rs705379 — PON1 PON1 promoter -108C>T

Promoter polymorphism that controls PON1 gene expression — the T allele (A on the plus strand) reduces transcription factor binding, halving arylesterase activity and lowering HDL-mediated antioxidant protection against LDL oxidation.

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PON1 Promoter -108C>T — The Gene Expression Switch for Your HDL's Antioxidant Guard

Paraoxonase-1 (PON1) is an enzyme that travels on HDL particles11 HDL particles
High-density lipoprotein — the so-called "good cholesterol" that carries cholesterol from tissues to the liver and provides antioxidant protection in the arterial wall and functions as your bloodstream's primary defense against oxidized LDL — the form of "bad cholesterol" that initiates plaque buildup in artery walls. While most research on PON1 focuses on the coding-region variants Q192R and L55M, the promoter polymorphism at position -108 (rs705379) is arguably the strongest single genetic determinant of how much PON1 your body actually produces. Less enzyme means less protection — and the T allele cuts that protection by roughly half.

The Mechanism

The PON1 gene sits on the minus (reverse) strand of chromosome 7. In the promoter region 108 base pairs upstream of the transcription start site, a C-to-T substitution (reported as G>A in plus-strand genome files) alters the binding affinity of a transcription factor that drives PON1 expression. The -108C/T variant accounts for 22.8% of the observed variability in PON1 expression levels22 The -108C/T variant accounts for 22.8% of the observed variability in PON1 expression levels in the human liver — more than any other single PON1 polymorphism, including the widely studied coding variants. Individuals homozygous for the T allele (TT genotype; AA in plus-strand notation) show arylesterase activity of only 67.5 U/ml on average, compared to 140.9 U/ml in CC carriers — a reduction of more than 50%. Heterozygotes (CT/AG) fall between these extremes.

Beyond its direct effect on expression, a 2021 multi-omics study33 a 2021 multi-omics study showed that the T allele also triggers DNA hypermethylation at CpG sites near the promoter, further silencing PON1 transcription. This epigenetic layer amplifies the initial transcription-factor effect, making the T allele's impact on expression self-reinforcing.

The Evidence

The expression-lowering effect of the T allele has downstream consequences for cardiovascular health. In type 2 diabetes patients, the TT genotype at the -108 position was significantly associated with elevated oxidized LDL/apoB ratios (P = 0.02)44 the TT genotype at the -108 position was significantly associated with elevated oxidized LDL/apoB ratios (P = 0.02), providing a direct biochemical link between reduced PON1 expression and impaired LDL antioxidant protection.

For cardiovascular outcomes, a Polish cohort of 865 hemodialysis patients found the TT genotype associated with cardiovascular mortality (HR 1.27, 95% CI 1.03-1.57, P = 0.025) and cardiac mortality (HR 1.34, 95% CI 1.05-1.71, P = 0.018)55 the TT genotype associated with cardiovascular mortality (HR 1.27, 95% CI 1.03-1.57, P = 0.025) and cardiac mortality (HR 1.34, 95% CI 1.05-1.71, P = 0.018). A companion study from the same group confirmed the cardiovascular mortality association was particularly pronounced in cigarette smokers with the TT genotype66 cigarette smokers with the TT genotype, with significant associations for cardiac non-CHD-related mortality (P = 0.001) — suggesting that combined low-PON1 and oxidative stress from smoking is especially dangerous.

Beyond the heart, a 2021 meta-analysis of Alzheimer's disease77 2021 meta-analysis of Alzheimer's disease covering 15 studies found the A allele (T in coding notation) significantly associated with AD risk in Caucasians (OR 1.21, 95% CI 1.05-1.39, P = 0.009), while the GG genotype was protective (OR 0.70, 95% CI 0.56-0.88, P = 0.002). PON1's antioxidant and anti-inflammatory actions in the brain may explain this connection.

Practical Implications

Since the T allele reduces PON1 production rather than altering its catalytic efficiency, the relevant interventions focus on compensating for reduced enzyme levels. Several dietary factors have been shown to upregulate PON1 expression or activity, regardless of genotype. Polyphenols — particularly pomegranate juice, olive oil, and red wine components88 pomegranate juice, olive oil, and red wine components — increase PON1 activity in human studies. Omega-3 fatty acids (EPA and DHA) enhance HDL functionality and support PON1's lipid-protective environment.

Smoking is the most important lifestyle factor to address: cigarette smoke both reduces PON1 activity and multiplies the cardiovascular mortality risk of the TT genotype, as demonstrated by the hemodialysis cohort data above.

Interactions

This variant interacts with both coding-region PON1 variants in the database. rs662 (Q192R)99 rs662 (Q192R) affects the enzymatic efficiency of the PON1 that is produced, while -108C>T controls how much PON1 is made. Carrying both the TT (low expression) and RR (low antioxidant efficiency) genotypes compounds cardiovascular risk beyond either alone. Similarly, rs854560 (L55M) affects PON1 protein stability and circulating concentrations, and unfavorable combinations across all three variants produce the lowest observed PON1 activity phenotypes. Describing the specific combined effects of these three genotypes belongs in compound actions.

Nutrient Interactions

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Genotype Interpretations

What each possible genotype means for this variant.

GG High Expresser Normal

Full PON1 promoter activity — high HDL antioxidant enzyme production

You have two copies of the C allele at the -108 promoter position (CC genotype in coding-strand notation), which maintains strong transcription factor binding and drives robust PON1 production. This is the genotype associated with the highest arylesterase activity (averaging ~140.9 U/ml), providing full HDL-associated antioxidant protection against LDL oxidation. About 39% of people of European descent share this genotype, though it is more common in African populations (~68%). Your PON1 enzyme levels are not limited by this promoter variant.

AG Intermediate Expresser Intermediate

Reduced PON1 promoter activity — moderately lower antioxidant enzyme production

The -108C/T heterozygote produces both the higher-expression C allele transcript and the lower-expression T allele transcript from the same liver cell. Net PON1 output is reduced relative to CC homozygotes, though the functional impact is more modest than in TT individuals. The additional epigenetic layer discovered in the 2021 multi-omics study (PMID 34389043) — where the T allele triggers CpG methylation — may progressively widen the gap between CT and CC individuals over time, particularly in the context of obesity or metabolic stress that modulates epigenetic marks.

AA Low Expresser Reduced

Substantially reduced PON1 expression — approximately half the normal arylesterase activity

The TT genotype's impact on PON1 expression operates through two mechanisms: direct impairment of transcription factor binding at the -108 site, and epigenetically — the T allele triggers CpG hypermethylation in the promoter region, which further silences PON1 transcription. This methylation-mediated amplification makes the expression deficit worse in metabolically stressed states (obesity, high-fat diet) and may explain why the TT genotype shows stronger associations with liver disease severity in obese individuals.

Because this is a regulatory (not coding) variant, PON1 enzymatic efficiency is unaffected — the enzyme produced by TT individuals works normally. The deficit is purely in how much enzyme is made, not in how well it functions per molecule. This distinction matters for interventions: approaches that upregulate PON1 transcription (dietary polyphenols, certain lifestyle factors) can partially compensate, whereas for coding variants affecting enzymatic efficiency, there is no equivalent compensation available.

The association with Alzheimer's disease (OR 1.21 in the meta-analysis of 15 studies, PMID 28954597) likely reflects PON1's anti-inflammatory role in the CNS — the same reduced enzyme levels that leave LDL more susceptible to oxidation also provide less neuroprotection in the aging brain.