ESR1 rs2206949 — The 6q25.1 Endometriosis Signal and Estrogen Receptor Regulation
The 6q25.1 chromosomal region is one of the most important genetic loci in female reproductive
biology. It contains the ESR1 gene (estrogen receptor alpha), which orchestrates estrogen
signaling across the endometrium, ovary, bone, brain, and cardiovascular system. Nearby sits
ARMT1 (Acidic Residue Methyltransferase 1), a gene co-located at 6q25.1 that shows
coordinated expression with estrogen-sensitive tissues. The rs2206949 variant — a C-to-T
substitution in an intron of ESR1 — is one of several independent signals at this locus
linking estrogen receptor biology to endometriosis risk.
The Mechanism
rs2206949 lies within an intronic region of ESR1 at chromosome 6, position 151,716,421
(GRCh38). Because it is intronic, it does not alter the amino acid sequence of estrogen
receptor alpha. Instead, intronic variants at this locus are thought to act through
regulatory mechanisms | intronic variants can affect gene expression by altering enhancer
activity, splicing efficiency, or chromatin organization
that modulate ERα expression levels or isoform ratios in hormone-responsive tissues.
The 6q25.1 region contains several genes — SYNE1, ESR1, CCDC170, and ARMT1 —
that show chromatin interactions and coordinated expression in the endometrium. Fine-mapping
studies using
Summary-based Mendelian Randomization | SMR tests whether a GWAS signal co-localizes
with a cis-eQTL, suggesting the GWAS variant acts through gene expression rather than
being a coding variant have identified ESR1
expression in blood and endometrial tissue as a mediator of endometriosis susceptibility
at this locus, with variants in strong LD acting as eQTLs for ESR1. The proximity of
rs2206949 to ARMT1 (~264 kb) also places it within a regulatory domain where chromatin
interactions between the two genes have been detected.
The Evidence
The clearest evidence for rs2206949 comes from a large international
GWAS meta-analysis in 17,045 endometriosis cases and 191,596 controls |
Sapkota et al. Meta-analysis identifies five novel loci associated with endometriosis
highlighting key genes involved in hormone metabolism. Nature Communications,
2017 that identified the ESR1/6q25.1 region
as harboring two independent association signals, with the ESR1 locus emerging as one
of five novel genome-wide significant findings. The T allele at rs2206949 carries a modest
but replicated effect (OR ~1.10, 95% CI 1.06–1.14, p=3×10⁻⁷) on endometriosis risk.
The 6q25.1 locus has since been substantially refined. In the largest endometriosis GWAS
to date, a
meta-analysis of 60,674 cases and 701,926 controls of European and East Asian ancestry |
Rahmioglu et al. The genetic basis of endometriosis and comorbidity with other pain and
inflammatory conditions. Nature Genetics, 2023,
conditional analysis revealed five distinct independent signals at the SYNE1/6q25.1
locus — more than any other locus in the genome — with rs73625113 within ESR1 intron
identified as a high-confidence causal variant (posterior probability 0.506). These signals
collectively underscore the critical role of this region in endometriosis pathogenesis.
Beyond reproductive disease, rs2206949 was identified in a
longitudinal GWAS of bone mineral density in 141,261 UK Biobank participants |
PMID 37500982, 2023 as a genome-wide
significant (p=2×10⁻⁸) determinant of BMD trajectory. This mirrors the well-known
pleiotropic effects of ESR1 variants on both reproductive and skeletal outcomes, as
estrogen receptor alpha mediates estrogen's bone-protective actions alongside its role
in endometrial function.
The T allele is substantially more common in African populations (~43%) and substantially
less common in East and South Asian populations (~13%), making ancestral background an
important consideration when interpreting this result.
Practical Actions
The effect of rs2206949 on endometriosis risk is modest — an OR of ~1.10 per T allele
means TT homozygotes carry roughly 1.21-fold elevated baseline risk compared to CC
homozygotes. This is not a diagnostic marker for endometriosis, and many factors beyond
this single variant determine individual susceptibility. However, the T allele sits within
a broader pattern of ESR1-region variation that, when combined with other 6q25.1 signals,
contributes meaningfully to the genetic architecture of the disease.
For T-allele carriers — especially TT homozygotes — the most actionable implication is
heightened awareness of endometriosis symptoms and avoiding the diagnostic delays (averaging
4–11 years in clinical practice) that are common for this condition. Symptoms warranting
specialist evaluation include severe dysmenorrhea, chronic pelvic pain, deep dyspareunia,
and unexplained infertility.
The bone mineral density association adds a secondary consideration: ESR1-region variants
track estrogen sensitivity in skeletal tissue, making proactive bone density monitoring
relevant for TT homozygotes — particularly as estrogen levels decline perimenopausally.
Interactions
rs9340799 and rs2234693 (ESR1 XbaI and PvuII): These are two other independent ESR1
intronic variants already well-characterized for endometriosis and reproductive outcomes.
rs2206949 represents a third, conditionally independent signal at the same locus — meaning
it adds information beyond what rs9340799 and rs2234693 capture. Women carrying risk alleles
at multiple ESR1 loci may have more pronounced estrogen-signaling dysregulation, though
formal combined-effect studies are needed.
rs12700667 (near HOXA10/HOXA11): The HOXA homeobox genes regulate endometrial
development and uterine receptivity. Risk alleles at both the ESR1 (rs2206949) and HOXA
loci may compound endometriosis susceptibility through independent pathways — ERα-mediated
signaling and HOX-mediated endometrial patterning respectively.
rs7521902 (near WNT4): WNT4 signaling is critical for female sex determination and
suppression of androgen biosynthesis. The WNT4 endometriosis locus is among the most
robustly replicated signals genome-wide. Carrying risk alleles at both ESR1 (rs2206949)
and WNT4 loci may confer additive endometriosis susceptibility through convergent hormonal
dysregulation, though epistatic interaction testing has not been published for this pair.
All Genotypes
No copies of the T risk allele — baseline endometriosis susceptibility at this locus
You carry two copies of the C (reference) allele at rs2206949. This is the most common genotype globally, present in approximately 47% of the population. At this specific ESR1 intronic locus, you carry no copies of the T allele that is associated with modestly elevated endometriosis risk in large GWAS studies. This result does not eliminate your risk for endometriosis — most of the genetic architecture of the disease lies outside this single variant, and environmental and hormonal factors play major roles. It does mean you do not carry additional risk from this particular ESR1 signal.
One copy of the T risk allele — modestly elevated endometriosis susceptibility
You carry one copy of the T allele at rs2206949. Under the additive model, each T allele increases endometriosis risk by approximately 10% (OR ~1.10 per allele), so CT heterozygotes have about 10% elevated baseline risk at this locus compared to CC carriers. Approximately 43% of people globally share this heterozygous genotype. This is a modest effect from a single variant — endometriosis is polygenic and influenced by many factors. The T allele at this ESR1 intronic locus is thought to influence estrogen receptor expression or regulation in endometrial tissue, subtly shifting how estrogen signaling is calibrated in the uterus and potentially in the peritoneum.
Two copies of the T risk allele — elevated endometriosis susceptibility at this ESR1 locus
You carry two copies of the T allele at rs2206949. Under the additive model, TT homozygotes carry approximately 21% elevated endometriosis risk at this locus compared to CC carriers (OR ~1.10² ≈ 1.21). About 10% of the global population carries this genotype. The T allele is more common in African ancestry populations (~43% allele frequency) and substantially less common in East and South Asian populations (~13%). This intronic ESR1 variant is one of at least five independent signals at the 6q25.1 locus associated with endometriosis. The cumulative effect of carrying risk alleles at multiple loci within this region may compound susceptibility more than any single variant in isolation.