rs4252185 — PLG

PLG Intron 1 Variant — A Signal at the Plasminogen Locus

Plasminogen is one of the body's most versatile proteases-in-waiting. Synthesised primarily in the liver, it circulates as an inactive zymogen until activated by tissue plasminogen activator (tPA) or urokinase (uPA)¹¹ tissue plasminogen activator (tPA) or urokinase (uPA)
serine proteases released at sites of injury, infection, or thrombosis to form plasmin — the active enzyme that dissolves fibrin clots, remodels damaged extracellular matrix, recruits macrophages to sites of inflammation, and regulates the complement cascade. Variants across the PLG locus on chromosome 6q26 are among the strongest known genetic determinants of circulating plasminogen levels and downstream fibrinolytic capacity.

Rs4252185 sits 66 base pairs into the first intron of PLG (NM_000301.5:c.49+66T>C), on the plus strand of chromosome 6 at position 160702419 (GRCh38). The C allele is the minor variant, occurring in approximately 9% of Europeans but nearly absent in East Asian populations (under 0.1%), a pattern of population stratification characteristic of PLG-region haplotypes under selection pressure. This early-intron position is notable: intron 1 frequently harbours regulatory elements — branch-point sequences, intronic enhancers, and early splice signals — that can influence transcription initiation and pre-mRNA processing efficiency.

The Mechanism

Rs4252185 is classified as an intronic variant with no protein-coding consequence. The C allele has a low CADD score of 0.73²² CADD score of 0.73
a composite deleteriousness score where scores below 10 suggest limited expected functional impact at the individual variant level and a negative GERP conservation score (-2.70), indicating the position is not under strong evolutionary constraint across mammals.

Despite the modest predicted functional impact, the PLG locus is known to exert strong haplotype-level effects on plasminogen levels. Ma et al. 2014 demonstrated in a GWAS of over 3,000 individuals³³ Ma et al. 2014 demonstrated in a GWAS of over 3,000 individuals
published in Blood, the leading haematology journal that 9 of 11 genome-wide significant loci for plasma plasminogen levels cluster near PLG/LPA on chr6q26. Rs4252185 sits within the same genomic neighbourhood, and its C allele shows the European-enriched, East-Asian-depleted pattern typical of the PLG regulatory haplotype documented in that study. Whether rs4252185 is itself causal or in linkage disequilibrium with a functional regulatory variant elsewhere in the locus has not been directly established.

The Evidence

Rs4252185 has been captured in genome-wide analyses of coronary artery disease. Nurnberg et al. 2016⁴⁴ Nurnberg et al. 2016
a functional genomics analysis of 58 established CAD GWAS loci published in Circulation Research and Charmet et al. 2018⁵⁵ Charmet et al. 2018
a GWAS of CAD in patients with type 1 diabetes, published in Cardiovascular Diabetology both include the PLG locus in cardiovascular genetic analyses. The biological rationale is direct: plasminogen is essential for fibrinolytic clot dissolution in coronary arteries, and reduced plasminogen activity accelerates thrombotic occlusion.

The broader PLG-locus biology is well characterised through related variants. Plasminogen deficiency in mice causes spontaneous chronic otitis media in 100% of animals within 18 weeks⁶⁶ spontaneous chronic otitis media in 100% of animals within 18 weeks
with fibrin deposition, bacterial colonisation, and persistent neutrophil/macrophage infiltration in the middle ear, establishing fibrinolytic clearance as rate-limiting for middle ear health. Plasminogen also plays a direct role in innate immunity: Ploplis & Castellino 2014⁷⁷ Ploplis & Castellino 2014 showed that plasminogen-deficient mice have 60–90% reduced macrophage phagocytic uptake of apoptotic cells and pathogens. Barthel et al. 2014⁸⁸ Barthel et al. 2014 demonstrated that plasmin cleaves complement fragment iC3b, providing an alternative complement regulatory pathway independent of cellular cofactors. Together, these findings place PLG at the intersection of fibrinolysis, macrophage function, and complement regulation.

The evidence for rs4252185 itself is currently at the GWAS-signal level — the variant appears in cardiovascular genetic datasets but has not been independently validated in expression studies or functional assays. The evidence level is therefore emerging for this specific SNP.

Practical Actions

For carriers of the C allele, the primary actionable signal from this PLG locus variant is cardiovascular: any factor that impairs plasminogen-dependent fibrinolysis (smoking, elevated PAI-1, coagulation disorders) compounds the potential effect of reduced PLG activity. Cardiovascular risk monitoring is warranted — particularly in the presence of other cardiovascular risk factors.

Because the C allele is rare in a homozygous state (under 1%), the CC genotype warrants the most specific follow-up. TC heterozygotes have a modest signal that does not change clinical management unless combined with other PLG-region variants or independent cardiovascular risk factors.

Interactions

Rs4252185 sits in the same PLG haplotype block as rs4252130 (a periodontitis- associated intronic variant) and is in the same gene as the rare pathogenic rs73015965 (K38E, p.Lys38Glu), which causes type I plasminogen deficiency. Carriers of both a common PLG regulatory variant (rs4252185 C, rs4252130 C) and the rare loss-of-function allele (rs73015965 G) would have lower total plasminogen output than either variant alone predicts — though no published human data quantify this compound effect directly.

The LPA gene immediately adjacent on 6q26 encodes lipoprotein(a), which is structurally homologous to plasminogen and competes for plasminogen receptor sites. High Lp(a) levels can interfere with plasmin-mediated fibrinolysis, so carriers of C alleles at PLG-region variants with concurrent high Lp(a) may have compounded vascular risk.