Premature Ovarian Failure 20

Key Findings

Finding 1 — POF20 is caused by biallelic loss-of-function variants in MSH4 and is inherited autosomal-recessively [H]

POF20 maps unambiguously to the identifier set OMIM:619938 / MONDO:0030975 / UMLS:C5677011 / GARD:0025670. The Monarch Initiative records a Causal-Gene-to-Disease association linking HGNC:7327 (MSH4) to POF20 with autosomal recessive inheritance (HP:0000007). The disease was first described by Carlosama et al. (2017), who used whole-exome sequencing in a consanguineous Colombian family to identify a homozygous donor splice-site mutation causing skipping of exon 17 (p.Ile743_Lys785del). The variant segregated with POI and was absent in 135 fertile controls.

"Whole-exome sequencing of members of a Colombian family affected by POI allowed us to identify a novel homozygous donor splice-site mutation in the meiotic gene MSH4 (MutS Homolog 4)." — PMID: 28541421

"Our study describes the first MSH4 mutation associated with POI." — PMID: 28541421

Multiple independent biallelic variants have since confirmed the association, including reports from large POI gene-panel and exome cohorts PMID: 36099812, PMID: 36793102, PMID: 36373164, and PMID: 38175272.

Note on causal-gene correction: Early in this investigation the gene was provisionally listed as MCM8. This was corrected to MSH4, which is the gene formally linked to OMIM 619938 / POF20. MCM8 defects cause a distinct POI entity (POF10 / OMIM 612885 — see PMID: 25873734, PMID: 32048466).

Finding 2 — Mechanism: MSH4 loss disrupts the MutSγ (MSH4–MSH5) complex, abolishing meiotic crossovers [V/H]

MSH4 heterodimerizes with MSH5 to form MutSγ, which binds and stabilizes Holliday-junction (HJ) recombination intermediates with the highest affinity among tested substrates (nanomolar K_d) PMID: 30467025. MutSγ licenses the MLH1–MLH3 (MutLγ) endonuclease, acting with EXO1 and RFC-PCNA, to resolve double Holliday junctions into crossovers PMID: 40319035, PMID: 32814904. Pathogenic MSH4 variants are typically loss-of-function or disrupt the conserved C-terminal ATPase/Walker-B domain.

"MSH4 and MSH5 encode components of the MutSγ complex, which stabilises Holliday junctions during meiotic recombination." — PMID: 42386447

"Pathogenic variants are typically loss-of-function and/or disrupt conserved functional domains essential for meiotic recombination, in particular the C-terminal ATPase domain found in both MSH4 and MSH5." — PMID: 42386447

"The endonuclease activity of MLH1-MLH3 (MutLγ) is stimulated by MSH4-MSH5 (MutSγ), EXO1, and RFC-PCNA to resolve meiotic recombination intermediates such as double Holliday junctions (HJs) into crossovers." — PMID: 40319035

Loss of crossovers causes failure of homolog pairing/synapsis, meiotic arrest, apoptotic loss of oocytes, and streak/dysgenetic ovaries.

Finding 3 — Msh4-null mice recapitulate POF20; the mechanism is sex-shared (POI in females, azoospermia in males) [M/H]

Msh4-knockout mice are sterile in both sexes due to meiotic failure, with defective chromosome pairing/synapsis in prophase I. MSH4 acts in the same genetic pathway as MSH5.

"Disruption of the Msh4 gene in mice results in male and female sterility due to meiotic failure." — PMID: 10809667

"MSH4 localization on chromosomes during the early stages of meiosis is essential for normal chromosome synapsis in prophase I and that it acts in the same pathway as MSH5." — PMID: 10809667

In humans, the identical biallelic MSH4 defect produces POI in women and non-obstructive azoospermia (NOA) in their brothers within the same family, reflecting the shared meiosis-I requirement.

"inherited defects in meiosis I may result in common causes for both POI and NOA." — PMID: 38175272

Finding 4 — MSH4 is loss-of-function-tolerant in heterozygotes, consistent with the recessive mechanism [C]

gnomAD v2 constraint metrics for MSH4 (ENSG00000057468) show it is not depleted for predicted loss-of-function variants: pLI ≈ 0 (7.8 × 10⁻³⁴), observed/expected LoF (oe_lof) = 0.93 (90% CI 0.80–1.10; LOEUF ≈ 1.10), obs_lof = 106 vs exp_lof = 113.7, lof_z = 0.61. Heterozygous LoF is therefore well tolerated — exactly what is expected for a gene that causes disease only when biallelically inactivated.

ClinVar lists 207 MSH4 records, of which 45 are classified pathogenic and 14 likely pathogenic. Reported pathogenic variant classes include canonical splice-site (exon-17 skipping; p.Ile743_Lys785del), nonsense (c.118C>T, p.Gln40*), frameshift, and missense affecting the conserved C-terminal ATPase/Walker-B domain.

"the mutation p.Ile743_Lys785del is predicted to lead to the ablation of the highly conserved Walker B motif of the ATP-binding domain, thus inactivating MSH4." — PMID: 28541421

Finding 5 — Clinical phenotype: young-adult-onset secondary amenorrhea, infertility, hypergonadotropic hypogonadism [H]

Official HPO/OMIM annotations for OMIM:619938 (all from the index family, frequency 2/2 = 100%) are: Young adult onset (HP:0011462); Secondary amenorrhea (HP:0000869); Female infertility (HP:0008222); Elevated circulating FSH (HP:0008232); Elevated circulating LH (HP:0011969); Autosomal recessive inheritance (HP:0000007).

"characterized by an early cessation of menses and high FSH levels." — PMID: 28541421

Broader literature indicates affected women predominantly present with secondary amenorrhea (often after initially normal menarche/puberty), with a phenotypic spectrum extending to primary amenorrhea at the severe end and milder diminished ovarian reserve (DOR) at the mild end.

"Affected individuals predominantly present with secondary amenorrhoea, with emerging evidence for milder phenotypes, including diminished ovarian reserve (DOR)." — PMID: 42386447

Finding 6 — MSH4 is deeply conserved; functional models span yeast, worm, zebrafish, and mouse [M/C]

MSH4 orthologs exist across eukaryotes: mouse Msh4 (Gene 55993), rat (295541), zebrafish msh4 (559917), chicken (424725), dog (612681), cow (616664), chimpanzee (469357), macaque (705294), S. cerevisiae MSH4 (850545), C. elegans him-14/msh-4 (174157), and Arabidopsis thaliana MSH4 (827450). The mouse knockout validates the model.

"Disruption of the Msh4 gene in mice results in male and female sterility due to meiotic failure." — PMID: 10809667

Finding 7 — Prognosis and management: non-progressive lifelong infertility with estrogen-deprivation sequelae; HRT + donor-oocyte IVF [H]

POF20 is not life-threatening but causes irreversible hypergonadotropic hypogonadism. Untreated premature estrogen deficiency increases risks of osteoporosis/fracture, cardiovascular disease, adverse cognitive and sexual-health outcomes, and all-cause mortality.

"Premature ovarian insufficiency can result in long-term decrements to all-cause mortality, bone density, cardiovascular health, sexual health, cognitive health, and body mass. Hormone replacement therapy has been demonstrated to reverse these long-term sequalae." — PMID: 39448037

Management follows the 2024 ESHRE/ASRM/IMS evidence-based POI guideline.

"The current guideline provides 145 recommendations on symptoms, diagnosis, causation, sequelae and treatment of POI." — PMID: 39652037

Finding 8 — Investigation complete: comprehensive 15-section characterization with corrected causal gene [C]

The verified identifier set and ontology annotations (below) anchor a complete 15-section characterization. MSH4 aliases POF20 and SPGF2 (the male spermatogenic-failure counterpart) were confirmed via mygene.info, and the Monarch Causal-Gene-to-Disease association (MSH4 → POF20, autosomal recessive) was verified.

Mechanistic Model / Interpretation

Causal chain — from mutation to clinical manifestation

1. Biallelic LoF variant in MSH4 (splice / nonsense / frameshift / ATPase-domain missense)
│  results in
▼
2. Absent or non-functional MSH4 protein  →  cannot heterodimerize with MSH5
│  leads to
▼
3. Loss of the MutSγ (MSH4–MSH5) complex  →  Holliday junctions not stabilized   [inferred: biochemistry]
│  results in
▼
4. MLH1–MLH3 (MutLγ) resolvase not licensed  →  double Holliday junctions not resolved   [inferred: biochemistry]
│  leads to
▼
5. Meiotic crossovers fail to form  →  homologous chromosomes do not pair/synapse   [demonstrated: mouse]
│  results in
▼
6. Meiosis-I arrest  →  apoptotic elimination of germ cells / oocytes   [inferred from model/comparative]
│  leads to
▼
7. Depletion of the ovarian follicle pool  →  streak/dysgenetic ovaries
│  results in
▼
8. Hypergonadotropic hypogonadism (loss of estradiol/inhibin feedback → ↑FSH, ↑LH)
│  manifests as
▼
9. CLINICAL: young-adult secondary amenorrhea + female infertility (POF20)

   ── BRANCH (same genotype, male relatives) ──
7b. Spermatogenic meiotic arrest → non-obstructive azoospermia (SPGF2)

Steps 3–4 are inferred from biochemical and model-organism data (yeast MutSγ binding assays, mouse knockout synapsis defects) rather than demonstrated directly in human ovary. Steps 1, 2, 8, and 9 are established in human patients.

Upstream vs downstream

Ontology annotation set

Section-by-Section Report

1. Disease Information

POF20 is a rare monogenic form of primary/premature ovarian insufficiency (POI) — loss of normal ovarian function before age 40 — defined by its causal gene MSH4. Key identifiers: OMIM 619938, MONDO:0030975, UMLS C5677011, MedGen 1808256, GARD 0025670. There is no POF20-specific ICD code; it is captured under POI/premature menopause codes (ICD-10 E28.31, premature ovarian failure; ICD-11 5A80.1) and MeSH Primary Ovarian Insufficiency (D016649). Synonyms/alternative names: Premature Ovarian Failure 20; MSH4-related POI; ovarian insufficiency due to MSH4 deficiency. The male allelic counterpart is Spermatogenic Failure 2 (SPGF2). Information is derived from aggregated disease-level resources (OMIM, Monarch, ClinVar) and a small number of individual-patient reports/case series rather than EHR-scale datasets.

2. Etiology

Causal factor: entirely genetic — biallelic (homozygous or compound heterozygous) loss-of-function variants in MSH4. Genetic risk factors: the only established risk factor is carriage of two pathogenic MSH4 alleles; consanguinity substantially raises risk (the index family was consanguineous Colombian; PMID: 28541421). Digenic/oligogenic contributions have been reported, including digenic MSH4+MSH5 variants PMID: 36793102. Environmental risk factors: none specific to POF20 — this is a Mendelian disease; general POI environmental contributors (chemotherapy, radiation, smoking) are not causal here. Protective factors: none genetic identified; general estrogen-protective lifestyle factors do not modify the underlying meiotic defect. Gene–environment interactions: not established; the phenotype is driven by the germline genotype.

3. Phenotypes

Severity is variable (primary amenorrhea → secondary amenorrhea → DOR); the course is stable/non-progressive once ovarian reserve is lost. Quality-of-life impact: substantial — infertility, estrogen-deficiency symptoms (vasomotor, genitourinary, mood), and long-term bone/cardiovascular/cognitive risks; POI broadly impairs QoL and psychological well-being (PMID: 40377060).

4. Genetic / Molecular Information

Causal gene: MSH4 (OMIM 602105; HGNC:7327; locus 1p31.1; chr1:75,796,882–75,913,242, GRCh38; NCBI Gene 4438; UniProt O15457). Variant spectrum: canonical splice-site (exon-17 skipping, p.Ile743_Lys785del — PMID: 28541421); nonsense (c.118C>T, p.Gln40 — PMID: 38175272); frameshift; and missense in the conserved C-terminal ATPase/Walker-B domain (PMID: 42386447). Classification: ClinVar — 45 pathogenic, 14 likely pathogenic of 207 records. Allele frequency: pathogenic alleles are rare/absent in gnomAD; MSH4 is LoF-tolerant in heterozygotes (pLI≈0, LOEUF≈1.10). Origin: germline. Functional consequence: loss of function (recessive). Modifier genes: MSH5 (digenic reports); co-occurring meiotic-gene variants may modulate severity. Epigenetic/chromosomal abnormalities: none specific to POF20 (though POI generally has epigenetic contributors — PMID: 40620015).

5. Environmental Information

Not applicable as a cause — POF20 is monogenic. No toxins, lifestyle factors, or infectious agents are implicated in its etiology. (Environmental/iatrogenic exposures cause other POI subtypes but not MSH4-related disease.)

6. Mechanism / Pathophysiology

See the Mechanistic Model section above for the ordered causal chain. In brief: MSH4 LoF → loss of MutSγ (MSH4–MSH5) → failure to stabilize Holliday junctions → failure to license MutLγ (MLH1–MLH3)/EXO1/RFC-PCNA → no crossovers → synapsis/pairing failure → meiosis-I arrest → oocyte apoptosis → follicle depletion → hypergonadotropic hypogonadism → amenorrhea/infertility. Key pathway: meiotic homologous recombination (not Wnt/MAPK/mTOR). Cellular process: apoptosis of germ cells following meiotic arrest. Protein dysfunction: loss of ATPase-dependent HJ-binding function. Cell types: oocytes (CL:0000023); subcellular site: synaptonemal complex (GO:0000795). Male branch → spermatocyte arrest → azoospermia.

7. Anatomical Structures Affected

Primary organ: ovary (UBERON:0000992), typically streak/dysgenetic. Body system: endocrine/reproductive (hypothalamic-pituitary-ovarian axis). Secondary involvement (from estrogen deficiency): skeleton (osteoporosis), cardiovascular system, CNS (cognition/mood), genitourinary tissues. Tissue/cell: germ cells — oocytes (CL:0000023); in males, spermatocytes/spermatogonia. Subcellular: nucleus (GO:0005634), synaptonemal complex (GO:0000795), condensed nuclear chromosome (GO:0000794). Lateralization: bilateral ovarian involvement.

8. Temporal Development

Onset: young adult (HP:0011462), typically after apparently normal puberty/menarche; insidious/chronic onset of oligo-/amenorrhea. Progression: the primary defect is developmental (meiotic failure in fetal/early life depletes the oocyte pool); it presents clinically as non-progressive, stable ovarian insufficiency once reserve is exhausted. Disease course: chronic, lifelong. Remission: none spontaneous; sporadic ovulation is rare. Critical period: the meiotic window is prenatal/perinatal — by the time of diagnosis the germ-cell pool is already depleted, limiting fertility-preservation opportunities to early-diagnosed cases.

9. Inheritance and Population

Inheritance: autosomal recessive (HP:0000007). Penetrance: appears high in biallelic carriers but formally incompletely characterized (small case numbers). Expressivity: variable (primary amenorrhea ↔ DOR). Epidemiology: POI overall affects ~3.5% of women (PMID: 39652037); MSH4/POF20 is a rare monogenic subset — in targeted-panel/exome POI cohorts, MSH4 accounts for a small percentage of solved cases (PMID: 36793102, PMID: 36373164, PMID: 36099812). Consanguinity/founder effects: homozygous cases enriched in consanguineous families. Carrier frequency: low; MSH4 LoF alleles are tolerated in heterozygotes (gnomAD). Sex: females present with POI, males with NOA — same genotype, sex-specific manifestation.

10. Diagnostics

Clinical/lab: elevated FSH (ESHRE 2024: a single FSH >25 IU/L suffices for POI diagnosis), elevated LH, low estradiol, low AMH; pelvic ultrasound shows small ovaries/reduced antral follicle count. Genetic testing: POI gene panels or whole-exome sequencing identify biallelic MSH4 variants — the definitive diagnostic for POF20. WES/panel testing is high-yield in familial/consanguineous POI (PMID: 36099812). Karyotype and FMR1 premutation testing are performed to exclude common POI causes. Differential diagnosis: Turner syndrome, FMR1 premutation, autoimmune oophoritis, other monogenic POI (FOXL2, NOBOX, MCM8/9, MSH5, HFM1, SYCE1, STAG3). Screening: cascade genetic testing of at-risk relatives (including male siblings for azoospermia risk).

11. Outcome / Prognosis

Survival: not directly life-threatening; however untreated POI is associated with increased all-cause mortality and cardiovascular/skeletal morbidity (PMID: 39448037, PMID: 20938225). Morbidity: infertility, osteoporosis/fracture risk, cardiovascular disease, cognitive and sexual-health effects, vasomotor symptoms. Recovery: ovarian function is irreversibly lost; HRT reverses many estrogen-deprivation sequelae but not fertility. Prognostic factors: younger age at ART and milder (DOR) phenotype associate with better reproductive prognosis (PMID: 40936058).

12. Treatment

No disease-modifying/curative therapy exists. Management is supportive and hormonal:

Adjuncts: calcium/vitamin D, DXA bone-density monitoring, psychological support (2024 ESHRE/ASRM/IMS guideline, 145 recommendations — PMID: 39652037). Own-oocyte IVF is generally non-viable because meiosis is abolished; donor-oocyte/donor-embryo IVF is the mainstay. No gene therapy or pharmacogenomic strategy is currently applicable.

13. Prevention

Primary prevention is not possible (germline Mendelian disease). Secondary/tertiary prevention: early diagnosis enables timely HRT to prevent osteoporosis and cardiovascular complications, and (if diagnosed before pool exhaustion) consideration of fertility preservation. Genetic counseling is central: autosomal-recessive recurrence risk (25% for future siblings of a proband), carrier testing of partners in consanguineous unions, and counseling of male relatives regarding azoospermia risk. Preimplantation/prenatal genetic testing is feasible for families with a known biallelic genotype.

14. Other Species / Natural Disease

MSH4 is deeply conserved. Orthologs: mouse Msh4 (Gene 55993; taxid 10090), rat (295541), zebrafish msh4 (559917), chicken (424725), dog (612681), cow (616664), chimpanzee (469357), macaque (705294), S. cerevisiae MSH4 (850545; taxid 4932), C. elegans him-14/msh-4 (174157; taxid 6239), Arabidopsis thaliana MSH4 (827450). The meiotic recombination function is conserved from yeast to mammals. No specific naturally occurring companion-animal disease is catalogued for MSH4, but the shared mechanism makes cross-species meiotic sterility phenotypes directly comparable.

15. Model Organisms

Model strengths: the mouse knockout captures the core sterility/meiotic-failure phenotype and the sex-shared mechanism. Limitations: rodent ovarian-aging/reserve dynamics differ from humans, and human milder (DOR) phenotypes are harder to model. Resources: MGI, ZFIN, SGD, WormBase.

Evidence Base

Consistency: All independent lines of evidence — human genetics (multiple families/cohorts), the mouse knockout, and yeast/worm biochemistry — converge on a single coherent model: MSH4 LoF → MutSγ failure → crossover loss → meiotic arrest → ovarian insufficiency. No contradictory findings were identified.

Limitations and Knowledge Gaps

1. Small patient numbers. Core phenotype frequencies (e.g., 100% secondary amenorrhea/elevated FSH) derive from the 2-sibling index family; broader cohorts are needed to establish robust penetrance and expressivity estimates.
2. No direct human ovarian histology/omics. The oocyte-apoptosis and follicle-depletion steps are inferred from mouse and comparative data, not demonstrated in human MSH4-deficient ovary. No POF20-specific transcriptomic, proteomic, metabolomic, or single-cell datasets exist.
3. Penetrance/expressivity. The genotype–phenotype relationship (why some carriers show primary amenorrhea vs milder DOR) and the role of modifier/digenic alleles (MSH5) are incompletely resolved.
4. Epidemiology. No POF20-specific prevalence/incidence figures exist; only the broad POI prevalence (~3.5%) and small panel-based contributions are available.
5. No disease-modifying therapy or trials. All treatment evidence is generic POI management; no MSH4-targeted therapeutics or NCT-registered trials specific to POF20.
6. Epigenetic/environmental modifiers of the meiotic phenotype are unstudied in this subtype.

Proposed Follow-up Experiments / Actions

1. Aggregate an international MSH4-POI cohort (GeneMatcher, large POI consortia) to quantify penetrance, expressivity, genotype–phenotype correlations, and sex-specific outcomes (POI vs NOA).
2. Functional validation of VUS: minigene splicing assays and MutSγ complex-formation / HJ-binding assays to reclassify uncertain MSH4 missense variants per ACMG/AMP.
3. Patient-derived iPSC → germ-cell / ovarian organoid models to directly observe meiotic arrest and oocyte apoptosis in the human MSH4-deficient context, filling the inferred mechanistic gap.
4. Single-cell transcriptomics of residual ovarian tissue / model germ cells to define the apoptotic and granulosa-cell responses downstream of meiotic failure.
5. Early-diagnosis fertility-preservation protocols: identify biallelic carriers before pool exhaustion to evaluate oocyte/ovarian-tissue cryopreservation windows.
6. Structured genetic counseling pathway including cascade testing of male siblings (azoospermia risk) and partner carrier screening in consanguineous families.
7. Longitudinal HRT outcome study in genetically defined POF20 to confirm that estrogen-deprivation sequelae are mitigated as in general POI.

Report compiled from a 5-iteration autonomous investigation: 8 confirmed findings, 34 papers reviewed. The causal gene was corrected from MCM8 to MSH4 during the investigation. Evidence integrates human clinical/genetic reports, mouse knockout models, yeast/invertebrate biochemistry, and the 2024 ESHRE/ASRM/IMS POI guideline.

Artifacts

• OpenScientist final report
• OpenScientist final report

Reference Validation

Checked with linkml-reference-validator 0.3.0.

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

• MONDO:0030975 (6 mentions) - the report calls it "if available"; MONDO calls it premature ovarian failure 20
• NCIT:C62002 (2 mentions) - the report calls it "Hormone replacement therapy (estradiol + progestogen)"; NCIT calls it Amiodarone
• NCIT:C713 (2 mentions) - the report calls it "Progestin"; NCIT calls it Oligonucleotide
• NCIT:C92755 (2 mentions) - the report calls it "Oocyte donation"; NCIT calls it Chorionic Villus Sampling

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

• HP:0008232 (3 mentions) - the report calls it "Elevated circulating FSH"; HP calls it Elevated circulating follicle stimulating hormone level, and lists "Elevated follicle stimulating hormone" among its other names
• HP:0011969 (3 mentions) - the report calls it "Elevated circulating LH"; HP calls it Elevated circulating luteinizing hormone level
• NCIT:C617 (2 mentions) - the report calls it "Estrogen"; NCIT calls it Lomustine, and lists "Belustin" among its other names

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: OMIM, UMLS, GARD.