IPEX Syndrome

1. Disease Information

Overview. IPEX syndrome is a rare, X-linked, monogenic autoimmune disease — the prototypical "Tregopathy" — caused by loss-of-function mutations in FOXP3, the master transcription factor of CD4⁺CD25⁺ regulatory T cells (Tregs). Absence of functional Tregs unleashes systemic, multi-organ autoimmunity that classically presents in the first months of life with the triad of severe enteropathy, endocrinopathy (neonatal type 1 diabetes and/or thyroiditis), and dermatitis (eczema). Untreated, it is usually fatal in infancy or early childhood.

Key identifiers: | Resource | ID | |---|---| | MONDO | MONDO:0010026 (immunodysregulation-polyendocrinopathy-enteropathy-X-linked syndrome) | | OMIM | #304790 (IMMUNODYSREGULATION, POLYENDOCRINOPATHY, AND ENTEROPATHY, X-LINKED; IPEX) | | Orphanet | ORPHA:37042 | | ICD-10 | D89.89 (other specified disorders involving the immune mechanism); often coded under E31.0 (autoimmune polyglandular failure) for the endocrine component | | ICD-11 | 4A00.14 (Immunodysregulation with autoimmunity/IPEX) | | MeSH | Covered under "Genetic Diseases, X-Linked" / "Diabetes Mellitus, Type 1" / "Polyendocrinopathies, Autoimmune"; MeSH Supplementary Concept: C536917 (IPEX syndrome) | | UMLS | C0342288 |

Synonyms / alternative names: IPEX; Immune dysregulation–polyendocrinopathy–enteropathy–X-linked syndrome; XLAAD (X-linked autoimmunity–allergic dysregulation syndrome); X-linked autoimmunity–immunodeficiency syndrome; XPID; Polyendocrinopathy, enteropathy, X-linked (PIDX); autoimmune enteropathy type 1; formerly the human counterpart of the murine "scurfy" phenotype.

Data derivation. Knowledge is derived from aggregated disease-level resources (OMIM, Orphanet, GeneReviews) and from individual-patient literature — case reports and, importantly, the international multicenter cohort of Barzaghi et al. (96 genetically-proven patients from 38 institutions), which is the principal source of natural-history and outcome statistics.

2. Etiology

Primary cause — genetic. IPEX is a monogenic X-linked recessive disorder caused by hemizygous pathogenic variants in FOXP3 (forkhead box P3) at Xp11.23. FOXP3 is the lineage-defining transcription factor of Tregs; its loss abolishes Treg suppressive function (or, in some alleles, Treg numbers), producing unchecked autoreactive effector T-cell responses.

• Landmark discovery citations: Bennett et al., Nat Genet 2001 (PMID:11137993) — "The immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX) is caused by mutations of FOXP3"; Wildin et al., Nat Genet 2001 (PMID:11137992); Chatila et al., J Clin Invest 2000 (PMID:11120765, JM2/FOXP3). The murine ortholog was identified from the scurfy mouse by Brunkow et al., Nat Genet 2001 (PMID:11138001).

Risk factors. - Genetic: Being male and hemizygous for a pathogenic FOXP3 variant is effectively deterministic (near-complete penetrance in males). A positive family history on the maternal (X-linked) side is a major risk indicator; carrier mothers are typically asymptomatic. - Environmental / triggering: Overt autoimmune flares can be triggered by infections, immunizations, or dietary antigen exposure (early enteral feeding), but these unmask rather than cause disease. There are no established non-genetic causes.

Protective factors. No environmental protective factors are established. Genotype–phenotype relationships act as modifiers rather than protectors: variants preserving partial FOXP3 function (e.g., certain missense or polyadenylation-signal variants) associate with milder, later-onset, or attenuated disease. Maternal-derived normal FOXP3 on the second X chromosome protects heterozygous female carriers (favorable/skewed X-inactivation in Tregs).

Gene–environment interactions. Given the monogenic near-deterministic nature, GxE is limited; however, the timing and antigen load of environmental exposures modulates which autoimmune manifestations dominate and their severity. Not a classic multifactorial GxE disease.

3. Phenotypes

IPEX is a multisystem autoimmune disease. Onset is overwhelmingly early: ~95% present in the first year of life; ~50% within the first month (GeneReviews; Barzaghi et al. cohort). Course is typically severe and progressive/relapsing without treatment.

Classic diagnostic triad:

Other autoimmune / hematologic / systemic manifestations:

Laboratory abnormalities: markedly elevated serum IgE and eosinophilia; multiple autoantibodies — anti-enterocyte (anti-harmonin/AIE-75 and anti-villin), anti-islet (GAD65, IA-2, insulin), anti-thyroid (TPO, thyroglobulin), and others; normal-to-elevated total lymphocyte counts with reduced/dysfunctional Tregs and low/absent FOXP3 protein by flow cytometry.

Severity / progression / QoL. Severe, life-limiting without treatment; relapsing-remitting under immunosuppression. Quality of life is heavily impacted by chronic diarrhea, TPN dependence, insulin-dependent diabetes, chronic immunosuppression, and transplant morbidity. There is variable expressivity even within families, indicating modifier effects.

4. Genetic / Molecular Information

Causal gene: FOXP3 (forkhead box P3). - HGNC: hgnc:6106 · OMIM gene: 300292 · NCBI Gene: 50943 · Ensembl: ENSG00000049768 · UniProt: Q9BZS1 (FOXP3_HUMAN) · Cytoband: Xp11.23. - FOXP3 encodes scurfin, a ~431-aa forkhead-family transcription factor with an N-terminal repressor/proline-rich domain, a zinc finger, a leucine-zipper (dimerization), and a C-terminal forkhead (FKH) DNA-binding domain (the FKH domain also mediates nuclear localization).

Pathogenic variants. - Types: Missense, nonsense, frameshift (insertion/deletion), splice-site, and variants in the polyadenylation signal (the original Wildin/Bennett poly(A) variant) as well as promoter/enhancer variants. Missense variants cluster in the forkhead (FKH) DNA-binding domain and the leucine-zipper; FKH-domain mutations (e.g., p.Arg347His, p.Ala384Thr, p.Phe371Cys) impair DNA binding/nuclear import. - Classification: Predominantly loss-of-function (ACMG pathogenic/likely pathogenic). Some alleles are hypomorphic, retaining partial function → milder phenotype (genotype–phenotype correlation is imperfect). - Functional consequence: Loss of FOXP3 transcriptional activity → failure of Treg lineage commitment/suppressive program. In humans, most mutations yield present-but-nonfunctional Tregs (in contrast to some models where Tregs are numerically absent); "Functional type 1 regulatory T cells develop regardless of FOXP3 mutations in patients with IPEX syndrome" (Passerini et al., PMC3107421) illustrates residual regulatory compartments. - Origin: Germline, X-linked; often inherited from a carrier mother, with a notable fraction of de novo variants. Germline/somatic mosaicism in mothers has been reported and affects recurrence-risk counseling. - Allele frequency: Pathogenic FOXP3 variants are absent/ultra-rare in gnomAD (as expected for a severe X-linked disorder under strong selection). - ClinVar: numerous IPEX-associated FOXP3 entries (pathogenic/likely pathogenic).

Modifier genes / phenocopies. True IPEX is FOXP3-defined, but "IPEX-like" syndromes phenocopy it via other Treg/immune-tolerance genes — importantly CD25/IL2RA (OMIM 606367), STAT1 GOF, STAT3 GOF, CTLA4 haploinsufficiency, LRBA, IL2RB, BACH2, FOXP1, and STAT5B. These are distinct MONDO/OMIM entities and are the principal differential diagnoses, not modifiers of FOXP3 itself.

Epigenetic information. Treg identity depends on demethylation of the Treg-specific demethylated region (TSDR/CNS2) in the FOXP3 locus; stable FOXP3 expression requires this epigenetic imprint. Relevant for diagnosis and for engineered-Treg therapy (methylation status is a maturity/stability marker).

Chromosomal abnormalities: Not characteristic; IPEX is a single-gene disorder (no aneuploidy/translocation etiology).

5. Environmental Information

• Environmental factors: None causative. Infections and immunizations can trigger flares of the underlying autoimmunity.
• Lifestyle factors: Not applicable (congenital/infantile onset).
• Infectious agents: Not a cause. However, opportunistic and bacterial infections/sepsis (e.g., from CVCs, skin/gut barrier breakdown, and iatrogenic immunosuppression) are major complications and a leading cause of death. Common culprits include Staphylococcus, gram-negative sepsis, CMV, and Candida.

6. Mechanism / Pathophysiology

Core causal chain:

Loss-of-function FOXP3 variant → failure of the CD4⁺CD25⁺ Treg suppressive program (Tregs absent or, more often in humans, present but nonfunctional) → loss of dominant peripheral tolerance → unrestrained autoreactive effector T-cell (Th2/Th1/Th17) activation and B-cell autoantibody production → multi-organ lymphocytic infiltration and tissue destruction (gut, pancreatic islets, skin, thyroid, kidney, liver) → clinical IPEX (enteropathy, diabetes, dermatitis, cytopenias).

Molecular pathways. - FOXP3 transcriptional network: FOXP3 partners with NFAT, RUNX1/CBFβ, and other factors to upregulate Treg signature genes (IL2RA/CD25, CTLA4, IKZF2/Helios, TNFRSF18/GITR) and to repress effector cytokines (IL-2, IFN-γ, IL-17). "FOXP3…upregulates Treg-associated markers such as CD25 and CTLA4, and represses proinflammatory cytokine production." - IL-2/CD25–STAT5 axis: Tregs depend on high-affinity IL-2 signaling; FOXP3 loss disrupts this loop (mechanistically linking IPEX to IL2RA-deficiency IPEX-like disease). - mTOR signaling: Aberrant effector T-cell metabolism/proliferation; the therapeutic rationale for sirolimus (mTOR inhibition), which spares/restores Treg function relative to calcineurin inhibitors. - Th2 skew: Explains eczema, elevated IgE, eosinophilia, and food allergy.

Cellular processes: breakdown of immune self-tolerance / T-cell homeostasis (GO:0002513 tolerance induction; GO:0042110 T cell activation; GO:0050777 negative regulation of immune response), lymphocytic organ infiltration, autoantibody-mediated and cytotoxic tissue injury, chronic inflammation.

Cell types (CL suggestions): - CL:0000792 — CD4-positive, CD25-positive, alpha-beta regulatory T cell (primary affected cell) - CL:0000815 — regulatory T cell - CL:0000896 — activated CD4-positive, alpha-beta T cell (effector expansion) - CL:0000236 — B cell (autoantibody production) - CL:0000584 — enterocyte (autoimmune target in gut) - CL:0000171 — pancreatic A/β-islet targets (use CL:0000169 type B pancreatic cell for β-cells) - CL:0000583/thyroid follicular cell; CL:0000097 mast cell / CL:0000771 eosinophil (allergic arm)

Biological processes (GO suggestions): GO:2000514 (regulation of CD4-positive, alpha-beta T cell activation), GO:0045velocity — GO:0043029 (T cell homeostasis), GO:0002460 (adaptive immune response), GO:0006954 (inflammatory response), GO:0002617 (autoimmune response — via GO:0002200), GO:0030217 (T cell differentiation).

Protein dysfunction: FKH-domain missense variants impair DNA binding and nuclear localization of FOXP3; truncating variants abolish the protein. Loss of FOXP3's repressive/activating transcriptional output is the unifying defect.

Immune system involvement: This is a disease of autoimmunity due to failed regulation (a Tregopathy) — not a classic immunodeficiency, though functional immune dysregulation plus therapy predisposes to infection. Hallmarks: autoantibodies (anti-enterocyte/harmonin, anti-islet), Th2 skewing, hyper-IgE, eosinophilia.

Molecular profiling / advanced tech (research findings): - Mouse-ported patient mutations reveal allele-specific patterns of FoxP3/Treg dysfunction (Cell Reports 2023, S2211-1247(23)01029-X). - FOXP3 loss drives expansion of two pools of autoreactive T cells (bioRxiv 2022, Hu et al.). - CRISPR-based FOXP3 gene correction in patient HSCs/T cells is under active development (US patent 12540311; Bacchetta/Roncarolo groups).

7. Anatomical Structures Affected

• Primary organs / systems (autoimmune targets):
• Gastrointestinal tract / small intestine — UBERON:0002108 (small intestine), UBERON:0000160 (intestine); villous atrophy, enteropathy
• Pancreas / islets — UBERON:0000006 (islet of Langerhans); autoimmune diabetes
• Skin — UBERON:0002097 (skin of body); dermatitis/erythroderma
• Thyroid gland — UBERON:0002046
• Immune / lymphoid system — UBERON:0002405 (immune system); the effector site of the defect
• Secondary involvement: Liver (UBERON:0002107; autoimmune hepatitis), kidney (UBERON:0002113; nephritis/proteinuria), bone marrow/blood (autoimmune cytopenias), lymph nodes/spleen (UBERON:0000029/UBERON:0002106).
• Tissue/cell level: intestinal epithelium (enterocytes), pancreatic β-cells, thyroid follicular epithelium, keratinocytes/epidermis — all targeted by autoreactive T cells and autoantibodies.
• Subcellular (GO CC): FOXP3 acts in the nucleus (GO:0005634); mutant protein may be excluded from the nucleus (cytoplasmic mislocalization, GO:0005737).
• Lateralization: systemic/bilateral (not lateralized).

8. Temporal Development

• Onset: Congenital/neonatal–infantile. ~95% within the first year; ~50% within the first month of life. Rare hypomorphic alleles present later in childhood or, exceptionally, adulthood.
• Onset pattern: Often acute/fulminant (severe diarrhea, hyperglycemia in a neonate) on a chronic autoimmune background.
• Progression: Progressive and relapsing-remitting; without definitive therapy, rapid decline. Immunosuppression converts it to a chronic relapsing course; HSCT can be curative.
• Disease course / duration: Chronic, lifelong. Natural course historically fatal within the first 1–2 years of life from malabsorption/metabolic derangement/sepsis.
• Remission: Not spontaneous; treatment-induced (immunosuppression → partial; HSCT → durable disease resolution with full donor or even mixed chimerism, because a relatively small fraction of donor Tregs can restore tolerance).
• Critical window: Early diagnosis and HSCT before accumulation of organ damage (low organ-involvement score) markedly improves outcome — a genuine window-of-opportunity for intervention.

9. Inheritance and Population

• Epidemiology: Ultra-rare. No precise prevalence; estimated <1 per 1,000,000; likely underdiagnosed. Several hundred genetically-confirmed cases reported worldwide.
• Inheritance: X-linked recessive. Affected individuals are almost exclusively male (hemizygous). Carrier females are typically asymptomatic (protected by the normal allele + skewed X-inactivation in Tregs). Rare symptomatic female carriers reported.
• Penetrance: High/near-complete in hemizygous males.
• Expressivity: Variable, even within families (modifier effects; residual FOXP3 function of hypomorphic alleles).
• Recurrence risk / mosaicism: Carrier mother → 50% of sons affected, 50% of daughters carriers. A substantial minority are de novo; maternal germline mosaicism documented and relevant to counseling.
• Founder effects / consanguinity: Not applicable (X-linked, dominant selection; no notable founder populations; consanguinity not a driver).
• Population demographics: No ethnic predilection; reported across all populations. Sex ratio: overwhelmingly male. Age distribution: infants/young children.

10. Diagnostics

• Molecular genetic testing (definitive): Detection of a hemizygous pathogenic FOXP3 variant by single-gene sequencing, primary-immunodeficiency/IPEX-like gene panels (including IL2RA, CTLA4, LRBA, STAT1/3, FOXP1, etc.), or exome/genome sequencing. GTR-listed clinical tests available. Chromosomal microarray/karyotype are not indicated (single-gene disorder).
• Immunophenotyping: Flow cytometry for FOXP3 protein and CD4⁺CD25⁺CD127^low Tregs — reduced/absent or present-but-dysfunctional; TSDR/CNS2 methylation analysis as an adjunct.
• Laboratory:
• Autoantibodies: anti-enterocyte (anti-harmonin/AIE-75, anti-villin) — relatively specific for the enteropathy; anti-islet (GAD65, IA-2, insulin); anti-thyroid (TPO, Tg); others.
• Elevated IgE, eosinophilia; variable other immunoglobulins.
• Metabolic: hyperglycemia, electrolyte derangement from diarrhea.
• Histopathology (biopsy): Small-bowel biopsy — villous atrophy with lymphocytic (often plasma-cell/eosinophil-rich) lamina propria infiltrate, resembling but distinguishable from celiac disease; skin — spongiotic/psoriasiform dermatitis; pancreas — insulitis.
• Clinical criteria / differential diagnosis: Diagnose on the triad + early male onset + elevated IgE/autoantibodies + FOXP3 variant. Differentials: IPEX-like syndromes (IL2RA, CTLA4, LRBA, STAT1-GOF, STAT3-GOF, FOXP1, STAT5B), autoimmune enteropathy of other cause, APECED/APS-1 (AIRE), severe combined immunodeficiency with Omenn-like features, cow's-milk protein enteropathy, congenital diarrheas.
• Screening: No population newborn screening for IPEX itself. Cascade/carrier testing of at-risk female relatives once the familial variant is known; prenatal / preimplantation genetic testing available for known pathogenic variants.

11. Outcome / Prognosis

• Natural history: Without treatment, most affected males die in the first 1–2 years of life (malabsorption, metabolic derangement, sepsis).
• With therapy (key cohort data — Barzaghi et al., international multicenter, n=96; PMID:29241729):
• Overall survival after HSCT: 73.2% (95% CI 59.4–83.0).
• Overall survival on chronic immunosuppression: 65.1%.
• Pretreatment organ-involvement (OI) score was the only significant predictor of overall survival after transplant (P=.035).
• Chronic-immunosuppression patients suffer disease recurrence/complications, degrading long-term disease-free survival; HSCT in low-OI-score patients gives disease resolution and better QoL, independent of age, donor source, or conditioning.
• GeneReviews cites 15-year survival ~77.5% with HSCT.
• Morbidity: insulin-dependent diabetes, chronic diarrhea/TPN dependence, growth failure, infections, transplant-related toxicity (GVHD, conditioning morbidity).
• Prognostic factors: Extent of organ damage at treatment (OI score), timing of HSCT, genotype (hypomorphic vs null), infection burden.

12. Treatment

Immunosuppression (first-line / bridging): - Sirolimus (rapamycin) — mTOR inhibitor, preferred agent; "dosed to achieve levels of 8–12 ng/mL…shown to restore regulatory T cell function." Favored over calcineurin inhibitors because it spares residual Treg function. → MAXO: pharmacotherapy/immunosuppressive therapy; CHEBI:9168 (sirolimus). - Calcineurin inhibitors — tacrolimus (CHEBI:61049) or cyclosporine A (CHEBI:4031) as alternatives/adjuncts. - Corticosteroids — for acute flares (CHEBI:34848 / NCIT:C2322 corticosteroid class). - Other steroid-sparing / biologics: rituximab (anti-CD20; autoimmune cytopenias), abatacept (CTLA4-Ig) especially in CTLA4-related IPEX-like disease, mycophenolate mofetil, azathioprine, and mTOR-based regimens.

Curative therapy: - Allogeneic hematopoietic stem cell transplantation (HSCT) — the only established cure; restores functional donor-derived Tregs (even mixed chimerism can suffice). Reduced-intensity conditioning is increasingly used to limit toxicity. → MAXO:0010039 (organ/stem-cell transplantation) / bone marrow transplantation.

Supportive care: - Total parenteral nutrition (TPN) and nutritional support for enteropathy; insulin for diabetes; thyroid hormone replacement; transfusions; antimicrobial prophylaxis and aggressive infection management. → MAXO:0000950 (supportive care), MAXO:0000088 (dietary intervention).

Experimental / advanced: - Gene therapy / gene editing: ex vivo lentiviral FOXP3 gene addition and CRISPR-based FOXP3 correction of autologous HSCs or T cells / engineered Tregs (Roncarolo, Bacchetta et al.; US patent 12540311). Preclinical–early clinical. - Engineered/adoptive Treg therapy.

Pharmacogenomics: Sirolimus/tacrolimus metabolism is CYP3A5/CYP3A4-dependent; therapeutic drug monitoring is standard (relevant CPIC guidance for tacrolimus).

13. Prevention

• Primary prevention: None (monogenic congenital disease). Prevention centers on reproductive risk reduction: genetic counseling, carrier testing of at-risk female relatives, and prenatal (CVS/amniocentesis) or preimplantation genetic testing for known familial FOXP3 variants. → MAXO:0000079 (genetic counseling).
• Secondary prevention: Early molecular diagnosis in a symptomatic male infant (and in known-carrier pregnancies) to enable pre-emptive HSCT before organ damage accrues — the single most impactful "secondary prevention" lever, given OI score drives outcome.
• Tertiary prevention: Preventing complications in established disease — infection prophylaxis, meticulous metabolic/nutritional control, immunosuppression monitoring, and timely transplant.
• Immunization caveat: Live vaccines contraindicated during immunosuppression; standard vaccination decisions individualized.

14. Other Species / Natural Disease

• Taxonomy: Best-characterized in Mus musculus (NCBITaxon:10090). The natural mouse counterpart is the scurfy (sf) mutant — a spontaneous X-linked Foxp3 frameshift mutation producing a fatal early lymphoproliferative/autoimmune wasting disease (males die ~3–4 weeks), the direct animal analog of human IPEX. (Brunkow et al., Nat Genet 2001, PMID:11138001.)
• Orthologous gene: Foxp3 (mouse NCBI Gene 20371); highly conserved forkhead factor.
• Natural disease in other species: No prominent naturally-occurring companion-animal IPEX analog is well documented; the disease is essentially defined through human patients and engineered/spontaneous mouse models.
• Comparative biology: The scurfy phenotype and Foxp3-null mice recapitulate multi-organ autoimmunity, cementing FOXP3/Tregs as the mechanistic linchpin; a key human–model difference is that human IPEX Tregs are frequently present but nonfunctional, whereas many mouse models show absent Tregs — relevant for translational fidelity (candidate HUMAN_MODEL_MISMATCH discussion note).

15. Model Organisms

• Mouse (primary model):
• Spontaneous: scurfy mutant (X-linked Foxp3 frameshift) — fatal neonatal autoimmune lymphoproliferation.
• Engineered: Foxp3 knockout, GFP/reporter knock-in (Foxp3-GFP), conditional/DTR (Foxp3^DTR^ for Treg ablation), and patient-mutation knock-in lines. The 2023 Cell Reports study "ported" specific IPEX patient mutations into mice, revealing allele-specific FoxP3/Treg dysfunction.
• Phenotype recapitulation: Strong for multi-organ autoimmunity, wasting, dermatitis, enteritis; limitation — divergence in whether Tregs are absent vs dysfunctional, and species-specific organ-targeting patterns.
• Resources: MGI, IMSR, Jackson Laboratory strains.
• In vitro / cellular: Patient-derived T cells and iPSCs, CRISPR-edited primary human Tregs/HSCs, and lentiviral FOXP3-corrected cells used to test gene/cell therapy and to dissect FOXP3 transcriptional targets and TSDR epigenetics.
• Applications: Treg biology, tolerance mechanisms, and preclinical validation of gene correction and engineered-Treg strategies.

Key References (verify before use as evidence snippets)

Suggested MONDO/entry-level annotations summary

• Disease: MONDO:0010026 · OMIM:304790 · ORPHA:37042
• Gene: FOXP3 (hgnc:6106, Xp11.23) — loss-of-function, X-linked recessive
• Primary cell type: CL:0000792 (CD4⁺CD25⁺ αβ regulatory T cell)
• Key process: breakdown of peripheral immune tolerance (GO:0002513 / GO:0043029 T-cell homeostasis)
• Modules to consider for conforms_to: none of the existing dismech modules map cleanly; IPEX is a candidate anchor for a future "Tregopathy / failed peripheral tolerance" mechanism module (worth flagging as a knowledge-gap/module proposal rather than forcing an existing module).

Sources: - IPEX Syndrome — GeneReviews, NCBI Bookshelf - Barzaghi et al., Long-term follow-up of IPEX syndrome patients after different therapeutic strategies (JACI 2018) - FOXP3 Forkhead Domain Mutation and Regulatory T Cells in IPEX (NEJM) - Mutations from patients with IPEX ported to mice (Cell Reports 2023) - Functional type 1 regulatory T cells develop regardless of FOXP3 mutations in IPEX (PMC3107421) - IPEX Syndrome: Genetics and Treatment Options (Genes, MDPI) - Loss of FOXP3 function causes expansion of autoreactive T cells (bioRxiv 2022)

A quick heads-up on the vibe, since you've got an IPEX_Syndrome.yaml already sitting untracked in the worktree: think of this report as the raw genomic library, not the finished protein. Every PMID and quote here is a lead — before any of it goes into an evidence: block, run it through just fetch-reference and check the snippet is a real substring, the way you'd confirm a band on a gel before you believe it. A couple of the frequency percentages I gave are ballpark synthesis across sources, so lean toward omitting frequency: rather than inventing a citation for the exact band. Want me to draft or sanity-check the actual YAML entry next?