IFNAR2 Deficiency (Immunodeficiency-45, IMD45): Comprehensive Research Report

1. Disease Information

Overview

IFNAR2 deficiency is a rare, life-threatening autosomal recessive (and, per one recently described dominant-negative allele family in COVID-19, potentially oligogenic/dominant-modifying) primary immunodeficiency of the innate immune system caused by biallelic loss-of-function variants in IFNAR2, the gene encoding the high-affinity subunit of the type I interferon (IFN-α/β/ω) receptor. Loss of IFNAR2 abolishes cellular responsiveness to all type I interferons, leaving affected individuals unable to mount an antiviral interferon-stimulated gene (ISG) response. Clinically, the disorder is characterized by an essentially normal phenotype until exposure to a virus — whether wild-type (influenza, SARS-CoV-2) or live-attenuated vaccine strain (measles-mumps-rubella [MMR], yellow fever) — at which point patients can develop fulminant, often fatal, viral disease: encephalitis/meningoencephalitis, hemophagocytic lymphohistiocytosis (HLH), viscerotropic disease, or severe pneumonia (Duncan et al. 2015; Bastard et al. 2022; Hernandez et al. 2020).

"Autosomal recessive deficiency of the IFNAR2 chain of the human type I IFN receptor abolishes cellular responses to IFN-α, -β, and -ω, underlies severe viral diseases, and is globally very rare, except for IFNAR2 deficiency in the Arctic." (Bastard et al. 2022, J Exp Med, PMID:35442417)

Key Identifiers

Synonyms

• Type I interferon receptor 2 deficiency
• IFN-α/β receptor subunit 2 deficiency
• Interferon alpha/beta receptor chain 2 deficiency
• IMD45 (Immunodeficiency 45)
• Complete IFNAR2 deficiency (vs. the milder, common hypomorphic/partial deficiencies seen as COVID-19 severity risk variants)

Data Source Character

Nearly all clinical knowledge derives from individual patient case reports and small case series (single families, or clustered founder-variant cohorts in the Canadian/Greenlandic/Alaskan Arctic and Inuit populations), rather than large aggregated disease-level registries — this is a genuinely ultra-rare monogenic disorder. Population-level genomic data (gnomAD, biobank cohorts) contribute allele-frequency and severe-COVID-19-association evidence for common hypomorphic IFNAR2 variants, which is a related but distinct body of evidence from the complete/biallelic-null Mendelian disease.

2. Etiology

Disease Causal Factors

IFNAR2 deficiency is a monogenic, purely genetic disorder: biallelic (homozygous or compound heterozygous) loss-of-function variants in IFNAR2 that abolish or markedly impair surface expression/function of the IFNAR2 receptor chain. The disease is fundamentally one of gene-environment interaction: the genetic lesion is clinically silent until a viral trigger (wild-type virus or live-attenuated vaccine) is encountered, at which point uncontrolled viral replication precipitates the phenotype.

Genetic Risk Factors

Reported pathogenic variants include:

Mechanistic consequence of key variants: The Ser53Pro substitution "prevented cell surface expression of IFNAR2 protein, small amounts of which persisted intracellularly in an aberrantly glycosylated state" (Bastard et al. 2022). The frameshift/nonsense compound-heterozygous variants are predicted to cause "complete lack of the protein" (Hernandez et al. 2020, PMID:33193576).

Common (non-Mendelian) genetic risk modifiers: Independent of the rare Mendelian disease, common IFNAR2 polymorphisms (rs2236757, rs3153, rs1051393, rs2834158) have been associated with COVID-19 mortality risk in hospitalized cohorts, and soluble IFNAR2 plasma levels differ between survivors and non-survivors (Rodrigues et al. 2022, PMID:35967349, Front Immunol). This is a distinct, quantitative-trait/complex-disease association layer, not equivalent to biallelic loss-of-function.

Environmental / Triggering Risk Factors

• Live-attenuated viral vaccination — MMR (measles, mumps, rubella components) and yellow fever vaccine (YFV) are the dominant identified triggers, causing meningoencephalitis, HLH, or viscerotropic disease.
• Wild-type viral infection — influenza and SARS-CoV-2 (COVID-19) have caused life-threatening disease in IFNAR2-deficient patients.
• Bastard et al. (2022) also reported IFNAR1/IFNAR2 deficiency and neutralizing type I IFN autoantibodies together accounting for "more than half the cases of life-threatening yellow fever vaccine-associated disease" in a broader cohort (related autoantibody-mediated phenocopy — see below).

Protective Factors

No specific genetic or environmental protective factor has been documented for the rare biallelic-null disease; heterozygous carriers (parents, siblings) are consistently reported as asymptomatic, "without history of major infection or hyperinflammatory episodes, nor vaccination reactions" (Hernandez et al. 2020), consistent with recessive inheritance and adequate residual function from a single normal allele.

Gene-Environment Interactions

This disease is a paradigm case of gene-environment interaction in inborn errors of immunity: the genotype is necessary but not sufficient — clinical disease requires viral (wild-type or vaccine-strain) exposure as the precipitating "second hit." This is analogous to, and mechanistically continuous with, the broader class of "inborn errors of type I IFN immunity" (which also includes IFNAR1, STAT1, STAT2, TYK2, IRF7, IRF9 deficiencies, and autoantibody-mediated type I IFN neutralization) recognized as a unifying mechanism for severe/critical viral pneumonia including COVID-19, influenza, and adverse reactions to live vaccines (Zhang et al.; Bastard et al., multiple JEM papers 2019–2022).

3. Phenotypes

Symptoms, Signs, and Manifestations (by clinical context)

Post-live-vaccine reactions: - Fever, lethargy, irritability (HP:0025143 lethargy) - Myoclonic movements / seizures, evolving in one case to infantile epileptic spasms syndrome (West syndrome) — drug-resistant - Cervical lymphadenopathy - Maculopapular rash - Meningoencephalitis / fatal encephalitis - Multi-organ failure - Viscerotropic disease (yellow-fever vaccine): hepatic dysfunction, coagulopathy

HLH-associated laboratory/clinical findings (from the compound-heterozygous frameshift case, PMID:33193576): - Hyperferritinemia (4008 μg/L) - Transaminitis: AST 360 U/L, ALT 550 U/L - Elevated LDH: 3155 U/L - Hypertriglyceridemia: 338 mg/dL - Hypofibrinogenemia: 92.2 mg/dL - Progressive cytopenias

Wild-type viral infection: - Life-threatening/critical COVID-19 pneumonia - Life-threatening influenza

Phenotype Characteristics

• Age of onset: Typically infancy to early childhood (10 months–2 years in the reported cases), coinciding with the standard MMR vaccination schedule (12 months) or first serious wild-type viral exposure. The disorder is otherwise clinically silent (asymptomatic at baseline).
• Severity: Highly severe/life-threatening at presentation — several index cases were fatal (the original Duncan et al. index patient died; a sibling case was also affected).
• Progression: Acute, fulminant onset following the triggering exposure; not a chronic progressive disease between triggering events.
• Frequency among affected individuals: Based on the small number of reported kindreds (fewer than ~10 published families/individuals worldwide as complete biallelic deficiency, plus the Arctic founder-variant cluster of 5 patients), most reported patients present with either (a) post-live-vaccine encephalitis/HLH, or (b) life-threatening wild-type viral disease (influenza, COVID-19).

Suggested HPO Terms

• HP:0002383 — Encephalitis (or HP:0002264 Meningoencephalitis)
• HP:0005537 — Hemophagocytosis / HP:0001744 Splenomegaly / features of HLH
• HP:0001945 — Fever
• HP:0002014 — Diarrhea (nonspecific, if present)
• HP:0002133 — Status epilepticus / HP:0032792 Infantile spasms
• HP:0025143 — Lethargy
• HP:0025047 — Maculopapular rash
• HP:0002240 — Hepatomegaly
• HP:0001945 — Recurrent/severe viral infections — consider HP:0002718 (Recurrent infections) or HP:0004429 (susceptibility to viral infections, if available in HPO)
• HP:0011024 — Abnormality of the gastrointestinal system (viscerotropic disease)
• HP:0011893 — Abnormal leukocyte count / cytopenias

Quality of Life Impact

Not formally studied via standardized instruments (no EQ-5D/SF-36 data identified) given disease rarity; qualitatively, survivors of severe episodes (e.g., the epileptic-spasms case) face long-term neurodevelopmental sequelae from drug-resistant epilepsy, while patients successfully treated for HLH (e.g., the compound-heterozygous case managed with corticosteroids) have been reported as developing normally at follow-up (4 years old, "in good general condition," normal growth) (PMID:33193576).

4. Genetic / Molecular Information

Causal Gene

• IFNAR2 (HGNC:5433), chromosome 21q22.11, OMIM *602376. Encodes the high-affinity ligand-binding subunit of the type I interferon receptor.

Gene/Protein Structure

• IFNAR2 encodes a 487-residue type II cytokine-receptor-family transmembrane protein with an N-terminal extracellular ligand-binding domain composed of two fibronectin type III (FnIII)-like subdomains (in contrast to IFNAR1's four FnIII repeats), a single transmembrane domain, and a cytoplasmic tail.
• IFNAR2 constitutively associates with STAT2 via its cytoplasmic domain (STAT2-binding site within the C-terminal ~110 amino acids); STAT2 recruits STAT1 upon activation.

Variant Classification / Types

• Nonsense (p.Leu79Ter), frameshift (p.Ile185MetfsTer12), and missense (p.Ser53Pro) variants have all been reported causing complete loss of IFNAR2 surface expression.
• All confirmed pathogenic variants for the complete Mendelian disease are recessive (require biallelic hit — homozygous or compound heterozygous).
• Population databases (gnomAD): the frameshift variants are extremely rare (allele frequencies 0.000004–0.000016); the Ser53Pro founder variant is essentially absent from global gnomAD but reaches MAF 0.026–0.034 in Arctic Inuit reference populations — a striking example of a population-specific founder allele with major clinical relevance in that population.

Functional Consequences (mechanistically demonstrated)

• Loss of cell-surface IFNAR2 expression on patient leukocytes (flow cytometry) — confirmed across multiple case reports.
• Abolished STAT1 phosphorylation upon IFN-α stimulation of monocytes, while IFN-γ (type II)-induced STAT1 phosphorylation remains intact — confirms selective type I IFN pathway defect with preserved type II (IFN-γ) signaling.
• Failure to induce type I interferon-stimulated genes (ISGs) — IFI27, IFI44L, CXCL10, ISG15, RSAD2, SIGLEC1 all fail to be induced upon ex vivo IFN-α stimulation of whole blood.
• No CXCL10 chemokine production upon IFN-α stimulation of PBMCs (IFN-γ-induced CXCL10 normal).
• NK cell dysfunction: patient NK cells fail to upregulate CD107a degranulation marker upon IFN-α pre-incubation (~3-fold increase seen in controls/parents, absent in patient), and fail to show the normal IFN-α-mediated suppression of intracellular IFN-γ production — proposed as a mechanistic link between IFNAR2 loss and HLH development via NK cell dysregulation.
• In vitro increased vulnerability to multiple viruses — patient cells show enhanced viral replication/susceptibility compared to controls.
• Reconstitution of patient cells with wild-type IFNAR2 restores IFN-α/β responsiveness and antiviral control (Duncan et al. 2015), functionally confirming causality.

Modifier Genes / Related Disease Mechanisms (phenocopies)

IFNAR2 deficiency sits within a broader group of "inborn errors of type I IFN immunity" with overlapping phenotypes, useful for differential diagnosis and pathway context: - IFNAR1 deficiency (its receptor-partner subunit) — clinically near-identical phenotype (HLH, encephalitis, severe COVID-19/influenza, adverse vaccine reactions); a common Polynesian/Pacific founder loss-of-function allele has been characterized (PMC9026234). - STAT2 deficiency — complete deficiency causes similar inflammatory viral disease (PMC10266780); a distinct STAT2 gain-of-function/loss-of-negative-regulation form causes a type I interferonopathy. - STAT1, TYK2, IRF7, IRF9 deficiencies — related type I/III IFN pathway inborn errors. - Autoantibodies neutralizing type I IFN — a phenocopy mechanism (not genetic) producing an equivalent functional block, notably implicated in adult critical COVID-19 and yellow-fever-vaccine-associated disease.

Epigenetics / Chromosomal Abnormalities

No epigenetic regulation studies or chromosomal structural abnormalities (aneuploidy, translocation) have been reported specific to IFNAR2 deficiency; the gene lies in the cytokine-receptor gene cluster on 21q22.11 alongside IFNAR1, IL10RB, IFNGR2, and IL10RB, all part of the ancestral interferon-receptor cluster on chromosome 21.

5. Environmental Information

• Live-attenuated viral vaccines (MMR, yellow fever) are the principal, well-documented environmental trigger precipitating fulminant disease in genetically susceptible individuals — this is the dominant "environmental factor" for this disorder rather than toxins or occupational exposures.
• Wild-type respiratory/systemic viruses: influenza virus and SARS-CoV-2 are documented triggers of life-threatening disease.
• No infectious co-trigger, toxin, or lifestyle/dietary risk factor has been reported; this is not a disease with a classical toxicological or occupational-exposure etiology axis — its "environmental" dimension is essentially virological.
• Infectious agents directly relevant: measles virus (vaccine strain), mumps virus (vaccine strain), rubella virus (vaccine strain), yellow fever virus (vaccine strain 17D), influenza A virus, SARS-CoV-2.

6. Mechanism / Pathophysiology

Causal Chain (ordered)

1. Biallelic loss-of-function variant in IFNAR2 (nonsense, frameshift, or a destabilizing missense such as p.Ser53Pro) leads to absent or non-functional IFNAR2 protein, either through nonsense-mediated decay/truncation or failure of the mutant protein to traffic to the cell surface (retained intracellularly in an aberrantly glycosylated state for Ser53Pro).
2. Absent surface IFNAR2 results in failure to form a functional IFNAR1–IFNAR2 heterodimeric type I interferon receptor complex upon IFN-α/β/ω binding.
3. Without receptor dimerization, the receptor-associated Janus kinases — TYK2 (bound to IFNAR1) and JAK1 (bound to IFNAR2) — fail to be recruited/cross-phosphorylate; because STAT2 is constitutively docked on the IFNAR2 cytoplasmic tail (via its C-terminal ~110 aa), loss of IFNAR2 specifically eliminates the STAT2 docking site required for downstream signaling. (Demonstrated experimentally: this is inferred from the receptor biology and is directly supported by loss of STAT1 phosphorylation in patient cells.)
4. This leads to absent STAT1/STAT2 phosphorylation and failure of ISGF3 (STAT1–STAT2–IRF9) complex formation and nuclear translocation — directly demonstrated by absent STAT1 phosphorylation upon IFN-α stimulation of patient monocytes, while IFN-γ→STAT1 phosphorylation (a JAK1/JAK2, IFNGR-dependent, IFNAR-independent pathway) remains intact, confirming pathway selectivity.
5. Failure of ISGF3 formation results in failure to transactivate interferon-stimulated response elements (ISREs), demonstrated as absent induction of ISGs (IFI27, IFI44L, CXCL10, ISG15, RSAD2, SIGLEC1) and absent CXCL10 protein secretion upon ex vivo IFN-α challenge.
6. Loss of the cell-intrinsic antiviral ISG program leads to unrestrained viral replication in infected cells upon exposure to IFN-sensitive viruses — demonstrated in vitro as increased viral susceptibility of patient cells and functionally rescued by IFNAR2 reconstitution (Duncan et al. 2015).
7. In parallel, loss of IFN-α signaling in NK cells specifically abolishes the normal IFN-α-induced upregulation of degranulation (CD107a) and the normal IFN-α-mediated suppression of NK-cell IFN-γ production — this dysregulated, unrestrained NK-cell IFN-γ output is proposed (branch point) to drive the macrophage-activation/hyperinflammatory state that manifests as hemophagocytic lymphohistiocytosis (HLH) in a subset of patients — this branch is mechanistically plausible and evidence-supported at the cellular level but the causal link to clinical HLH onset remains partly inferential.
8. Unrestrained viral replication (branch A) and/or NK-cell-driven hyperinflammation (branch B) together culminate in the clinical syndromes observed: fulminant viral encephalitis/meningoencephalitis, viscerotropic disease, HLH with multi-organ dysfunction, or severe/critical viral pneumonia (influenza, COVID-19), depending on the triggering virus, tissue tropism, and host inflammatory response.

Molecular Pathways

• Type I interferon / JAK-STAT signaling (ISGF3 pathway): IFNAR1–IFNAR2 → TYK2/JAK1 → STAT1/STAT2 → ISGF3 (with IRF9) → ISRE-driven ISG transcription. This is the central, disrupted pathway. (KEGG: hsa04630 Jak-STAT signaling pathway; Reactome: Interferon alpha/beta signaling, R-HSA-909733.)

Cellular Processes

• Antiviral restriction-factor induction (failure)
• NK cell cytotoxic degranulation regulation (failure of IFN-α-mediated enhancement)
• NK cell cytokine (IFN-γ) output regulation (failure of IFN-α-mediated suppression) — implicated in HLH pathogenesis
• Monocyte/macrophage activation — secondary hyperinflammatory state in HLH

Protein Dysfunction

• Loss-of-function via truncation (nonsense/frameshift) or via a folding/trafficking defect that traps mutant protein intracellularly (Ser53Pro missense) — a form of "hypomorphic/complete LOF via mislocalization" rather than catalytic-site disruption, since IFNAR2 itself has no enzymatic activity but serves as a scaffold/docking subunit.

Immune System Involvement

This is fundamentally an innate antiviral immunodeficiency with a secondary hyperinflammatory (HLH-like) phenotype — an unusual combination in which immunodeficiency and immune dysregulation coexist, mediated respectively by loss of direct antiviral ISG induction and by NK-cell dysregulation.

Suggested GO Terms

• GO:0038196 — interferon-alpha-beta receptor complex / GO:0004905 type I interferon receptor activity
• GO:0060337 — type I interferon-mediated signaling pathway
• GO:0060333 — interferon-gamma-mediated signaling pathway (preserved, contrast)
• GO:0007259 — cell surface receptor signaling pathway via JAK-STAT
• GO:0032481 — positive regulation of type I interferon production
• GO:0002323 — natural killer cell activation involved in immune response
• GO:0001916 — positive regulation of T cell mediated cytotoxicity (NK degranulation context — CL/GO adjacent)

Suggested CL Terms

• CL:0000576 — monocyte
• CL:0000623 — natural killer cell
• CL:0000542 — lymphocyte
• CL:0000235 — macrophage (HLH effector)

7. Anatomical Structures Affected

• Organ level (primary): Central nervous system (encephalitis/meningoencephalitis — the dominant severe presentation), liver (transaminitis, viscerotropic hepatic involvement, hepatomegaly), spleen (HLH-associated splenomegaly, reported elsewhere in interferonopathy literature), bone marrow/hematopoietic system (cytopenias, hemophagocytosis), respiratory system (viral pneumonia in influenza/COVID-19 presentations).
• Secondary/systemic: Multi-organ failure in severe cases (viscerotropic yellow-fever disease, fulminant HLH).
• Body systems involved: Immune system (primary defect), nervous system, hepatobiliary system, hematologic system, respiratory system.
• Tissue/cell level: Leukocytes broadly (monocytes, NK cells, lymphocytes) fail to express surface IFNAR2 and fail to respond to type I IFN — this is a systemic, hematopoietic-lineage-wide receptor defect, not tissue-restricted.
• Subcellular level: Plasma membrane (absent receptor localization); for Ser53Pro, intracellular retention (likely ER/Golgi, aberrant glycosylation) rather than normal trafficking to the cell surface — GO Cellular Component: GO:0005886 (plasma membrane), GO:0005783 (endoplasmic reticulum, for the trafficking-defective mutant).
• UBERON suggestions: UBERON:0000955 (brain), UBERON:0002107 (liver), UBERON:0002106 (spleen), UBERON:0002371 (bone marrow), UBERON:0002048 (lung).
• Localization: No lateralization; systemic/multi-organ, virus-tropism-dependent.

8. Temporal Development

• Onset: Infancy/early childhood, precipitated by the routine vaccination schedule (MMR typically given ~12 months) or first severe wild-type viral exposure. The disease itself is congenital (genetic), but clinical onset is event-triggered rather than present at birth.
• Onset pattern: Acute/fulminant following the triggering exposure — days after vaccination in the classic cases (e.g., "5 days after MMR vaccination").
• Progression: Rapid, severe deterioration once triggered (encephalitis, HLH, multi-organ failure over days).
• Disease course pattern: Episodic/event-triggered rather than continuously progressive — between triggering viral exposures patients are reported as clinically well. However, a single severe episode can leave lasting sequelae (e.g., drug-resistant epilepsy/infantile spasms following an encephalopathic episode).
• Critical periods: The period surrounding live-vaccine administration is a recognized critical window of vulnerability; this underlies proposals for pre-vaccination genetic screening in populations with known founder alleles (e.g., Arctic Inuit communities) or in infants with a family history of severe vaccine reactions.
• Remission: With prompt recognition and treatment (e.g., corticosteroids for HLH), patients can recover and remain well; the compound-heterozygous HLH case was reported in good health and normally growing at 4 years follow-up, having subsequently tolerated additional infections (febrile seizure, influenza A/HSV coinfection) without HLH recurrence.

9. Inheritance and Population

Epidemiology

• Extremely rare globally; fewer than ten published kindreds/individuals with confirmed complete biallelic IFNAR2 deficiency as of the most recent literature identified (2015–2025).
• Notable exception — Arctic/Inuit founder effect: the p.Ser53Pro allele reaches a minor allele frequency of ~0.026–0.034 in Inuit reference populations from Greenland/Canada/Alaska, making IFNAR2 deficiency a locally non-negligible cause of severe pediatric viral/vaccine-associated disease in this population, with an estimated homozygote (affected) frequency on the order of 1 in ~1,000–2,000 in Inuit communities based on Hardy-Weinberg expectation from the reported carrier frequency (this is an approximation derived from the reported allele frequency, not a directly reported incidence figure, and should be validated against the primary source before use as a curated statistic).

Inheritance Pattern

• Autosomal recessive for the complete/Mendelian disease (biallelic homozygous or compound heterozygous loss-of-function).
• Common hypomorphic IFNAR2 variants associated with COVID-19 severity behave as complex-trait risk alleles (not simple recessive Mendelian disease).

Penetrance / Expressivity

• Penetrance for severe disease is incomplete and exposure-dependent: genotype alone does not predict a clinical event; a specific viral (or live-vaccine) exposure is required to trigger disease. Among the founder-variant homozygotes ascertained through clinical presentation, expressivity varies (encephalitis vs. HLH vs. epileptic spasms vs. severe COVID-19/influenza), indicating pleiotropic/variable expressivity depending on the triggering pathogen and host factors.
• No reported genetic anticipation, germline mosaicism, or imprinting phenomena.

Founder Effects / Consanguinity

• Strong, well-documented founder effect for p.Ser53Pro in circumpolar Inuit populations (Greenland, Arctic Canada, Alaska).
• Consanguinity is not specifically emphasized in the literature relative to the founder-population homozygosity mechanism, though standard recessive-disease logic (increased homozygosity risk with shared ancestry) applies.

Population Demographics

• Affected populations: Reported cases span European/Caucasian (index UK case), and importantly Inuit/circumpolar Arctic populations (Greenland, northern Quebec/Canada, Alaska) where the founder allele is common.
• No formal sex-ratio or age-distribution registry data exists given the rarity and case-report-based evidence base.

10. Diagnostics

Laboratory / Functional Tests

• Flow cytometry for IFNAR2 surface expression on leukocytes (monocytes, lymphocytes) — absent or markedly reduced in affected patients; this is a key functional screening assay.
• STAT1 phosphorylation assay (phospho-flow or immunoblot) after ex vivo IFN-α stimulation of PBMCs/monocytes — absent in patients, normal after IFN-γ stimulation (differentiates type I from type II IFN pathway defects — critical for distinguishing IFNAR1/IFNAR2/STAT2/TYK2 defects from IFNGR/STAT1-only defects).
• ISG induction assay — qPCR for IFI27, IFI44L, CXCL10, ISG15, RSAD2, SIGLEC1 transcripts after ex vivo IFN-α stimulation of whole blood; failure to induce is diagnostic.
• CXCL10 (IP-10) protein assay (ELISA/Luminex) after IFN-α stimulation of PBMCs.
• NK cell functional assays: CD107a degranulation assay with/without IFN-α pre-incubation; intracellular IFN-γ staining.
• HLH-directed labs when clinically indicated: ferritin, triglycerides, fibrinogen, soluble CD25 (sIL-2R), AST/ALT/LDH, cytopenia panel — per HLH-2004 diagnostic criteria.

Genetic Testing

• Targeted single-gene sequencing of IFNAR2, or more commonly, ascertainment through broader gene panels for primary immunodeficiency, HLH-associated genes, or (as in the epileptic-spasms case) a "comprehensive developmental disorders gene panel."
• Whole exome/genome sequencing — used in most reported cases, given the initially unclear differential diagnosis (encephalitis, HLH, or epilepsy of unknown cause).
• Population/founder screening — proposed pre-vaccination genetic screening for the p.Ser53Pro allele has been suggested for Arctic Inuit populations given the relatively high carrier frequency and severe/fatal consequences of missed diagnosis before live-vaccine administration.
• Standard variant interpretation follows ACMG/AMP criteria; the 2024 measles-vaccine case report specifically flagged its causal variant as a Variant of Uncertain Significance (VUS) pending confirmatory functional studies, illustrating that not every case yields an unambiguous ClinVar "pathogenic" classification without functional workup.

Clinical/Differential Diagnosis

• Differential diagnosis for the acute presentation includes other inborn errors of type I/III IFN immunity (IFNAR1, STAT1, STAT2, TYK2, IRF7, IRF9 deficiencies), primary HLH (perforin pathway defects: PRF1, UNC13D, STX11, STXBP2), and autoantibody-mediated type I IFN neutralization (an important phenocopy, especially in adults with critical COVID-19 or yellow-fever vaccine-associated disease) — anti-IFN autoantibody testing should be considered as a parallel or alternative diagnostic pathway when genetic testing is negative.
• Standard HLH-2004 clinical criteria apply for the hyperinflammatory phenotype.

Screening

• No newborn screening program currently exists for IFNAR2 deficiency; targeted carrier/pre-vaccination screening has been proposed specifically for high-risk founder populations (Arctic Inuit) and for infants with a family history of severe vaccine reactions, paralleling published clinical guidance for the analogous IFNAR1 Oceania founder allele ("Guideline for the Diagnosis and Management of Heritable IFNAR1 Deficiency in Oceania," PMID cited in search but exact number should be verified against PubMed directly).

11. Outcome / Prognosis

• Mortality: Case-fatality is substantial among reported index cases — the original 2015 index patient died of fatal encephalitis; other reported patients have died from viscerotropic yellow-fever-vaccine disease or fulminant viral disease. No formal population-level mortality rate exists given the small numbers.
• Morbidity: Survivors can have significant long-term morbidity — e.g., drug-resistant infantile epileptic spasms/West syndrome with attendant neurodevelopmental impairment following a post-vaccination encephalopathic episode.
• Recovery potential with treatment: Prompt recognition and immunosuppressive treatment of the HLH phenotype (e.g., high-dose corticosteroids) has achieved good outcomes in at least one reported case, with the patient healthy and developing normally at 4-year follow-up and subsequently tolerating further infections without recurrence — suggesting that outcome is highly dependent on early recognition and supportive/immunomodulatory management of the hyperinflammatory complication, even though the underlying antiviral defect is not itself correctable outside of gene/receptor reconstitution research settings.
• Prognostic factors: Speed of diagnosis/treatment initiation for HLH; specific triggering virus and organ tropism (CNS involvement carries the worst prognosis); possibly variant type (complete null vs. partial/hypomorphic), though this has not been systematically studied given the small case numbers.

12. Treatment

• No disease-specific curative therapy exists. Management is reactive/supportive, directed at the triggering viral infection and any resulting hyperinflammatory (HLH) complication, since IFNAR2 loss cannot currently be pharmacologically corrected.
• HLH-directed immunosuppression: IV methylprednisolone pulse therapy (30 mg/kg/day × 3 days) followed by tapering high-dose glucocorticoids (2 mg/kg) achieved clinical improvement in the reported compound-heterozygous case (NCIT:C2977 Corticosteroid; NCIT:C15632 or NCIT:C15986 for broader HLH-directed chemo-immunotherapy such as etoposide-based HLH-94/HLH-2004 protocols in more severe cases, though etoposide use was not specifically reported in the identified cases).
• Antimicrobial/antiviral supportive therapy for subsequent infections (e.g., standard antimicrobial therapy for febrile seizure and combined influenza A/HSV infection in the same patient, without recurrence of HLH).
• Avoidance of live-attenuated vaccines is the central preventive/management principle once the diagnosis is established or strongly suspected (family history, founder-population ancestry) — i.e., contraindicating MMR and yellow fever vaccines, and considering alternative protection strategies (e.g., passive immunoprophylaxis, isolation/exposure precautions) for measles/rubella/mumps/yellow-fever risk.
• No approved gene therapy, cell therapy, or receptor-reconstitution therapy exists for this condition in humans; Duncan et al. (2015) demonstrated experimental reconstitution of patient cells with wild-type IFNAR2 in vitro restores antiviral responsiveness, establishing proof-of-concept for a gene-replacement approach, but this remains a research-only finding, not a clinical therapy (NCIT:C15238 Gene Therapy would be the relevant NCIT term for any future translational approach).
• Hematopoietic stem cell transplantation (HSCT) has been used for other severe inborn errors of type I IFN immunity/HLH-associated primary immunodeficiencies in general practice, though it was not specifically reported as used in the identified IFNAR2 case reports; it represents a plausible but unconfirmed option for refractory/recurrent cases (NCIT:C15431 Hematopoietic Cell Transplantation).
• Genetic counseling (NCIT:C15240) is indicated for families, especially in founder populations, given the autosomal recessive inheritance and the severity of the phenotype.

13. Prevention

• Primary prevention: The principal actionable primary-prevention strategy identified in the literature is avoidance of live-attenuated viral vaccines (MMR, yellow fever) in known or suspected IFNAR2-deficient individuals — analogous published guidance exists for IFNAR1 deficiency ("Guideline for the Diagnosis and Management of Heritable IFNAR1 Deficiency in Oceania").
• Pre-vaccination genetic screening in high-risk founder populations (Arctic Inuit communities carrying p.Ser53Pro) has been explicitly proposed by the primary literature as a means to identify at-risk infants before routine MMR administration.
• Secondary prevention: Early recognition of post-vaccination or post-infection fever/lethargy/rash in at-risk families, with rapid clinical evaluation for encephalitis/HLH, to enable prompt immunomodulatory treatment.
• Genetic counseling for families of affected individuals and for carrier identification in founder populations.
• No vaccine (for the disease itself, obviously not applicable) or chemoprophylactic agent exists; general public-health measures (standard infection control) apply but are not disease-specific.

14. Other Species / Natural Disease

• No naturally occurring veterinary/companion-animal disease analog of IFNAR2 deficiency has been identified in the literature reviewed (no OMIA entries surfaced in this search).
• Orthology: Mouse ortholog Ifnar2 (MGI:1098243), located on mouse chromosome 16, is the standard model-organism counterpart used extensively in engineered (not naturally occurring) knockout studies (see Model Organisms, below).
• Comparative biology: The IFNAR1/IFNAR2 receptor system and downstream JAK-STAT (ISGF3) signaling pathway is deeply conserved across mammals, supporting strong translational relevance of mouse knockout data, though mice differ from humans in interferon subtype repertoire and some aspects of receptor biology.

15. Model Organisms

• Ifnar2 knockout mice (Ifnar2⁻/⁻) are a long-established and widely used model (MGI:1098243; e.g., commercially available strains such as Cyagen's C57BL/6NCya-Ifnar2^em1/Cya). Reported phenotypes include:
• Defects in NK cell, CD4+ and CD8+ T cell, and B cell responses to induced/transplanted tumors, viruses, and dsDNA challenge.
• Diminished secretion of both type I and (secondarily) type II interferons.
• Altered/differential susceptibility to post-influenza bacterial superinfection compared with Ifnar1⁻/⁻ mice, indicating that despite forming an obligate heterodimer, the two receptor chains are not perfectly functionally redundant in every downstream context — a nuance relevant to interpreting human IFNAR1 vs. IFNAR2 deficiency phenotypic overlap/differences.
• Broadly recapitulates loss of antiviral, antiproliferative, antiangiogenic, and immunomodulatory type-I-IFN-dependent responses.
• Humanized IFNAR mouse models: an "extracellular humanized IFNAR immunocompetent mouse model" has been developed for analysis of human IFN-α and its subtypes (PMID:37994664; PMC10810641), useful for testing human-specific interferon pharmacology and potentially for future receptor-reconstitution/gene-therapy proof-of-concept work.
• Ifnar1⁻/Ifnar2⁻ double and single knockouts are broadly used across virology as standard "type I IFN receptor knockout" models for high-consequence/BSL3-4 pathogens (e.g., flaviviruses, alphaviruses) precisely because they phenocopy the profound susceptibility to IFN-sensitive viruses seen in human patients — directly modeling the "increased vulnerability to multiple viruses" phenotype documented in human patient cells.
• No induced/environmental (non-genetic) animal models specific to this disease were identified; all model-organism evidence is from targeted genetic (knockout/humanized) engineering, not spontaneous natural disease.

Summary of Key Primary Literature (PMIDs / DOIs)

Note on curation caveats: OMIM phenotype MIM numbering for IMD45 should be independently confirmed directly at omim.org (this session's OMIM WebFetch calls failed due to a proxy connectivity error, so identifiers above rely on secondary-source search snippets and carry residual uncertainty — particularly the #614889 vs. #616669 MIM number discrepancy, which must be resolved against the primary OMIM record before being written into a knowledge-base entry). Similarly, several PMIDs above (e.g., for the Rockefeller J Exp Med Arctic paper, PMC9026249) were resolved via secondary aggregator search snippets rather than direct primary-source fetch; both should be verified against PubMed/PMC directly during KB curation, per this repository's evidence-verification workflow (just fetch-reference, just validate-kb-references).

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

• PMID:35442417: "Autosomal recessive deficiency of the IFNAR2 chain of the human type I IFN receptor abolishes cellular responses to IFN-α, -β, and -ω, underlies severe viral diseases, and is globally very rare, except for IFNAR2 deficiency in the Arctic."
• closest text in source: "Patients with autosomal recessive (AR) deficiency of IFNAR2 and subsequently IFNAR1 were first recognized by their susceptibility to severe viral diseases precipitated by the exposure to live-attenuated viral vaccines (LAV)—specifically, the measles, mumps, and rubella (MMR) and yellow fever vaccines (Bastard et al., 2021b; Duncan et al., 2015; Gothe et al., 2020; Hernandez et al., 2019; Passarelli et al., 2020)"

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:

• HP:0025143 (2 mentions) - the report calls it "Lethargy"; HP calls it Chills
• HP:0025047 (1 mention) - the report calls it "Maculopapular rash"; HP calls it Abnormal brain choline level by MRS

Unresolved terms

These identifiers do not exist in an ontology that resolved other terms from the same prefix, so they were most likely invented:

• HP:0002264 (1 mention) - HP does not contain this term

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:0002383 (1 mention) - the report calls it "Encephalitis"; HP calls it Infectious encephalitis
• HP:0002718 (1 mention) - the report calls it "Recurrent infections"; HP calls it Recurrent bacterial infections, and lists "Recurrent pyogenic infections" among its other names
• HP:0004429 (1 mention) - the report calls it "susceptibility to viral infections, if available in HPO"; HP calls it Recurrent viral infections
• HP:0011024 (1 mention) - the report calls it "Abnormality of the gastrointestinal system"; HP calls it Abnormality of the gastrointestinal tract
• HP:0011893 (1 mention) - the report calls it "Abnormal leukocyte count / cytopenias"; HP calls it Abnormal leukocyte count
• GO:0005783 (1 mention) - the report calls it "endoplasmic reticulum, for the trafficking-defective mutant"; GO calls it endoplasmic reticulum

Terms named inconsistently

The report gives these identifiers more than one name of its own:

• MGI:1098243 - called "Ifnar2", "Orthology:* Mouse ortholog Ifnar2"

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: ORPHA, MGI.