, Norway
6  Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway
,
Bernd Thiede
7  Department of Biosciences, University of Oslo, Oslo, Norway
,
Heidi Glosli
8  Department of Pediatric Research, Division of Pediatric and Adolescent Medicine, Oslo University Hospital, Oslo, Norway
9  Centre for Rare Disorders, Division of Pediatric and Adolescent Medicine, Oslo University Hospital, Oslo, Norway
,
Carola Elisabeth Henriksson
6  Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway
10  Institute of Clinical Medicine, University of Oslo, Oslo, Norway
,
Nina Iversen
3  Department of Medical Genetics, Oslo University Hospital, Oslo, Norway
› Author Affiliations
Funding This work was funded by the South-Eastern Norway Regional Health Authority. Mass spectrometry-based proteomic analyses were performed by the Proteomics Core Facility, Department of Biosciences, University of Oslo. This facility is a member of the National Network of Advanced Proteomics Infrastructure (NAPI), which is funded by the Research Council of Norway INFRASTRUKTUR-program (project number: 295910).

Abstract

Clinical parameters have been extensively studied in factor (F) VII deficiency, but the knowledge of molecular mechanisms of this disease is scarce. We report on three probands with intracranial bleeds at an early age, one of which had concomitant high titer of FVII inhibitor. The aim of the present study was to identify the causative mutations and to elucidate the underlying molecular mechanisms. All nine F7 exons were sequenced in the probands and the closest family members. A homozygous deletion in exon 1, leading to a frame shift and generation of a premature stop codon (p.C10Pfs*16), was found in proband 1. Probands 2 and 3 (siblings) were homozygous for a missense mutation in exon 8, resulting in a glycine (G) to arginine (R) substitution at amino acid 240 (p.G240R). All probands had severely reduced FVII activity (FVII:C < 1 IU/dL). Treatment consisted of recombinant FVIIa and/or plasma concentrate, and proband 1 developed a FVII inhibitor shortly after initiation of treatment. The FVII variants were overexpressed in mammalian cell lines. No FVII protein was produced in cells expressing the p.C10Pfs*16 variant, and the inhibitor development in proband 1 was likely linked to the complete absence of circulating FVII. Structural analysis suggested that the G to R substitution in FVII found in probands 2 and 3 would destabilize the protein structure, and cell studies demonstrated a defective intracellular transport and increased endoplasmic reticulum stress. The molecular mechanism underlying the p.G240R variant could be reduced secretion caused by protein destabilization and misfolding.

Author Contributions

E.A. and M.E.C. designed and performed the research, analyzed the data, and wrote the manuscript. M.S., B.S., E.A., P.H.B., B.T., H.G., C.E.H., and N.I. designed and performed the research and analyzed the data. N.I. conceived the study. All authors critically read the manuscript and approved the final version.


Note

Written consent to publish the clinical data was obtained from the parents, as the probands and siblings were minors, and ethical approval was obtained from the data protection officer at the hospital.


* E.A. and M.E.C. are co-first authors.


Supplementary Material



Publication History

Received: 19 February 2021

Accepted: 12 March 2021

Publication Date:
19 March 2021 (online)

© 2021. Thieme. All rights reserved.

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany