rs7061710 — FMO3

Intronic FMO3 variant associated with reduced hepatic oxidation of garlic-derived sulfur compounds (S-allylcysteine) and trimethylamine; C allele carriers accumulate higher circulating levels of unprocessed sulfur metabolites

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FMO3 rs7061710 — Your Garlic Metabolism Gene

The flavin-containing monooxygenase 3 enzyme (FMO311 FMO3
A liver-expressed NADPH-dependent oxygenase that adds an oxygen atom to nitrogen- and sulfur-containing molecules, converting them to their N-oxide or S-oxide forms for easier urinary excretion) is the liver's chemical processing station for two major classes of dietary compounds: trimethylamine from choline-rich foods (eggs, meat, fish) and sulfur-containing compounds from allium vegetables (garlic, onions, leeks). rs7061710 is an intronic variant in FMO3 — it sits within the gene but does not change the protein sequence. Instead, it likely acts as a regulatory variant22 regulatory variant
An intronic or non-coding variant that alters transcription factor binding sites, splice enhancers, or chromatin accessibility to change how much of the protein is produced rather than what the protein looks like that modifies how much FMO3 protein the liver produces.

Carriers of the C allele show significantly higher circulating levels of S-allylcysteine33 S-allylcysteine
The primary sulfur compound from aged garlic extract; a water-soluble amino acid with antioxidant and anti-inflammatory properties that FMO3 converts to S-allylcysteine sulfoxide for urinary excretion — a garlic-derived sulfur compound that FMO3 normally clears from the bloodstream. The association is genome-wide significant (p = 3×10⁻¹⁴), indicating a real, replicable difference in FMO3 activity linked to this variant. A second garlic-pathway metabolite, X-11786-methylcysteine, is similarly elevated (p = 8×10⁻¹⁴), reinforcing the signal.

The Mechanism

FMO3 is expressed almost exclusively in adult liver tissue, where it performs NADPH-dependent S-oxygenation44 NADPH-dependent S-oxygenation
A chemical reaction that adds an oxygen to a sulfur atom, converting R-S-R' to R-S(=O)-R' (a sulfoxide), making the compound more water-soluble and easier to excrete in urine on a wide range of substrates — from trimethylamine (TMA, the "fishy" compound from gut bacterial metabolism of choline) to garlic-derived thiosulfinate breakdown products. The rs7061710 C allele does not disrupt the protein structure of FMO3. Rather, as an intronic variant, it most likely alters splicing efficiency or enhancer element binding, resulting in lower FMO3 transcript levels or less efficient exon inclusion.

The practical consequence is measurable: genome-wide metabolomics studies55 genome-wide metabolomics studies
Large studies that measure hundreds of blood metabolites simultaneously in thousands of people, then test every genetic variant across the genome for associations — a powerful way to map which genes control circulating metabolite levels in more than 7,800 Europeans (Shin et al. 2014) and over 11,800 multi-ethnic participants (Feofanova et al. 2023) independently identified this variant as a significant predictor of elevated garlic-sulfur metabolite levels in blood. Because FMO3 handles both TMA and sulfur compounds through the same enzymatic mechanism, reduced FMO3 activity from this variant is also expected to modestly increase circulating TMAO66 TMAO
Trimethylamine N-oxide — produced when FMO3 oxidizes trimethylamine (TMA) from gut bacterial metabolism of choline, carnitine, and lecithin in meat, eggs, and fish levels, though direct TMAO association data for rs7061710 specifically are not yet published.

The Evidence

The foundational link between FMO3 genetic variation and cardiovascular risk comes from Wang et al. 201177 Wang et al. 2011
Wang Z et al. Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease. Nature, 2011, which demonstrated that gut bacteria produce TMA from dietary choline, FMO3 converts this to TMAO in the liver, and FMO3 expression levels in mice directly tracked with atherosclerosis susceptibility. Mice with higher FMO3 expression had more TMAO and more atherosclerosis; mice with lower FMO3 had less.

For the rs7061710 variant specifically, two independent metabolomics studies provide strong evidence. Shin et al. 201488 Shin et al. 2014
Shin SY et al. An atlas of genetic influences on human blood metabolites. Nature Genetics, 2014 mapped 400+ blood metabolites to genetic loci in 7,824 adults, finding rs7061710-C strongly associated with elevated X-11786-methylcysteine (a cysteine-containing metabolite) at p = 8×10⁻¹⁴. Feofanova et al. 202399 Feofanova et al. 2023
Feofanova EV et al. Whole-genome sequencing analysis of human metabolome in multi-ethnic populations. Nature Communications, 2023 replicated the signal in 11,840 participants spanning multiple ancestries, finding rs7061710-C associated with elevated S-allylcysteine at p = 3×10⁻¹⁴ — both results are far beyond standard genome-wide thresholds. The direct biochemical evidence that FMO3 processes S-allylcysteine in vivo was established by Cashman et al. 20021010 Cashman et al. 2002
Cashman JR et al. Sulfoxides as urinary metabolites of S-allyl-L-cysteine in rats: evidence for the involvement of flavin-containing monooxygenases. Drug Metab Dispos, 2002, confirming that FMO inhibition reduces sulfoxide metabolite recovery.

For the broader cardiovascular implications of FMO3 variation, Robinson-Cohen et al. 20161111 Robinson-Cohen et al. 2016
Robinson-Cohen C et al. Association of FMO3 Variants and Trimethylamine N-Oxide Concentration, Disease Progression, and Mortality in CKD Patients. PLoS One, 2016 found that each copy of the FMO3 E158K reduced-activity allele was associated with 0.38 μg/mL higher circulating TMAO and a roughly 2-fold higher mortality risk in patients with chronic kidney disease. This establishes the principle that inherited variation in FMO3 activity has clinically meaningful effects on TMAO levels and downstream health outcomes.

Practical Actions

For GC and CC carriers, the most relevant dietary consideration is choline intake. The same enzyme that processes garlic sulfur compounds also converts TMA (produced by gut bacteria from choline and carnitine) to TMAO. With reduced FMO3 capacity, the TMA-to-TMAO conversion is less efficient — potentially allowing more unconverted TMA to circulate. Rather than avoiding choline-rich foods entirely (which would reduce TMAO precursor load), a more targeted approach focuses on gut microbiome composition, since the gut bacteria that produce TMA are the first step in the pathway. Dietary patterns that reduce TMAO-producing gut bacteria (lower red meat, higher fiber, fermented foods) address the root of elevated TMAO independently of FMO3 genotype.

For garlic specifically: reduced FMO3 clearance of S-allylcysteine means C allele carriers may experience stronger or longer-lasting effects from garlic and aged garlic extract supplements, since the active compound clears from the blood more slowly. This is more of a pharmacokinetic observation than a risk — S-allylcysteine itself has antioxidant properties and is not harmful at typical dietary levels.

Interactions

rs7061710 belongs to a cluster of FMO3 variants. The coding variants rs2266782 (E158K) and rs2266780 (E308G) are the best-characterized functional variants in the same gene — together, the E158K;E308G compound variant1212 E158K;E308G compound variant
When a person carries both amino acid changes simultaneously, the combination reduces FMO3 enzyme activity more than either alone — an additive or synergistic loss-of-function effect documented in in vitro expression studies substantially reduces FMO3 enzyme activity. Whether rs7061710 is in linkage disequilibrium1313 linkage disequilibrium
Non-random co-inheritance of nearby variants — if two variants are always (or almost always) co-inherited, they appear statistically equivalent as predictors even if only one is functionally relevant with either coding variant is not established in the published literature; rs7061710 may be an independent regulatory signal or a proxy for one of the coding variants. For people who carry rs7061710-CC and also carry E158K or E308G, the cumulative reduction in FMO3 metabolic capacity is likely greater, and dietary choline management becomes more important. A compound action proposal is included in the harvesting notes.

Nutrient Interactions

trimethylamine (from choline, carnitine, TMAO precursors) altered_metabolism
S-allylcysteine (from garlic) altered_metabolism

Genotype Interpretations

What each possible genotype means for this variant.

GG Normal FMO3 Metabolizer Normal

Normal FMO3 activity — efficient clearance of dietary sulfur compounds and TMA

GG homozygotes show reference-level FMO3 metabolic activity in genome-wide metabolomics studies. In the Feofanova et al. 2023 analysis of 11,840 participants, the GG genotype defined the baseline S-allylcysteine level against which C allele carriers showed significantly elevated levels. Your liver's FMO3 enzyme is efficiently converting garlic sulfur compounds and trimethylamine through normal NADPH-dependent oxygenation, producing sulfoxides and TMAO that clear in urine.

Inter-individual variation in FMO3 expression can still reach 20-fold in the general population due to factors beyond genetics — age, sex (FMO3 is downregulated in males by androgens), hormonal status, and diet all influence liver FMO3 levels. This genotype does not protect against non-genetic causes of elevated TMAO.

CG Intermediate FMO3 Metabolizer Intermediate

One C allele — moderately elevated garlic sulfur metabolite accumulation

The C allele appears to act as a regulatory variant that reduces FMO3 expression or activity. With one copy, you likely produce moderately less FMO3 protein or have slightly less efficient splicing of the FMO3 transcript, resulting in intermediate enzymatic capacity. The genome-wide associations at p = 3×10⁻¹⁴ for S-allylcysteine and p = 8×10⁻¹⁴ for X-11786-methylcysteine are additive — heterozygotes fall between GG and CC homozygotes.

Because the same enzyme handles TMA from choline-rich foods, moderately reduced FMO3 activity at this variant may contribute a modest increase in the amount of TMA that escapes conversion to TMAO. The clinical significance of this for TMA metabolism specifically is not yet directly quantified for rs7061710, though analogous data from coding-variant studies (Robinson-Cohen et al. 2016) support the principle that graded FMO3 variation produces graded TMAO-level differences.

CC Reduced FMO3 Metabolizer Reduced

Two C alleles — significantly elevated garlic sulfur metabolites, reduced TMA processing

With two C alleles at this regulatory site, FMO3 expression or enzymatic efficiency is likely at its lowest among the three genotypes. The genome-wide associations for both S-allylcysteine (p = 3×10⁻¹⁴) and X-11786-methylcysteine (p = 8×10⁻¹⁴) are additive, placing CC carriers at the high end of circulating sulfur metabolite levels. This does not cause trimethylaminuria (the classic fish-odor syndrome requires severe loss-of-function from missense variants like E308G homozygosity or compound E158K;E308G) — the intronic rs7061710 C allele is a modifier that shifts activity within the normal range, not a null allele.

The reduced TMA→TMAO conversion capacity may be clinically relevant for cardiovascular risk, especially in the context of high-choline diets. Analogy to coding FMO3 variants: Robinson-Cohen et al. (2016) found each FMO3 reduced-activity allele raised circulating TMAO by 0.38 μg/mL and approximately doubled mortality risk in CKD patients. The quantitative effect of rs7061710 CC specifically on TMAO has not been separately measured, but the biological mechanism is the same.

If you also carry the FMO3 missense variants rs2266782 (E158K) or rs2266780 (E308G), the cumulative reduction in FMO3 capacity is likely additive. Such combinations may warrant more proactive dietary management and direct TMAO monitoring.