rs201408742 — GPR174

GPR174 Xq21.1 — An X-Linked Immune Receptor Locus and Rheumatoid Arthritis Risk

On the X chromosome at band Xq21.1 sits a gene that the immune system relies on to tune the behaviour of T cells and dendritic cells: GPR174 (G protein-coupled receptor 174)¹¹ GPR174 (G protein-coupled receptor 174)
formerly annotated as LOC107985690 in earlier genome builds; Gene ID replaced by 84636 (GPR174) in 2020. GPR174 encodes a seven-transmembrane GPCR expressed at high levels in lymph nodes, appendix, and lymphoid tissue. Its cognate ligand — identified only in the last decade — is lysophosphatidylserine (LysoPS)²² lysophosphatidylserine (LysoPS)
a bioactive lipid mediator generated from membrane phosphatidylserine during apoptosis and immune activation; acts on GPR174 to modulate T cell chemotaxis and dendritic cell responses. Because GPR174 is X-linked, women carry two copies while men carry one; this dosage difference likely contributes to the well-known female predominance of autoimmune diseases.

rs201408742 is an intergenic variant at chrX:79209119 (GRCh38), located approximately 37 kb downstream of the GPR174 coding region in a putative regulatory region. It falls within the same Xq21.1 GWAS signal block as the well-characterised functional variant rs3827440 (S162P)³³ rs3827440 (S162P)
the primary coding GPR174 variant — changes serine to proline at position 162 of the receptor protein; associated with Graves' disease, autoimmune Addison's disease, and rheumatoid arthritis in multiple populations and the confirmed RA index SNPs rs6619397 and rs6615512. rs201408742 itself has no annotated functional consequence in dbSNP; it is a tag SNP for the broader locus LD block, likely in linkage disequilibrium with the functional variants, particularly in East Asian populations where the A allele is substantially more common (~47%).

The Mechanism

The GPR174 protein relays LysoPS signals from the cell surface into downstream G protein cascades. In dendritic cells, GPR174 stimulation has been shown to suppress colitis-driving inflammatory responses. In T cells, GPR174 modulates chemotactic migration — directing T cells toward lymph nodes and inflammatory sites. Variants in GPR174 that alter protein function or expression levels could therefore shift the balance of T cell trafficking and antigen presentation in ways that favour autoimmune tissue attack.

The rs3827440 functional variant⁴⁴ rs3827440 functional variant
a missense change at codon 162, shifting serine to proline; this alters a region of the receptor involved in ligand recognition and downstream signalling coupling is associated with altered GPR174 mRNA levels in immune-relevant tissues (p=0.002 in eQTL analysis). rs201408742 sits in the regulatory flanking region where enhancer elements modulating GPR174 expression in lymphoid tissue would be expected. However, no direct eQTL or functional evidence specifically linking rs201408742 to gene expression changes has been published. It is classified here as a regulatory tag SNP based on its genomic position and LD context.

The Evidence

The GPR174/Xq21.1 locus has now been independently associated with multiple autoimmune diseases across several ancestries. The Graves' disease signal is best characterised: Chu et al. 2013⁵⁵ Chu et al. 2013
X chromosome-wide association study in Chinese Han (1,536 GD cases, 1,516 controls) with replication in 4,564 cases and 3,968 controls found rs3827440 associated with GD at combined p=5.5×10⁻²¹ (OR 1.69, 95% CI 1.53–1.86). The same variant was replicated in Polish Caucasians at OR 1.19 (p=0.021) by Szymański et al. 2014⁶⁶ Szymański et al. 2014
756 GD patients, 946 controls; first Caucasian replication. For autoimmune Addison's disease, Napier et al. 2015⁷⁷ Napier et al. 2015
286 AAD cases, 288 UK controls found an OR of 1.80 (p=0.010) for the same GPR174 variant.

The rheumatoid arthritis association at this locus was established by large-scale trans-ancestral GWAS. Ha et al. 2021⁸⁸ Ha et al. 2021
meta-analysis of 311,292 Korean, Japanese, and European individuals identified rs6619397 at GPR174 as a significant RA signal (OR 1.11, p=6×10⁻¹²), and Ishigaki et al. 2020⁹⁹ Ishigaki et al. 2020
212,453 Japanese subjects across 42 diseases found rs6615512 (OR 1.127, p=6×10⁻⁹) at the same locus. rs201408742 was identified as part of the broader X-chromosome RA signal block in this locus; among the ~42 X-chromosome SNPs associated with RA in the region, most have ORs between 1.01–1.2, reflecting a modest risk effect consistent with a common regulatory variant in linkage disequilibrium with the causal functional change.

The allele frequency structure of rs201408742 is unusual: the A allele (risk) is rare in Europeans (~0.9%) and Africans (~0.8%) but approaches equal frequency with the reference in East Asian populations (~47% in 1000G East Asian, ~44% in Korean databases, ~41% in Japanese). This population stratification means RA risk modification from this specific variant is primarily relevant for individuals of East Asian ancestry.

Practical Implications

The modest effect size (OR ~1.1) for this tag SNP means it contributes a small, quantifiable increment to RA susceptibility rather than a high-penetrance risk. For individuals of East Asian ancestry carrying the A allele, awareness of inflammatory joint symptoms and periodic assessment of inflammatory markers is reasonable, particularly given the additive nature of polygenic RA risk. Early recognition of RA symptoms — symmetric joint pain and morning stiffness lasting more than 30 minutes — enables timely intervention before irreversible joint damage occurs.

The broader GPR174 locus also raises the question of cross-autoimmune risk. Individuals with the RA-associated A allele at this locus may carry slightly elevated susceptibility to other GPR174-associated autoimmune conditions (thyroid autoimmunity, Addison's disease), particularly if they also carry the functional rs3827440 variant.

Interactions

The GPR174 locus houses multiple variants in linkage disequilibrium. The primary functional variant rs3827440¹⁰¹⁰ rs3827440
a missense S162P change in the GPR174 receptor protein; OR 1.69 for Graves' disease, OR 1.80 for autoimmune Addison's disease; also in the RA signal block is the likely causal variant underlying the rs201408742 signal. Individuals carrying both rs201408742-A and rs3827440-T (the risk allele) may have additive risk from the combined haplotype effect. The nearby variant rs5912761, also in this LD block, shows some of the strongest thyroid peroxidase antibody associations (p=2×10⁻²⁸), suggesting the GPR174 locus exerts broad influence across thyroid and joint autoimmune phenotypes.

On the autosomal side, the canonical RA risk loci (HLA-DRB1 shared epitope, PTPN22 rs2476601, STAT4 rs7574865, TRAF1-C5 rs10818488) each contribute independently to polygenic RA risk. The X-linked GPR174 signal adds to — but does not multiply — this autosomal risk architecture.