rs3890745 — MMEL1 MMEL1 rs3890745

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.