rs4253238 — KLKB1 KLKB1 intronic variant

Intronic KLKB1 variant whose T allele elevates plasma kallikrein enzymatic activity and associates with higher circulating endothelin and adrenomedullin surrogate markers — vasoactive peptides predictive of cardiac stress and heart failure

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KLKB1 — The Contact Activation Regulator Linking Coagulation, Bradykinin, and Vasoactive Peptides

KLKB111 KLKB1
Kallikrein B1 — encodes plasma prekallikrein (Fletcher factor), a serine protease that circulates in blood as an inactive zymogen complexed with high-molecular-weight kininogen (HK) is the central enzyme of the plasma contact activation pathway. When factor XII (Hageman factor)22 factor XII (Hageman factor)
the initiating serine protease of the intrinsic coagulation cascade, activated by contact with negatively charged surfaces is activated, it converts plasma prekallikrein into plasma kallikrein — an active protease with far-reaching effects on coagulation, inflammation, blood pressure, and vascular tone. The rs4253238 intronic variant in KLKB1 modulates how much plasma kallikrein activity the liver produces, with downstream consequences for bradykinin generation, endothelin regulation, and thrombotic risk.

The Mechanism

rs4253238 sits in an intron of KLKB1 on chromosome 4q35.2. Although it does not change the plasma prekallikrein protein sequence, research by Sidarovich and Fink33 Sidarovich and Fink
Sidarovich V, Fink E. The 3'-terminal 13-bp segment of intron 1 is sufficient to promote transcriptional activity in the KLKB1 gene. Gene, 2009 demonstrated that the KLKB1 intron 1 harbors a 13-bp regulatory element sufficient to promote transcriptional activity and recruit alternative promoters. Intronic variants in this regulatory region plausibly alter the level of KLKB1 mRNA produced in the liver and kidney, where the gene is predominantly expressed. The T allele at rs4253238 is associated with increased plasma kallikrein enzymatic activity.

Active plasma kallikrein has multiple substrates. Its classical function is to cleave high-molecular-weight kininogen44 high-molecular-weight kininogen
the plasma protein that serves as the precursor to bradykinin, the vasodilatory, pro-inflammatory peptide central to ACE-inhibitor activity to release bradykinin. Beyond bradykinin, plasma kallikrein also cleaves precursors of endothelin-1 (ET-1) and adrenomedullin (ADM)55 endothelin-1 (ET-1) and adrenomedullin (ADM)
ET-1 is a potent vasoconstrictor and predictor of cardiac death; ADM is a vasodilatory peptide elevated in heart failure into smaller peptide fragments. The measurement of CT-pro-endothelin-1 and MR-pro-adrenomedullin as circulating surrogates of ET-1 and ADM activity means that higher plasma kallikrein activity registers as elevated levels of these cardiovascular biomarkers.

The Evidence

The primary cardiovascular evidence comes from a large genome-wide association study of plasma CT-proET-1 and MR-proADM66 genome-wide association study of plasma CT-proET-1 and MR-proADM
Verweij N et al. Genome-wide association study on plasma levels of midregional-proadrenomedullin and C-terminal-pro-endothelin-1. Hypertension, 2013 conducted in 3,444 discovery participants with replication in 3,230 additional European participants. Minor variants in KLKB1, including rs4253238, showed genome-wide significant associations with both MR-proADM (P=4.46×10⁻⁵²) and CT-proET-1 (P=1.23×10⁻¹²²). The researchers demonstrated mechanistically that purified plasma kallikrein can directly cleave both ADM and ET-1 precursor proteins into multiple smaller peptides, providing a biochemical explanation for the genetic association. Elevated CT-proET-1 and MR-proADM are established predictors of cardiac death and heart failure.

An independent genome-wide protein QTL study77 genome-wide protein QTL study
Portelli MA et al. Genome-wide protein QTL mapping identifies human plasma kallikrein as a post-translational regulator of serum uPAR levels. FASEB J, 2014 in 584 control/asthma participants and 219 COPD participants confirmed that the rs4253238 T:T genotype is directly associated with elevated plasma kallikrein enzymatic activity (combined P=5.04×10⁻¹²). Higher kallikrein activity was inversely correlated with circulating soluble uPAR levels, a receptor involved in vascular repair and inflammatory signaling.

The cardiovascular implications of altered plasma kallikrein activity were clarified by Stavrou et al.88 Stavrou et al.
Stavrou EX et al. Reduced thrombosis in Klkb1-/- mice is mediated by increased Mas receptor, prostacyclin, Sirt1, and KLF4 and decreased tissue factor. Blood, 2015 who found that Klkb1-knockout mice show significantly delayed arterial thrombosis — the paradoxical protection arising from upregulation of the Mas receptor/prostacyclin axis and suppression of tissue factor. This study establishes plasma kallikrein as a net pro-thrombotic driver in the contact activation pathway; higher KLKB1 activity from the T allele thus associates with a modestly more pro-thrombotic vascular environment.

A review by Feener et al.99 Feener et al.
Feener EP et al. Role of plasma kallikrein in diabetes and metabolism. Thromb Haemost, 2013 confirmed that common KLKB1 variants associate with blood metabolite levels, hypertension, and coagulation in population studies. Notably, the Rohmann 20191010 Rohmann 2019
Rohmann JL et al. Genetic determinants of activity and antigen levels of contact system factors. J Thromb Haemost, 2019 GWAS found that contact activation variants were not significantly associated with myocardial infarction or stroke risk in women under 50, suggesting that the kallikrein-modulating effect of rs4253238 primarily manifests as altered biomarker levels rather than directly elevated event risk in isolation.

Practical Implications

The T allele elevates plasma kallikrein activity, which simultaneously elevates bradykinin (vasodilatory, cardioprotective) and increases cleavage of ET-1 precursors (elevating circulating CT-proET-1, a cardiac stress marker). The net clinical significance of this variant is not fully resolved — elevated bradykinin is protective in ischemic conditioning and may enhance ACE-inhibitor effects, while elevated CT-proET-1 signals greater endothelin pathway activity associated with cardiac load. Heterozygotes (CT) have intermediate kallikrein activity levels. Monitoring cardiovascular biomarkers (particularly high-sensitivity CRP, BNP/NT-proBNP, and if available CT-proET-1) provides the most actionable information for TT genotype carriers.

Interactions

rs4253238 (KLKB1) has a documented epistatic interaction with rs2731672 (F12, coagulation factor XII), the upstream activating protease in the contact system. Together, KLKB1 and F12 variants modulate the full throughput of the contact activation cascade — bradykinin generation, complement activation, and endothelin surrogate levels. The Verweij 2013 GWAS identified both rs4253238 (KLKB1) and rs2731672 (F12) as independent contributors to CT-proET-1 and MR-proADM plasma levels, consistent with additive effects along the same proteolytic axis. The Gianni 2017 study (PMID 29130992) also demonstrated that combined KLKB1-428 and F12-46C/T variants produce an 8.8-year delay in hereditary angioedema onset — confirming meaningful gene-gene epistasis between these two contact system proteins. Carriers of risk genotypes in both rs4253238 (KLKB1) and rs2731672 (F12) likely have the highest contact-activation throughput and greatest endothelin/adrenomedullin surrogate elevation.

Genotype Interpretations

What each possible genotype means for this variant.

CC Lower Kallikrein Activity Normal

Reference genotype — lower plasma kallikrein activity, typical endothelin and adrenomedullin surrogate levels

The CC genotype represents homozygosity for the GRCh38 reference allele at this intronic KLKB1 locus. The Portelli 2014 genome-wide protein QTL study (PMID 24249636) found that T:T homozygotes had the highest plasma kallikrein activity; CC carriers represent the lower end of the kallikrein activity spectrum. Lower kallikrein activity means less cleavage of ET-1 and ADM precursors (lower CT-proET-1 and MR-proADM surrogates) and modestly reduced bradykinin generation through the contact activation pathway relative to TT carriers.

Importantly, the Rohmann 2019 study (PMID 30288888) found that contact system genetic variants were not significantly associated with MI or stroke risk in an age-matched population, suggesting that the kallikrein level differences captured by rs4253238 primarily translate to biomarker differences rather than independently elevated event risk.

CT Intermediate Kallikrein Activity Intermediate

One T allele — intermediate plasma kallikrein activity and moderately elevated vasoactive peptide surrogate levels

Under the additive model documented in the Verweij 2013 GWAS, each T allele incrementally elevates plasma kallikrein activity and the resulting vasoactive peptide surrogates. CT heterozygotes sit midway between CC and TT in kallikrein output. The biological significance is nuanced: elevated plasma kallikrein generates more bradykinin (a vasodilatory, cardioprotective peptide that also potentiates ACE-inhibitor effects on blood pressure) while simultaneously producing more ET-1 and ADM fragments. The Stavrou 2015 animal model (PMID 25339356) showed that Klkb1 activity promotes a mildly pro-thrombotic vascular environment through contact system activation and tissue factor upregulation.

For CT carriers, the individual-level risk from this single variant is modest. The cardiovascular significance is amplified if co-inherited with F12 variants (rs2731672), which operate upstream in the same contact activation cascade.

TT Higher Kallikrein Activity High Risk

Two T alleles — highest plasma kallikrein activity, elevated endothelin and adrenomedullin surrogates, and mildly pro-thrombotic contact activation

TT homozygosity places you at the highest end of the plasma kallikrein activity spectrum for this locus. The Verweij 2013 GWAS demonstrated genome-wide significance for the KLKB1 locus effect on CT-proET-1 (P=1.23×10⁻¹²²) — one of the strongest associations reported for a cardiovascular biomarker GWAS — reflecting the large effect of this gene on vasoactive peptide regulation. Plasma kallikrein's role extends beyond biomarker levels: the Stavrou 2015 mouse model (PMID 25339356) established that higher kallikrein activity promotes a pro-thrombotic vascular state by reducing prostacyclin production and upregulating tissue factor.

However, the same TT genotype also generates more bradykinin — a vasodilatory peptide that mediates part of the cardiovascular protection from ACE inhibitors. The Rohmann 2019 GWAS found no significant independent association between contact system variants and MI or stroke in women under 50, suggesting that rs4253238 alone does not substantially elevate event risk. The clinical significance is amplified in combination with F12 variants (rs2731672) and in the context of other cardiovascular risk factors (hypertension, dyslipidemia, inflammation). Monitoring and targeted biomarker surveillance are the most actionable responses.

ACE inhibitor therapy is particularly relevant: TT carriers on ACE inhibitors may experience stronger bradykinin accumulation, increasing the probability of ACE-inhibitor cough or, rarely, angioedema.