Autoimmune Disease, Multisystem, Infantile-Onset, 2 (ADMIO2) — Comprehensive Disease Report

Disease: Autoimmune Disease, Multisystem, Infantile-Onset, 2 (ADMIO2) MONDO ID: MONDO:0014861 · OMIM: 617006 · DOID: 0061161 · Category: Mendelian (autosomal recessive inborn error of immunity) Causal gene: ZAP70 (HGNC:12858, NCBI Gene 7535, UniProt P43403, locus 2q11.2)

Summary

Autoimmune disease, multisystem, infantile-onset, 2 (ADMIO2; MONDO:0014861 / OMIM 617006) is an ultra-rare, autosomal-recessive inborn error of immunity defined molecularly by biallelic missense mutations in ZAP70, the Syk-family tyrosine kinase that is the proximal signaling node of the T-cell antigen receptor (TCR). The disease was delineated in a single sibling pair (a brother and sister) who were compound heterozygous for two private ZAP70 alleles: a hypomorphic allele, p.Arg192Trp (R192W), in the C-terminal SH2 domain that reduces binding to the phosphorylated ζ-chain, and an activating allele, p.Arg360Pro (R360P), in the N-lobe of the catalytic domain that disrupts kinase autoinhibition to produce a weakly hyperactive enzyme (PMID: 26783323). This particular allelic combination distinguishes ADMIO2 from the more common classic ZAP70-deficiency combined immunodeficiency (CID; OMIM 269840), which is caused by biallelic loss-of-function alleles.

The defining pathophysiologic concept is that altered TCR signal strength — not simple loss of signaling — breaks T-cell tolerance. Attenuated/altered ZAP70 kinase activity raises the thresholds of thymic (central) selection so that self-reactive thymocytes that should be negatively selected instead escape deletion and are positively selected, while the activating allele raises the sensitivity of mature peripheral T cells to weak self-ligands. The clinical result is severe, early-onset (first year of life) multiorgan autoimmunity — uncontrollable bullous pemphigoid, colitis, nephrotic syndrome with minimal-change glomerulonephritis, and a factor VIII autoantibody causing acquired hemophilia — superimposed on a partial combined immunodeficiency with CD8 lymphopenia. Both affected children required and were cured by allogeneic hematopoietic stem cell transplantation (HSCT).

This report synthesizes the molecular genetics, mechanism, phenotype, epidemiology, diagnostics, prognosis, treatment, and model-organism evidence for ADMIO2. Because ADMIO2 sensu stricto is known from a single family, much supporting mechanistic and clinical detail is extrapolated from (a) functional studies of the specific R360P and R192W alleles, (b) the broader literature on biallelic ZAP70 deficiency (~49 reported patients), and (c) mouse models — the SKG hypomorphic mutant (Zap70 W163C) and an R360P knock-in — that respectively model the two human alleles. Importantly, ADMIO2 must be distinguished from the clinically similar but mechanistically unrelated STAT3 gain-of-function syndrome (ADMIO1; OMIM 615952), which was also surveyed during this investigation.

1. Disease Information

Overview. ADMIO2 is a monogenic (Mendelian) disorder of immune dysregulation presenting in infancy with multisystem autoimmunity. Mechanistically it is an inborn error of TCR signaling: biallelic ZAP70 variants alter the quality and strength of TCR signal transduction, breaking immune tolerance while simultaneously impairing protective T-cell immunity.

Key identifiers.

These cross-references were confirmed via OLS4/MONDO (MONDO:0014861 equivalentTo OMIM:617006).

Synonyms / alternative names. "ADMIO2"; the disease is best referred to by its OMIM title "Autoimmune disease, multisystem, infantile-onset, 2." The underlying gene-level entity is "ZAP70-related combined immunodeficiency / immune dysregulation." ADMIO1 (OMIM 615952) is the distinct STAT3-GOF syndrome.

Information source. Disease-level knowledge derives from aggregated resources (OMIM, MONDO, HPO) that are themselves built on a single primary clinical report of two patients (PMID: 26783323). This is a disease-level (literature-aggregated) rather than EHR/individual-patient derived entry, and the small n (2) is the dominant limitation throughout.

2. Etiology

Primary cause — genetic. ADMIO2 is caused by biallelic (compound heterozygous) missense mutations in ZAP70. Whole-exome sequencing of a five-member family identified the two affected siblings as compound heterozygous for two unique missense variants; healthy relatives were heterozygous carriers, establishing autosomal-recessive inheritance (PMID: 26783323):

"revealed the affected siblings to be compound heterozygous for two unique missense mutations in the 70-kD T cell receptor ζ-chain associated protein (ZAP-70)"

The two alleles have opposite biochemical effects:

"Mutation R192W in the C-SH2 domain exhibited reduced binding to phosphorylated ζ-chain, whereas mutation R360P in the N lobe of the catalytic domain disrupted an autoinhibitory mechanism, producing a weakly hyperactive ZAP-70 protein"

Genetic risk factors. The disease-causing variants are themselves the risk factor; both were private to the index family and are not population polymorphisms. There are no established common-variant susceptibility loci or validated modifier genes for ADMIO2 specifically, though inter-individual variability in broader ZAP70 deficiency (even between siblings carrying identical alleles) implies the existence of unidentified genetic/environmental modifiers (PMID: 41790376).

Environmental risk factors. None are established as causal. As with other combined immunodeficiencies, infectious exposures (e.g., CMV) can precipitate or worsen clinical course in ZAP70-deficient patients (PMID: 33484432), and endogenous retroviral superantigens modulate autoimmunity in the mouse model (see §6). Consanguinity is a risk factor for biallelic ZAP70 disease generally (enriching homozygous LoF deficiency in Middle Eastern/North African populations), though the ADMIO2 index family was compound heterozygous rather than consanguineous.

Protective factors. No genetic or environmental protective factors are defined for ADMIO2. By inference from gnomAD constraint (below), heterozygous carriers are asymptomatic — a single wild-type ZAP70 allele is protective/sufficient.

Gene–environment interactions. The best-characterized GxE axis is from the SKG mouse model: endogenous mouse-mammary-tumor-virus (MMTV) superantigens and the microbiota are required to convert the genetic lesion into overt arthritis, and antiretroviral therapy curtails disease (PMID: 39589811; PMID: 37394552). Whether analogous triggers operate in human ADMIO2 is unknown.

3. Phenotypes

All ADMIO2 HPO annotations derive from the two siblings in PMID: 26783323:

"A brother and sister developed a previously undescribed constellation of autoimmune manifestations within their first year of life, with uncontrollable bullous pemphigoid, colitis, and proteinuria. The boy had hemophilia due to a factor VIII autoantibody and nephrotic syndrome"

Phenotype characteristics. Onset: neonatal–infantile (within the first year). Severity: severe ("uncontrollable" bullous pemphigoid; nephrotic-range proteinuria; bleeding from acquired hemophilia). Progression: progressive/refractory to conventional immunosuppression, ultimately requiring HSCT. Frequency: autoimmunity and the immunologic lab abnormalities were present in both siblings; organ-specific features were variably present.

Broader ZAP70-deficiency phenotype (context). A systematic review of 49 biallelic ZAP70 patients (PMID: 32431715) and a 13-patient HSCT cohort (PMID: 41080547) describe profound CD8 lymphopenia (84.6% in the cohort), recurrent respiratory infections, cutaneous disease, and autoimmunity, with median symptom onset ~1 month:

"Eleven of thirteen patients (84.6%) exhibited profound CD8" (PMID: 41080547)

Quality-of-life impact. No disease-specific QoL instruments (EQ-5D/SF-36/PROMIS) have been applied to ADMIO2. By inference, untreated disease is life-threatening and severely disabling (refractory multiorgan autoimmunity + immunodeficiency); successful HSCT can restore normal immune function and resolve autoimmunity (see §11–12).

4. Genetic / Molecular Information

Causal gene. ZAP70 (Zeta-chain Associated Protein kinase 70 kDa), HGNC:12858, OMIM gene 176947, locus 2q11.2; protein UniProt P43403 — a 619-aa cytoplasmic Syk-family protein tyrosine kinase with two tandem N-terminal SH2 domains (binding doubly-phosphorylated ITAMs) and a C-terminal catalytic kinase domain.

ADMIO2 pathogenic variants (private to index family).

Both are missense substitutions. In the context of this family with functional support, both would be classified pathogenic/likely-pathogenic, but they are absent from population databases (private), consistent with their non-recurrent nature.

Variant classification per ACMG/AMP: functional evidence (PS3), compound heterozygosity with segregation (PM3/PP1), absence from controls (PM2), and in-silico support place both alleles at least as likely pathogenic in this disease context.

Allele frequency. The R192W and R360P alleles are not catalogued as recurrent population variants (private). For the gene overall, gnomAD constraint (ENSG00000115085): pLI = 0.88, LOEUF (oe_lof) = 0.173 (90% CI 0.09–0.364), observed/expected LoF = 5/28.8, missense Z = 2.76 — indicating that ZAP70 is intolerant of heterozygous loss of function, yet heterozygous carriers are clinically healthy (biallelic hit required for disease).

Somatic vs germline. Germline; inherited from heterozygous carrier parents.

Functional consequences. A combination of loss-of-function (R192W reduces ITAM engagement) and gain-of-function (R360P releases autoinhibition) — the net effect is altered/dysregulated TCR signaling, not simple nullizygosity.

ClinVar variant landscape (gene-level). ClinVar (NCBI E-utilities, 2026) returns ~616 ZAP70 records: ~79 pathogenic, ~21 likely-pathogenic, ~354 VUS, ~422 benign/likely-benign. Most pathogenic/likely-pathogenic alleles are LoF/hypomorphic variants causing classic ZAP70-deficiency CID (OMIM 269840) — e.g., homozygous p.Ala463Val (PMID: 33484432) — whereas the ADMIO2-defining p.Arg192Trp and p.Arg360Pro alleles remain private to the index family.

Modifier genes / epigenetics / chromosomal abnormalities. No ADMIO2-specific modifier genes, epigenetic marks, or chromosomal/structural abnormalities are established. Phenotypic divergence among siblings with identical ZAP70 genotypes in the broader literature implies unidentified modifiers (PMID: 41790376).

5. Environmental Information

ADMIO2 is a monogenic disease with no required environmental cause. Relevant non-genetic modifiers/triggers, largely by inference or from models:

• Infectious agents. Not causal, but infections (notably CMV) complicate the associated immunodeficiency and can unmask/worsen disease in ZAP70-deficient infants (PMID: 33484432). In the SKG mouse, Brucella infection drives a spondyloarthritis-like phenotype on the susceptible Zap70 background (PMID: 40027658).
• Endogenous retrovirus / microbiota. MMTV-derived superantigens and gut microbiota are required to convert the mouse genetic lesion into overt autoimmune arthritis (PMID: 39589811; PMID: 37394552).
• Lifestyle factors. Not applicable (infantile-onset Mendelian disease).

6. Mechanism / Pathophysiology

Ordered causal chain

1. Biallelic ZAP70 missense mutations (R192W hypomorphic + R360P activating) are inherited → altered ZAP70 protein with reduced phospho-ζ binding (R192W) and weakened kinase autoinhibition (R360P). (Demonstrated — functional assays, PMID: 26783323.)
2. Altered ZAP70 changes the strength/quality of TCR signal transduction at the proximal node (ZAP70 is recruited to doubly-phosphorylated CD3/ζ ITAMs, activated by Lck, and phosphorylates LAT/SLP76 to drive Ca²⁺/NFAT, Ras–MAPK, and NF-κB). (Pathway demonstrated; allele-specific effect inferred.)
3. In the thymus (central tolerance): attenuated/altered TCR signaling raises selection thresholds, so self-reactive thymocytes that should be negatively selected instead escape deletion and are positively selected → export of self-reactive T cells. (Demonstrated in SKG mouse, PMID: 37394552.)
4. In the periphery (peripheral tolerance): the R360P activating allele increases mature T-cell sensitivity to weak/self ligands that would normally be ignored → activation of autoreactive T cells. (Demonstrated in R360P knock-in mouse, PMID: 33531381.)
5. Activation of autoreactive CD4⁺ (and dysregulated) T cells drives T-follicular-helper (Tfh) expansion and aberrant B-cell help → production of pathogenic autoantibodies (anti-basement-membrane IgG, anti-factor VIII, anti-podocyte/glomerular). (Tfh expansion demonstrated in mouse [PMID: 33531381]; autoantibodies demonstrated in patients [PMID: 26783323].)
6. Autoantibody- and T-cell–mediated tissue injury at specific organs → clinical manifestations: bullous pemphigoid (skin basement membrane), colitis (gut), minimal-change nephrotic syndrome with podocyte foot-process effacement (kidney), acquired hemophilia A (factor VIII neutralization). (Demonstrated — clinical/pathology, [PMID: 26783323].)
7. In parallel (branch): the hypomorphic R192W allele plus overall signaling impairment reduces CD8⁺ T-cell development and T-cell function → partial combined immunodeficiency (CD8 lymphopenia, impaired PHA response, poor specific antibody) → susceptibility to infection. (Demonstrated — immunophenotype, [PMID: 26783323]; broader cohorts [PMID: 32431715].)

 ZAP70 biallelic missense (R192W hypomorphic + R360P activating)
            │
            ▼
   Altered TCR signal STRENGTH (not absent)
        ┌───────────────┴───────────────┐
        ▼                               ▼
 Raised thymic selection          Increased peripheral T-cell
 thresholds → self-reactive       sensitivity to weak/self
 thymocytes escape deletion       ligands (R360P)
 (central tolerance break)        (peripheral tolerance break)
        └───────────────┬───────────────┘
                        ▼
          Autoreactive T cells + Tfh expansion
                        ▼
              Pathogenic autoantibodies
                        ▼
   Multiorgan autoimmunity: skin (bullous pemphigoid),
   gut (colitis), kidney (nephrotic syndrome), FVIII inhibitor
                        │
            (parallel branch via hypomorphic allele)
                        ▼
   CD8 lymphopenia + impaired T-cell function → infection risk

Supporting detail

• Molecular pathways. Proximal TCR signaling: Lck → CD3/ζ ITAM phosphorylation → ZAP70 recruitment/activation → LAT/SLP76 phosphorylation → PLCγ1 (Ca²⁺/NFAT), Ras–MAPK/ERK, PKCθ–NF-κB. (Reactome "TCR signaling"; KEGG hsa04660.)
• Autoinhibition structural basis. The tandem-SH2 (tSH2) module locks the kinase in a closed, inactive conformation; ITAM binding or ζ-phosphorylation triggers the closed→open transition (PMID: 26237552):

  "TCR binding or phosphorylation of Zap70 triggers a transition from a closed, autoinhibited conformation to an open conformation" The ADMIO2 R360P substitution lies in the N-lobe and structurally weakens this autoinhibition. TCR dwell time tunes kinase output (PMID: 26237552); tSH2 dynamics differ between Syk and ZAP-70, explaining ZAP-70's tighter autoinhibition (PMID: 34601763).

• Immune system involvement. Autoimmunity + partial immunodeficiency (immune dysregulation). Tolerance is broken in both compartments; autoantibodies are the proximate effectors of organ injury.
• Cellular processes / cell types. CD4⁺ T cells (CL:0000624), CD8⁺ T cells (CL:0000625; depleted), Tfh cells, thymocytes undergoing selection, and downstream autoantibody-producing B cells/plasma cells.
• GO terms. T-cell receptor signaling pathway (GO:0050852); positive/negative thymic T-cell selection (GO:0045059 / GO:0045060); T-cell tolerance induction (GO:0002517); protein tyrosine kinase activity (GO:0004713); regulation of immune response (GO:0050776).
• Functional proof of the two-allele model.

  "disruption of ZAP70 autoinhibition by the R360P mutation enables increased mature T cell sensitivity to self-antigens that would normally be ignored by wild-type T cells, a mechanism that may contribute to the break of tolerance in human patients with R360P mutation" (PMID: 33531381) "Defective TCR signaling by ZAP70 mutation alters thymic selection thresholds and allows the positive selection of otherwise negatively selected self-reactive T cells" (PMID: 37394552)

• Spectrum concept. Graded reduction of ZAP70/TCR signal produces a continuum from immunodeficiency to autoimmunity (PMID: 41770842):

  "the effects of graded TCR signal reduction manifest as a disease spectrum encompassing T cell immune deficiency, latent autoimmunity, and overt autoimmune disease"

7. Anatomical Structures Affected

Organ level (primary targets of autoimmunity):

Secondary involvement. Infectious complications of the immunodeficiency (e.g., respiratory tract, systemic CMV) affect the respiratory system (UBERON:0001004) and others.

Tissue / cell level. Epithelial basement membrane (skin), renal podocytes (CL:0000653), colonic mucosa; immunologically, thymocytes and peripheral T lymphocytes. Targeted/dysregulated cell populations: CD4⁺ αβ T cell (CL:0000624), CD8⁺ αβ T cell (CL:0000625, depleted), T-follicular-helper cell, autoantibody-secreting B cell/plasma cell (CL:0000786/CL:0000980).

Subcellular level. ZAP70 functions at the inner-leaflet plasma membrane / TCR complex (GO:0005886; GO:0042101 T-cell receptor complex) in the cytoplasm (GO:0005737). Podocyte foot-process effacement is an ultrastructural (cytoskeletal) lesion.

Lateralization. Systemic/bilateral (skin, kidneys, gut) — not lateralized.

8. Temporal Development

• Onset. Congenital predisposition with clinical onset in infancy — within the first year of life (HP:0003593). Pattern is subacute-to-progressive.
• Progression. Severe and refractory/progressive under conventional immunosuppression; the index siblings progressed to requiring HSCT. In the broader ZAP70-deficiency literature, median symptom onset is ~1 month, and untreated disease is life-threatening.
• Disease course. Chronic and progressive until definitively treated; curable (remission) by allogeneic HSCT (treatment-induced remission). No spontaneous remission is described.
• Critical period / window of intervention. Early recognition and HSCT before irreversible organ damage or fatal infection is the key therapeutic window; the infant thymus is more amenable to reconstitution (relevant to experimental intrathymic gene therapy, PMID: 16075064).

9. Inheritance and Population

• Inheritance. Autosomal recessive (HP:0000007), confirmed by compound heterozygosity in affected siblings and heterozygous healthy carriers (PMID: 26783323):

  "Healthy relatives were heterozygous mutation carriers"

• Penetrance / expressivity. Within the single family, biallelic genotype was fully penetrant for autoimmunity in both siblings, with variable organ-specific expressivity (e.g., hemophilia and nephrotic syndrome only in the boy). Broader ZAP70 disease shows variable expressivity even among identical-genotype siblings (PMID: 41790376).
• Epidemiology. Ultra-rare. ADMIO2 sensu stricto is reported in a single sibling pair; formal prevalence is not estimated (<1 per 1,000,000). The broader biallelic ZAP70-deficiency entity has ~49 reported cases worldwide (PMID: 32431715).
• Carrier frequency / constraint. Heterozygous carriers are healthy; gnomAD shows ZAP70 is LoF-constrained (pLI 0.88, LOEUF 0.173) but disease requires two hits.
• Founder effects / consanguinity. The ADMIO2 alleles are private (no founder effect). Classic ZAP70 deficiency is enriched in consanguineous Middle Eastern/North African populations (PMID: 41080547; PMID: 41790376).
• Sex ratio / demographics. No sex predilection (AR); the index pair comprised one male and one female. No established ethnic predilection for ADMIO2 specifically.

10. Diagnostics

Immunologic laboratory tests (characteristic pattern). - Flow cytometry: CD8 lymphopenia / low CD8⁺ T cells → increased CD4:CD8 ratio (HP:0033221). In classic ZAP70 deficiency, intracellular ZAP70 is absent/reduced on gated T cells (PMID: 33484432). - Impaired T-cell proliferation to mitogens (PHA/ConA) (HP:0025834). - Humoral: variable; decreased specific (pneumococcal) antibody response in one sibling. - Autoimmune workup: anti–basement-membrane IgG (direct immunofluorescence shows linear IgG along the epidermal basement-membrane zone), factor VIII inhibitor assay (acquired hemophilia), urinalysis for proteinuria.

Biopsy / pathology. Skin DIF (bullous pemphigoid pattern); renal biopsy showing minimal-change glomerulonephritis with podocyte foot-process effacement on electron microscopy; colonic biopsy for colitis.

Newborn screening caveat. TREC-based SCID newborn screening may be normal in ZAP70 / CID, so a normal TREC screen does not exclude the diagnosis (PMID: 33484432; PMID: 22664165).

Genetic testing (diagnostic gold standard). WES/WGS or a primary-immunodeficiency / inborn-errors-of-immunity gene panel including ZAP70 is the definitive test; the disease was discovered by WES (PMID: 26783323). Confirm biallelic ZAP70 variants, segregation (parental carriers), and functional validation (phospho-ζ binding, kinase activity, TCR-induced proliferation/IL-2) because ADMIO2 alleles are private and otherwise VUS.

Clinical criteria / differential diagnosis. No formal consensus criteria exist. Key differentials for infantile multiorgan autoimmunity: - STAT3 gain-of-function (ADMIO1, OMIM 615952) — early-onset polyautoimmunity, lymphoproliferation, double-negative T cells, responsive to JAK inhibitors (PMID: 36228738). - IPEX (FOXP3), CTLA4 haploinsufficiency, LRBA deficiency, APECED (AIRE), and classic ZAP70-deficiency CID (OMIM 269840). Distinguishing feature of ADMIO2: biallelic ZAP70 with the specific hypomorphic+activating combination and CD8 lymphopenia with autoimmunity.

11. Outcome / Prognosis

• Natural course (untreated). Severe, refractory, life-threatening multiorgan autoimmunity plus immunodeficiency; both index children required HSCT after failing conventional therapy.
• With definitive treatment. Allogeneic HSCT is curative and resolved the autoimmunity in both ADMIO2 siblings (PMID: 26783323). In the broader ZAP70-deficiency literature, long-term outcomes after HSCT are excellent: 8/8 patients alive at median 13.5 years, with restored T-cell function and resolution of infections and autoimmunity (PMID: 27438785).
• Complications. Pre-transplant: bleeding (FVIII inhibitor), nephrotic complications, colitis, infection. Transplant-related: graft failure, GVHD, conditioning toxicity.
• Prognostic factors. Timeliness of diagnosis and HSCT; control of autoimmunity and infection pre-transplant; donor source/conditioning. CD8 reconstitution post-HSCT is generally good.

12. Treatment

Definitive / curative. - Allogeneic hematopoietic stem cell transplantation (HSCT) — curative; the only established cure (NCIT: Allogeneic Hematopoietic Stem Cell Transplantation, C15349). Both ADMIO2 siblings were cured by HCT:

"Both children required allogeneic hematopoietic cell transplantation (HCT), which resolved their autoimmunity" (PMID: 26783323) Supported by durable success in ZAP70 deficiency broadly (8/8 alive at 13.5 yr, PMID: 27438785; curative in majority of a 13-patient cohort, PMID: 41080547).

Supportive / bridging immunosuppression (pre-HSCT, symptom control). - Corticosteroids (NCIT C682); IVIG (C29368); rituximab / B-cell depletion for autoantibody-mediated disease (FVIII inhibitor, pemphigoid) (NCIT C1702); calcineurin inhibitors; standard management of nephrotic syndrome and colitis.

Experimental / preclinical — gene therapy. - ZAP70-deficient mice have been corrected by retroviral/lentiviral HSC gene transfer (PMID: 12149205), intrathymic lentiviral delivery (PMID: 16075064), and intrathymic AAV8/9/10 gene transfer restoring thymopoiesis and long-term peripheral T-cell function (PMID: 31513879):

"Intrathymic AAV-transduced progenitors promote a rapid restoration of the thymic architecture, with a single wave of thymopoiesis generating long-term peripheral T-cell function" Note: gene addition addresses the deficiency component; the ADMIO2 activating (R360P) allele is dominant-acting at the cellular level, so a correction strategy for the autoimmune component may require allele-specific considerations.

Mechanism-informed experimental approaches (from models). In the SKG hypomorphic model, antiretroviral therapy and depletion of superantigen-reactive T cells curtailed arthritis (PMID: 39589811); JAK inhibition is effective in the mechanistically analogous STAT3-GOF syndrome (PMID: 36228738) but is not established for ADMIO2.

Pharmacogenomics. None established specific to ADMIO2.

13. Prevention

• Primary prevention. Not applicable in the usual sense (monogenic recessive disease). Genetic counseling for carrier couples; carrier/cascade testing in affected families; prenatal diagnosis / preimplantation genetic testing (PGT) is possible once familial variants are known.
• Secondary prevention. Early diagnosis via immunophenotyping + genetic testing in infants with multiorgan autoimmunity or CID; note TREC newborn screening can miss ZAP70 disease.
• Tertiary prevention. Infection prophylaxis (antimicrobial, antiviral, IVIG), prompt treatment of autoimmunity, and timely HSCT to prevent irreversible organ damage.
• Counseling. 25% recurrence risk per pregnancy for carrier couples (AR).

14. Other Species / Natural Disease

• Taxonomy / ortholog. Mouse (Mus musculus, NCBI Taxon 10090); ortholog Zap70 (NCBI Gene 22637). ZAP70 is evolutionarily conserved; TCR-proximal signaling architecture (Lck + ZAP-70/Syk, ITAM recognition) is conserved even in teleosts (rainbow trout homology modeling, PMID: 41240985).
• Natural disease in other species. No well-characterized naturally-occurring companion-animal homolog of ADMIO2 is documented; relevance is primarily through engineered rodent models.
• Comparative biology. The mouse allelic series (below) recapitulates the human deficiency↔autoimmunity spectrum, underscoring conserved mechanisms.

15. Model Organisms

Direct quotes:

"Mice with a ZAP70 R360P mutation and polyclonal TCR repertoires exhibited relatively normal T cell development but showed evidence of increased signaling" (PMID: 33531381)

"the effects of graded TCR signal reduction manifest as a disease spectrum encompassing T cell immune deficiency, latent autoimmunity, and overt autoimmune disease" (PMID: 41770842)

Model types: mammalian (mouse) in vivo; knock-in, knockout, and point-mutant (ENU-derived SKG) lines. Recapitulation: the two alleles are each separately modeled and together support the "altered-signal-strength breaks tolerance" mechanism; the knockout models the immunodeficiency arm. Limitations: no single mouse carries the exact human compound-heterozygous R192W/R360P genotype, so the combined/epistatic effect of the two alleles together is modeled only indirectly; mouse autoimmune targets (arthritis) differ from the human organ spectrum (skin/kidney/gut), reflecting species-specific self-antigens and superantigen biology. Resources: MGI (Zap70, SKG allele), IMPC/IMSR.

Mechanistic Model / Interpretation

ADMIO2 is best understood as a "Goldilocks" disorder of TCR signal strength. ZAP70 sits at the apex of TCR signaling, and the amount of kinase output a thymocyte or T cell experiences determines its fate: too little signal → failed positive selection / immunodeficiency; intermediate aberrant signal → escape from negative selection + peripheral hyper-responsiveness → autoimmunity; normal signal → tolerance + protective immunity. The ADMIO2 genotype pairs a hypomorphic allele (R192W; less ITAM engagement, raising selection thresholds like SKG) with an activating allele (R360P; released autoinhibition, lowering the threshold for peripheral responses to self). The net effect is a signaling milieu that simultaneously (a) allows self-reactive T cells to be positively selected and exported and (b) renders mature T cells inappropriately responsive to weak self-ligands — a double break of central and peripheral tolerance — while still leaving CD8 development and overall T-cell function partially impaired. The downstream effector arm is autoantibody-mediated, explaining the specific, disparate organ targets (skin basement membrane, glomerular podocyte, colon, clotting factor VIII). This model is anchored by direct biochemistry of the two alleles (PMID: 26783323), structural understanding of ZAP70 autoinhibition (PMID: 26237552, PMID: 34601763), and two complementary mouse models (PMID: 37394552, PMID: 33531381).

Evidence Base

Limitations and Knowledge Gaps

1. Single family (n=2). All ADMIO2-specific clinical and genetic data come from one sibling pair. Prevalence, penetrance, expressivity, full phenotype spectrum, and genotype–phenotype correlations cannot be generalized.
2. Private alleles. R192W and R360P are not recurrent; no population allele-frequency or additional segregation data beyond the index family.
3. No combined-genotype animal model. The two alleles are modeled separately (SKG and R360P knock-in); the epistatic effect of the exact human compound-heterozygous genotype is inferred, not demonstrated.
4. Effector mechanism partly inferred. The link from altered T-cell tolerance to the specific autoantibody targets (pemphigoid, podocyte, FVIII) is clinically observed but mechanistically underexplored for ADMIO2.
5. No ADMIO2-specific trials or QoL/natural-history data. Treatment and prognosis rest on the single report plus extrapolation from the broader ZAP70-deficiency literature.
6. Therapeutic uncertainty for the activating allele. Whether standard gene-addition gene therapy (effective for deficiency) would correct the dominant cellular effect of R360P is unknown; JAK-inhibitor utility (as in STAT3-GOF) is untested here.

Proposed Follow-up Experiments / Actions

1. International case-finding / GeneMatcher. Actively solicit additional ADMIO2 families via GeneMatcher, inborn-errors-of-immunity consortia, and ClinVar to expand the phenotype and genotype spectrum and estimate penetrance.
2. Compound-heterozygous model. Engineer a mouse or patient-derived iPSC → thymic organoid carrying both R192W and R360P to test the predicted additive/epistatic tolerance break and reproduce human-relevant autoimmunity.
3. Autoantibody repertoire and target mapping. Define the autoantigen specificities (skin BP180/BP230, podocyte antigens, FVIII epitopes) and the Tfh/B-cell dynamics driving them in ADMIO2 (and in R360P knock-in mice).
4. Therapeutic screen. Test JAK inhibition, B-cell depletion, abatacept/CTLA4-Ig, and allele-selective approaches in cellular/animal models to identify bridge therapies that control autoimmunity pre-HSCT.
5. Gene-therapy feasibility for the activating allele. Evaluate allele-specific knockdown/base-editing of R360P versus gene-addition in ZAP70 models to determine whether gene therapy can address both the deficiency and autoimmune arms.
6. Diagnostic yield of functional validation. Formalize a functional assay panel (phospho-ζ binding, kinase activity, TCR-induced IL-2/proliferation, Ca²⁺ flux) to reclassify ZAP70 VUS and flag hypomorphic+activating combinations.

Report compiled from 7 confirmed findings and 35 reviewed papers over 5 investigation iterations. Evidence sources span human clinical (single defining family + broader cohorts), model organism (mouse SKG, R360P knock-in, knockout), in vitro/biochemical (allele functional assays, ZAP70 structural dynamics), and computational (gnomAD constraint, ClinVar aggregation, OLS4/MONDO cross-references).