rs3890745 — MMEL1 MMEL1 rs3890745

Intronic variant near MMEL1 and TNFRSF14 on chromosome 1p36; the C allele is associated with increased susceptibility to rheumatoid arthritis and other autoimmune conditions through disrupted immune costimulatory signaling at the HVEM/LIGHT/BTLA axis

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MMEL1-TNFRSF14 — A Regulatory Checkpoint Between Peptide Processing and Immune Costimulation

On the short arm of chromosome 1, at position 1p36, two genes sit in close proximity with distinct but complementary roles in immune homeostasis: MMEL1, encoding a neprilysin-like metalloendopeptidase, and TNFRSF14, encoding HVEM11 HVEM
Herpes Virus Entry Mediator, also known as CD270 — a TNF receptor superfamily member that regulates both activating and inhibitory T-cell signals. The rs3890745 intronic SNP22 SNP
Single nucleotide polymorphism — a single-letter DNA difference that varies between people; this one lies within MMEL1 but is in linkage disequilibrium with regulatory elements affecting both neighboring genes has been consistently associated with rheumatoid arthritis susceptibility in multiple genome-wide association studies. The C allele, carried at approximately 32% frequency in Europeans but up to 53% in African populations, tags a risk haplotype at this locus.

The Mechanism

rs3890745 falls within an intron of MMEL1 (membrane metalloendopeptidase like 1), also known as NEP2 or neprilysin II. MMEL1 is a zinc-dependent neutral endopeptidase that cleaves bioactive peptides including neuropeptides and inflammatory mediators — a function that positions it as a regulator of local peptide signaling in immune and neural contexts. MMEL1 is expressed broadly, with highest levels in testis and small intestine, and weaker expression in brain, kidney, and immune tissues.

The more immunologically prominent neighbor is TNFRSF14 (HVEM/CD270). HVEM operates as a dual-function immune checkpoint: it can deliver activating signals to T cells via binding LIGHT33 LIGHT
TNFSF14, a ligand expressed on activated T cells that delivers costimulatory signals through HVEM, promoting T-cell proliferation and cytokine production, but it also transmits inhibitory signals through BTLA44 inhibitory signals through BTLA
B- and T-lymphocyte attenuator — an inhibitory receptor expressed on lymphocytes that signals "stop" when bound to HVEM, analogous to CTLA-4 and PD-1. This bidirectional control makes HVEM a critical rheostat in peripheral immune tolerance. Disruption of the HVEM/BTLA inhibitory axis has been implicated in multiple autoimmune conditions, including rheumatoid arthritis, celiac disease, and inflammatory bowel disease.

As an intronic variant, rs3890745 does not change the MMEL1 protein sequence. It is presumed to act as a regulatory tag SNP in linkage disequilibrium with functional variants that alter expression levels of MMEL1, TNFRSF14, or both in immune cell populations. Expression quantitative trait locus (eQTL) data from immune cells would be required to identify the precise causal variant; the rs3890745 association most likely reflects a haplotype-level regulatory effect spanning both genes.

The Evidence

The MMEL1-TNFRSF14 locus was first established as an RA susceptibility region in a 2008 genome-wide association meta-analysis55 genome-wide association meta-analysis
Study design combining multiple GWAS cohorts to increase statistical power — more samples yield more reliable effect estimates by Raychaudhuri and colleagues (Nature Genetics), which analyzed 3,393 cases and 12,462 controls in the discovery phase and 3,929 anti-CCP-positive RA cases and 5,807 controls in replication. The rs3890745 signal at this locus reached an overall p-value of 1.1×10⁻⁷, placing it among confirmed RA susceptibility loci alongside CD40, KIF5A, and CDK6.

The association was replicated in the large trans-ethnic RA GWAS meta-analysis66 large trans-ethnic RA GWAS meta-analysis
Trans-ethnic meta-analysis pooling cohorts of European, East Asian, and mixed ancestry — improves fine-mapping precision by narrowing LD blocks by Okada et al. (Nature, 2014), which confirmed an odds ratio of 1.18 (95% CI 1.10–1.27) for the risk allele at this locus. An independent GWAS meta-analysis by Stahl et al. (Nature Genetics, 2010)77 Stahl et al. (Nature Genetics, 2010)
Discovery phase: 5,539 RA cases and 20,169 controls from European populations; replication phase: 6,768 cases and 8,806 controls confirmed the MMEL1 locus at p=4×10⁻⁶. A 2019 cross-trait GWAS analysis88 2019 cross-trait GWAS analysis
Examining shared genetic architecture between autoimmune diseases and non-Hodgkin lymphomas using regional overlap and polygenic risk scores identified rs3890745 with OR 1.14 at genome-wide significance (p=2×10⁻⁸) in a combined RA/DLBCL analysis, supporting shared immune-regulatory genetic architecture across B-cell-driven conditions.

Beyond RA, variants at the MMEL1-TNFRSF14 locus have been associated with multiple sclerosis and primary biliary cirrhosis in separate GWAS, consistent with the broad role of HVEM-mediated immune costimulation in peripheral tolerance across different autoimmune phenotypes.

The per-allele odds ratio of approximately 1.12–1.18 classifies this as a moderate-effect susceptibility locus. This is consistent with the polygenic architecture of RA, where dozens of loci each contribute small incremental risk — the clinical impact of rs3890745 alone is modest, but it gains significance when combined with high-risk HLA-DRB1 shared epitope alleles or PTPN22 R620W.

Practical Actions

For C allele carriers, particularly CC homozygotes, the priority is early recognition of seropositive RA — the anti-CCP (ACPA)-positive, erosive subtype with the strongest genetic component. Because rs3890745 tags shared autoimmune genetic architecture, individuals with joint symptoms, unexplained morning stiffness, or a strong family history of RA should prioritize early autoantibody testing. Vitamin D3 supplementation has demonstrated a 22% reduction in incident autoimmune disease in the VITAL RCT and acts as a direct NF-kB and T-cell regulatory modulator.

Interactions

rs3890745 sits in the same chromosomal neighbourhood as a broader 1p36 autoimmune risk region. TNFRSF14/HVEM interacts directly with BTLA on T cells and B cells — variants in the BTLA locus (rs9288952) have been associated with RA in some GWAS, suggesting a potential compound effect through the HVEM-BTLA inhibitory axis. MMEL1 has homology with neprilysin (NEP/CD10), which processes inflammatory neuropeptides; the folate-methylation pathway (MTHFR, rs1801133) intersects with DNA methylation patterns at immune loci that regulate TNFRSF14 expression.

The strongest RA risk loci that may compound with rs3890745 include PTPN22 rs2476601 (T-cell signaling threshold), TRAF1-C5 rs10818488 (NF-kB regulation), and HLA-DRB1 shared epitope alleles (antigen presentation). These operate through distinct pathways and their combined carriage incrementally raises absolute RA risk.

Genotype Interpretations

What each possible genotype means for this variant.

TT Typical MMEL1-TNFRSF14 Regulation Normal

Low-risk genotype at the MMEL1-TNFRSF14 locus; no HVEM-pathway susceptibility signal

You carry two copies of the T reference allele at rs3890745, the lower-risk genotype at the MMEL1-TNFRSF14 locus. Approximately 47% of people share this genotype globally, rising to about 47% in Europeans. The TT genotype is not associated with elevated rheumatoid arthritis risk through this locus; HVEM-mediated immune costimulation and MMEL1 peptide-processing activity at this haplotype are at baseline population levels.

CT One Risk Allele Intermediate

One copy of the C risk allele — modestly elevated RA susceptibility through HVEM immune checkpoint variation

The C allele tags a haplotype spanning the MMEL1-TNFRSF14 intergenic region on chromosome 1p36. TNFRSF14 encodes HVEM (CD270), a dual-function immune receptor that can both activate T cells (via LIGHT) and inhibit them (via BTLA). Disruption of the inhibitory HVEM/BTLA axis is a recognized mechanism in autoimmune disease pathogenesis, particularly in conditions driven by loss of peripheral T-cell tolerance.

The CT heterozygous genotype represents an intermediate exposure to the risk haplotype. Seropositivity (anti-CCP and/or rheumatoid factor) is the RA subtype most strongly influenced by genetic susceptibility variants at non-HLA loci. Early autoantibody testing when joint symptoms arise is the most actionable implication.

CC Two Risk Alleles High Risk

Two copies of the C risk allele — higher RA susceptibility through HVEM immune checkpoint dysregulation

CC homozygosity at rs3890745 places you in the top tier of genetic susceptibility at this 1p36 locus. The TNFRSF14/HVEM protein encoded near this variant operates as a dual-function immune checkpoint — it can activate T cells through LIGHT binding and suppress them through BTLA engagement. The risk haplotype tagged by the C allele is thought to alter TNFRSF14 or MMEL1 expression levels in immune cell populations, tipping the balance away from HVEM-mediated immune suppression and toward a lower threshold for autoreactive T-cell activation.

The cross-trait association of this locus with both RA and diffuse large B-cell lymphoma (OR 1.14 at p=2×10⁻⁸) indicates broad perturbation of B-cell and T-cell immune homeostasis, not just RA-specific mechanisms. Other autoimmune conditions (multiple sclerosis, primary biliary cirrhosis) show associations at this locus in some populations, suggesting CC homozygotes may have a generally elevated autoimmune threshold.

Prioritize early anti-CCP antibody and rheumatoid factor baseline testing. Both markers can be positive 5–10 years before clinical RA onset; positive serology without symptoms enables structured watchful waiting and faster treatment initiation when needed.