rs340875 — PROX1

Intronic variant in PROX1, the master transcription factor for lymphatic endothelial identity and valve development, associated with increased varicose veins risk through impaired lymphatic-venous drainage

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PROX1 rs340875 — A Lymphatic Valve Gene Variant Behind Varicose Veins

Deep beneath the skin, an invisible infrastructure of lymphatic vessels works alongside your veins to return fluid to circulation. The gene PROX1 — prospero homeobox 111 prospero homeobox 1
a transcription factor named for the Drosophila gene prospero, which controls cell identity — is the master regulator of lymphatic endothelial cell identity. Without PROX1, lymphatic vessels fail to form correctly; without properly formed lymphatic vessels and their valves, venous pressure rises and varicose veins develop. The rs340875 variant lies within an intron of PROX1, likely influencing how much of this transcription factor is produced in the endothelial cells that line lymphatic and venous valves.

The Mechanism

PROX1 sits at the apex of a transcriptional cascade that determines whether an endothelial progenitor cell becomes a lymphatic endothelial cell (LEC) rather than a blood vascular cell. It does this by forming a complex with β-catenin and TCF7L122 forming a complex with β-catenin and TCF7L1
components of the Wnt signaling pathway, which translates mechanical and biochemical cues into gene expression changes to amplify expression of two subordinate transcription factors, FOXC2 and GATA2, that are essential for the assembly and maintenance of lymphatic valve leaflets.

When PROX1 is deleted from valvular endothelial cells33 When PROX1 is deleted from valvular endothelial cells
Ho et al. 2023 Circulation Research, the consequence is progressive valve degeneration: aortic and mitral valves become thick and myxomatous, FOXC2 expression falls, and extracellular matrix composition is disrupted with excess proteoglycan accumulation. PROX1 suppresses PDGF-B signaling to maintain healthy valve architecture; without it, PDGF-B runs unchecked and the valve structure breaks down.

rs340875 is an intronic variant — it does not change the PROX1 protein sequence, but intronic variants in transcription factor genes can alter splicing efficiency, mRNA stability, or regulatory element activity, affecting the total amount of functional protein produced in endothelial tissues. The C allele is the risk-associated allele identified at the PROX1 locus in varicose veins genetics.

The Evidence

Ahmed et al. 202244 Ahmed et al. 2022
Genome-wide association analysis and replication in 810,625 individuals with varicose veins, Nature Communications conducted the largest varicose veins GWAS to date: 135,514 cases and 675,111 controls drawn from UK Biobank (401,656 individuals) and the 23andMe research cohort (408,969 individuals). The study identified 49 independent genetic signals across 46 susceptibility loci, mapping 237 genes. Pathway analysis confirmed enrichment in lymphangiogenesis — implicating genes like PROX1 that regulate lymphatic vessel formation and valve integrity.

The PROX1 gene's role in valve disease extends beyond varicose veins. PROX1 is classified as required for the development of both lymphatic and venous valves; its loss from endothelial cells is sufficient to cause progressive myxomatous degeneration55 sufficient to cause progressive myxomatous degeneration
myxomatous meaning the valves accumulate abnormal proteoglycan-rich matrix that makes them floppy and incompetent of aortic and mitral valves. High PROX1 expression in specific endothelial cells is also the initiating signal for lymphatic valve specification66 initiating signal for lymphatic valve specification
Qu et al. 2015 Developmental Biology; cells that fail to upregulate PROX1 do not enter the valve-forming program.

The evidence level for rs340875 specifically is moderate: the PROX1 locus is robustly identified in a very large GWAS, and the biological mechanism is well-established, but the specific functional effect of rs340875 on PROX1 expression or splicing has not been independently characterized at the molecular level.

Practical Actions

For people carrying one or two C alleles at rs340875, the most directly relevant interventions address the lymphatic-venous drainage impairment that underlies varicose veins and venous insufficiency. Compression therapy is the first-line evidence-based intervention for venous reflux regardless of cause; for carriers of a lymphatic gene variant, it directly compensates for the drainage deficit that PROX1 reduction creates. Elevation reduces hydrostatic pressure in the dependent leg veins. Avoiding prolonged static postures — standing or sitting without movement — is specifically important when lymphatic pump function is genetically compromised.

Interactions

PROX1 operates at the top of the lymphatic transcriptional hierarchy. Its downstream targets include FOXC2 (encoded by FOXC2 at chromosome 16q24.1 — mutations in FOXC2 cause lymphedema- distichiasis syndrome) and GATA2. Variants in FOXC2, GATA2, or other lymphatic valve genes interacting with PROX1 may compound the risk of venous insufficiency in carriers of the rs340875 C allele, although specific gene-gene interaction data for this variant are not yet published.

Genotype Interpretations

What each possible genotype means for this variant.

GG Typical Lymphatic Valve Function Normal

No elevated PROX1-related venous insufficiency risk

You carry two copies of the reference G allele at rs340875. Your PROX1 gene at this locus follows the typical pattern not associated with elevated varicose veins risk from this variant. About 27% of people of European descent share this genotype. Standard measures to maintain venous circulation apply.

CG One Risk Allele Intermediate

Modestly elevated varicose veins risk from one copy of the PROX1 C allele

PROX1 sits at the top of the lymphatic transcriptional hierarchy. It initiates the formation of lymphatic valve leaflets by upregulating FOXC2 and GATA2 in valve-forming cells; it also maintains valve integrity by suppressing PDGF-B-mediated matrix breakdown. As a heterozygous C carrier, you have one allele at rs340875 that may reduce PROX1 transcription efficiency in lymphatic and venous endothelial cells, producing an intermediate phenotype: mildly compromised lymphatic drainage capacity and modestly elevated hydrostatic venous pressure in dependent limbs over time.

The clinical consequence is an increased tendency toward varicose veins, chronic venous insufficiency, and leg heaviness or swelling — especially with prolonged standing or sitting, obesity, or pregnancy. The risk is not deterministic; many people with this genotype never develop symptomatic varicose veins, particularly if they maintain good leg muscle pump activity and avoid prolonged venous stasis.

CC Two Risk Alleles High Risk

Elevated varicose veins and venous insufficiency risk from two copies of the PROX1 C allele

Carrying two C alleles at rs340875 likely produces the largest reduction in PROX1 expression from this intronic regulatory variant. PROX1 drives valve-forming endothelial cells to upregulate FOXC2 and GATA2, which assemble and maintain lymphatic valve leaflets. It also suppresses PDGF-B signaling to protect valve extracellular matrix from myxomatous degeneration. When PROX1 levels fall, lymphatic valve leaflets may be reduced in size, asymmetric, or structurally compromised — impairing their ability to prevent retrograde lymph flow and maintain the low interstitial fluid pressures that allow veins to drain.

The consequence is a genetic predisposition to chronic venous insufficiency, varicose veins, and leg edema. The risk is compounded by lifestyle factors that increase venous hydrostatic pressure: prolonged standing, sedentary sitting, obesity, pregnancy, and prior venous thrombosis. For CC carriers, proactive compression and venous surveillance are genetically informed prevention strategies. If varicose veins are already present and symptomatic, discussing vascular evaluation with a physician is appropriate — thermal ablation, sclerotherapy, and other minimally invasive options are highly effective and have largely replaced surgical stripping.