rs492602 — FUT2 FUT2 secretor status proxy

A synonymous FUT2 proxy variant in strong LD with the W143X nonsense allele (rs601338), tagging secretor status and associated with Crohn's disease susceptibility, psoriasis risk, and gut microbiome composition; the G allele marks the secretor phenotype

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FUT2 Secretor Proxy — The Gut-Skin Axis at a Genetic Crossroads

Your FUT2 gene is the master switch for secretor status11 secretor status
Whether you express ABO blood group antigens on mucosal surfaces and in saliva, tears, and intestinal mucus — a trait that fundamentally shapes your gut microbiome and immune landscape. rs492602 is a synonymous proxy variant that tags this biological divide: the G allele travels with the secretor phenotype, while the A allele travels with the non-secretor phenotype that arises from the nearby W143X nonsense mutation22 W143X nonsense mutation
rs601338 (G428A) creates a premature stop codon at amino acid 143 of FUT2, producing a truncated, non-functional enzyme; this is the primary FUT2 non-secretor variant in Europeans and Africans (rs601338). Although rs492602 itself is a silent coding change (alanine-68 codon remains alanine), it serves as a reliable genomic proxy for the functional variant in most populations.

The platform already tracks rs601338 in the vitamins-nutrients category, where the focus is on B12 absorption. This entry covers the orthogonal angle: the gut-skin axis33 gut-skin axis
The bidirectional communication between the intestinal microbiome and skin immune function, increasingly recognised as a driver of inflammatory skin diseases including psoriasis and autoimmune susceptibility that rs492602 tags independently. The two entries address distinct clinical implications of the same underlying biology.

The Mechanism

FUT2 encodes alpha(1,2)-fucosyltransferase44 alpha(1,2)-fucosyltransferase
An enzyme that adds the six-carbon sugar fucose to glycan chains on the surface of intestinal epithelial cells and into secreted mucus, creating the H antigen on which A and B blood group specificities are built. In secretors, fucosylated glycans line the gut wall and are shed into the intestinal lumen where they serve two purposes: attachment scaffolds for certain pathogens (and therefore pathogen resistance signals) and a dedicated carbon source for Bifidobacterium55 Bifidobacterium
A genus of beneficial gut bacteria that have evolved specialised fucosidase enzymes to harvest fucose from host glycans as their primary food source in the gut species that have co-evolved with human secretors.

Non-secretors produce no functional FUT2 enzyme and therefore no mucosal fucosylated glycans. The immediate consequence is a profoundly altered intestinal microbiome — reduced Bifidobacterium richness and diversity, and an enrichment of bacteria that drive Th17-promoting inflammation. The gut of a non-secretor is structurally predisposed to a different immunological state from birth.

The Evidence

The secretor-microbiome connection was firmly established by Wacklin et al. 201166 Wacklin et al. 2011
Wacklin P et al. Secretor genotype (FUT2 gene) is strongly associated with the composition of Bifidobacteria in the human intestine. PLoS One, 2011: in 71 healthy volunteers, non-secretors showed significantly reduced bifidobacterial richness (p<0.0001) and several key species (B. bifidum, B. adolescentis, B. catenulatum) were absent or rare in non-secretors but common in secretors.

The link between FUT2 non-secretor status and Crohn's disease was established by a genome-wide association study in 4,100 Caucasian participants77 4,100 Caucasian participants
McGovern DPB et al. Fucosyltransferase 2 (FUT2) non-secretor status is associated with Crohn's disease. Hum Mol Genet, 2010 reaching genome-wide significance (P=4.90×10⁻⁸). Mechanistically, Tong et al. 201488 Tong et al. 2014
Tong M et al. Reprograming of gut microbiome energy metabolism by the FUT2 Crohn's disease risk polymorphism. ISME J, 2014 demonstrated that the non-secretor microbiome shows depleted amino-acid biosynthesis and enriched carbohydrate catabolism pathways, accompanied by sub-clinical mucosal inflammation in non-secretors even before disease onset.

The psoriasis association was identified in a Han Chinese case-control study Liu et al. 202199 Liu et al. 2021
Liu Y et al. Association of Polymorphisms of Metabolism-Related Genes with Psoriasis Vulgaris in Han Chinese. Biomed Res Int, 2021 of 1,030 psoriasis patients and 965 controls (OR=1.86, P=0.005). The association was stronger in individuals without the HLA-C*06:02 allele (OR=2.04), suggesting rs492602 contributes to psoriasis risk through a pathway partially independent of the canonical HLA-driven pathway. This is consistent with the gut-skin axis hypothesis: altered microbial composition drives systemic immune dysregulation that manifests in skin inflammation. Importantly, rs492602 sits in a genomic region with documented shared susceptibility for both psoriasis and Crohn's disease, supporting a common gut-immune mechanism.

A large Dutch microbiome GWAS Lopera-Maya et al. 20221010 Lopera-Maya et al. 2022
Lopera-Maya EA et al. Effect of host genetics on the gut microbiome in 7,738 participants of the Dutch Microbiome Project. Nat Genet, 2022 confirmed FUT2/secretor status as one of only two robust genome-wide significant genetic determinants of gut microbial composition, with a p-value below 1.89×10⁻¹⁰ — placing this among the most reproducible host-microbiome genetic associations in the human genome.

LD with rs601338: rs492602 is in strong LD with the functional W143X nonsense variant (rs601338) in European and African populations. The two variants are highly correlated, which is why rs492602 served as the GWAS tag SNP for B12 levels in the original Hazra et al. 2008 discovery. In East Asian populations, both variants are rare; the primary non-secretor allele there is rs1047781 (A385T). This entry focuses on the autoimmune and gut-skin axis biology; see the rs601338 entry for B12 absorption details.

Practical Actions

For non-secretors (AA), the gut-immune implications are the most actionable aspect of this variant. Supporting microbial diversity through prebiotic-rich foods and targeted Bifidobacterium probiotics can partially compensate for the structural deficit in mucosal glycan availability. Monitoring for early signs of gut inflammation is warranted given the elevated Crohn's risk.

For psoriasis specifically, the gut-skin axis implication means that gut microbiome health strategies may have downstream benefit for skin inflammation — though direct clinical evidence for probiotics modifying psoriasis severity in non-secretors specifically is not yet available.

Interactions

This variant is in strong LD with rs601338 (FUT2 W143X), which is separately catalogued for B12 metabolism. If you carry the A allele at rs492602, you very likely also carry the A (non-secretor) allele at rs601338. The two entries address different clinical angles of the same biology.

rs602662 (FUT2 S258G) is also in LD with this locus and shows similar Crohn's disease associations. In East Asian populations, rs1047781 (A385T) is the primary secretor-status determinant and should be checked in that ancestry context.

Genotype Interpretations

What each possible genotype means for this variant.

GG Secretor Beneficial

Full secretor — optimal gut microbiome diversity and reduced autoimmune risk

The GG genotype at rs492602 tags the secretor haplotype. Your gut epithelium produces fucosylated H-type antigens that serve as both a carbon source for Bifidobacterium species and — in a physiologically ironic twist — an attachment scaffold for certain enteric pathogens (norovirus, rotavirus) that require H-type antigens to infect gut cells.

The microbial consequence is well-characterised: GG carriers tend to harbour richer, more diverse bifidobacterial communities, including B. bifidum, B. adolescentis, and B. catenulatum — species that are sparse or absent in non-secretors. This microbial architecture is associated with lower mucosal inflammation and reduced risk of the immune dysregulation thought to underlie Crohn's disease and psoriasis.

Note: Being a secretor does not confer any specific proactive supplementation requirement — this is the genetic baseline. See rs601338 for the B12 absorption angle on secretor status.

AA Non-Secretor High Risk

Non-secretor — reduced gut microbiome diversity, elevated Crohn's disease and psoriasis risk

The AA genotype at rs492602 reliably tags functional FUT2 loss in European and African populations through its tight linkage disequilibrium with the W143X nonsense mutation (rs601338). With no functional enzyme, your intestinal epithelium cannot add fucose to glycan chains on the mucosal surface. The downstream consequences span three domains:

Gut microbiome: Wacklin et al. 2011 demonstrated significantly reduced bifidobacterial richness and diversity (p<0.0001). Tong et al. 2014 showed functional reprogramming of the non-secretor microbiome — enriched carbohydrate/lipid catabolism pathways and depleted amino-acid biosynthesis, with sub-clinical mucosal inflammation detectable even before disease onset. Cheng et al. 2021 identified elevated Th17-inducing bacteria in non-secretors with IBD, suggesting a pro-inflammatory microbial tilt.

Crohn's disease risk: GWAS in 4,100 Caucasians established genome-wide significant association (P=4.90×10⁻⁸). The postulated mechanism is straightforward: gut dysbiosis → impaired barrier → immune activation → chronic intestinal inflammation.

Psoriasis risk: A case-control study (n=1,995 Han Chinese) found OR=1.86 (P=0.005) for psoriasis vulgaris in A allele carriers. The association was stronger in HLA-C*06:02-negative individuals (OR=2.04), implicating the gut-skin axis as the operative mechanism rather than the canonical HLA-driven pathway.

B12 note: Non-secretor status also affects B12 metabolism (covered in detail under rs601338). Standard total serum B12 tests may overestimate functional status; holotranscobalamin or methylmalonic acid testing is more informative.

AG Secretor (Carrier) Carrier

Secretor with one non-secretor allele — full secretor function, carrier status

Heterozygous AG carriers produce enough functional FUT2 enzyme from their single G allele to fucosylate mucosal glycans at levels that sustain a secretor microbiome. Studies consistently group AG and GG individuals together as "secretors" because their microbial communities, infection susceptibility profiles, and autoimmune risk are essentially indistinguishable.

If both parents carry one A allele each, there is a 25% probability of producing an AA (non-secretor) child.