rs72755295 — EXO1 EXO1 mismatch repair variant

Intronic regulatory variant in EXO1 (exonuclease 1) that increases EXO1 enhancer activity; the G allele is associated with earlier age at natural menopause (ovarian ageing) and elevated breast cancer risk through upregulated EXO1 expression

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EXO1 rs72755295 — A Dual-Role DNA Repair Variant Linking Ovarian Ageing and Cancer Risk

Exonuclease 1 (EXO1) is a multifunctional nuclease that participates in two of the most consequential DNA maintenance processes in human biology: mismatch repair (MMR)11 mismatch repair (MMR)
the proofreading system that corrects base substitution errors after DNA replication, protecting cells from accumulating mutations and meiotic recombination — the process that generates genetic diversity and ensures proper chromosome segregation during egg and sperm formation. The rs72755295 variant is an intronic regulatory SNP that alters how much EXO1 protein the cell produces, with consequences that reach from the ovary to breast tissue.

The Mechanism

rs72755295 sits within an intron of EXO1 on chromosome 1 (GRCh38 position 241,870,961). It does not change the EXO1 protein sequence but instead modifies a regulatory enhancer element. Shi et al. 202222 Shi et al. 2022
Breast cancer-associated SNP rs72755295 is a cis-regulatory variation for human EXO1. Genetics and Molecular Biology, 2022 demonstrated that the G allele creates a stronger binding site for the transcription factor PAX6, which drives higher enhancer activity at this locus. The result is elevated EXO1 expression in cells carrying the G allele.

In the ovary, this matters because EXO1 is essential for meiotic crossover formation. Gioia et al. 202333 Gioia et al. 2023
Exo1 protects DNA nicks from ligation to promote crossover formation during meiosis. PLoS Biology, 2023 showed that EXO1 shields DNA nick sites during meiosis I prophase, preventing them from being prematurely sealed by ligase enzymes and thereby enabling the Mlh1-Mlh3 endonuclease complex to initiate crossovers. Too little EXO1 means crossovers fail; but the relationship between EXO1 dosage and ovarian ageing is more nuanced — the GWAS signal at this locus suggests altered EXO1 activity or expression in granulosa and oocyte cells influences the pace at which the primordial follicle pool is depleted over a woman's lifetime.

The Evidence

The ovarian ageing connection was first established by Stolk et al. 201244 Stolk et al. 2012
Meta-analyses identify 13 loci associated with age at menopause and highlight DNA repair and immune pathways. Nature Genetics, 44:260–268, a landmark meta-analysis of 22 GWAS in 38,968 European women with replication in 14,435 additional women. EXO1 was among eight DNA repair genes at newly identified loci reaching genome-wide significance (P < 5 × 10⁻⁸). The striking enrichment of DNA-repair genes at menopause-timing loci — including EXO1, HELQ, UIMC1, FANCI, TLK1, POLG, and PRIM1 — points to a central biological principle: accurate DNA maintenance in oocytes is rate-limiting for ovarian reserve longevity55 accurate DNA maintenance in oocytes is rate-limiting for ovarian reserve longevity
Oocytes are arrested in meiotic prophase I for decades, during which accumulated DNA damage is a primary driver of follicle apoptosis and reserve depletion.

Ruth et al. 202166 Ruth et al. 2021
Genetic insights into biological mechanisms governing human ovarian ageing. Nature, 596:393–397 extended this work to a much larger multi-ancestry cohort exceeding 200,000 women, confirming the EXO1 locus among genetic determinants of age at natural menopause (ANM). The estimated per-allele effect at the EXO1 locus is approximately 0.32 years (~17 weeks) later ANM per G allele — meaning carriers of the G allele have, on average, a slightly later menopause. However, because the G allele is rare (~2% globally), it is the A/A common genotype that defines the population mean, and understanding this SNP requires recognising that the G allele appears to modulate EXO1 expression in a direction that influences ovarian reserve trajectory.

The breast cancer dimension adds an important clinical layer. The same rs72755295-G allele that alters ovarian biology also increases EXO1 expression in breast tissue. Since EXO1 is overexpressed in breast carcinoma samples, Shi et al. 2022 demonstrated that the SNP functions as a cis-regulatory element explaining part of the breast cancer GWAS signal at chromosome 1q43.

Practical Actions

For women carrying the G allele, the dual EXO1 signal — modified ovarian reserve trajectory and elevated breast cancer risk through EXO1 overexpression — warrants specific monitoring targeted to each pathway. Ovarian reserve monitoring via AMH measurement provides the most direct readout of reserve trajectory. Breast awareness and adherence to recommended screening schedules is warranted, and women with a family history of breast cancer should discuss this genetic context with their clinician.

Interactions

EXO1 sits within the DNA-repair cluster of ovarian ageing genes identified in both the Stolk 2012 and Ruth 2021 GWAS. Other genes in this cluster — TLK1 (rs10183486), MCM8 (rs16991615), HELQ (rs1046089), and POLG (rs7759938) — each contribute additive risk through related but distinct repair pathways. Women carrying G alleles at rs72755295 combined with risk alleles at TLK1 or MCM8 may have greater cumulative DNA-repair burden in the ovary, though formal compound analyses of the EXO1 pair with these loci have not been published. Pathway-level enrichment analyses from Ruth 2021 show that the meiotic crossover genes and MMR genes collectively explain a disproportionate fraction of menopause-timing variance.

Genotype Interpretations

What each possible genotype means for this variant.

AA Normal

Common EXO1 genotype — typical ovarian reserve trajectory and cancer baseline

You carry two copies of the A allele at rs72755295, which is the reference genotype at this EXO1 locus and is found in approximately 96% of the global population. Your EXO1 enhancer activity at this locus is at the population-average level, and your ovarian ageing trajectory and breast cancer risk from this specific variant are not elevated. The genetic architecture of ovarian reserve is polygenic; this result is simply one component of a broader picture.

AG One G Allele Intermediate

One copy of the EXO1 G allele — mildly elevated EXO1 expression and altered ovarian ageing signal

The biological interpretation of the G allele's direction of effect on ovarian ageing is nuanced. The GWAS signal at the EXO1 locus for age at natural menopause reflects that altered EXO1 activity in the ovary changes the rate of follicle attrition — but whether this manifests as earlier or later menopause for G allele carriers depends on the specific tissue context and whether increased EXO1 expression helps or hinders meiotic crossover fidelity. The key clinical point is that this locus sits in a well-established DNA-repair gene cluster governing ovarian reserve, and the G allele distinguishes you from the ~96% of people at the population mean.

For breast cancer risk, the mechanism is more direct: elevated EXO1 expression driven by the G allele's enhanced enhancer activity parallels the overexpression pattern seen in breast carcinoma tissue, suggesting a plausible cis-regulatory pathway to increased susceptibility. This does not mean breast cancer is likely — the absolute risk increment from a single intronic regulatory variant is modest — but it is actionable via standard screening vigilance.

GG Two G Alleles High Risk

Two copies of the EXO1 G allele — rare genotype with elevated EXO1 expression and dual ovarian/breast signal

Because GG homozygosity at rs72755295 is so rare (G allele frequency ~2%), essentially no published studies have characterised the GG genotype specifically — all effect size estimates come from additive allele models. The per-allele GWAS beta of ~0.32 years for menopause timing, if additive, would predict GG homozygotes have approximately 0.64 years (~7.5 months) difference in ANM compared with AA individuals. Whether this is earlier or later menopause depends on the precise mechanism (EXO1 upregulation could impair meiotic crossover fidelity if expression exceeds an optimal range, accelerating follicle attrition).

For breast cancer, the mechanistic argument from Shi et al. 2022 is that G allele dosage correlates with increasing EXO1 enhancer activity via PAX6 binding. GG carriers represent the tail of the expression distribution. While the absolute risk from this single variant is unlikely to be dramatic, it is one of several molecular inputs into breast cancer susceptibility and warrants incorporation into clinical risk stratification alongside family history, BRCA status, and breast density.

Importantly, EXO1's role in mismatch repair means elevated EXO1 expression also intersects with colorectal cancer biology (MLH1-EXO1 pathway). At this stage, the literature is insufficient to quantify colorectal cancer risk from rs72755295 GG specifically, but the dual MMR/fertility biology of EXO1 makes broader cancer awareness appropriate.