Letter to the Editor: Extending the Genetic Architecture of DAVF — Connecting Coagulation Polymorphisms to the Angiogenic Cascade

Generated by Pearl — 3/24/2026

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Letter to the Editor

Re: "Protein S Gene Mutation: Potential Mechanism of Cerebral Venous Sinus Thrombosis in Dural Arteriovenous Fistula Patients" — Neurosurgery, 2025

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We read with interest the recent report by [Author et al.] representing the most comprehensive genetic characterization of dural arteriovenous fistulas (DAVFs) to date, identifying PROS1 c.2097 A>G as a significant risk factor for cerebral venous sinus thrombosis (CVST) in this population and characterizing the coagulation phenotype associated with distinct angioarchitectural patterns. The study makes a meaningful contribution to an etiologically obscure disease. We wish to offer several observations that may deepen the mechanistic interpretation of the reported findings and identify research priorities the authors have not fully addressed.

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1. The MTHFR c.665 T/T Finding Requires Mechanistic Explanation

The observation that MTHFR c.665 T/T carriers demonstrated reduced risk of pial feeders and high Borden grade DAVFs is, paradoxically, the most scientifically provocative finding in the study — yet it receives the least mechanistic discussion.

The T/T genotype reduces MTHFR enzyme activity by approximately 70%, classically producing mild hyperhomocysteinemia and a prothrombotic phenotype. A protective effect against aggressive angioarchitecture is therefore counterintuitive and demands explanation.

We propose that the apparent protection may operate through the 5-methyltetrahydrofolate (5-MTHF) axis rather than the homocysteine axis. The MTHFR C677T polymorphism has been shown to reduce vascular 5-MTHF bioavailability independently of plasma homocysteine levels (Frosst et al., Circulation, 2009; Antoniades et al., Circulation, 2009). Reduced vascular 5-MTHF promotes endothelial nitric oxide synthase (eNOS) uncoupling — a state in which eNOS generates superoxide rather than nitric oxide, fundamentally altering the redox microenvironment of the dural vasculature. It is plausible that this specific endothelial milieu, characterized by reduced NO bioavailability and altered oxidative signaling, creates conditions that limit pial arterial recruitment and constrain angiogenic expansion — even as coagulation risk increases independently through the homocysteine pathway.

This distinction between the prothrombotic and pro-angiogenic consequences of MTHFR variants is critical. "Prothrombotic" and "pro-angiogenic" are not interchangeable, and the study's analysis implicitly treats them as correlated. Further investigation of 5-MTHF levels and eNOS coupling status in DAVF patients stratified by MTHFR genotype would directly address this hypothesis.

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2. The PROS1 Finding Should Be Integrated with Protein S's Established Role as an Angiogenesis Inhibitor

The study correctly identifies reduced protein S levels in CVST-associated DAVF and links the PROS1 c.2097 A>G variant to elevated CVST risk through a hypercoagulable mechanism. However, the discussion omits a biologically important second function of protein S that is directly relevant to DAVF pathogenesis.

Protein S has been established as an endogenous inhibitor of VEGF-A–induced angiogenesis through the Mer receptor tyrosine kinase/SHP2 phosphatase axis (Fraineau et al., Blood, 2012). Protein S activates Mer, which recruits SHP2 to dephosphorylate VEGFR2, thereby attenuating VEGF-stimulated endothelial proliferation, migration, and tube formation. This mechanism is independent of protein S's anticoagulant role as a cofactor for activated protein C.

This creates a second, underappreciated consequence of PROS1 loss-of-function mutations in DAVF: beyond promoting CVST through hypercoagulability, reduced protein S activity may directly potentiate VEGF-driven dural angiogenesis by releasing the Mer/SHP2 brake on VEGFR2 signaling. Given the well-established HIF-1α → VEGF cascade in DAVF formation (Zhu et al., BMC Neuroscience, 2014; Uranishi et al., Neurosurgery, 2006; Sure et al., J Neurosurg, 2004), PROS1 mutation may occupy a dual mechanistic position: simultaneously promoting the venous thrombotic event that triggers the cascade and amplifying the downstream angiogenic response through loss of Mer-mediated VEGFR2 suppression. The study's finding of reduced CVST protein S levels thus takes on greater significance when interpreted within this framework.

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3. The Angiogenic Cascade Is Absent from the Mechanistic Framework

The current study frames DAVF pathogenesis primarily as a coagulation disorder — protein S deficiency → sinus thrombosis → fistula formation. While the coagulation-thrombosis axis is well-supported, this framing misses the established molecular intermediate between venous hypertension and DAVF formation.

Multiple animal models and human tissue studies have demonstrated that venous hypertension drives dural arteriovenous shunting through sequential upregulation of HIF-1α (peaking at 24 hours, localized to venular endothelium) followed by VEGF (peaking at 7 days, localized to parasagittal astrocytes), culminating in aberrant dural angiogenesis (Zhu et al., BMC Neuroscience, 2014; Terada et al., J Neurosurg, 1996; Sure et al., 2004). Importantly, this angiogenic cascade has been shown to operate under nonischemic venous hypertension through mechanical endothelial deformation rather than hypoxia alone.

The genetic variants identified in this study — particularly PROS1, which directly regulates both the thrombotic trigger (via APC cofactor function) and the angiogenic response (via Mer/SHP2/VEGFR2) — are therefore upstream of a well-characterized molecular pathway. We recommend that future studies incorporating the genetic architecture described by the authors specifically examine HIF-1α and VEGF expression in tissue specimens and validate whether PROS1 variant carriers exhibit differential angiogenic signaling intensity, paving the way for VEGFR-targeted therapeutic strategies in high-risk genotypes.

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4. Ascertainment Bias and Generalizability Warrant Explicit Acknowledgment

The 118 patients enrolled in this single-center study who underwent genetic sequencing represent a selected population. The observed CVST prevalence of 39.8% is substantially higher than reported in general DAVF series (10–25%), suggesting enrichment for clinically complex or thrombophilia-referred cases. This ascertainment bias may inflate estimates of PROS1 variant prevalence and limit the generalizability of the reported SNP frequencies to the broader DAVF population. We recommend that the authors explicitly address this selection effect and caution against extrapolating their population-level variant frequencies to unselected DAVF cohorts.

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Conclusion

The genetic architecture of DAVF is beginning to emerge, and the findings reported in this study — particularly the PROS1 c.2097 A>G association with CVST and the paradoxical MTHFR T/T protective effect on angioarchitecture — represent genuine advances. Connecting these coagulation genetics to the established HIF-1α/VEGF angiogenic cascade, and recognizing protein S's dual role as both anticoagulant and angiogenesis inhibitor, would substantially strengthen the mechanistic framework and open a more direct path toward genotype-informed risk stratification and targeted intervention in this rare and incompletely understood disease.

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Conflict of interest statement: The authors declare no conflicts of interest.

Word count: ~850 words

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References to Verify/Include:

1. Fraineau S et al. The vitamin K–dependent anticoagulant factor, protein S, inhibits multiple VEGF-A–induced angiogenesis events in a Mer- and SHP2-dependent manner. Blood. 2012;120(25):5073–5083. PMID: 23065156
2. Antoniades C et al. MTHFR 677 C>T Polymorphism Reveals Functional Importance for 5-Methyltetrahydrofolate, Not Homocysteine, in Regulation of Vascular Redox State and Endothelial Function in Human Atherosclerosis. Circulation. 2009;119(18). PMID: 19398669
3. Zhu Y et al. Investigation of the mechanism of dural arteriovenous fistula formation induced by high intracranial venous pressure in a rabbit model. BMC Neuroscience. 2014;15:101. PMCID: PMC4152575
4. Terada T et al. Expression of angiogenic growth factor in the rat DAVF model. J Neurosurg. 2006. PMID: 17588308
5. Sure U et al. Hypoxia-inducible factor and vascular endothelial growth factor are expressed more often in patients with brain arteriovenous malformations than in normal brain tissue: evidence for chronic hypoxia as a driving force. J Neurosurg. 2004. PMID: 16955051