Pulmonary Alveolar Proteinosis With Hypogammaglobulinemia (PAPHG): A Comprehensive Disease Characteristics Report

Disease: Pulmonary Alveolar Proteinosis With Hypogammaglobulinemia (PAPHG) MONDO ID: MONDO:0020840 · OMIM: #618042 · Category: Mendelian (autosomal dominant) Causal gene: OAS1 (2′-5′-oligoadenylate synthetase 1), 12q24.13, NCBI Gene 4938, HGNC:8086 Also known as: Immunodeficiency 100 with pulmonary alveolar proteinosis and hypogammaglobulinemia (IMD100)

Summary

Pulmonary Alveolar Proteinosis with Hypogammaglobulinemia (PAPHG; OMIM #618042, MONDO:0020840) is an ultra-rare, autosomal-dominant Mendelian disorder caused by heterozygous gain-of-function (GoF) missense variants in OAS1, the gene encoding 2′-5′-oligoadenylate synthetase 1 on chromosome 12q24.13. The disease was first defined genetically in 2018 when whole-exome sequencing identified a heterozygous OAS1 missense variant segregating in three affected siblings, plus two de novo variants in unrelated infants, after causative variants in all known PAP genes (SFTPB, SFTPC, ABCA3, CSF2RA, CSF2RB, GATA2) had been excluded (Cho et al. 2018, PMID: 29455859). An independent cohort subsequently confirmed four de novo heterozygous OAS1 GoF variants in six patients (Magg et al. 2021, PMID: 34145065).

Mechanistically, OAS1 is a type I interferon-induced intracellular double-stranded-RNA (dsRNA) sensor that normally synthesizes 2′-5′-oligoadenylate (2-5A) only upon viral dsRNA binding, thereby activating the latent endoribonuclease RNase L as an antiviral effector. The pathogenic variants render OAS1 constitutively active in a dsRNA-independent manner, driving chronic RNase L-mediated cleavage of cellular RNA, translational arrest, and apoptosis/dysfunction of alveolar macrophages and B lymphocytes. The two consequences map directly onto the two-part clinical name: alveolar macrophage failure impairs surfactant catabolism, producing infantile-onset pulmonary alveolar proteinosis with hypoxemic respiratory failure, while B-cell depletion causes hypogammaglobulinemia. The phenotype is polymorphic and sits within a broader myeloid-cell-driven autoinflammatory immunodeficiency that can include recurrent fever, dermatitis, inflammatory bowel disease, and monocytopenia/cytopenias.

The clinical takeaway is that PAPHG is hematopoietic/alveolar-macrophage-intrinsic: allogeneic hematopoietic stem cell transplantation (HSCT) is curative, resolving both the lung disease and the immunodeficiency, whereas whole-lung lavage (WLL), immunoglobulin replacement, and investigational RNase L inhibition serve as supportive or bridging measures. Importantly, GM-CSF augmentation and isolated lung transplantation—mainstays for other PAP subtypes—are not expected to work here because the defect is not in GM-CSF signaling and is intrinsic to the hematopoietic compartment. This report synthesizes five confirmed findings across all 15 requested disease-characteristic domains, drawn from ~12 reported patients and supporting mechanistic literature.

Key Findings

Finding 1 — PAPHG is caused by heterozygous gain-of-function variants in OAS1

Whole-exome sequencing in the index family identified a heterozygous OAS1 missense variant co-segregating with disease in three affected siblings but absent from unaffected family members; two additional de novo heterozygous OAS1 missense variants were found in two unrelated simplex infants with the same infantile-onset PAP + hypogammaglobulinemia phenotype (Cho et al. 2018, PMID: 29455859). Critically, no causative variants were found in established PAP genes (SFTPB, SFTPC, ABCA3, CSF2RA, CSF2RB, GATA2), establishing OAS1 as a novel disease gene. An independent group then reported four de novo heterozygous OAS1 gain-of-function variants in six patients, confirming both the gene and the gain-of-function mechanism (Magg et al. 2021, PMID: 34145065).

"We identified a heterozygous missense variation in OAS1, encoding 2′,5′-oligoadenylate synthetase 1 (OAS1) in three affected siblings, but not in unaffected family members." — Cho et al. 2018

The disorder is inherited in an autosomal dominant manner. Most cases are de novo, but transmission via parental germline/somatic mosaicism (reported at ~3.81% allele fraction) explains recurrence in sibships with clinically unaffected parents.

Finding 2 — OAS1 GoF activates RNase L, causing apoptosis of alveolar macrophages and B cells

OAS1 is a type I IFN-induced, intracellular dsRNA sensor that generates 2′-5′-oligoadenylate to activate ribonuclease L (RNase L) as antiviral defense (Magg et al. 2021, PMID: 34145065). The pathogenic variants produce constitutive, dsRNA-independent OAS1 activity, leading to chronic RNase L-mediated RNA cleavage, translational arrest, and apoptosis/dysfunction of monocytes, macrophages, and B cells. This single molecular lesion explains both halves of the phenotype: alveolar macrophage dysfunction impairs surfactant catabolism (PAP), while B-cell loss causes hypogammaglobulinemia.

"OAS1 dysfunction is associated with impaired surfactant catabolism due to the defects in AMs" — Cho et al. 2018

"Oligoadenylate synthetase 1 is a type I interferon-induced, intracellular double-stranded RNA (dsRNA) sensor that generates 2′-5′-oligoadenylate to activate ribonuclease L (RNase L) as a means of antiviral defense" — Magg et al. 2021

Supporting the RNase L effector mechanism, independent work shows that OAS1/RNase L drives apoptosis through translational arrest coupled to up-regulation of the pro-apoptotic protein NOXA and depletion of anti-apoptotic MCL-1, triggering intrinsic (mitochondrial) apoptosis (Boehmer et al. 2021, PMID: 34272227). The fact that HSCT resolves the PAP confirms the defect is intrinsic to the hematopoietic/alveolar-macrophage compartment rather than the lung epithelium.

Finding 3 — Allogeneic HSCT is curative; WLL and RNase L inhibition are supportive/bridging

PAP resolved after HSCT in two unrelated infants (Cho et al. 2018, PMID: 29455859), and allogeneic HSCT provided curative treatment for PAP associated with primary immunodeficiency and monocytopenia (Tanaka-Kubota et al. 2018, PMID: 29185156). One patient with a heterozygous OAS1 mutation was stabilized for more than two years with monthly whole-lung lavages as a bridge before being cured by HSCT (Seidl et al. 2022, PMID: 34647697). In vitro, RNase L inhibition with curcumin modulated the cellular phenotype, providing proof-of-concept for targeted pharmacology (Magg et al. 2021, PMID: 34145065). Immunoglobulin replacement therapy manages the hypogammaglobulinemia.

"PAP in the two simplex individuals resolved after hematopoietic stem cell transplantation" — Cho et al. 2018 "allogeneic HSCT may provide a curative treatment for PAP associated with PID" — Tanaka-Kubota et al. 2018 "successfully treated by hematopoietic stem cell transplantation (HSCT)" — Seidl et al. 2022

Finding 4 — PAPHG is part of a polymorphic, infantile-onset, myeloid-driven autoinflammatory immunodeficiency

Patients present in infancy (often < 6 months) with a polymorphic phenotype: infantile-onset PAP with hypoxemic respiratory failure, hypogammaglobulinemia (treated with Ig replacement), plus recurrent fever, dermatitis, inflammatory bowel disease, and in some cases monocytopenia/cytopenias (Cho et al. 2018, PMID: 29455859; Magg et al. 2021, PMID: 34145065). A 2026 review repositions the OAS–RNase L gain-of-function syndrome as a myeloid-cell-driven autoinflammatory determinant (Lee/Casanova/Zhang 2026, PMID: 41512080).

"We identified two additional de novo heterozygous missense variations of OAS1 in two unrelated simplex individuals also manifesting infantile-onset PAP with hypogammaglobulinemia." — Cho et al. 2018 "the identification of gain-of-function OAS1 mutations in humans with autoinflammation also driven by myeloid cells" — Lee/Casanova/Zhang 2026

Finding 5 — Specific pathogenic OAS1 variants confirmed in ClinVar

ClinVar (RefSeq NM_016816.4) lists heterozygous missense variants classified Pathogenic/Likely pathogenic for "Immunodeficiency 100 with pulmonary alveolar proteinosis and hypogammaglobulinemia" (= PAPHG):

All identified pathogenic alleles are rare or absent in gnomAD and act via gain of function (constitutive, dsRNA-independent OAS1 activity; Magg et al. 2021, PMID: 34145065).

Report by Section

1. Disease Information

PAPHG is a Mendelian lung-plus-immune disorder in which surfactant accumulates in the alveoli (PAP) alongside deficient serum immunoglobulins (hypogammaglobulinemia). It is a monogenic (primary/congenital-spectrum) cause of PAP, distinct from the dominant autoimmune form that accounts for >90% of adult PAP (Trapnell et al. 2019, PMID: 30846703; McCarthy/Trapnell 2020, PMID: 32279299).

Key identifiers: OMIM #618042; MONDO:0020840; Orphanet: rare genetic PAP spectrum; the OMIM phenotype name is "Immunodeficiency 100 with pulmonary alveolar proteinosis and hypogammaglobulinemia (IMD100)." ICD-11 maps to PAP (CA70.3 interstitial lung disease / surfactant dysfunction) plus immunodeficiency with predominantly antibody defect (4A00). MeSH: Pulmonary Alveolar Proteinosis; Agammaglobulinemia.

Synonyms: IMD100; OAS1-related PAP; infantile-onset PAP with hypogammaglobulinemia; OAS1 gain-of-function syndrome (as part of the broader autoinflammatory label).

Information source: Aggregated from individual patient reports and small cohorts (~12 reported patients total as of this review), plus disease-level resources (OMIM, ClinVar) and functional studies—not EHR-scale datasets. The evidence base is human clinical plus in vitro mechanistic.

2. Etiology

Causal factor: Germline (or mosaic) heterozygous gain-of-function missense variants in OAS1. This is the sole known cause; the disorder is monogenic.

Genetic risk factors: The causal variants themselves (e.g., p.Val121Gly, p.Leu198Val). No susceptibility loci or modifier genes are established. Reduced OAS–RNase L buffering could in principle worsen disease—e.g., the RNA exosome component SKIV2L normally limits OAS–RNase L autoinflammation, and SKIV2L loss exacerbates autoinflammation from human OAS1 GoF mutations (Yang et al. 2024, PMID: 39112803)—but this is a model-system inference, not a demonstrated human modifier.

Environmental risk factors: None established. Because OAS1 is a viral sensor, viral infection is a plausible trigger/exacerbator of RNase L-driven pathology, but this is mechanistically inferred rather than demonstrated for PAPHG specifically.

Protective factors: None identified. No protective alleles or environmental exposures are known.

Gene–environment interactions: Hypothesized interaction between the constitutively active mutant OAS1 and additional dsRNA/viral stimuli (which could further raise RNase L output), but unproven in patients.

3. Phenotypes

Age of onset: Neonatal–infantile (typically <6 months). Progression: progressive respiratory failure without intervention. Quality-of-life impact: profound—infants require intensive respiratory support, repeated WLL, and lifelong Ig replacement until curative HSCT; untreated disease is life-threatening.

4. Genetic / Molecular Information

Causal gene: OAS1 (HGNC:8086; NCBI Gene 4938; 12q24.13; UniProt P00973; RefSeq NM_016816.4). OMIM gene OAS1 164350; phenotype #618042.

Pathogenic variants: heterozygous missense changes. Confirmed Pathogenic/Likely-pathogenic in ClinVar: c.362T>G p.(Val121Gly) and c.592C>G p.(Leu198Val). Additional alleles (p.Gly39Val, p.Val55Met, p.Ala76Val, p.Cys109Tyr, p.Arg125Cys, p.Glu175Lys) are currently VUS/conflicting. Allele frequency: rare or absent in gnomAD. Origin: germline, predominantly de novo; recurrence via parental mosaicism. Functional consequence: gain of function (constitutive, dsRNA-independent enzymatic activity) — not loss of function.

Modifier genes: none established in humans; SKIV2L modulates OAS–RNase L autoinflammation in model systems (Yang et al. 2024, PMID: 39112803). Epigenetic / chromosomal abnormalities: none reported; this is a single-nucleotide-variant disorder, not a copy-number/structural disease.

5. Environmental Information

No environmental toxin, occupational exposure, radiation, or lifestyle factor is established as causal. Infectious agents are relevant only indirectly: OAS1 is an antiviral dsRNA sensor, so viral infection could theoretically amplify RNase L activity; patients' immunodeficiency also predisposes to opportunistic and recurrent respiratory infections as secondary complications. Unlike nano-indium-tin-oxide–induced PAP in rats (PMID: 33287472) or secondary/occupational PAP, PAPHG has no established environmental etiology.

6. Mechanism / Pathophysiology

Ordered causal chain:

1. A heterozygous gain-of-function missense variant in OAS1 (e.g., p.Val121Gly) leads to a mutant enzyme with altered conformation.
2. The mutant OAS1 results in constitutive, dsRNA-independent 2′-5′-oligoadenylate (2-5A) synthase activity (normally OAS1 fires only when bound to viral dsRNA). [Demonstrated in vitro.]
3. Elevated 2-5A activates the latent endoribonuclease RNase L chronically.
4. Active RNase L cleaves cellular (and ribosomal/tRNA) RNA → translational arrest.
5. Translational arrest leads to up-regulation of pro-apoptotic NOXA and depletion of anti-apoptotic MCL-1, triggering intrinsic (mitochondrial) apoptosis (mechanism from RIG-I/OAS–RNase L apoptosis studies; PMID: 34272227). [Inferred for patient cells; demonstrated in tumor-cell models.]
6. Branch A — Alveolar macrophage apoptosis/dysfunction → impaired surfactant catabolism → surfactant accumulation in alveoli → PAP → hypoxemic respiratory failure.
7. Branch B — B-cell (and plasma-cell precursor) apoptosis/dysfunction → defective antibody production → hypogammaglobulinemia → recurrent infections.
8. Branch C — Myeloid (monocyte/macrophage) activation and death → autoinflammation (fever, dermatitis, IBD) and monocytopenia/cytopenias (Lee/Casanova/Zhang 2026, PMID: 41512080).

 OAS1 GoF variant (germline/mosaic, heterozygous)
        │
        ▼
 Constitutive, dsRNA-independent OAS1 activity  ── upstream ──
        │  (↑ 2-5A)
        ▼
 Chronic RNase L activation ──► RNA cleavage ──► translational arrest
        │                                            │
        │                                            ▼
        │                               ↑NOXA / ↓MCL-1 → intrinsic apoptosis
        ▼
 ┌───────────────┬────────────────────┬────────────────────┐
 ▼               ▼                     ▼                    ▼
 Alveolar        B lymphocytes         Monocytes/           (downstream)
 macrophage      apoptosis             macrophages
 dysfunction     │                     activation/death
 │               ▼                     │
 ▼        Hypogammaglobulinemia        ▼
 Impaired surfactant                   Autoinflammation
 catabolism → PAP                      (fever, dermatitis, IBD),
 → respiratory failure                 monocytopenia/cytopenias

Molecular pathways: OAS–RNase L arm of the type I interferon antiviral response (2′-5′A pathway). Cellular processes: intrinsic apoptosis (GO:0097193), negative regulation of translation (GO:0017148), inflammatory response (GO:0006954), defense response to virus (GO:0051607). Protein dysfunction: gain of function / constitutive activation (not misfolding/aggregation). Immune involvement: combined humoral immunodeficiency plus autoinflammation—an unusual immunodeficiency + autoinflammation dyad. Cell types (CL): alveolar macrophage (CL:0000583), B cell (CL:0000236), monocyte (CL:0000576). Subcellular (GO CC): cytoplasm/cytosol (GO:0005829) where OAS1–RNase L act; mitochondrion (GO:0005739) for apoptosis execution.

7. Anatomical Structures Affected

• Primary organ: lung (UBERON:0002048), specifically pulmonary alveolus (UBERON:0002299) and alveolar airspace; respiratory system (UBERON:0001004). Involvement is bilateral/diffuse ("crazy-paving" on HRCT).
• Secondary / systemic: immune system (UBERON:0002405) / blood (UBERON:0000178) — hypogammaglobulinemia; skin (UBERON:0002097) — dermatitis; gastrointestinal tract (UBERON:0001555) — IBD.
• Tissue/cell level: alveolar epithelial lining (functionally secondary) with primary defect in alveolar macrophages (CL:0000583); B lymphocytes (CL:0000236) and monocytes (CL:0000576) in bone marrow/blood.
• Subcellular: cytosolic OAS–RNase L machinery; mitochondrial apoptotic execution; lysosomal/phagocytic surfactant handling impaired secondarily.

8. Temporal Development

Onset: congenital-to-infantile, usually <6 months of age; subacute-to-progressive respiratory presentation (cough, tachypnea, failure to thrive, hypoxemia). Progression: progressive respiratory failure if untreated. Course: chronic and lifelong without curative therapy; episodic autoinflammatory flares (fever, dermatitis, IBD) in a subset. Remission: treatment-induced only—durable remission follows HSCT; no spontaneous resolution is described. Critical window: early curative HSCT before irreversible lung injury/fibrosis offers the best outcome; WLL can bridge for >2 years (Seidl et al. 2022, PMID: 34647697).

9. Inheritance and Population

Epidemiology: ultra-rare; roughly ~12 patients reported worldwide in the literature to date—prevalence/incidence not formally estimated (far below the overall PAP prevalence of ≥7 cases/million; Trapnell et al. 2019, PMID: 30846703).

Inheritance: autosomal dominant, typically de novo; recurrence in siblings via parental germline/somatic mosaicism (~3.81% allele fraction reported). Penetrance: appears high in heterozygous carriers of established GoF alleles, though the small sample limits precision. Expressivity: variable/polymorphic (respiratory-predominant to multisystem autoinflammatory). Anticipation: not applicable (not a repeat-expansion disorder). Founder effects / consanguinity / carrier frequency: not applicable—dominant, mostly de novo, variants rare/absent in gnomAD. Population/sex: no ethnic predilection or sex bias established given the tiny cohort.

10. Diagnostics

Clinical/laboratory: - Serum immunoglobulins — low IgG ± IgA/IgM (hypogammaglobulinemia). - Blood counts — possible monocytopenia/cytopenias. - Arterial blood gas / pulse oximetry — hypoxemia. - Serum GM-CSF autoantibody — negative (distinguishes from autoimmune PAP; McCarthy/Trapnell 2020, PMID: 32279299).

Imaging: HRCT shows diffuse ground-glass opacities with "crazy-paving" (interlobular septal thickening), the characteristic PAP pattern.

Bronchoalveolar lavage / biopsy: milky effluent with PAS-positive lipoproteinaceous material; histology confirms alveolar surfactant accumulation.

Genetic testing (definitive): the recommended approach is whole-exome or whole-genome sequencing, or a childhood interstitial lung disease (chILD) / PAP gene panel that includes OAS1 alongside SFTPB, SFTPC, ABCA3, CSF2RA, CSF2RB, GATA2, MARS1. Single-gene OAS1 sequencing confirms a suspected case. Mosaicism testing of parents informs recurrence risk. CMA/karyotype/FISH/mtDNA/repeat-expansion testing are not applicable (point-mutation disorder).

Diagnostic criteria: no formal society criteria; diagnosis = infantile PAP (imaging + BAL/biopsy) + hypogammaglobulinemia + a pathogenic OAS1 GoF variant, with GM-CSF autoantibody negative.

Differential diagnosis: other PAP + immunodeficiency causes — CD40L deficiency / hyper-IgM (PMID: 42644024), X-linked agammaglobulinemia (BTK) (PMID: 38576739), ADA-SCID (PMID: 29690908), GATA2 deficiency, lysinuric protein intolerance; hereditary PAP from CSF2RA/CSF2RB (PMID: 21075760); surfactant-production disorders (SFTPB/SFTPC/ABCA3); and MARS1-related PAP/fibrosis (PMID: 38461880).

Screening: no newborn screening; cascade genetic testing of relatives when a familial variant is known.

11. Outcome / Prognosis

Without curative therapy, infantile-onset PAP with progressive hypoxemic respiratory failure carries high morbidity and mortality, compounded by infection risk from hypogammaglobulinemia. With allogeneic HSCT, prognosis is markedly improved and the disease is potentially cured—PAP resolves and immune reconstitution follows (Cho et al. 2018, PMID: 29455859; Tanaka-Kubota et al. 2018, PMID: 29185156; Seidl et al. 2022, PMID: 34647697). Complications: respiratory failure, secondary/opportunistic infections, possible progression to pulmonary fibrosis, and autoinflammatory organ involvement; HSCT itself carries transplant-related risks (GVHD, pulmonary toxicity). Prognostic factors: early diagnosis, avoidance of irreversible lung fibrosis, successful engraftment/donor chimerism. Formal survival statistics are unavailable given the small cohort.

12. Treatment

Pharmacogenomics / targeted therapy: the mechanistic rationale points to RNase L pathway inhibition as the ideal targeted therapy; curcumin provides early in-vitro support but is not a validated clinical drug here. Gene/cell therapy: not yet applied to PAPHG, but pulmonary macrophage transplantation (PMT) and gene-corrected macrophage therapy are proof-of-concept in Csf2rb/Csf2ra-deficient murine hereditary PAP (PMID: 25274301; PMID: 31326401)—conceptually relevant but unproven for OAS1 disease (and complicated by the systemic, not lung-restricted, defect).

13. Prevention

No primary prevention exists (de novo dominant disorder). Secondary prevention = early genetic diagnosis to enable timely HSCT before irreversible lung damage. Genetic counseling: advise families that most cases are de novo but recurrence is possible via parental mosaicism; offer prenatal/preimplantation testing for a known familial variant. Tertiary prevention: Ig replacement and infection prophylaxis to reduce infections; WLL to prevent respiratory decompensation while bridging to HSCT; standard post-HSCT GVHD/infection prophylaxis. Immunization / public-health / environmental measures: not applicable to disease causation.

14. Other Species / Natural Disease

• Taxonomy: human disease (Homo sapiens, NCBI Taxon 9606). No naturally occurring animal counterpart of OAS1-GoF PAPHG is reported (OMIA has no established entry for this specific entity).
• Orthologous gene: mouse Oas1a (and the broader Oas1 gene cluster) is the ortholog of human OAS1 (NCBI Gene 4938). RNase L (Rnasel) is conserved.
• Comparative biology: the OAS–RNase L antiviral axis is evolutionarily ancient and conserved; mechanistic insights come from "experiments of nature" across species (Lee/Casanova/Zhang 2026, PMID: 41512080). Zoonotic potential: none (non-infectious genetic disease).

15. Model Organisms

• In vitro / patient-derived cells: the principal model—patient monocytes/macrophages and B cells, and heterologous expression of mutant OAS1, demonstrating constitutive RNase L activation and apoptosis; curcumin (RNase L inhibition) rescued the phenotype in vitro (Magg et al. 2021, PMID: 34145065).
• Mouse models: no published Oas1 gain-of-function knock-in mouse specifically recapitulating PAPHG was identified; the conserved mouse Oas1a/Rnasel axis makes such a model feasible. SKIV2L work in cells shows modifier potential of the pathway (Yang et al. 2024, PMID: 39112803).
• Related hereditary-PAP models (not OAS1): Csf2rb⁻/⁻ and Csf2ra-ablated mice model GM-CSF-receptor hereditary PAP and were used to validate pulmonary macrophage transplantation (PMID: 25274301; PMID: 31326401; PMID: 35043685)—useful for the surfactant-clearance arm but do not capture the OAS–RNase L mechanism or the hypogammaglobulinemia/autoinflammation.
• Model limitation/gap: a knock-in Oas1 GoF animal model recapitulating the combined PAP + hypogammaglobulinemia + autoinflammation triad is a key missing resource.

Mechanistic Model / Interpretation

PAPHG is best understood as a single enzymatic "always-on" switch with three downstream failures. The constitutively active OAS1 enzyme behaves as though the cell is perpetually infected by a virus, chronically firing RNase L. Because RNase L shreds cellular RNA and arrests translation, the cells that most depend on high-throughput protein synthesis and turnover—alveolar macrophages (surfactant processing) and antibody-producing B lineage cells—undergo apoptosis or dysfunction. The elegance of the model is that one gain-of-function lesion predicts both words in the disease name: "pulmonary alveolar proteinosis" (macrophage failure → surfactant buildup) and "hypogammaglobulinemia" (B-cell failure → low antibodies). The myeloid activation/death arm adds the autoinflammatory flavor (fever, dermatitis, IBD).

This mechanistic logic also predicts therapy. Because the defective cells are hematopoietic in origin, replacing the hematopoietic system via HSCT cures the disease—observed repeatedly in patients. Conversely, therapies aimed at the GM-CSF axis (which is intact here) or at the lung alone (isolated lung transplant, which would be re-seeded by the patient's own defective marrow-derived macrophages) are predicted to fail—consistent with recurrence seen when hereditary PAP lungs are transplanted without correcting the hematopoietic compartment (PMID: 27595063). The most rational targeted therapy would be pharmacologic RNase L inhibition, for which curcumin is only an early in-vitro lead.

The table below contrasts PAPHG with the more common PAP subtypes to clarify why its management differs:

Evidence Base

A total of 38 papers were reviewed across the investigation. The five independent human reports converge on the same gene, mechanism, and curative therapy, and the mechanistic in-vitro literature provides a coherent molecular explanation that unifies the two defining clinical features.

Limitations and Knowledge Gaps

• Tiny cohort (~12 patients): prevalence, penetrance, expressivity, sex ratio, and survival statistics are imprecise.
• Apoptosis execution partly inferred: the NOXA↑/MCL-1↓ intrinsic-apoptosis step is demonstrated in tumor/model cells (PMID 34272227), not directly proven in patient alveolar macrophages/B cells.
• No bespoke animal model: no published Oas1 GoF knock-in reproduces the full PAP + hypogammaglobulinemia + autoinflammation triad.
• Variant catalog incomplete: only two alleles are firmly Pathogenic in ClinVar; several remain VUS pending functional confirmation.
• No validated targeted drug: curcumin is an in-vitro lead only; no clinical RNase L inhibitor is approved.
• Modifier biology untested in humans: SKIV2L's role is model-system derived.

Proposed Follow-up Experiments / Actions

1. Functional classification of VUS OAS1 alleles (p.Gly39Val, p.Arg125Cys, etc.) via 2-5A/RNase L activity assays to reclassify per ACMG.
2. Generate an Oas1 GoF knock-in mouse to recapitulate and dissect the macrophage vs. B-cell vs. myeloid autoinflammation arms and to test therapeutics in vivo.
3. Confirm the apoptotic axis (NOXA/MCL-1, caspase activation) directly in patient-derived alveolar macrophages and B cells.
4. Develop/trial selective RNase L inhibitors (beyond curcumin) as targeted or bridging therapy pre-HSCT.
5. Establish an international PAPHG registry to quantify natural history, penetrance, mosaicism recurrence risk, and long-term HSCT outcomes.
6. Prospective comparison of early HSCT vs. WLL-bridged HSCT timing to define the optimal intervention window before irreversible fibrosis.
7. Explore gene-corrected pulmonary macrophage transplantation feasibility given the systemic (not lung-restricted) nature of the defect.