GREB1

GREB1 — An Estrogen-Responsive Gene at the Heart of Endometriosis Susceptibility

Endometriosis — tissue similar to the uterine lining growing outside the uterus — affects an
estimated 10% of women of reproductive age and accounts for a substantial share of chronic
pelvic pain and infertility. The condition is driven by estrogen | estrogen is the primary
hormonal fuel for endometriotic lesion growth; ectopic implants express elevated levels of
aromatase, generating their own local estrogen supply
and sustained by immune tolerance at ectopic implant sites. Roughly half of endometriosis
susceptibility is heritable, and rs13394619 in GREB1 is one of the most consistently
replicated common genetic risk signals discovered to date.

GREB1 — Growth Regulation by Estrogen in Breast Cancer 1 — was first identified as an early
estrogen response gene in breast cancer cell lines. It encodes a nuclear co-factor that
physically interacts with hormone receptors to amplify their transcriptional activity.
The gene sits on chromosome 2p25.1, and rs13394619 lies in an intronic region between
exons 9 and 10 with predicted effects on local splicing activity.

The Mechanism

GREB1 operates as a pan-steroid hormone cofactor | Chadchan et al. Nature Communications,
2024 that behaves differently depending on
the hormonal and cellular context. In healthy endometrium during the secretory phase, GREB1
is progesterone-responsive: it physically binds the progesterone receptor and amplifies
expression of downstream targets including WNT4 and FOXO1A, which drive the stromal
decidualization required for embryo implantation.

In endometriotic lesions the circuit flips. Ectopic tissue accumulates estrogen through
locally upregulated aromatase, and in this estrogen-dominant environment GREB1 switches to
functioning as an estrogen receptor cofactor — amplifying estrogen-driven gene expression
and proliferation of ectopic cells. Mouse models with GREB1 knockout show significantly
reduced endometriotic lesion volume and mass. Human endometriotic cells with GREB1 knockdown
proliferate more slowly when exposed to estrogen.

The intronic rs13394619 variant may influence how GREB1 is spliced or expressed in
endometrial tissue. Although eQTL analyses have not identified a single dramatically
altered transcript, fine-mapping studies have identified multiple nearby variants with
stronger individual associations, suggesting the region contains regulatory elements
relevant to endometrial gene expression.
GREB1 mRNA and protein are significantly elevated in peritoneal endometriotic lesions
compared with eutopic endometrium from unaffected women | Pellegrini et al. Fertility
and Sterility, 2012, supporting GREB1 as
a functionally active contributor to estrogen-dependent lesion growth.

The Evidence

rs13394619 was identified in a
genome-wide association meta-analysis of 4,604 endometriosis cases and 9,393 controls
of Japanese and European ancestry | Nyholt et al. Nature Genetics, 2012
.
The G allele reached genome-wide significance (OR 1.15, 95% CI 1.09–1.20, P = 6.1 × 10⁻⁸)
in the combined analysis, with consistent direction of effect across all contributing cohorts.

A subsequent
meta-analysis of eight GWAS datasets encompassing European and Japanese populations | Rahmioglu
et al. Human Reproduction Update, 2014
confirmed the association: OR 1.13 (95% CI 1.07–1.20, P = 2.9 × 10⁻⁸). Notably, five of
the six confirmed endometriosis loci — including the GREB1 locus — showed stronger effects
when restricted to Stage III/IV (moderate-to-severe) disease, with the Stage III/IV enriched
estimate for rs13394619 reaching P = 3.5 × 10⁻⁸ and OR = 1.15.

Independent replication in a
Belgian cohort of 998 cases and 783 controls | Sapkota et al. Twin Research and Human
Genetics, 2015 confirmed nominally significant
association, which reached genome-wide significance in the updated meta-analysis. The G allele
frequency shows marked ancestry stratification: approximately 0.51 in Europeans and 0.50 in
East Asians, but only approximately 0.14 in African populations.

Practical Implications

Carrying G alleles at rs13394619 raises the population-level probability of developing
endometriosis, with the greatest estimated effect on moderate-to-severe disease. The absolute
risk added by a single common variant of this effect size (OR ~1.13–1.15 per allele) is
modest, but the biological pathway — GREB1's estrogen-driven amplification of ectopic
tissue growth — points to concrete surveillance and specialist engagement strategies.

The most actionable implication is awareness of cardinal symptoms and willingness to escalate
evaluation early. Endometriosis average diagnostic delay remains approximately 7–9 years in
many healthcare systems. Severe dysmenorrhea, deep dyspareunia, cyclic bowel or bladder
symptoms, and unexplained infertility are the key presentations to act on rather than
normalize.

For GG homozygotes — who carry the highest common genetic load at this locus — the elevated
probability of moderate-to-severe disease specifically supports proactive fertility counseling,
early ovarian reserve assessment, and lower thresholds for specialist referral if symptoms
emerge.

Interactions

rs12700667 (7p15.2, near HOXA10/HOXA11): rs12700667 is the other major replicated
endometriosis GWAS locus, operating through a distinct candidate pathway — long-range
regulation of homeobox genes that orchestrate endometrial development and receptivity.
While formal statistical interaction testing between rs13394619 and rs12700667 has not been
published, both variants show independent additive genome-wide significant effects on
endometriosis risk, both show stronger effects for Stage III/IV disease, and women carrying
risk alleles at both loci may represent a subgroup with substantially elevated cumulative
susceptibility.

For a supervisor compound action proposal: women carrying the G risk allele at rs13394619
(GG or AG) AND the A risk allele at rs12700667 (AA or AG) carry the two strongest and most
replicated common endometriosis GWAS signals simultaneously. The combined recommendation
would be: lower threshold for specialist gynecological referral for any pelvic symptoms,
earlier baseline ovarian reserve testing (AMH + antral follicle count), and proactive
fertility counseling by age 28–30. Evidence level: moderate (both loci independently
established; combined effect inferred from consistent additive direction rather than
formal interaction analysis).

rs11674184 (GREB1): A second intronic GREB1 variant also associated with endometriosis
risk. Studies in Greek populations testing rs11674184 as a proxy for the GREB1 locus found
non-significant results in a small cohort, illustrating the population-level heterogeneity
in this region. Both variants lie within GREB1 and may tag overlapping haplotypes.