rs146906133 — FRMD5 FRMD5 UTI susceptibility variant

Intronic variant in FRMD5 — a cell-adhesion scaffolding gene — where the rare C allele is associated with reduced recurrent urinary tract infection susceptibility, implicating uroepithelial barrier integrity in innate mucosal defense

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FRMD5 — A Scaffold Protein at the Uroepithelial Frontier

Urinary tract infections (UTIs) are among the most common bacterial infections in humans, affecting roughly 50% of women at least once in their lifetime and frequently recurring in a subset genetically predisposed to mucosal colonization by uropathogenic E. coli. While immune signaling genes like TLR4 have long been linked to UTI susceptibility, a 2017 genome-wide association study identified a second independent locus — an intronic variant in FRMD511 FRMD5
FERM domain-containing protein 5, a cytoskeletal scaffolding protein expressed at epithelial cell junctions — pointing to uroepithelial barrier integrity as a distinct axis of innate UTI defense.

The Mechanism

FRMD5 is a member of the FERM (Four-point-one, Ezrin, Radixin, Moesin) domain superfamily — a class of proteins that physically link the actin cytoskeleton to transmembrane adhesion molecules and junction complexes. FRMD5 localizes to cell adherens junctions and interacts with p120-catenin22 FRMD5 localizes to cell adherens junctions and interacts with p120-catenin
p120-catenin is a key regulator of E-cadherin stability and epithelial barrier function at cell-cell contacts. It also binds directly to the cytoplasmic tail of integrin β5 and inhibits ROCK1-mediated myosin phosphorylation33 binds directly to the cytoplasmic tail of integrin β5 and inhibits ROCK1-mediated myosin phosphorylation
ROCK1 drives stress fiber contraction; FRMD5 acts as a brake on this pathway to stabilize cell-matrix adhesion, promoting tight cell-surface attachment over migratory, loosely adherent states.

The rs146906133 variant is intronic and does not alter the FRMD5 protein sequence. It likely acts as a regulatory variant affecting FRMD5 transcription or splicing in uroepithelial tissue, although the exact mechanism has not yet been functionally characterized. The plausible biological model is that altered FRMD5 expression changes the structural stiffness of the uroepithelial cell layer — either making it more or less permeable to bacterial attachment and the cytoskeletal remodeling that uropathogenic E. coli exploit during invasion. The rare C allele may increase FRMD5 expression in bladder epithelium, reinforcing tight junction stability and reducing the cytoskeletal rearrangements that allow bacteria to access and persist within uroepithelial cells.

FRMD5 has also been identified as upregulated during Plasmodium berghei infection44 upregulated during Plasmodium berghei infection
a rodent malaria parasite, in a serum proteomics study, consistent with the idea that FRMD5 participates in the cell-to-cell adhesion dynamics exploited by intracellular and epithelium-invading pathogens more broadly.

The Evidence

The association at rs146906133 was discovered by Tian et al. in a 2017 Nature Communications genome-wide study55 Tian et al. in a 2017 Nature Communications genome-wide study
23andMe research group, analyzing 23 infection phenotypes in over 200,000 individuals of European ancestry. The study identified 59 genome-wide significant associations across all infections, of which the FRMD5 locus was the second independent hit for UTI frequency (the first being a locus near the TLR4 pathway). The T allele (reference, common in >98% of Europeans) was associated with higher self-reported UTI frequency (beta = 0.38, 95% CI 0.32–0.45, p = 2.02×10⁻⁸). Importantly, this study used UTI frequency as a quantitative phenotype, so the beta represents the change in standardized UTI frequency score per allele copy.

The evidence level is emerging: the GWAS signal is genome-wide significant, but the study was observational and self-reported, functional validation of the FRMD5 intronic variant in uroepithelial cells has not been published, and no independent replication cohort has been reported specifically for rs146906133. The biological plausibility is high given FRMD5's established roles in epithelial adhesion, but the mechanistic link to UTI remains inferred.

The C allele is notably more common in East Asian populations (~5.8% allele frequency) than in Europeans (~0.75%) or Africans (<0.1%). Whether the C allele confers the same magnitude of protection in non-European populations has not been tested.

Practical Implications

For the rare carriers of the protective C allele (approximately 1.5% of Europeans carry at least one copy), the genetic data suggest a meaningfully lower biological susceptibility to recurrent UTIs — not immunity, but a measurable difference in how readily uropathogenic bacteria establish persistent mucosal infection. This likely reflects more resilient uroepithelial barrier function rather than any difference in classical immune signaling.

Given that the mechanism involves epithelial structural integrity, factors that further support mucosal barrier health — particularly adequate hydration to maintain urinary flow, and probiotic approaches that compete with uropathogenic colonizers at the vaginal and periurethral mucosa — may complement the genetic protection.

Conversely, the TT genotype (the common reference state) simply reflects the normal population-level baseline susceptibility to UTIs. This genotype alone does not predict recurrent UTIs — many other genetic and behavioral factors (sexual activity frequency, contraceptive choice, anatomical features, other UTI-susceptibility variants) shape overall UTI burden.

Interactions

The FRMD5 locus (rs146906133) and the TLR4 signaling locus represent two independent genetic axes of UTI susceptibility: barrier integrity versus innate immune signaling, respectively. Variants in TLR4 (rs4986790, rs4986791), the secretor status gene FUT2 (which governs whether uropathogens can adhere to certain blood group antigen substrates on the uroepithelium), and complement system genes are all relevant to overall UTI susceptibility and represent distinct pathways from FRMD5's cell adhesion role.

Genotype Interpretations

What each possible genotype means for this variant.

TT Normal

Common baseline uroepithelial adhesion profile with typical UTI susceptibility

You carry two copies of the common reference T allele at rs146906133 in the FRMD5 gene. This is the most common genotype, found in approximately 98.5% of people globally. Your FRMD5 expression in uroepithelial tissue is at the typical population level, and your mucosal adhesion scaffold functions in the standard way. This genotype does not confer any special protection against UTIs, nor does it indicate elevated risk relative to the general population — it simply reflects the common baseline susceptibility from which the rare C allele departs.

CT Partial FRMD5 Protection Beneficial

One copy of the rare protective C allele — reduced uroepithelial susceptibility to UTI colonization

FRMD5 localizes to cell adherens junctions, where it interacts with p120-catenin and integrin β5 to stabilize the uroepithelial cell layer against invasion and cytoskeletal remodeling. Uropathogenic E. coli (UPEC) bind to uroplakin and mannose-terminated glycoproteins on the bladder surface, then trigger actin cytoskeletal remodeling to invade intracellularly — a process that a more rigid, FRMD5-reinforced cytoskeleton may impede. Heterozygous carriers of the C allele carry one copy of whatever regulatory variant influences this process, likely resulting in intermediate protection compared to the homozygous CC state.

The GWAS data (PMID 28928442) do not separately report effect sizes for CT vs TT; an additive model is assumed, meaning each C allele confers approximately 0.38 units of reduction in standardized UTI frequency score. For CT heterozygotes, the expected protection is approximately half that of CC homozygotes.

CC Homozygous FRMD5 Protection Beneficial

Two copies of the rare protective C allele — strongest genetic reduction in uroepithelial UTI susceptibility at this locus

FRMD5 functions as a scaffolding protein at cell adherens junctions, linking the actin cytoskeleton to both p120-catenin (junction stability) and integrin β5 (cell-matrix adhesion). Uropathogenic E. coli must trigger host cytoskeletal remodeling to invade uroepithelial cells and form the intracellular bacterial communities that enable chronic, recurrent infection. A more rigid, well-anchored uroepithelial cytoskeleton — hypothesized to result from the CC genotype's effect on FRMD5 expression — may reduce the compliance of the cell surface to this cytoskeletal hijacking, limiting bacterial invasion depth.

As a CC homozygote, you carry the protective allele dosage that confers the maximum genetic reduction in UTI frequency at this locus. The evidence is from a single large GWAS and has not been independently replicated; no functional cellular studies have confirmed the proposed uroepithelial mechanism. Treat this as a meaningful genetic signal with emerging but not established evidence.