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Classifications

IUIS Category

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Inheritance

1

Autosomal recessive inheritance HP:0000007

Biallelic pathogenic ZAP70 variants are required; heterozygous parents are obligate carriers and are clinically well. Roughly three quarters of reported patients are homozygous rather than compound heterozygous, which reflects the high rate of consanguinity and the Old Order Mennonite founder allele in the published series rather than anything about the allele itself.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:20301777 SUPPORT Human Clinical

"ZAP70 deficiency is inherited in an autosomal recessive manner."

GeneReviews states the mode of inheritance directly.

PMID:32431715 SUPPORT Human Clinical

"Zeta-Chain Associated Protein Kinase 70 kDa (ZAP-70) deficiency is a rare combined immunodeficiency (CID) caused by recessive homozygous/compound heterozygous loss-of-function mutations in the ZAP70 gene."

Records that both homozygous and compound heterozygous biallelic states cause the disease.

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Discussions and Knowledge Gaps

3

Can a Zap70-null mouse be used to predict the T-cell compartment of a human ZAP70-deficient patient, when the null allele arrests both lineages in the mouse and only the CD8 lineage in people?

HUMAN MODEL MISMATCH mouse_null_does_not_model_lineage_selectivity

Attached to

pathophysiology#Block of CD8 Single-Positive Thymocyte Selection animal_models#Zap70-null mouse

The mismatch is not a difference of degree, and it is the whole diagnostic signature of the human disease that goes missing. Complete Zap70 loss arrests murine thymocytes at the double-positive stage with no mature peripheral T cells at all; the same loss in a patient produces a thymus with CD4 single-positive cells in the medulla and a periphery with normal or elevated CD4 counts. The proposed cause is concrete rather than hand-waving — SYK is expressed far more highly in human than in murine thymocytes and can carry the lower signalling threshold the CD4 lineage requires — and it is supported from both directions: forcing Syk expression into zap-70-/- mice restores thymocyte development, and the residual CD8 cells in patients are the ones expressing SYK. The practical rule this yields is narrow enough to be useful. The null mouse is informative about what ZAP-70 does in selection and about signalling mechanism; it is not informative about which lineage survives, about the peripheral immunophenotype, or about anything downstream of having a CD4 compartment — which includes the antibody-help defect and the autoimmune arm. For those, the hypomorphic strains are the better read, and the human cohort data are the only real answer.

Show evidence (3 references)

PMID:41080547 SUPPORT Other

"The absence of ZAP70 protein thus results in selective CD8+ T-cell deficiency with impaired signal transduction in CD4+ T-cells in humans, whereas in murine models, complete ZAP70 deficiency leads to an arrest in both CD4+ and CD8+ T-cell development because of insufficient Syk expression (17)."

States the mismatch and its proposed cause in one sentence.

PMID:9324357 SUPPORT Model Organism

"Syk expression restored both thymocyte development and function."

Supplies the experimental half of the argument: SYK is sufficient to carry the developmental function in the mouse, so its abundance is a plausible determinant of the species difference.

PMID:26187144 SUPPORT Human Clinical

"Our findings highlight the differential requirements of ZAP70 and SYK during thymic development, peripheral homeostasis as well as effector functions of CD4 and CD8 T cells."

Supplies the human half: SYK dependence differs by lineage in patients, which is the same axis the species difference runs along.

Why does allele class fail to predict clinical severity in ZAP70 deficiency, when it predicts residual protein function well?

KNOWLEDGE GAP no_genotype_phenotype_correlation

Attached to

genetic#ZAP70 pathophysiology#Impaired Negative Selection and Thymic Regulatory T Cell Output

The largest systematic review found no significant genotype-phenotype correlation between classical and leaky alleles or across mutation types, which is awkward, because the mechanistic story predicts one: residual function should map onto residual T-cell survival, and residual T-cell survival is what the autoimmune arm needs. Candidate explanations have not been separated — the cohort may simply be too small and too heterogeneously ascertained to detect a real correlation; SYK expression varies between patients and could dominate allele effect; or the determinant of the autoimmune arm may be TCR repertoire skewing, which allele class does not predict in a simple way. Until this is settled, prognostic counselling cannot be based on the variant.

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Based on the current evidence, there is no genotype-phenotype correlation in ZAP-70 deficient patients."

The finding the gap is about: allele class does not predict clinical severity in the largest pooled cohort.

Should newborn screening programmes in populations carrying the Mennonite founder allele supplement TREC screening with a CD8-based or targeted genetic test?

OPEN QUESTION trec_screening_blind_spot

Attached to

diagnosis#Newborn TREC screening pathophysiology#Block of CD8 Single-Positive Thymocyte Selection

TREC screening measures thymic output, and in this disorder thymic output continues through an intact CD4 lineage, so an affected infant can screen normal. That is not a marginal failure mode; it follows directly from the lineage selectivity that defines the disease. Genetically confirmed patients with retrospectively normal TREC screens are on record. Whether the answer is a supplementary CD8 count in founder communities, a targeted ZAP70 assay, or accepting the gap and relying on clinical suspicion has not been settled, and the trade-off depends on local prevalence that has never been measured.

Show evidence (2 references)

PMID:26187144 SUPPORT Human Clinical

"Retrospective TCR excision circle newborn screening was normal in both patients."

The patient-level observation that grounds the question: confirmed patients with normal TREC screens.

PMID:32431715 SUPPORT Human Clinical

"ZAP-70 has not been frequently picked up during the >10 year screening experience in the United States (49), despite a significant Mennonite population and the large number of reported ZAP-70 patients."

The programme-level counterpart, and the reason the question is about screening policy rather than about two patients.

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Pathophysiology

11

ZAP70 Loss of Kinase Function

Biallelic ZAP70 variants remove the kinase from the T-cell receptor cascade. Most reported alleles abolish protein expression or catalytic activity and cluster in the kinase domain, but there is a second, mechanistically distinct class in the C-terminal SH2 domain: R170C and R192W sit in the arginine pocket that docks the kinase onto the phosphorylated TCR zeta chain, so they abolish recruitment rather than catalysis. Preserved protein expression is documented for R170C specifically; R192W was confirmed pathogenic in two siblings without its expression level being reported in the same terms. Both classes reach the same place, a kinase that is not doing its job at the receptor, which is why a normal ZAP-70 protein level on flow cytometry does not exclude the diagnosis.

Genetic context variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION

ZAP-70 tyrosine kinase activity GO:0004715 ↓ DECREASED

Downstream

Attenuated Residual TCR Signaling The hypomorphic and docking-defective allele classes reduce rather than abolish the kinase's contribution, so this edge is the one those alleles take.

Failure of TCR-Proximal Signal Propagation The kinase is the obligate link between the phosphorylated receptor and its adaptors, so its loss stops the cascade at that step.

Show evidence (3 references)

PMID:8124727 SUPPORT Human Clinical

"We show here that STD patients carry a mutation of zap-70, resulting in loss of the activity of this kinase."

The founding observation that the disease allele destroys kinase activity.

PMID:8202712 SUPPORT Human Clinical

"A homozygous mutation in the kinase domain of ZAP-70, a T cell receptor-associated protein tyrosine kinase, produced a distinctive form of human severe combined immunodeficiency."

Locates the founding allele in the kinase domain and states the disease consequence.

PMID:37313400 SUPPORT Human Clinical

"While the R170C mutant was highly expressed, there was an absence of TCR-induced proliferation, associated with significantly attenuated TCR-induced ZAP-70 phosphorylation and a lack of binding of ZAP-70 to TCR-zeta."

Establishes the docking-defective allele class, in which protein expression is preserved and only receptor engagement is lost.

Failure of TCR-Proximal Signal Propagation

Without ZAP-70 the phosphorylated CD3 and zeta ITAMs have nothing to recruit, so the adaptors LAT and SLP-76 are never phosphorylated and the signalosome that would carry the signal onward is never assembled. In patient T cells this reads out as markedly reduced tyrosine phosphorylation, no interleukin-2, and no proliferation to receptor stimulation — with the cells otherwise present and normal in number.

alpha-beta T cell CL:0000789

T cell receptor signaling pathway GO:0050852 ↓ DECREASED

Downstream

Block of CD8 Single-Positive Thymocyte Selection Positive selection reads the strength of the TCR signal, so a cascade that cannot propagate cannot deliver the selecting signal.

Functional Anergy of Peripheral CD4 T Cells The CD4 cells that escape the thymus carry the same broken cascade, so they are numerically normal and functionally inert.

Show evidence (2 references)

PMID:41080547 SUPPORT Other

"ZAP70 then phosphorylates key downstream molecules, including SLP-76 and LAT, thereby initiating signaling cascades essential for T-cell activation, differentiation, cytokine production, adhesion, and motility (14)."

Names the substrates whose phosphorylation fails when the kinase is absent, and the processes downstream of them.

PMID:8124727 SUPPORT Human Clinical

"Peripheral CD4+ T cells from the zap-70-/- patients exhibit markedly reduced tyrosine phosphorylation, fail to produce interleukin-2, and do not proliferate in response to T cell receptor stimulation by mitogens or antigens."

The direct measurement of the propagation failure in patient cells.

Block of CD8 Single-Positive Thymocyte Selection

Double-positive thymocytes accumulate normally in the cortex, but only CD4 single-positive cells reach the medulla. The asymmetry has a two-part explanation, each part separately sourced: the CD4 and CD8 lineages are selected at different ZAP-70 signalling thresholds, CD4 being the lower of the two, and human thymocytes express enough of the paralogous kinase SYK to carry that lower threshold. The rescue is human-specific. Mouse thymocytes express far less SYK, which is why complete Zap70 loss arrests both lineages in the mouse and only the CD8 lineage in patients.

CD4-positive CD8-positive double-positive thymocyte CL:0000809

positive thymic T cell selection GO:0045059 ↓ DECREASED

thymus UBERON:0002370 thymic cortex UBERON:0002123

Animal models

Zap70-null mouse Mouse partially recapitulates Reproduces the thymic selection block and its dependence on ZAP-70, but not its lineage selectivity.

Downstream

Peripheral CD8 T Cell Lymphopenia The peripheral CD8 compartment is filled by thymic export, so a selection block empties it.

Show evidence (4 references)

PMID:8124727 SUPPORT Human Clinical

"The thymi of zap-70-/- patients show the presence of CD4+CD8+ cells in the cortex; however, only CD4, not CD8, single-positive cells are present in the medulla."

Direct histological demonstration of the lineage-selective block in patient thymus.

PMID:41080547 SUPPORT Other

"Importantly, ZAP70 plays a central role in the positive selection of CD8+ thymocytes, whereas CD4+ T-cell development is relatively spared because of compensation by the related kinase Syk, which is more highly expressed in human thymocytes than in murine thymocytes (15)."

Supplies the SYK-compensation half of the explanation for why the block spares the CD4 lineage in humans. This is a background statement in a clinical cohort paper, attributed to its own reference, hence OTHER.

PMID:20332428 SUPPORT Model Organism

"This temporal gradient in the amount of Zap70 protein enabled the selection of CD4(+) and CD8(+) repertoires in separate temporal windows and at different TCR signaling thresholds, thereby facilitating discrimination of distinct positive selection signals in these lineages."

Supplies the other half, which the compensation claim depends on and which is otherwise asserted without a source: the two lineages are selected at different ZAP-70 signalling thresholds. Demonstrated in an inducible mouse system, so the threshold itself is a model result even though the SYK abundance that exploits it is a human observation.

+ 1 more reference

Peripheral CD8 T Cell Lymphopenia

The signature laboratory finding: profoundly reduced or absent circulating CD8 T cells against a normal or elevated total lymphocyte count, with normal B and NK numbers. It is present in essentially every patient, and it is the finding that should trigger ZAP70 sequencing. Rare exceptions with near-normal CD8 counts and impaired function are reported, so a normal count does not exclude the diagnosis when function is abnormal.

CD8-positive, alpha-beta T cell CL:0000625

Animal models

Zap70-null mouse Mouse fails to recapitulate The model does not reproduce the selective peripheral CD8 deficit, because it has no mature peripheral T cells of either lineage.

Downstream

Impaired Cellular Immunity Against Opportunistic Pathogens

Impaired Cytotoxic Surveillance of Virus-Infected Cells

Decreased total CD8+ T cell count

Show evidence (3 references)

PMID:32431715 SUPPORT Human Clinical

"Patients with ZAP-70 deficiency often present with normal to elevated numbers of circulating lymphocytes, including B cells, CD3+, and CD4+ T cells, but an absence of CD8+ T cells in the peripheral blood."

Describes the full immunophenotype, including the preserved compartments that make the CD8 deficit conspicuous.

PMID:41080547 SUPPORT Human Clinical

"Eleven of thirteen patients (84.6%) exhibited profound CD8+ T-cell lymphopenias and two had near-normal CD8+ T-cell counts with impaired T-cell function."

Quantifies the finding in a single-centre series and records the near-normal-count exception.

PMID:26187144 SUPPORT Human Clinical

"In contrast to CD4 T cells, the majority of the few CD8 T cells showed expression of the ZAP70-related tyrosine kinase SYK that correlated with residual TCR signaling including calcium flux and degranulation."

Shows that the small surviving CD8 population is enriched for SYK expression, which correlates with the residual TCR signalling those cells retain. The paper measures signalling rather than survival, so it does not by itself explain why those cells were selected.

Functional Anergy of Peripheral CD4 T Cells

CD4 T cells are present in normal or elevated numbers and are functionally inert: they fail to flux calcium, make interleukin-2, or proliferate in response to receptor engagement or mitogen. This is the half of the disease a cell count misses, and it is why the mitogen proliferation assay is a first-line rather than a confirmatory test.

CD4-positive, alpha-beta T cell CL:0000624

T cell activation GO:0042110 ↓ DECREASED T cell proliferation GO:0042098 ↓ DECREASED

Downstream

Impaired Cellular Immunity Against Opportunistic Pathogens

Defective T-Dependent Antibody Responses B cells are numerically normal here, so the humoral defect is a failure of T-cell help rather than a B-cell-intrinsic one.

Impaired T-cell proliferative response to mitogens

Increased circulating IgE concentration

Show evidence (1 reference)

PMID:8124727 SUPPORT Human Clinical

"Peripheral CD4+ T cells from the zap-70-/- patients exhibit markedly reduced tyrosine phosphorylation, fail to produce interleukin-2, and do not proliferate in response to T cell receptor stimulation by mitogens or antigens."

Documents the anergic behaviour of the peripheral CD4 compartment directly.

Attenuated Residual TCR Signaling

A distinct state from the complete propagation failure above, and the two should not be conflated: hypomorphic and docking-defective alleles leave the cascade running weakly rather than not at all. That distinction is what makes the tolerance branch possible, because a thymocyte receiving no signal is not selected whereas one receiving a weak signal can be selected wrongly. This node is therefore reached only from the subset of alleles that retain residual function, which is why allele class and clinical presentation are related even though the pooled cohort finds no formal correlation.

Genetic context variant_origin: GERMLINE functional_impact_category: PARTIAL_LOSS_OF_FUNCTION

T cell receptor signaling pathway GO:0050852 ↓ DECREASED

Downstream

Impaired Negative Selection and Thymic Regulatory T Cell Output Negative selection and thymic regulatory T-cell development read the same signal strength that positive selection does, so a weakened cascade degrades both.

Show evidence (1 reference)

PMID:37313400 SUPPORT Human Clinical

"Deleterious mutations in the SH2-C domain result in attenuated ZAP-70 function and clinical manifestations of immunodeficiency."

Establishes attenuated rather than abolished function as a distinct human allele class.

Impaired Negative Selection and Thymic Regulatory T Cell Output

Autoreactive thymocytes that a normal signal would delete survive selection, in a thymus simultaneously producing too few regulatory T cells to contain them afterwards. Both halves are thymic events, which is why this node is scoped to the thymus rather than to tolerance in general. The human evidence is an association between residual-function alleles and the dysregulation-predominant presentation; the mechanistic dissection is in mouse hypomorphs.

regulatory T cell CL:0000815

negative thymic T cell selection GO:0045060 ↓ DECREASED

thymus UBERON:0002370

Animal models

Zap70 YYAA knock-in mouse Mouse recapitulates Reproduces the tolerance failure that attenuated ZAP-70 signalling produces, including the regulatory T-cell deficit.

Downstream

Autoimmunity and Immune Dysregulation Autoreactive clones that survive selection, in a compartment with too few regulatory T cells to restrain them, is the standard route from tolerance failure to autoimmune disease.

Show evidence (2 references)

PMID:19841086 SUPPORT Model Organism

"YYAA mice, like SKG mice, develop rheumatoid factor antibodies, but fail to develop autoimmune arthritis."

Shows that attenuated ZAP-70 signalling produces autoantibody reactivity, and separates that from overt autoimmune disease, which needs more.

PMID:37313400 SUPPORT INDIRECT Human Clinical

"Deleterious mutations in the SH2-C domain result in attenuated ZAP-70 function and clinical manifestations of immunodeficiency."

Establishes the attenuated-function allele class in humans, which is the genotype associated with the dysregulation-predominant presentation; the link to tolerance loss itself is an inference from that association.

Impaired Cellular Immunity Against Opportunistic Pathogens

The combined loss of cytotoxic CD8 cells and functional CD4 help leaves patients open to the pathogens that cellular immunity normally handles: Pneumocystis jirovecii, Candida, CMV, varicella, and — where BCG is given before diagnosis — disseminated BCG disease.

Downstream

Recurrent respiratory infections

Pneumocystis jirovecii pneumonia

Pneumonia

BCGosis

Failure to thrive

Chronic diarrhea

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"ZAP-70 deficiency presents with a history of recurrent opportunistic infections, although, Pneumocystis jirovecii pneumonia and Cytomegalovirus (CMV) pneumonitis are less common (10)."

Records the opportunistic-infection pattern and, usefully, that the two classic SCID opportunists are less prominent here than the label would suggest.

PMID:26187144 SUPPORT Human Clinical

"The patients presented as infant-onset CID with severe infections caused by varicella zoster virus and live vaccines."

Documents live-vaccine and herpesvirus disease as presenting infections, which is what the cellular defect predicts.

Defective T-Dependent Antibody Responses

B cells are present in normal numbers and serum IgM and IgA are usually normal, but specific antibody responses to protein and polysaccharide antigens fail in a majority of patients, and IgG is normal or reduced. The humoral defect is therefore functional rather than quantitative, which is why immunoglobulin replacement is offered even to patients whose total IgG looks acceptable.

Downstream

Impaired specific antibody response

Decreased circulating immunoglobulin concentration

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"All patients have normal or reduced serum immunoglobulin (Ig) G, while IgM and IgA levels are often normal (15)."

Records the immunoglobulin pattern that makes the defect functional rather than a global hypogammaglobulinaemia.

Impaired Cytotoxic Surveillance of Virus-Infected Cells

Without a cytotoxic CD8 compartment, EBV-infected B cells are not cleared, and a minority of patients develop EBV-driven lymphoproliferation or lymphoma. This is a downstream branch of the CD8 deficit rather than an independent tumour-suppressor lesion.

CD8-positive, alpha-beta cytotoxic T cell CL:0000794

Downstream

Neoplasm

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Three patients (8.1%) developed malignant diseases (Table 2) including EBV-associated diffuse large B-cell lymphoma, non-EBV-associated large B cell lymphoma, and non-Hodgkin lymphoma."

Supports the EBV attribution this node makes and simultaneously records that not every lymphoma in the cohort is EBV-driven, which is why the node is scoped to a subset.

Autoimmunity and Immune Dysregulation

Roughly a fifth of reported patients have autoimmune or dysregulatory disease — cytopenias, colitis and enteropathy, nephritis, skin involvement — and this arm can dominate the presentation in patients whose alleles leave residual function. It coexists with, rather than replaces, the infectious susceptibility.

Downstream

Autoimmunity

Eczematoid dermatitis Non-infectious cutaneous disease in this disorder is part of the dysregulation arm rather than an infectious complication; skin infiltration by dysfunctional CD4 T cells is the described route.

Lymphadenopathy

Hepatomegaly

Splenomegaly

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"ZAP-70 deficient patients have been reported in the literature with a broad spectrum of clinical manifestations including recurrent respiratory infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of..."

Quantifies autoimmunity, lymphoproliferation and enteropathy in the pooled cohort.

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Pathograph

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Phenotypes

18

Blood 5

Decreased total CD8+ T cell count VERY_FREQUENT HP:5210426

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"The predominant immunologic phenotype was low CD8+ T cell counts (97.9%)."

Gives the frequency of the finding across 49 pooled patients.

Increased total lymphocyte count HP:0100827

Show evidence (1 reference)

PMID:32431715 SUPPORT BACKGROUND Human Clinical

"Patients with ZAP-70 deficiency often present with normal to elevated numbers of circulating lymphocytes, including B cells, CD3+, and CD4+ T cells, but an absence of CD8+ T cells in the peripheral blood."

States that total lymphocyte counts run normal to elevated despite the absent CD8 compartment.

Impaired T-cell proliferative response to mitogens VERY_FREQUENT Decreased mitogen-induced T-cell proliferation HP:0031381

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Immunologic profiling showed defective antibody production (57%) and decreased lymphocyte responses to mitogenic stimuli such as phytohemagglutinin (PHA) (95%)."

Gives the frequency of the mitogen-proliferation defect in the pooled cohort.

Decreased circulating immunoglobulin concentration OCCASIONAL Decreased circulating IgG concentration HP:0004315

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"All patients have normal or reduced serum immunoglobulin (Ig) G, while IgM and IgA levels are often normal (15)."

States the immunoglobulin pattern, including that reduction is confined to IgG.

PMID:32431715 SUPPORT Human Clinical

"serum immunoglobulin levels were mostly reported to be normal, but some cases showed decreased levels of IgG (n = 12 out of 44, 27.3%), IgA (n = 6 out of 45, 13.3%), and IgM (n = 5 out of 45, 11.1%)."

Quantifies how often each isotype is actually low, which is the basis for the OCCASIONAL frequency and for confining the claim to IgG.

Increased circulating IgE concentration HP:0003212

Show evidence (2 references)

PMID:26783323 SUPPORT Human Clinical

"Some ZAP-70 deficient patients also have skin infiltration with dysfunctional CD4 T cells, elevated serum IgE, and eosinophilia"

States the association of raised IgE and eosinophilia with the cutaneous manifestations in this disorder.

PMID:20301777 SUPPORT INDIRECT Human Clinical

"later-onset presentations with dysregulated immunity such as autoimmunity, atopy, and even malignancy"

GeneReviews names atopy among the later-onset manifestations; the raised IgE is the laboratory correlate of that, which is the inference step.

Cardiovascular 2

Lymphadenopathy FREQUENT HP:0002716

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"ZAP-70 deficient patients have been reported in the literature with a broad spectrum of clinical manifestations including recurrent respiratory infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of..."

Gives the frequency of lymphoproliferation in the pooled cohort.

Splenomegaly OCCASIONAL HP:0001744

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Splenomegaly (%) | 36 | 5 (13.9)"

The cohort table row giving the splenomegaly frequency.

Digestive 2

Chronic diarrhea FREQUENT HP:0002028

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Pneumonia (n = 30, 71.4%), diarrhea (n = 19, 50%), and upper respiratory tract infections"

Gives the diarrhoea frequency directly, rather than borrowing the separate enteropathy figure.

Hepatomegaly OCCASIONAL HP:0002240

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Hepatomegaly (%) | 36 | 7 (19.4)"

The cohort table row giving the hepatomegaly frequency.

Immune 7

Impaired specific antibody response FREQUENT HP:0012475

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Immunologic profiling showed defective antibody production (57%) and decreased lymphocyte responses to mitogenic stimuli such as phytohemagglutinin (PHA) (95%)."

Reports defective antibody production in 57% of pooled patients.

Recurrent respiratory infections VERY_FREQUENT HP:0002205

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"ZAP-70 deficient patients have been reported in the literature with a broad spectrum of clinical manifestations including recurrent respiratory infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of..."

Gives the frequency of recurrent respiratory infection in the pooled cohort.

PMID:41080547 SUPPORT Human Clinical

"The most frequent initial presentations were recurrent respiratory infections and cutaneous manifestations."

Independently confirms respiratory infection as the leading presentation in a separate cohort.

Eczematoid dermatitis FREQUENT HP:0000964

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"ZAP-70 deficient patients have been reported in the literature with a broad spectrum of clinical manifestations including recurrent respiratory infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of..."

Gives the frequency of cutaneous involvement in the pooled cohort.

Autoimmunity OCCASIONAL HP:0002960

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Autoimmunity or manifestations of immune dysregulation such as ulcerative colitis and blood cytopenias (11), pustular skin lesions and subcutaneous nodules (12), lymphoma (13), Omenn syndrome, and hemophagocytic lymphohistiocytosis (HLH) (14) have also been reported."

Enumerates the autoimmune and dysregulatory manifestations reported in this disorder.

Pneumocystis jirovecii pneumonia HP:0020102

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"ZAP-70 deficiency presents with a history of recurrent opportunistic infections, although, Pneumocystis jirovecii pneumonia and Cytomegalovirus (CMV) pneumonitis are less common (10)."

Records Pneumocystis pneumonia as part of the opportunistic spectrum while noting it is less common than in classical SCID.

PMID:37313400 SUPPORT Human Clinical

"Genetic characterization of an infant who presented with pneumocystis pneumonia, mycobacterial infection, and an absence of CD8 T cells revealed a novel homozygous mutation in the C-terminal SH2 domain (SH2-C) of the ZAP70 gene (c.C343T, p.R170C)."

A patient-level example of Pneumocystis pneumonia as the presenting infection.

Pneumonia FREQUENT HP:0002090

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Pneumonia (n = 30, 71.4%), diarrhea (n = 19, 50%), and upper respiratory tract infections"

Gives the pneumonia frequency in the pooled cohort.

BCGosis OCCASIONAL HP:0020087

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"bacteria (n = 14, 36.8%) (mainly BCG [18.4%]), fungal pathogens (n = 14, 38.9%) [predominantly Candida albicans (28.9%)]"

Gives the BCG-disease frequency alongside the other reported pathogen classes in the pooled cohort.

Growth 1

Failure to thrive FREQUENT HP:0001508

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Enteropathy (18.4%) and failure to thrive (43.6%) were other reported manifestations."

Gives the disease-specific frequency in the pooled cohort, rather than the generic SCID presenting syndrome.

Neoplasm 1

Neoplasm OCCASIONAL HP:0002664

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"ZAP-70 deficient patients have been reported in the literature with a broad spectrum of clinical manifestations including recurrent respiratory infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of..."

Gives the malignancy frequency in the pooled cohort.

PMID:37101133 SUPPORT Human Clinical

"Case 1 presented with leaky severe combined immunodeficiency with low to the absence of CD8 + T cells, while case 2 suffered from a recurrent respiratory infection and had a past medical history of non-EBV-associated Hodgkin's lymphoma."

A patient-level lymphoma report, and a reminder that not every lymphoma in this disorder is EBV-driven.

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Genetic Associations

2

ZAP70

Gene: ZAP70 hgnc:12858 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (5 references)

PMID:8202713 SUPPORT Human Clinical

"Here, three siblings are described with an autosomal recessive form of severe combined immunodeficiency disease (SCID) in which ZAP-70, a non-Src PTK, is absent as a result of mutations in the ZAP-70 gene."

The founding gene-disease report, establishing biallelic ZAP70 mutation as the cause.

PMID:32431715 SUPPORT Human Clinical

"Mutations of the ZAP70 gene were located throughout the gene, and there was no mutational hotspot. However, most of the mutations were located in the kinase domain."

Describes the distribution of disease alleles across the gene.

PMID:32431715 SUPPORT Human Clinical

"38 (77.5%) patients (in 33 families) had homozygous mutations, 10 (16.3%) patients (in 8 families) had compound heterozygous ZAP70 mutations"

Gives the homozygous-versus-compound-heterozygous split quoted in the inheritance section and in these notes.

+ 2 more references

SYK

Gene: SYK hgnc:11491 relationship_type: MODIFIER variant_origin: GERMLINE

Show evidence (2 references)

PMID:26187144 SUPPORT Human Clinical

"In contrast to CD4 T cells, the majority of the few CD8 T cells showed expression of the ZAP70-related tyrosine kinase SYK that correlated with residual TCR signaling including calcium flux and degranulation."

Shows SYK expression correlating with preserved signalling in patient CD8 T cells, which is the modifier claim.

PMID:9324357 SUPPORT Model Organism

"Hence, ZAP-70 and Syk can play overlapping functions and exhibit similar regulatory mechanisms in mediating alphabeta T cell development."

Demonstrates experimentally that SYK can carry ZAP-70's developmental function, which is the mechanism the human modifier claim rests on.

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Medical Actions

8

Allogeneic Hematopoietic Stem Cell Transplantation

Action: allogeneic haematopoietic stem cell transplantation Ontology label: Allogeneic Hematopoietic Stem Cell Transplantation NCIT:C46089

Platform: Cell therapy

The only curative treatment, and effective in the reported series. Those series use matched sibling, matched unrelated, haploidentical and cord blood donors, with and without conditioning; myeloablative conditioning gives more durable reconstitution, while reduced-intensity or unconditioned transplant remains a life-saving option for a critically ill infant. Long-term survival in published cohorts is good and both the infectious and the autoimmune manifestations resolve.

Mechanism Target:

ZAP70 Loss of Kinase Function — Replaces the patient's haematopoietic compartment with donor cells that carry functional ZAP70, so the lesion is bypassed at its origin rather than compensated downstream.

Show evidence (3 references)

PMID:20301777 SUPPORT Other

"Targeted therapy: The only curative therapy for ZAP70 deficiency is allogeneic HSCT."

States that transplantation is the sole curative option.

PMID:27438785 SUPPORT Human Clinical

"At a median of 13.5-year post-HSCT, 8/8 (100 %) patients are alive."

Long-term survival data from a single-centre transplanted cohort.

PMID:41080547 SUPPORT Human Clinical

"HSCT remains the only curative treatment for ZAP70 deficiency. Myeloablative conditioning regimens appear to promote more robust and durable immune reconstitution."

Confirms curative status and records the conditioning-intensity finding.

Immunoglobulin Replacement Therapy

Action: immunoglobulin replacement therapy Ontology label: Immunoglobulin Therapy NCIT:C62710

Platform: Protein replacement

Given for the functional antibody defect, which is present even in patients whose total IgG is normal. Several patients in the long-term transplant series were able to stop it once specific antibody responses returned after engraftment.

Mechanism Target:

Defective T-Dependent Antibody Responses — Supplies the specific antibody the patient cannot generate; it replaces the product of the failed response rather than repairing the response.

Show evidence (2 references)

PMID:20301777 SUPPORT Other

"Supportive care: IgG replacement therapy; antibacterial, antifungal, antiviral, and Pneumocystis jiroveci prophylaxis to control and reduce the occurrence of infections."

Names immunoglobulin replacement as standard supportive care.

PMID:27438785 SUPPORT Human Clinical

"In total, seven have discontinued immunoglobulin replacement."

Records that replacement can be withdrawn after successful transplantation.

Antimicrobial Prophylaxis

Action: anti-infective prophylaxis Ontology label: Supportive Care NCIT:C15747

Platform: Small molecule

Antibacterial, antifungal, antiviral and Pneumocystis prophylaxis while awaiting transplantation, and for patients in whom transplantation is not an option. GeneReviews is explicit that conservative management on prophylaxis and immunoglobulin alone leaves patients at high risk, so it is a holding measure rather than a definitive one.

Mechanism Target:

Impaired Cellular Immunity Against Opportunistic Pathogens — Suppresses the organisms the absent cellular immunity would otherwise control; it substitutes for the missing defence rather than restoring it.

Show evidence (1 reference)

PMID:20301777 SUPPORT Human Clinical

"Although more conservative approaches that rely on immunoglobulin (Ig) G replacement therapy and antimicrobial prophylaxis have been utilized, especially when HSCT is not an option, individuals on these therapies remain at high risk for severe infections as well as autoimmunity and..."

States both the role of prophylaxis and its insufficiency as definitive management.

Infection-Risk Avoidance and Blood Product Precautions

Action: infection-risk avoidance and blood product precautions Ontology label: Supportive Care NCIT:C15747

Platform: Behavioral / lifestyle

The GeneReviews "agents and circumstances to avoid" list. These are consequential rather than merely precautionary in this disorder. Live viral vaccines are contraindicated for the infant and for household contacts; blood products must be irradiated, leukoreduced and CMV-safe to avoid transfusion-associated graft-versus-host disease; breastfeeding is withheld until maternal CMV status is known; and construction or soil-disturbance environments are avoided for fungal-exposure risk. Disseminated BCG disease in infants vaccinated before diagnosis is a recurring real-world harm in BCG-endemic settings.

Mechanism Target:

Impaired Cellular Immunity Against Opportunistic Pathogens — Removes the exposures that a patient without cellular immunity cannot survive, particularly live vaccine organisms and viable donor lymphocytes.

Show evidence (3 references)

PMID:20301777 SUPPORT Other

"live viral vaccines for the infant and household contacts; transfusion of non-irradiated blood products; and areas of construction or soil manipulation, as they increase the risk for fungal exposure."

The GeneReviews list of exposures to avoid, quoted from the agents/circumstances section.

PMID:20301777 SUPPORT Other

"breastfeeding and breast milk until maternal CMV status is established by CMV serologies"

The breastfeeding item of the same list, quoted separately because the description states it as its own precaution.

PMID:26187144 SUPPORT Human Clinical

"The patients presented as infant-onset CID with severe infections caused by varicella zoster virus and live vaccines."

A patient-level demonstration of live-vaccine harm, which is why the avoidance is not merely precautionary.

Genetic Counseling

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Platform: Behavioral / lifestyle

Autosomal recessive counselling with a 25% recurrence risk per pregnancy, carrier testing for at-risk relatives, and prenatal or preimplantation testing once the familial variants are known. Particularly consequential in the Mennonite founder communities and in consanguineous families, where testing at-risk siblings allows diagnosis before the first severe infection.

Show evidence (2 references)

PMID:20301777 SUPPORT Other

"Molecular genetic testing for the familial ZAP70 pathogenic variants is strongly recommended for all at-risk sibs to allow earliest possible diagnosis and treatment."

States the at-risk-relative testing recommendation and its rationale.

PMID:20301777 SUPPORT Other

"each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier"

The recurrence-risk figures the description quotes.

Gene Therapy

Action: gene therapy Ontology label: Gene Therapy NCIT:C15238

Platform: Gene therapy

Investigational only, with no clinical application in this disease. The preclinical work is unusual in targeting the thymus directly rather than the stem cell compartment: intrathymic AAV delivery of ZAP70 into Zap70-null mice restores thymic architecture and produces gene-corrected peripheral T cells that persist for months, and intrathymic injection of wild-type progenitors reconstitutes those mice faster and with fewer cells than intravenous delivery. Both remain mouse results.

Mechanism Target:

Block of CD8 Single-Positive Thymocyte Selection — Restores kinase function in thymocytes themselves, which is where the selection block sits, rather than in the upstream stem cell.

Show evidence (2 references)

PMID:31513879 SUPPORT Model Organism

"Intrathymic injection of an AAV8-ZAP-70 vector into ZAP-70-/- mice resulted in a rapid thymocyte differentiation associated with the development of a thymic medulla."

The preclinical proof of concept for intrathymic gene correction in this disorder.

PMID:16174749 SUPPORT Model Organism

"Upon intrathymic HSC injection, there was a more rapid T cell differentiation, with mature thymocytes detected by 4 weeks after transplantation."

Supports the intrathymic delivery route in the same disease model.

Post-Transplant Surveillance

Action: post-transplant immune and organ surveillance Ontology label: Supportive Care NCIT:C15747

Platform: Behavioral / lifestyle

Close follow-up for the first year after transplantation and then every six to twelve months, tracking lineage-specific donor chimerism, growth, immune and lung function, and gastrointestinal and dermatological problems. Where conditioning chemotherapy was used, organ function and neurodevelopment are monitored long-term. Patients who have not been transplanted need periodic reassessment of immune function instead, because it can deteriorate.

Show evidence (1 reference)

PMID:20301777 SUPPORT Other

"Surveillance: After successful HSCT, evaluate individuals very closely for the first year and then every six to 12 months to monitor lineage-specific donor cell engraftment, growth, immune and lung function, and gastrointestinal and dermatologic issues."

The GeneReviews surveillance schedule this entry follows.

Corticosteroid Therapy

Action: corticosteroid therapy Ontology label: Pharmacotherapy NCIT:C15986

Platform: Small molecule

Recorded here for what the sources actually support, which is narrower than it first appears. In the pooled cohort steroids were given around transplantation — as prophylaxis or to control transplant complications — in about a third of transplanted patients, with five clinically responsive; in the single-centre series corticosteroids were first-line for graft-versus-host disease. Neither source documents steroids as a quantified treatment for the disorder's own autoimmune arm, so no `target_mechanisms` link to the dysregulation node is asserted here. The deep-research report for this entry described this same 32% figure as corticosteroid use for autoimmune manifestations, which misreads the sentence.

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"Steroids and intravenous immunoglobulin (IVIG) have been tried as a prophylactic or to control adverse side effects of transplantation in 8 (32%) and 18 (36.7%) patients, respectively. Among the patients receiving steroids, five were clinically responsive (35)."

Records both the indication (peri-transplant, not disease autoimmunity) and the response rate.

PMID:41080547 SUPPORT Human Clinical

"All patients received corticosteroids as first-line therapy, and additional immunomodulatory treatments were used as required."

The graft-versus-host disease indication in the single-centre series.

🌍

Environmental Factors

1

BCG vaccination before diagnosis

Left unbound after searching. ECTO has no term for BCG or Mycobacterium bovis vaccine exposure. The generic `ECTO:2000129` (exposure to vaccination) exists in OLS but is absent from the ECTO build this repository validates against, so it fails both the ontology lookup and the `ExposureTerm` dynamic enum; the only other vaccination-adjacent hit is an Orthopoxvirus vaccinia term, which names a different vaccine. Binding a term that does not resolve is worse than binding none, so the concept stays in `preferred_term` until ECTO carries something that validates.

Live attenuated Mycobacterium bovis BCG, given at birth in countries with universal BCG programmes, before the immunodeficiency is known. In a child with no functional cellular immunity the vaccine strain is not contained and disseminates. It is the commonest bacterial exposure in the pooled cohort and the concrete reason live vaccines are withheld until immune reconstitution is confirmed. This is an iatrogenic precipitant, not a cause of the disease, and the edge is drawn accordingly. It triggers the BCGosis phenotype; it does not cause the impaired cellular immunity that permits it, which would invert the direction of the mechanism.

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"bacteria (n = 14, 36.8%) (mainly BCG [18.4%]), fungal pathogens (n = 14, 38.9%) [predominantly Candida albicans (28.9%)]"

Establishes BCG exposure as a documented and frequent event in this patient population.

PMID:20301777 SUPPORT Other

"delaying immunizations until immune reconstitution is confirmed"

The management counterpart. This is the general immunization statement rather than the live-viral-vaccine item from the agents-to-avoid list: BCG is a live attenuated bacterial vaccine, so the viral-specific sentence would not cover it.

Mechanism Target:

TRIGGERS BCGosis — Administration of the live vaccine strain is the exposure that produces disseminated BCG disease in an infant who cannot contain it.

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"bacteria (n = 14, 36.8%) (mainly BCG [18.4%]), fungal pathogens (n = 14, 38.9%) [predominantly Candida albicans (28.9%)]"

Records BCG as the predominant bacterial exposure in the pooled cohort, which is the exposure this edge draws.

🔬

Diagnosis

3

Lymphocyte subset flow cytometry

The first-line test and the one that makes the diagnosis suggestible. Absent or profoundly reduced CD8 T cells against a normal or elevated total lymphocyte count, with normal CD19 B cells and normal NK cells, is a pattern no classical SCID produces. Note the exception: a small number of patients have near-normal CD8 counts with impaired function, so a normal count in a child with a compatible clinical picture does not close the question.

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"Newborns with consanguineous parents, positive family history of CID, and low CD8+ T cell counts should be considered for ZAP-70 deficiency screening, since early diagnosis and treatment with HSCT can lead to a more favorable outcome."

States the CD8-count-based diagnostic trigger recommended by the largest review.

PMID:41080547 SUPPORT Human Clinical

"Eleven of thirteen patients (84.6%) exhibited profound CD8+ T-cell lymphopenias and two had near-normal CD8+ T-cell counts with impaired T-cell function."

Documents the near-normal-count exception that limits the test's negative predictive value.

Molecular genetic testing of ZAP70

Confirmatory. Single-gene sequencing is appropriate when the immunophenotype is characteristic; broader combined-immunodeficiency panels or exome sequencing are used when the presentation is atypical, which in practice means autoimmunity-predominant.

Show evidence (1 reference)

PMID:20301777 SUPPORT Other

"The diagnosis of ZAP70 deficiency is established in a proband with suggestive findings and biallelic pathogenic variants in ZAP70 identified by molecular genetic testing."

States the diagnostic criterion.

Newborn TREC screening

Recorded for its limitation rather than its yield. TREC-based newborn SCID screening can miss ZAP70 deficiency, because thymic output continues through the intact CD4 lineage even while CD8 selection fails, so TRECs can sit above the screening cutoff in an affected infant. Do not treat a normal newborn screen as excluding the diagnosis. This is a recognised limitation rather than an incidental miss: it has been noted prospectively across more than a decade of US screening, in a population that includes the Mennonite founder community where most reported patients come from.

Show evidence (3 references)

PMID:32431715 SUPPORT Human Clinical

"ZAP-70 has not been frequently picked up during the >10 year screening experience in the United States (49), despite a significant Mennonite population and the large number of reported ZAP-70 patients."

States the programme-level failure of TREC screening to detect this disorder, which is stronger than any single-patient observation.

PMID:37313400 SUPPORT Human Clinical

"While infants with IEI due to mutations in ZAP70 might not present with TREC numbers that are below the threshold for diagnosis"

States the mechanism of the miss: TRECs can sit above the screening threshold in an affected infant.

PMID:26187144 SUPPORT Human Clinical

"Retrospective TCR excision circle newborn screening was normal in both patients."

Two genetically confirmed patients whose retrospective TREC screen was normal, which is the screening blind spot stated as an observation.

📈

Progression

4

Infantile presentation

Almost all patients present within the first year. In the pooled review the median age at presentation was 4 months, the median age at diagnosis 10.4 months, and the median diagnostic delay 5 months — the delay driven largely by the immunophenotype being read first as classical SCID. A single-centre series reports an earlier median symptom onset of 1 month; the two cohorts are reported separately here because their figures are not interchangeable.

Show evidence (3 references)

PMID:32431715 SUPPORT Human Clinical

"Our review illustrated that 97.3% of the patients presented within 12 months of age with a median age of 4 months."

Gives the pooled cohort's own age at presentation, which is the figure the diagnostic delay below is measured against.

PMID:32431715 SUPPORT Human Clinical

"The median (IQR) age of diagnosis was 10.4 (7.0-18.7) months with a median (IQR) diagnostic delay of 5 (1.2-11.5) months."

Gives the diagnostic age and delay from the same cohort as the presentation age.

PMID:41080547 SUPPORT Human Clinical

"Thirteen patients with a median age at symptom onset of 1 month were identified."

The separate single-centre onset figure, reported alongside rather than merged with the pooled one.

Untreated course

Without transplantation, infants presenting with severe infection in the first year of life generally do not survive their second.

Show evidence (1 reference)

PMID:20301777 SUPPORT Human Clinical

"Children who present in their first year of life with severe infections are expected to have a declining quality of life and usually do not survive past their second year without allogeneic hematopoietic stem cell transplantation (HSCT)."

States the untreated natural history directly.

Outcome by transplant status

Transplantation is the dominant prognostic variable and the effect is large: mortality in the pooled cohort was significantly lower in transplanted patients. Age at transplant matters too — post-transplant complications in that cohort were concentrated in patients transplanted after six months.

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"As presented in the plot, the mortality rate was significantly lower in patients who underwent HSCT (p < 0.001)."

The survival comparison between transplanted and non-transplanted patients.

PMID:32431715 SUPPORT Human Clinical

"Eight out of twelve patients (66%) with the above mentioned complications post-HSCT were older than 6 months at the time of transplantation."

Supports age at transplant as a prognostic factor within the transplanted group.

Post-transplant

After successful transplantation, infectious and autoimmune manifestations resolve and mitogen responses normalise; long-term survival in reported series is good.

Show evidence (1 reference)

PMID:27438785 SUPPORT Human Clinical

"Infectious complications in 5/5 and autoimmune thrombocytopenia in one patient resolved post-HSCT."

Records resolution of both the infectious and the autoimmune arms after transplantation.

📊

Prevalence

1

Worldwide, published literature

Cases In Literature Ultra Rare

No population-based prevalence or incidence estimate exists. The largest systematic review pooled 49 unique patients from 33 articles; a 2025 single-centre series adds 13 more. Ancestry is heavily skewed in the published series by the Mennonite founder allele and by consanguinity, so these counts describe the literature rather than the disease's distribution.

Show evidence (2 references)

PMID:32431715 SUPPORT Human Clinical

"A total of 49 ZAP-70 deficient patients were identified from 33 articles."

Gives the size of the pooled published cohort.

PMID:32431715 SUPPORT Human Clinical

"Most of the patients were of Mennonite (30.6%) descent, followed by Turkish (22.4%), Japanese and Caucasian ethnicity (each 6.1%)."

Records the ancestry skew that makes these counts a description of the literature rather than of population distribution.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from ZAP70 Deficiency:

Classical SCID (IL2RG, JAK3, IL7R)

Overlapping Features The initial misdiagnosis in most cases, because both present as an infant with severe infection. The discriminator is the lymphocyte subset panel rather than the clinical picture: classical SCID has profound total T-cell lymphopenia, while ZAP70 deficiency has normal or elevated total lymphocytes and CD4 cells with an isolated CD8 deficit. The NK compartment separates the SCID genes from one another rather than from this disorder, and is worth stating precisely: IL2RG and JAK3 defects are T-B+NK-, because the common gamma chain is required for IL-15 signalling and therefore for NK development, whereas IL7R defects are T-B+NK+. ZAP70 deficiency is T+B+NK+ and is not a SCID by cell count at all.

Show evidence (1 reference)

PMID:32431715 SUPPORT Human Clinical

"Patients with ZAP-70 deficiency often present with normal to elevated numbers of circulating lymphocytes, including B cells, CD3+, and CD4+ T cells, but an absence of CD8+ T cells in the peripheral blood."

States the subset pattern that separates this disorder from classical SCID at the bench.

ZAP70 combined hypomorphic and activating variant syndrome

Overlapping Features A separate disease at the same locus, listed by IUIS under its own OMIM number (617006), and worth keeping separate rather than folding in as a subtype. Compound heterozygosity for a hypomorphic SH2-domain allele and an activating allele that disrupts autoinhibition produces early-onset severe autoimmunity — bullous pemphigoid, colitis, nephrotic syndrome, a factor VIII autoantibody — rather than the CD8-lymphopenic immunodeficiency. The mechanism is a hyperactive kinase, not an absent one, so the pathophysiology chain in this entry does not describe it.

Show evidence (3 references)

PMID:26783323 SUPPORT Human Clinical

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

Establishes the two-allele mechanism that distinguishes this entity from loss-of-function ZAP70 deficiency.

PMID:35748970 SUPPORT Other

"ZAP-70 combined hypomorphic and activating mutations ZAP70 AR (LOF/GOF) 617006"

The IUIS row for this entity, carrying its own OMIM number and its own LOF/GOF mechanism annotation. This is what makes keeping it out of has_subtypes a sourced decision rather than a curator preference.

PMID:26783323 SUPPORT Human Clinical

"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."

Describes the autoimmune-dominant presentation that separates this entity clinically.

🐁

Animal Models

2

Zap70-null mouse

The standard null model. Thymocyte development arrests at the CD4+CD8+ double-positive stage, so neither lineage matures — a more complete block than patients show, and the reason this model is better read as a model of TCR signal-dependent selection than of the human disease's immunophenotype.

Species

Mouse

Genotype

Zap70 knockout (zap-70-/-)

Publication

PMID:9324357

Pathograph links

Block of CD8 Single-Positive Thymocyte Selection partially recapitulates fidelity: moderate observes: cellular Reproduces the thymic selection block and its dependence on ZAP-70, but not its lineage selectivity.

Limitations: The block extends to the CD4 lineage, which is spared in patients. Mouse thymocytes express much less SYK than human thymocytes, so the paralogue cannot carry the lower CD4 threshold; the model therefore reports a complete developmental arrest where the human disease produces a selective CD8 deficit with an intact, dysfunctional CD4 compartment.

Show evidence (1 reference)

PMID:9324357 SUPPORT Model Organism

"Thymocyte development in zap-70-/- mice is blocked at the CD4+CD8+ TCR(lo) stage."

States the model's developmental block, which is the phenotype it is cited for.

Peripheral CD8 T Cell Lymphopenia fails to recapitulate fidelity: low observes: organism The model does not reproduce the selective peripheral CD8 deficit, because it has no mature peripheral T cells of either lineage.

Limitations: The species difference is the point rather than an incidental caveat: insufficient Syk expression in mouse thymocytes converts a lineage-selective human deficit into a complete arrest. A study reading peripheral T-cell subsets off this model would misdescribe the human immunophenotype.

Show evidence (1 reference)

PMID:41080547 SUPPORT Other

"The absence of ZAP70 protein thus results in selective CD8+ T-cell deficiency with impaired signal transduction in CD4+ T-cells in humans, whereas in murine models, complete ZAP70 deficiency leads to an arrest in both CD4+ and CD8+ T-cell development because of insufficient Syk expression (17)."

States the divergence between the model and the human disease, and its mechanistic cause.

Show evidence (1 reference)

PMID:9324357 SUPPORT Model Organism

"To determine if Syk can play a role in thymocyte development, we generated zap-70-/- mice expressing a human syk cDNA."

Establishes the model and the SYK-complementation experiment performed in it.

Zap70 YYAA knock-in mouse

A hypomorphic knock-in in which the interdomain B tyrosines Y315 and Y319 are mutated to alanine, attenuating rather than abolishing signalling. Together with the spontaneous SKG strain it is the model for the tolerance arm of the disease: impaired positive and negative selection, markedly reduced thymic regulatory T cells, and autoantibody production.

Species

Mouse

Genotype

Zap70 Y315A/Y319A knock-in (YYAA)

Publication

PMID:19841086

Pathograph links

Impaired Negative Selection and Thymic Regulatory T Cell Output recapitulates fidelity: moderate observes: cellular Reproduces the tolerance failure that attenuated ZAP-70 signalling produces, including the regulatory T-cell deficit.

Limitations: Autoantibody reactivity does not progress to overt autoimmune disease in this strain, whereas the SKG strain on the same axis develops arthritis, so the model separates reactivity from disease rather than modelling the human autoimmune presentation end to end. The specific autoimmune manifestations differ from those reported in patients.

Show evidence (1 reference)

PMID:19841086 SUPPORT Model Organism

"Both YYAA and SKG mice have impaired T cell development and hyporesponsiveness to TCR stimulation, markedly reduced numbers of thymic T regulatory cells and defective positive and negative selection."

The phenotype this model is cited for: tolerance failure with a regulatory T-cell deficit.

Show evidence (1 reference)

PMID:19841086 SUPPORT Model Organism

"To address the importance of the scaffolding function, we generated a zap70 mutant mouse (YYAA mouse) with Y315 and Y319 both mutated to alanines."

Establishes the model's construction and allele, which is what makes it the hypomorphic counterpart to the null strain.

{ }

Source YAML

click to show

name: ZAP70 Deficiency
creation_date: "2026-09-09T01:45:00Z"
category: Mendelian
synonyms:
- ZAP-70 deficiency
- combined immunodeficiency due to ZAP70 deficiency
- ZAP70-related combined immunodeficiency
- selective T-cell defect
- selective CD8 lymphocyte deficiency
- immunodeficiency 48
- IMD48
description: >-
  ZAP70 deficiency is an autosomal recessive combined immunodeficiency caused by
  biallelic loss-of-function variants in ZAP70, the Syk-family cytoplasmic
  tyrosine kinase that couples the engaged T-cell receptor to its downstream
  signalling machinery. On TCR engagement, LCK phosphorylates the ITAMs of the
  CD3 and zeta chains; ZAP-70 docks on those phospho-ITAMs through its tandem SH2
  domains and, once activated, phosphorylates the adaptors LAT and SLP-76 that
  nucleate the rest of the cascade. Losing the kinase therefore leaves the
  receptor intact but uncoupled from everything downstream of it.

  What makes the disorder distinctive is that the disconnection is not uniform
  across the T-cell lineages, and the resulting laboratory picture is the
  diagnosis. CD8 single-positive thymocytes fail positive selection almost
  completely, so patients have profound CD8 lymphopenia; CD4 single-positive
  development proceeds largely intact, because the paralogous kinase SYK is
  expressed highly enough in human thymocytes to carry the lower signalling
  threshold that the CD4 lineage requires. The CD4 cells that emerge are present
  in normal or elevated numbers and are functionally dead to TCR stimulation.
  A normal or high lymphocyte count with normal B and NK cells and absent CD8 T
  cells matches no classical SCID, and the largest published review recommends
  screening for ZAP70 deficiency on that pattern. It is also a pattern standard
  TREC newborn screening can miss, because CD4 thymic output continues.

  Clinically it spans a wide range: infantile SCID-like disease with
  opportunistic infection at one end, and later-onset immune dysregulation with
  autoimmunity, atopy and lymphoma at the other. Untreated infants who present in
  the first year rarely survive past the second. Allogeneic haematopoietic stem
  cell transplantation is the only curative treatment and is highly effective.
disease_term:
  preferred_term: ZAP70 deficiency
  term:
    id: MONDO:0010023
    label: combined immunodeficiency due to ZAP70 deficiency
parents:
- Primary Immunodeficiency
- Combined Immunodeficiency
classifications:
  iuis_category:
    classification_value: combined immunodeficiency
    notes: >-
      IUIS 2022 phenotypic classification of inborn errors of immunity, Table 1
      (immunodeficiencies affecting cellular and humoral immunity). The table
      records ZAP-70 loss of function as autosomal recessive with low CD8 numbers
      and normal CD4 numbers of poor function, and normal B and NK compartments —
      the T+B+NK+ pattern that separates it from the T-B+NK+ and T-B-NK- SCIDs
      listed alongside it. IUIS carries the combined hypomorphic/activating
      ZAP70 entity (OMIM 617006) as a separate row; see differential_diagnoses.
    evidence:
    - reference: PMID:35748970
      reference_title: "Human Inborn Errors of Immunity: 2022 Update on the Classification from the International Union of Immunological Societies Expert Committee."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        ZAP-70 deficiency (ZAP70 LOF) ZAP70 AR 269840 Low CD8 number, normal CD4
        number but with poor function Normal Normal May have immune
        dysregulation, autoimmunity
      explanation: >-
        The IUIS classification row for ZAP70 loss of function, recording the
        recessive inheritance, the selective CD8 deficit with functionally poor
        CD4 cells, and the preserved B and NK compartments.
references:
- reference: PMID:20301777
  title: "ZAP70 Deficiency."
  tags:
  - GeneReviews
inheritance:
- name: Autosomal recessive inheritance
  description: >-
    Biallelic pathogenic ZAP70 variants are required; heterozygous parents are
    obligate carriers and are clinically well. Roughly three quarters of reported
    patients are homozygous rather than compound heterozygous, which reflects the
    high rate of consanguinity and the Old Order Mennonite founder allele in the
    published series rather than anything about the allele itself.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP70 deficiency is inherited in an autosomal recessive manner.
    explanation: >-
      GeneReviews states the mode of inheritance directly.
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Zeta-Chain Associated Protein Kinase 70 kDa (ZAP-70) deficiency is a rare
      combined immunodeficiency (CID) caused by recessive
      homozygous/compound heterozygous loss-of-function mutations in the ZAP70
      gene.
    explanation: >-
      Records that both homozygous and compound heterozygous biallelic states
      cause the disease.
pathophysiology:
- name: ZAP70 Loss of Kinase Function
  description: >-
    Biallelic ZAP70 variants remove the kinase from the T-cell receptor cascade.
    Most reported alleles abolish protein expression or catalytic activity and
    cluster in the kinase domain, but there is a second, mechanistically distinct
    class in the C-terminal SH2 domain: R170C and R192W sit in the arginine pocket
    that docks the kinase onto the phosphorylated TCR zeta chain, so they abolish
    recruitment rather than catalysis. Preserved protein expression is documented
    for R170C specifically; R192W was confirmed pathogenic in two siblings without
    its expression level being reported in the same terms. Both classes reach the
    same place, a kinase that is not doing its job at the receptor, which is why a
    normal ZAP-70 protein level on flow cytometry does not exclude the diagnosis.
  biological_scale: MOLECULAR
  genetic_context:
    variant_origin: GERMLINE
    functional_impact_category: LOSS_OF_FUNCTION
  molecular_functions:
  - preferred_term: ZAP-70 tyrosine kinase activity
    modifier: DECREASED
    term:
      id: GO:0004715
      label: non-membrane spanning protein tyrosine kinase activity
  downstream:
  - target: Attenuated Residual TCR Signaling
    causal_link_type: DIRECT
    description: >-
      The hypomorphic and docking-defective allele classes reduce rather than
      abolish the kinase's contribution, so this edge is the one those alleles
      take.
  - target: Failure of TCR-Proximal Signal Propagation
    causal_link_type: DIRECT
    description: >-
      The kinase is the obligate link between the phosphorylated receptor and its
      adaptors, so its loss stops the cascade at that step.
    evidence:
    - reference: PMID:8202713
      reference_title: "ZAP-70 deficiency in an autosomal recessive form of severe combined immunodeficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        This absence is associated with defects in TCR signal transduction,
        suggesting an important functional role for ZAP-70.
      explanation: >-
        Ties the absence of the protein directly to the failure of receptor
        signal transduction in patient cells.
  evidence:
  - reference: PMID:8124727
    reference_title: "Defective T cell receptor signaling and CD8+ thymic selection in humans lacking zap-70 kinase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We show here that STD patients carry a mutation of zap-70, resulting in
      loss of the activity of this kinase.
    explanation: >-
      The founding observation that the disease allele destroys kinase activity.
  - reference: PMID:8202712
    reference_title: "Human severe combined immunodeficiency due to a defect in ZAP-70, a T cell tyrosine kinase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A homozygous mutation in the kinase domain of ZAP-70, a T cell
      receptor-associated protein tyrosine kinase, produced a distinctive form of
      human severe combined immunodeficiency.
    explanation: >-
      Locates the founding allele in the kinase domain and states the disease
      consequence.
  - reference: PMID:37313400
    reference_title: "Combined immunodeficiency caused by pathogenic variants in the ZAP70 C-terminal SH2 domain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      While the R170C mutant was highly expressed, there was an absence of
      TCR-induced proliferation, associated with significantly attenuated
      TCR-induced ZAP-70 phosphorylation and a lack of binding of ZAP-70 to
      TCR-zeta.
    explanation: >-
      Establishes the docking-defective allele class, in which protein
      expression is preserved and only receptor engagement is lost.
- name: Failure of TCR-Proximal Signal Propagation
  description: >-
    Without ZAP-70 the phosphorylated CD3 and zeta ITAMs have nothing to recruit,
    so the adaptors LAT and SLP-76 are never phosphorylated and the signalosome
    that would carry the signal onward is never assembled. In patient T cells this
    reads out as markedly reduced tyrosine phosphorylation, no interleukin-2, and
    no proliferation to receptor stimulation — with the cells otherwise present
    and normal in number.
  biological_scale: MOLECULAR
  biological_processes:
  - preferred_term: T cell receptor signaling pathway
    modifier: DECREASED
    term:
      id: GO:0050852
      label: T cell receptor signaling pathway
  cell_types:
  - preferred_term: alpha-beta T cell
    term:
      id: CL:0000789
      label: alpha-beta T cell
  downstream:
  - target: Block of CD8 Single-Positive Thymocyte Selection
    causal_link_type: DIRECT
    description: >-
      Positive selection reads the strength of the TCR signal, so a cascade that
      cannot propagate cannot deliver the selecting signal.
    evidence:
    - reference: PMID:8124727
      reference_title: "Defective T cell receptor signaling and CD8+ thymic selection in humans lacking zap-70 kinase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Thus, Zap-70 kinase appears to be indispensable for the development of
        CD8 single-positive T cells as well as for signal transduction and
        function of single-positive CD4 T cells.
      explanation: >-
        States that the same signalling requirement underlies both the
        developmental block and the peripheral functional defect.
  - target: Functional Anergy of Peripheral CD4 T Cells
    causal_link_type: DIRECT
    description: >-
      The CD4 cells that escape the thymus carry the same broken cascade, so they
      are numerically normal and functionally inert.
    evidence:
    - reference: PMID:8202712
      reference_title: "Human severe combined immunodeficiency due to a defect in ZAP-70, a T cell tyrosine kinase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Manifestations of this disorder included profound immunodeficiency,
        absence of peripheral CD8+ T cells, and abundant peripheral CD4+ T cells
        that were refractory to T cell receptor-mediated activation.
      explanation: >-
        Records the abundant but activation-refractory peripheral CD4
        compartment that this edge produces.
  evidence:
  - reference: PMID:41080547
    reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      ZAP70 then phosphorylates key downstream molecules, including SLP-76 and
      LAT, thereby initiating signaling cascades essential for T-cell activation,
      differentiation, cytokine production, adhesion, and motility (14).
    explanation: >-
      Names the substrates whose phosphorylation fails when the kinase is
      absent, and the processes downstream of them.
  - reference: PMID:8124727
    reference_title: "Defective T cell receptor signaling and CD8+ thymic selection in humans lacking zap-70 kinase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Peripheral CD4+ T cells from the zap-70-/- patients exhibit markedly
      reduced tyrosine phosphorylation, fail to produce interleukin-2, and do not
      proliferate in response to T cell receptor stimulation by mitogens or
      antigens.
    explanation: >-
      The direct measurement of the propagation failure in patient cells.
- name: Block of CD8 Single-Positive Thymocyte Selection
  description: >-
    Double-positive thymocytes accumulate normally in the cortex, but only CD4
    single-positive cells reach the medulla. The asymmetry has a two-part
    explanation, each part separately sourced: the CD4 and CD8 lineages are
    selected at different ZAP-70 signalling thresholds, CD4 being the lower of
    the two, and human thymocytes express enough of the paralogous kinase SYK to
    carry that lower threshold. The rescue is human-specific. Mouse thymocytes
    express far less SYK, which is why complete Zap70 loss arrests both lineages
    in the mouse and only the CD8 lineage in patients.
  biological_scale: CELLULAR
  biological_processes:
  - preferred_term: positive thymic T cell selection
    modifier: DECREASED
    term:
      id: GO:0045059
      label: positive thymic T cell selection
  cell_types:
  - preferred_term: CD4-positive CD8-positive double-positive thymocyte
    term:
      id: CL:0000809
      label: double-positive, alpha-beta thymocyte
  locations:
  - preferred_term: thymus
    term:
      id: UBERON:0002370
      label: thymus
  - preferred_term: thymic cortex
    term:
      id: UBERON:0002123
      label: cortex of thymus
  downstream:
  - target: Peripheral CD8 T Cell Lymphopenia
    causal_link_type: DIRECT
    description: >-
      The peripheral CD8 compartment is filled by thymic export, so a selection
      block empties it.
    evidence:
    - reference: PMID:41080547
      reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        The absence of ZAP70 protein thus results in selective CD8+ T-cell
        deficiency with impaired signal transduction in CD4+ T-cells in humans,
        whereas in murine models, complete ZAP70 deficiency leads to an arrest in
        both CD4+ and CD8+ T-cell development because of insufficient Syk
        expression (17).
      explanation: >-
        States the causal link from the thymic block to the selective peripheral
        CD8 deficit, and the species difference behind it.
  evidence:
  - reference: PMID:8124727
    reference_title: "Defective T cell receptor signaling and CD8+ thymic selection in humans lacking zap-70 kinase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The thymi of zap-70-/- patients show the presence of CD4+CD8+ cells in the
      cortex; however, only CD4, not CD8, single-positive cells are present in
      the medulla.
    explanation: >-
      Direct histological demonstration of the lineage-selective block in
      patient thymus.
  - reference: PMID:41080547
    reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Importantly, ZAP70 plays a central role in the positive selection of CD8+
      thymocytes, whereas CD4+ T-cell development is relatively spared because of
      compensation by the related kinase Syk, which is more highly expressed in
      human thymocytes than in murine thymocytes (15).
    explanation: >-
      Supplies the SYK-compensation half of the explanation for why the block
      spares the CD4 lineage in humans. This is a background statement in a
      clinical cohort paper, attributed to its own reference, hence OTHER.
  - reference: PMID:20332428
    reference_title: "Regulation of Zap70 expression during thymocyte development enables temporal separation of CD4 and CD8 repertoire selection at different signaling thresholds."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      This temporal gradient in the amount of Zap70 protein enabled the selection
      of CD4(+) and CD8(+) repertoires in separate temporal windows and at
      different TCR signaling thresholds, thereby facilitating discrimination of
      distinct positive selection signals in these lineages.
    explanation: >-
      Supplies the other half, which the compensation claim depends on and which
      is otherwise asserted without a source: the two lineages are selected at
      different ZAP-70 signalling thresholds. Demonstrated in an inducible mouse
      system, so the threshold itself is a model result even though the SYK
      abundance that exploits it is a human observation.
  - reference: PMID:9324357
    reference_title: "Restoration of thymocyte development and function in zap-70-/- mice by the Syk protein tyrosine kinase."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Syk expression restored both thymocyte development and function.
    explanation: >-
      Shows experimentally that SYK can substitute for ZAP-70 in thymocyte
      development, which is the mechanism proposed for the human CD4 rescue.
- name: Peripheral CD8 T Cell Lymphopenia
  description: >-
    The signature laboratory finding: profoundly reduced or absent circulating
    CD8 T cells against a normal or elevated total lymphocyte count, with normal
    B and NK numbers. It is present in essentially every patient, and it is the
    finding that should trigger ZAP70 sequencing. Rare exceptions with near-normal
    CD8 counts and impaired function are reported, so a normal count does not
    exclude the diagnosis when function is abnormal.
  biological_scale: ORGANISM
  cell_types:
  - preferred_term: CD8-positive, alpha-beta T cell
    term:
      id: CL:0000625
      label: CD8-positive, alpha-beta T cell
  downstream:
  - target: Impaired Cellular Immunity Against Opportunistic Pathogens
    causal_link_type: DIRECT
  - target: Impaired Cytotoxic Surveillance of Virus-Infected Cells
    causal_link_type: DIRECT
  - target: Decreased total CD8+ T cell count
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients with ZAP-70 deficiency often present with normal to elevated
      numbers of circulating lymphocytes, including B cells, CD3+, and CD4+ T
      cells, but an absence of CD8+ T cells in the peripheral blood.
    explanation: >-
      Describes the full immunophenotype, including the preserved compartments
      that make the CD8 deficit conspicuous.
  - reference: PMID:41080547
    reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Eleven of thirteen patients (84.6%) exhibited profound CD8+ T-cell
      lymphopenias and two had near-normal CD8+ T-cell counts with impaired
      T-cell function.
    explanation: >-
      Quantifies the finding in a single-centre series and records the
      near-normal-count exception.
  - reference: PMID:26187144
    reference_title: "SYK expression endows human ZAP70-deficient CD8 T cells with residual TCR signaling."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In contrast to CD4 T cells, the majority of the few CD8 T cells showed
      expression of the ZAP70-related tyrosine kinase SYK that correlated with
      residual TCR signaling including calcium flux and degranulation.
    explanation: >-
      Shows that the small surviving CD8 population is enriched for SYK
      expression, which correlates with the residual TCR signalling those cells
      retain. The paper measures signalling rather than survival, so it does not
      by itself explain why those cells were selected.
- name: Functional Anergy of Peripheral CD4 T Cells
  description: >-
    CD4 T cells are present in normal or elevated numbers and are functionally
    inert: they fail to flux calcium, make interleukin-2, or proliferate in
    response to receptor engagement or mitogen. This is the half of the disease a
    cell count misses, and it is why the mitogen proliferation assay is a
    first-line rather than a confirmatory test.
  biological_scale: CELLULAR
  biological_processes:
  - preferred_term: T cell activation
    modifier: DECREASED
    term:
      id: GO:0042110
      label: T cell activation
  - preferred_term: T cell proliferation
    modifier: DECREASED
    term:
      id: GO:0042098
      label: T cell proliferation
  cell_types:
  - preferred_term: CD4-positive, alpha-beta T cell
    term:
      id: CL:0000624
      label: CD4-positive, alpha-beta T cell
  downstream:
  - target: Impaired Cellular Immunity Against Opportunistic Pathogens
    causal_link_type: DIRECT
  - target: Defective T-Dependent Antibody Responses
    causal_link_type: DIRECT
    description: >-
      B cells are numerically normal here, so the humoral defect is a failure of
      T-cell help rather than a B-cell-intrinsic one.
    evidence:
    - reference: PMID:32431715
      reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Immunologic profiling showed defective antibody production (57%) and
        decreased lymphocyte responses to mitogenic stimuli such as
        phytohemagglutinin (PHA) (95%).
      explanation: >-
        Pairs the antibody-production defect with the T-cell proliferation
        defect in the same cohort. That the defect is one of T-cell help rather
        than B-cell number rests on the separate observation of normal B-cell
        counts, cited on the Peripheral CD8 T Cell Lymphopenia node.
  - target: Impaired T-cell proliferative response to mitogens
    causal_link_type: DIRECT
  - target: Increased circulating IgE concentration
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:8124727
    reference_title: "Defective T cell receptor signaling and CD8+ thymic selection in humans lacking zap-70 kinase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Peripheral CD4+ T cells from the zap-70-/- patients exhibit markedly
      reduced tyrosine phosphorylation, fail to produce interleukin-2, and do not
      proliferate in response to T cell receptor stimulation by mitogens or
      antigens.
    explanation: >-
      Documents the anergic behaviour of the peripheral CD4 compartment
      directly.
- name: Attenuated Residual TCR Signaling
  description: >-
    A distinct state from the complete propagation failure above, and the two
    should not be conflated: hypomorphic and docking-defective alleles leave the
    cascade running weakly rather than not at all. That distinction is what makes
    the tolerance branch possible, because a thymocyte receiving no signal is not
    selected whereas one receiving a weak signal can be selected wrongly. This
    node is therefore reached only from the subset of alleles that retain residual
    function, which is why allele class and clinical presentation are related even
    though the pooled cohort finds no formal correlation.
  biological_scale: MOLECULAR
  genetic_context:
    variant_origin: GERMLINE
    functional_impact_category: PARTIAL_LOSS_OF_FUNCTION
  biological_processes:
  - preferred_term: T cell receptor signaling pathway
    modifier: DECREASED
    term:
      id: GO:0050852
      label: T cell receptor signaling pathway
  downstream:
  - target: Impaired Negative Selection and Thymic Regulatory T Cell Output
    causal_link_type: DIRECT
    description: >-
      Negative selection and thymic regulatory T-cell development read the same
      signal strength that positive selection does, so a weakened cascade
      degrades both.
    evidence:
    - reference: PMID:19841086
      reference_title: "A hypomorphic allele of ZAP-70 reveals a distinct thymic threshold for autoimmune disease versus autoimmune reactivity."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Both YYAA and SKG mice have impaired T cell development and
        hyporesponsiveness to TCR stimulation, markedly reduced numbers of thymic
        T regulatory cells and defective positive and negative selection.
      explanation: >-
        Shows in two independent hypomorphic Zap-70 strains that attenuated
        signalling degrades negative selection and thymic regulatory T-cell
        output alongside positive selection.
  evidence:
  - reference: PMID:37313400
    reference_title: "Combined immunodeficiency caused by pathogenic variants in the ZAP70 C-terminal SH2 domain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Deleterious mutations in the SH2-C domain result in attenuated ZAP-70
      function and clinical manifestations of immunodeficiency.
    explanation: >-
      Establishes attenuated rather than abolished function as a distinct human
      allele class.
- name: Impaired Negative Selection and Thymic Regulatory T Cell Output
  description: >-
    Autoreactive thymocytes that a normal signal would delete survive selection,
    in a thymus simultaneously producing too few regulatory T cells to contain
    them afterwards. Both halves are thymic events, which is why this node is
    scoped to the thymus rather than to tolerance in general. The human evidence
    is an association between residual-function alleles and the
    dysregulation-predominant presentation; the mechanistic dissection is in mouse
    hypomorphs.
  biological_scale: CELLULAR
  biological_processes:
  - preferred_term: negative thymic T cell selection
    modifier: DECREASED
    term:
      id: GO:0045060
      label: negative thymic T cell selection
  cell_types:
  - preferred_term: regulatory T cell
    term:
      id: CL:0000815
      label: regulatory T cell
  locations:
  - preferred_term: thymus
    term:
      id: UBERON:0002370
      label: thymus
  downstream:
  - target: Autoimmunity and Immune Dysregulation
    causal_link_type: DIRECT
    description: >-
      Autoreactive clones that survive selection, in a compartment with too few
      regulatory T cells to restrain them, is the standard route from tolerance
      failure to autoimmune disease.
    evidence:
    - reference: PMID:19841086
      reference_title: "A hypomorphic allele of ZAP-70 reveals a distinct thymic threshold for autoimmune disease versus autoimmune reactivity."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      directness: INDIRECT
      snippet: >-
        By uncoupling the relative contribution from T regulatory cells and TCR
        repertoire during thymic selection, our data help to identify events that
        may be important, but alone are insufficient, for the development of
        autoimmune disease.
      explanation: >-
        Supports the edge while stating its own limit: attenuated ZAP-70
        signalling supplies necessary but not sufficient conditions for
        autoimmune disease, which is why this edge is drawn from a mouse
        hypomorph rather than from human mechanism.
  evidence:
  - reference: PMID:19841086
    reference_title: "A hypomorphic allele of ZAP-70 reveals a distinct thymic threshold for autoimmune disease versus autoimmune reactivity."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      YYAA mice, like SKG mice, develop rheumatoid factor antibodies, but fail to
      develop autoimmune arthritis.
    explanation: >-
      Shows that attenuated ZAP-70 signalling produces autoantibody reactivity,
      and separates that from overt autoimmune disease, which needs more.
  - reference: PMID:37313400
    reference_title: "Combined immunodeficiency caused by pathogenic variants in the ZAP70 C-terminal SH2 domain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      Deleterious mutations in the SH2-C domain result in attenuated ZAP-70
      function and clinical manifestations of immunodeficiency.
    explanation: >-
      Establishes the attenuated-function allele class in humans, which is the
      genotype associated with the dysregulation-predominant presentation; the
      link to tolerance loss itself is an inference from that association.
- name: Impaired Cellular Immunity Against Opportunistic Pathogens
  description: >-
    The combined loss of cytotoxic CD8 cells and functional CD4 help leaves
    patients open to the pathogens that cellular immunity normally handles:
    Pneumocystis jirovecii, Candida, CMV, varicella, and — where BCG is given
    before diagnosis — disseminated BCG disease.
  biological_scale: ORGANISM
  downstream:
  - target: Recurrent respiratory infections
    causal_link_type: DIRECT
  - target: Pneumocystis jirovecii pneumonia
    causal_link_type: DIRECT
  - target: Pneumonia
    causal_link_type: DIRECT
  - target: BCGosis
    causal_link_type: DIRECT
  - target: Failure to thrive
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Chronic diarrhea
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP-70 deficiency presents with a history of recurrent opportunistic
      infections, although, Pneumocystis jirovecii pneumonia and Cytomegalovirus
      (CMV) pneumonitis are less common (10).
    explanation: >-
      Records the opportunistic-infection pattern and, usefully, that the two
      classic SCID opportunists are less prominent here than the label would
      suggest.
  - reference: PMID:26187144
    reference_title: "SYK expression endows human ZAP70-deficient CD8 T cells with residual TCR signaling."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patients presented as infant-onset CID with severe infections caused by
      varicella zoster virus and live vaccines.
    explanation: >-
      Documents live-vaccine and herpesvirus disease as presenting infections,
      which is what the cellular defect predicts.
- name: Defective T-Dependent Antibody Responses
  description: >-
    B cells are present in normal numbers and serum IgM and IgA are usually
    normal, but specific antibody responses to protein and polysaccharide antigens
    fail in a majority of patients, and IgG is normal or reduced. The humoral
    defect is therefore functional rather than quantitative, which is why
    immunoglobulin replacement is offered even to patients whose total IgG looks
    acceptable.
  biological_scale: ORGANISM
  downstream:
  - target: Impaired specific antibody response
    causal_link_type: DIRECT
  - target: Decreased circulating immunoglobulin concentration
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients have normal or reduced serum immunoglobulin (Ig) G, while IgM
      and IgA levels are often normal (15).
    explanation: >-
      Records the immunoglobulin pattern that makes the defect functional rather
      than a global hypogammaglobulinaemia.
- name: Impaired Cytotoxic Surveillance of Virus-Infected Cells
  description: >-
    Without a cytotoxic CD8 compartment, EBV-infected B cells are not cleared, and
    a minority of patients develop EBV-driven lymphoproliferation or lymphoma.
    This is a downstream branch of the CD8 deficit rather than an independent
    tumour-suppressor lesion.
  biological_scale: ORGANISM
  cell_types:
  - preferred_term: CD8-positive, alpha-beta cytotoxic T cell
    term:
      id: CL:0000794
      label: CD8-positive, alpha-beta cytotoxic T cell
  downstream:
  - target: Neoplasm
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Three patients (8.1%) developed malignant diseases (Table 2) including
      EBV-associated diffuse large B-cell lymphoma, non-EBV-associated large B
      cell lymphoma, and non-Hodgkin lymphoma.
    explanation: >-
      Supports the EBV attribution this node makes and simultaneously records
      that not every lymphoma in the cohort is EBV-driven, which is why the node
      is scoped to a subset.
- name: Autoimmunity and Immune Dysregulation
  description: >-
    Roughly a fifth of reported patients have autoimmune or dysregulatory disease
    — cytopenias, colitis and enteropathy, nephritis, skin involvement — and this
    arm can dominate the presentation in patients whose alleles leave residual
    function. It coexists with, rather than replaces, the infectious
    susceptibility.
  biological_scale: ORGANISM
  downstream:
  - target: Autoimmunity
    causal_link_type: DIRECT
  - target: Eczematoid dermatitis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Non-infectious cutaneous disease in this disorder is part of the
      dysregulation arm rather than an infectious complication; skin infiltration
      by dysfunctional CD4 T cells is the described route.
    evidence:
    - reference: PMID:26783323
      reference_title: "A novel human autoimmune syndrome caused by combined hypomorphic and activating mutations in ZAP-70."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Some ZAP-70 deficient patients also have skin infiltration with
        dysfunctional CD4 T cells, elevated serum IgE, and eosinophilia
      explanation: >-
        Names the cellular route from dysfunctional CD4 T cells to the cutaneous
        manifestations.
  - target: Lymphadenopathy
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Hepatomegaly
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Splenomegaly
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP-70 deficient patients have been reported in the literature with a broad
      spectrum of clinical manifestations including recurrent respiratory
      infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation
      (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of
      malignancies (8.1%).
    explanation: >-
      Quantifies autoimmunity, lymphoproliferation and enteropathy in the pooled
      cohort.
phenotypes:
- category: Laboratory
  name: Decreased total CD8+ T cell count
  description: >-
    The defining laboratory abnormality, present in essentially all patients and
    the single finding most likely to lead to the diagnosis.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Decreased total CD8+ T cell count
    term:
      id: HP:5210426
      label: Decreased total CD8+ T cell count
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The predominant immunologic phenotype was low CD8+ T cell counts (97.9%).
    explanation: >-
      Gives the frequency of the finding across 49 pooled patients.
- category: Laboratory
  name: Increased total lymphocyte count
  description: >-
    Total lymphocyte counts are typically normal or elevated, because the CD4
    and B-cell compartments are preserved or expanded even as CD8 T cells are
    absent. This dissociation — a normal-or-raised count masking a profound
    CD8 defect — is the pattern that distinguishes ZAP70 deficiency from
    classical SCID and the reason TREC-based newborn screening can miss it.
  phenotype_term:
    preferred_term: Increased total lymphocyte count
    term:
      id: HP:0100827
      label: Increased total lymphocyte count
  diagnostic: true
  reports_on:
  - target: Peripheral CD8 T Cell Lymphopenia
    relationship: READOUT_OF
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      The total count is preserved by the intact CD4 and B compartments, so a
      normal-or-raised value sits alongside — and masks — the CD8 deficit. This
      dissociation is why TREC-based newborn screening can miss the disease.
      Recorded as an observational readout rather than a causal edge: losing a
      lymphocyte subset cannot raise the total, and the cited sentence reports
      co-occurrence, not causation.
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: >-
      Patients with ZAP-70 deficiency often present with normal to elevated
      numbers of circulating lymphocytes, including B cells, CD3+, and CD4+ T
      cells, but an absence of CD8+ T cells in the peripheral blood.
    explanation: >-
      States that total lymphocyte counts run normal to elevated despite the
      absent CD8 compartment.
- category: Laboratory
  name: Impaired T-cell proliferative response to mitogens
  description: >-
    Reduced lymphocyte proliferation to phytohaemagglutinin, reflecting the
    receptor-signalling block in the numerically normal CD4 compartment.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Decreased mitogen-induced T-cell proliferation
    term:
      id: HP:0031381
      label: Decreased mitogen-induced T-cell proliferation
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Immunologic profiling showed defective antibody production (57%) and
      decreased lymphocyte responses to mitogenic stimuli such as
      phytohemagglutinin (PHA) (95%).
    explanation: >-
      Gives the frequency of the mitogen-proliferation defect in the pooled
      cohort.
- category: Laboratory
  name: Impaired specific antibody response
  description: >-
    Poor antibody responses to protein and polysaccharide vaccine antigens
    despite normal B-cell numbers.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Impaired specific antibody response
    term:
      id: HP:0012475
      label: Impaired specific antibody response
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Immunologic profiling showed defective antibody production (57%) and
      decreased lymphocyte responses to mitogenic stimuli such as
      phytohemagglutinin (PHA) (95%).
    explanation: >-
      Reports defective antibody production in 57% of pooled patients.
- category: Laboratory
  name: Decreased circulating immunoglobulin concentration
  description: >-
    Serum IgG is normal or reduced; IgM and IgA are usually normal, so this is a
    partial rather than a global hypogammaglobulinaemia, which is why the binding
    is the IgG-specific term rather than the general immunoglobulin one.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Decreased circulating IgG concentration
    term:
      id: HP:0004315
      label: Decreased circulating IgG concentration
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients have normal or reduced serum immunoglobulin (Ig) G, while IgM
      and IgA levels are often normal (15).
    explanation: >-
      States the immunoglobulin pattern, including that reduction is confined to
      IgG.
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      serum immunoglobulin levels were mostly reported to be normal, but some
      cases showed decreased levels of IgG (n = 12 out of 44, 27.3%), IgA (n = 6
      out of 45, 13.3%), and IgM (n = 5 out of 45, 11.1%).
    explanation: >-
      Quantifies how often each isotype is actually low, which is the basis for
      the OCCASIONAL frequency and for confining the claim to IgG.
- category: Clinical
  name: Recurrent respiratory infections
  description: >-
    The commonest presenting problem, and together with skin involvement the
    usual reason a child comes to attention.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Recurrent respiratory infections
    term:
      id: HP:0002205
      label: Recurrent respiratory infections
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP-70 deficient patients have been reported in the literature with a broad
      spectrum of clinical manifestations including recurrent respiratory
      infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation
      (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of
      malignancies (8.1%).
    explanation: >-
      Gives the frequency of recurrent respiratory infection in the pooled
      cohort.
  - reference: PMID:41080547
    reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most frequent initial presentations were recurrent respiratory
      infections and cutaneous manifestations.
    explanation: >-
      Independently confirms respiratory infection as the leading presentation
      in a separate cohort.
- category: Clinical
  name: Eczematoid dermatitis
  description: >-
    Cutaneous involvement covers a range — eczematous rash, erythroderma,
    ichthyosis, pustular lesions — and is the second commonest presenting
    feature. Skin infiltration by dysfunctional CD4 T cells has been described,
    often with raised IgE and eosinophilia.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Eczematoid dermatitis
    term:
      id: HP:0000964
      label: Eczematoid dermatitis
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP-70 deficient patients have been reported in the literature with a broad
      spectrum of clinical manifestations including recurrent respiratory
      infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation
      (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of
      malignancies (8.1%).
    explanation: >-
      Gives the frequency of cutaneous involvement in the pooled cohort.
- category: Clinical
  name: Chronic diarrhea
  description: >-
    Diarrhoea is reported in half of pooled patients and contributes to the growth
    failure that usually accompanies presentation. Enteropathy is counted
    separately and less often (18.4%), so the two figures are not
    interchangeable; the frequency here is the diarrhoea one.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Chronic diarrhea
    term:
      id: HP:0002028
      label: Chronic diarrhea
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pneumonia (n = 30, 71.4%), diarrhea (n = 19, 50%), and upper respiratory
      tract infections
    explanation: >-
      Gives the diarrhoea frequency directly, rather than borrowing the separate
      enteropathy figure.
- category: Clinical
  name: Failure to thrive
  description: >-
    Growth failure in infancy, driven by the combination of recurrent infection
    and enteropathy.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Enteropathy (18.4%) and failure to thrive (43.6%) were other reported
      manifestations.
    explanation: >-
      Gives the disease-specific frequency in the pooled cohort, rather than the
      generic SCID presenting syndrome.
- category: Clinical
  name: Lymphadenopathy
  description: >-
    Lymphoproliferation, including lymphadenopathy and hepatosplenomegaly, in
    roughly a third of reported patients.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Lymphadenopathy
    term:
      id: HP:0002716
      label: Lymphadenopathy
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP-70 deficient patients have been reported in the literature with a broad
      spectrum of clinical manifestations including recurrent respiratory
      infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation
      (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of
      malignancies (8.1%).
    explanation: >-
      Gives the frequency of lymphoproliferation in the pooled cohort.
- category: Clinical
  name: Autoimmunity
  description: >-
    Autoimmune cytopenias, ulcerative colitis, nephritis and autoimmune skin
    disease, in about a fifth of reported patients.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Autoimmunity
    term:
      id: HP:0002960
      label: Autoimmunity
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autoimmunity or manifestations of immune dysregulation such as ulcerative
      colitis and blood cytopenias (11), pustular skin lesions and subcutaneous
      nodules (12), lymphoma (13), Omenn syndrome, and hemophagocytic
      lymphohistiocytosis (HLH) (14) have also been reported.
    explanation: >-
      Enumerates the autoimmune and dysregulatory manifestations reported in
      this disorder.
- category: Clinical
  name: Pneumocystis jirovecii pneumonia
  description: >-
    Opportunistic pneumonia reflecting the cellular immune defect. Reported, but
    less prominent here than in classical SCID. No frequency is recorded: the
    cited sources place it qualitatively rather than giving a rate.
  phenotype_term:
    preferred_term: Pneumocystis jirovecii pneumonia
    term:
      id: HP:0020102
      label: Pneumocystis jirovecii pneumonia
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP-70 deficiency presents with a history of recurrent opportunistic
      infections, although, Pneumocystis jirovecii pneumonia and Cytomegalovirus
      (CMV) pneumonitis are less common (10).
    explanation: >-
      Records Pneumocystis pneumonia as part of the opportunistic spectrum while
      noting it is less common than in classical SCID.
  - reference: PMID:37313400
    reference_title: "Combined immunodeficiency caused by pathogenic variants in the ZAP70 C-terminal SH2 domain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genetic characterization of an infant who presented with pneumocystis
      pneumonia, mycobacterial infection, and an absence of CD8 T cells revealed
      a novel homozygous mutation in the C-terminal SH2 domain (SH2-C) of the
      ZAP70 gene (c.C343T, p.R170C).
    explanation: >-
      A patient-level example of Pneumocystis pneumonia as the presenting
      infection.
- category: Clinical
  name: Neoplasm
  description: >-
    Increased malignancy risk, predominantly EBV-associated lymphoproliferative
    disease and lymphoma, in a minority of patients.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Neoplasm
    term:
      id: HP:0002664
      label: Neoplasm
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP-70 deficient patients have been reported in the literature with a broad
      spectrum of clinical manifestations including recurrent respiratory
      infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation
      (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of
      malignancies (8.1%).
    explanation: >-
      Gives the malignancy frequency in the pooled cohort.
  - reference: PMID:37101133
    reference_title: "Two patients with ZAP-70 deficiency in China present with a different genetic, immunological, and clinical phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Case 1 presented with leaky severe combined immunodeficiency with low to
      the absence of CD8 + T cells, while case 2 suffered from a recurrent
      respiratory infection and had a past medical history of non-EBV-associated
      Hodgkin's lymphoma.
    explanation: >-
      A patient-level lymphoma report, and a reminder that not every lymphoma in
      this disorder is EBV-driven.
- category: Clinical
  name: Pneumonia
  description: >-
    The single most frequent individual infection in the pooled cohort, and the
    reason recurrent respiratory infection dominates the presenting picture.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Pneumonia
    term:
      id: HP:0002090
      label: Pneumonia
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pneumonia (n = 30, 71.4%), diarrhea (n = 19, 50%), and upper respiratory
      tract infections
    explanation: >-
      Gives the pneumonia frequency in the pooled cohort.
- category: Clinical
  name: BCGosis
  description: >-
    Disseminated disease from the BCG vaccine strain in infants vaccinated before
    the immunodeficiency was recognised. This is an iatrogenic manifestation
    confined to BCG-endemic settings rather than a feature of the disease
    everywhere, and it is the concrete harm behind the live-vaccine avoidance in
    the treatment section.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: BCGosis
    term:
      id: HP:0020087
      label: BCGosis
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      bacteria (n = 14, 36.8%) (mainly BCG [18.4%]), fungal pathogens (n = 14,
      38.9%) [predominantly Candida albicans (28.9%)]
    explanation: >-
      Gives the BCG-disease frequency alongside the other reported pathogen
      classes in the pooled cohort.
- category: Clinical
  name: Hepatomegaly
  description: >-
    Part of the lymphoproliferative arm, usually alongside splenomegaly and
    lymphadenopathy rather than in isolation.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hepatomegaly (%) | 36 | 7 (19.4)
    explanation: >-
      The cohort table row giving the hepatomegaly frequency.
- category: Clinical
  name: Splenomegaly
  description: >-
    The other half of the organomegaly seen in the lymphoproliferative arm.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Splenomegaly
    term:
      id: HP:0001744
      label: Splenomegaly
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Splenomegaly (%) | 36 | 5 (13.9)
    explanation: >-
      The cohort table row giving the splenomegaly frequency.
- category: Laboratory
  name: Increased circulating IgE concentration
  description: >-
    Raised IgE accompanies the atopic and cutaneous end of the spectrum, which
    GeneReviews names as atopy among the later-onset dysregulated presentations.
    The pooled cohort reports a median IgE well above the paediatric reference
    range with a wide spread, so this is a feature of part of the cohort rather
    than of all of it; no frequency is recorded because the source gives a
    distribution rather than a proportion.
  phenotype_term:
    preferred_term: Increased circulating IgE concentration
    term:
      id: HP:0003212
      label: Increased circulating IgE concentration
  evidence:
  - reference: PMID:26783323
    reference_title: "A novel human autoimmune syndrome caused by combined hypomorphic and activating mutations in ZAP-70."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Some ZAP-70 deficient patients also have skin infiltration with
      dysfunctional CD4 T cells, elevated serum IgE, and eosinophilia
    explanation: >-
      States the association of raised IgE and eosinophilia with the cutaneous
      manifestations in this disorder.
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      later-onset presentations with dysregulated immunity such as autoimmunity,
      atopy, and even malignancy
    explanation: >-
      GeneReviews names atopy among the later-onset manifestations; the raised
      IgE is the laboratory correlate of that, which is the inference step.
genetic:
- name: ZAP70
  notes: >-
    Encodes the 70 kDa zeta-chain-associated protein kinase, a Syk-family
    non-receptor tyrosine kinase at 2q11.2. Reported disease alleles are spread
    through the gene with no hotspot, though the majority sit in the kinase
    domain; the C-terminal SH2 alleles R170C and R192W are the mechanistically
    distinct docking-defective class. The splice variant c.1624-11G>A is a
    founder allele in Old Order Mennonite families, which is why that ancestry is
    over-represented in every published series.

    Note on the identifier: the correct HGNC id for ZAP70 is hgnc:12858. The
    deep-research report for this entry offered "HGNC:7535", which is the NCBI
    Gene id for ZAP70 rather than an HGNC id, and HGNC has no record 7535 at all.
    Gene CURIEs are skipped by the report-side term validator, so this was caught
    only by resolving the symbol against HGNC directly.
  gene_term:
    preferred_term: ZAP70
    term:
      id: hgnc:12858
      label: ZAP70
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  evidence:
  - reference: PMID:8202713
    reference_title: "ZAP-70 deficiency in an autosomal recessive form of severe combined immunodeficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, three siblings are described with an autosomal recessive form of
      severe combined immunodeficiency disease (SCID) in which ZAP-70, a non-Src
      PTK, is absent as a result of mutations in the ZAP-70 gene.
    explanation: >-
      The founding gene-disease report, establishing biallelic ZAP70 mutation as
      the cause.
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutations of the ZAP70 gene were located throughout the gene, and there was
      no mutational hotspot. However, most of the mutations were located in the
      kinase domain.
    explanation: >-
      Describes the distribution of disease alleles across the gene.
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      38 (77.5%) patients (in 33 families) had homozygous mutations, 10 (16.3%)
      patients (in 8 families) had compound heterozygous ZAP70 mutations
    explanation: >-
      Gives the homozygous-versus-compound-heterozygous split quoted in the
      inheritance section and in these notes.
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The splice site mutation c.1624-11G>A (p.K541_K542insLEQ) was the most
      frequent mutation, as it was identified in 10 different families most of
      which were of Mennonite descent.
    explanation: >-
      Sources the founder allele, its consequence, and its association with the
      Mennonite communities.
  - reference: PMID:37313400
    reference_title: "Combined immunodeficiency caused by pathogenic variants in the ZAP70 C-terminal SH2 domain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Structural modeling of this region revealed the critical nature of the
      arginines at positions 170 and 192, in concert with R190, forming a binding
      pocket for the phosphorylated TCR-zeta chain.
    explanation: >-
      Establishes the SH2-C allele class and the structural basis for its
      docking defect.
- name: SYK
  notes: >-
    Not a disease gene here — a modifier. SYK is the ZAP-70 paralogue and can
    substitute for it at the T-cell receptor. Its relatively high expression in
    human thymocytes is the accepted explanation for why the CD4 lineage survives
    in patients when it does not in Zap70-null mice, and its expression in
    individual surviving CD8 cells tracks with how much residual signalling those
    cells retain.
  gene_term:
    preferred_term: SYK
    term:
      id: hgnc:11491
      label: SYK
  relationship_type: MODIFIER
  variant_origin: GERMLINE
  evidence:
  - reference: PMID:26187144
    reference_title: "SYK expression endows human ZAP70-deficient CD8 T cells with residual TCR signaling."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In contrast to CD4 T cells, the majority of the few CD8 T cells showed
      expression of the ZAP70-related tyrosine kinase SYK that correlated with
      residual TCR signaling including calcium flux and degranulation.
    explanation: >-
      Shows SYK expression correlating with preserved signalling in patient CD8
      T cells, which is the modifier claim.
  - reference: PMID:9324357
    reference_title: "Restoration of thymocyte development and function in zap-70-/- mice by the Syk protein tyrosine kinase."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Hence, ZAP-70 and Syk can play overlapping functions and exhibit similar
      regulatory mechanisms in mediating alphabeta T cell development.
    explanation: >-
      Demonstrates experimentally that SYK can carry ZAP-70's developmental
      function, which is the mechanism the human modifier claim rests on.
prevalence:
- population: Worldwide, published literature
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No population-based prevalence or incidence estimate exists. The largest
    systematic review pooled 49 unique patients from 33 articles; a 2025
    single-centre series adds 13 more. Ancestry is heavily skewed in the
    published series by the Mennonite founder allele and by consanguinity, so
    these counts describe the literature rather than the disease's distribution.
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A total of 49 ZAP-70 deficient patients were identified from 33 articles.
    explanation: >-
      Gives the size of the pooled published cohort.
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most of the patients were of Mennonite (30.6%) descent, followed by Turkish
      (22.4%), Japanese and Caucasian ethnicity (each 6.1%).
    explanation: >-
      Records the ancestry skew that makes these counts a description of the
      literature rather than of population distribution.
progression:
- phase: Infantile presentation
  notes: >-
    Almost all patients present within the first year. In the pooled review the
    median age at presentation was 4 months, the median age at diagnosis 10.4
    months, and the median diagnostic delay 5 months — the delay driven largely by
    the immunophenotype being read first as classical SCID. A single-centre series
    reports an earlier median symptom onset of 1 month; the two cohorts are
    reported separately here because their figures are not interchangeable.
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our review illustrated that 97.3% of the patients presented within 12
      months of age with a median age of 4 months.
    explanation: >-
      Gives the pooled cohort's own age at presentation, which is the figure the
      diagnostic delay below is measured against.
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The median (IQR) age of diagnosis was 10.4 (7.0-18.7) months with a median
      (IQR) diagnostic delay of 5 (1.2-11.5) months.
    explanation: >-
      Gives the diagnostic age and delay from the same cohort as the
      presentation age.
  - reference: PMID:41080547
    reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thirteen patients with a median age at symptom onset of 1 month were
      identified.
    explanation: >-
      The separate single-centre onset figure, reported alongside rather than
      merged with the pooled one.
- phase: Untreated course
  notes: >-
    Without transplantation, infants presenting with severe infection in the
    first year of life generally do not survive their second.
  evidence:
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Children who present in their first year of life with severe infections are
      expected to have a declining quality of life and usually do not survive
      past their second year without allogeneic hematopoietic stem cell
      transplantation (HSCT).
    explanation: >-
      States the untreated natural history directly.
- phase: Outcome by transplant status
  notes: >-
    Transplantation is the dominant prognostic variable and the effect is large:
    mortality in the pooled cohort was significantly lower in transplanted
    patients. Age at transplant matters too — post-transplant complications in
    that cohort were concentrated in patients transplanted after six months.
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      As presented in the plot, the mortality rate was significantly lower in
      patients who underwent HSCT (p < 0.001).
    explanation: >-
      The survival comparison between transplanted and non-transplanted
      patients.
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Eight out of twelve patients (66%) with the above mentioned complications
      post-HSCT were older than 6 months at the time of transplantation.
    explanation: >-
      Supports age at transplant as a prognostic factor within the transplanted
      group.
- phase: Post-transplant
  notes: >-
    After successful transplantation, infectious and autoimmune manifestations
    resolve and mitogen responses normalise; long-term survival in reported
    series is good.
  evidence:
  - reference: PMID:27438785
    reference_title: "Long-Term Outcomes of Hematopoietic Stem Cell Transplantation for ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Infectious complications in 5/5 and autoimmune thrombocytopenia in one
      patient resolved post-HSCT.
    explanation: >-
      Records resolution of both the infectious and the autoimmune arms after
      transplantation.
diagnosis:
- name: Lymphocyte subset flow cytometry
  description: >-
    The first-line test and the one that makes the diagnosis suggestible. Absent
    or profoundly reduced CD8 T cells against a normal or elevated total
    lymphocyte count, with normal CD19 B cells and normal NK cells, is a pattern
    no classical SCID produces. Note the exception: a small number of patients
    have near-normal CD8 counts with impaired function, so a normal count in a
    child with a compatible clinical picture does not close the question.
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Newborns with consanguineous parents, positive family history of CID, and
      low CD8+ T cell counts should be considered for ZAP-70 deficiency
      screening, since early diagnosis and treatment with HSCT can lead to a more
      favorable outcome.
    explanation: >-
      States the CD8-count-based diagnostic trigger recommended by the largest
      review.
  - reference: PMID:41080547
    reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Eleven of thirteen patients (84.6%) exhibited profound CD8+ T-cell
      lymphopenias and two had near-normal CD8+ T-cell counts with impaired
      T-cell function.
    explanation: >-
      Documents the near-normal-count exception that limits the test's negative
      predictive value.
- name: Molecular genetic testing of ZAP70
  description: >-
    Confirmatory. Single-gene sequencing is appropriate when the immunophenotype
    is characteristic; broader combined-immunodeficiency panels or exome
    sequencing are used when the presentation is atypical, which in practice
    means autoimmunity-predominant.
  evidence:
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The diagnosis of ZAP70 deficiency is established in a proband with
      suggestive findings and biallelic pathogenic variants in ZAP70 identified
      by molecular genetic testing.
    explanation: >-
      States the diagnostic criterion.
- name: Newborn TREC screening
  description: >-
    Recorded for its limitation rather than its yield. TREC-based newborn SCID
    screening can miss ZAP70 deficiency, because thymic output continues through the intact CD4
    lineage even while CD8 selection fails, so TRECs can sit above the screening
    cutoff in an affected infant. Do not treat a normal newborn screen as
    excluding the diagnosis. This is a recognised limitation rather than an
    incidental miss: it has been noted prospectively across more than a decade of
    US screening, in a population that includes the Mennonite founder community
    where most reported patients come from.
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP-70 has not been frequently picked up during the >10 year screening
      experience in the United States (49), despite a significant Mennonite
      population and the large number of reported ZAP-70 patients.
    explanation: >-
      States the programme-level failure of TREC screening to detect this
      disorder, which is stronger than any single-patient observation.
  - reference: PMID:37313400
    reference_title: "Combined immunodeficiency caused by pathogenic variants in the ZAP70 C-terminal SH2 domain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      While infants with IEI due to mutations in ZAP70 might not present with
      TREC numbers that are below the threshold for diagnosis
    explanation: >-
      States the mechanism of the miss: TRECs can sit above the screening
      threshold in an affected infant.
  - reference: PMID:26187144
    reference_title: "SYK expression endows human ZAP70-deficient CD8 T cells with residual TCR signaling."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Retrospective TCR excision circle newborn screening was normal in both
      patients.
    explanation: >-
      Two genetically confirmed patients whose retrospective TREC screen was
      normal, which is the screening blind spot stated as an observation.
environmental:
- name: BCG vaccination before diagnosis
  description: >-
    Live attenuated Mycobacterium bovis BCG, given at birth in countries with
    universal BCG programmes, before the immunodeficiency is known. In a child
    with no functional cellular immunity the vaccine strain is not contained and
    disseminates. It is the commonest bacterial exposure in the pooled cohort and
    the concrete reason live vaccines are withheld until immune reconstitution is
    confirmed.

    This is an iatrogenic precipitant, not a cause of the disease, and the edge
    is drawn accordingly. It triggers the BCGosis phenotype; it does not cause
    the impaired cellular immunity that permits it, which would invert the
    direction of the mechanism.
  exposure_term:
    preferred_term: exposure to BCG vaccination
  notes: >-
    Left unbound after searching. ECTO has no term for BCG or Mycobacterium
    bovis vaccine exposure. The generic `ECTO:2000129` (exposure to
    vaccination) exists in OLS but is absent from the ECTO build this
    repository validates against, so it fails both the ontology lookup and the
    `ExposureTerm` dynamic enum; the only other vaccination-adjacent hit is an
    Orthopoxvirus vaccinia term, which names a different vaccine. Binding a term
    that does not resolve is worse than binding none, so the concept stays in
    `preferred_term` until ECTO carries something that validates.
  influences_mechanisms:
  - target: BCGosis
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Administration of the live vaccine strain is the exposure that produces
      disseminated BCG disease in an infant who cannot contain it.
    evidence:
    - reference: PMID:32431715
      reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        bacteria (n = 14, 36.8%) (mainly BCG [18.4%]), fungal pathogens (n = 14,
        38.9%) [predominantly Candida albicans (28.9%)]
      explanation: >-
        Records BCG as the predominant bacterial exposure in the pooled cohort,
        which is the exposure this edge draws.
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      bacteria (n = 14, 36.8%) (mainly BCG [18.4%]), fungal pathogens (n = 14,
      38.9%) [predominantly Candida albicans (28.9%)]
    explanation: >-
      Establishes BCG exposure as a documented and frequent event in this
      patient population.
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      delaying immunizations until immune reconstitution is confirmed
    explanation: >-
      The management counterpart. This is the general immunization statement
      rather than the live-viral-vaccine item from the agents-to-avoid list:
      BCG is a live attenuated bacterial vaccine, so the viral-specific
      sentence would not cover it.
treatments:
- name: Allogeneic Hematopoietic Stem Cell Transplantation
  description: >-
    The only curative treatment, and effective in the reported series. Those
    series use matched sibling, matched unrelated, haploidentical and cord blood donors, with and
    without conditioning; myeloablative conditioning gives more durable
    reconstitution, while reduced-intensity or unconditioned transplant remains a
    life-saving option for a critically ill infant. Long-term survival in
    published cohorts is good and both the infectious and the autoimmune
    manifestations resolve.
  therapeutic_modality: CELL_THERAPY
  treatment_term:
    preferred_term: allogeneic haematopoietic stem cell transplantation
    term:
      id: NCIT:C46089
      label: Allogeneic Hematopoietic Stem Cell Transplantation
  target_mechanisms:
  - target: ZAP70 Loss of Kinase Function
    description: >-
      Replaces the patient's haematopoietic compartment with donor cells that
      carry functional ZAP70, so the lesion is bypassed at its origin rather
      than compensated downstream.
  evidence:
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Targeted therapy: The only curative therapy for ZAP70 deficiency is
      allogeneic HSCT.
    explanation: >-
      States that transplantation is the sole curative option.
  - reference: PMID:27438785
    reference_title: "Long-Term Outcomes of Hematopoietic Stem Cell Transplantation for ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At a median of 13.5-year post-HSCT, 8/8 (100 %) patients are alive.
    explanation: >-
      Long-term survival data from a single-centre transplanted cohort.
  - reference: PMID:41080547
    reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      HSCT remains the only curative treatment for ZAP70 deficiency.
      Myeloablative conditioning regimens appear to promote more robust and
      durable immune reconstitution.
    explanation: >-
      Confirms curative status and records the conditioning-intensity finding.
- name: Immunoglobulin Replacement Therapy
  description: >-
    Given for the functional antibody defect, which is present even in patients
    whose total IgG is normal. Several patients in the long-term transplant
    series were able to stop it once specific antibody responses returned after
    engraftment.
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: immunoglobulin replacement therapy
    term:
      id: NCIT:C62710
      label: Immunoglobulin Therapy
  target_mechanisms:
  - target: Defective T-Dependent Antibody Responses
    description: >-
      Supplies the specific antibody the patient cannot generate; it replaces the
      product of the failed response rather than repairing the response.
  evidence:
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Supportive care: IgG replacement therapy; antibacterial, antifungal,
      antiviral, and Pneumocystis jiroveci prophylaxis to control and reduce the
      occurrence of infections.
    explanation: >-
      Names immunoglobulin replacement as standard supportive care.
  - reference: PMID:27438785
    reference_title: "Long-Term Outcomes of Hematopoietic Stem Cell Transplantation for ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In total, seven have discontinued immunoglobulin replacement.
    explanation: >-
      Records that replacement can be withdrawn after successful
      transplantation.
- name: Antimicrobial Prophylaxis
  description: >-
    Antibacterial, antifungal, antiviral and Pneumocystis prophylaxis while
    awaiting transplantation, and for patients in whom transplantation is not an
    option. GeneReviews is explicit that conservative management on prophylaxis
    and immunoglobulin alone leaves patients at high risk, so it is a holding
    measure rather than a definitive one.
  therapeutic_modality: SMALL_MOLECULE
  notes: >-
    Bound to the generic supportive-care action deliberately. NCIT:C51993
    (Antibiotic Prophylaxis) is the obvious narrower candidate and was rejected:
    the regimen GeneReviews describes is antibacterial *and* antifungal *and*
    antiviral *and* anti-Pneumocystis, so that term would assert less than the
    treatment does. No NCIT clinical-action term covers the combined regimen, and
    no `therapeutic_agent` is bound because the agents differ by centre and by
    which arm of the regimen is meant.
  treatment_term:
    preferred_term: anti-infective prophylaxis
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Impaired Cellular Immunity Against Opportunistic Pathogens
    description: >-
      Suppresses the organisms the absent cellular immunity would otherwise
      control; it substitutes for the missing defence rather than restoring it.
  evidence:
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Although more conservative approaches that rely on immunoglobulin (Ig) G
      replacement therapy and antimicrobial prophylaxis have been utilized,
      especially when HSCT is not an option, individuals on these therapies
      remain at high risk for severe infections as well as autoimmunity and
      lymphoproliferative manifestations.
    explanation: >-
      States both the role of prophylaxis and its insufficiency as definitive
      management.
- name: Infection-Risk Avoidance and Blood Product Precautions
  description: >-
    The GeneReviews "agents and circumstances to avoid" list. These are
    consequential rather than merely precautionary in this disorder. Live viral
    vaccines are contraindicated for the infant and for household contacts; blood products must be irradiated,
    leukoreduced and CMV-safe to avoid transfusion-associated graft-versus-host
    disease; breastfeeding is withheld until maternal CMV status is known; and
    construction or soil-disturbance environments are avoided for fungal-exposure
    risk. Disseminated BCG disease in infants vaccinated before diagnosis is a
    recurring real-world harm in BCG-endemic settings.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: infection-risk avoidance and blood product precautions
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Impaired Cellular Immunity Against Opportunistic Pathogens
    description: >-
      Removes the exposures that a patient without cellular immunity cannot
      survive, particularly live vaccine organisms and viable donor lymphocytes.
  evidence:
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      live viral vaccines for the infant and household contacts; transfusion of
      non-irradiated blood products; and areas of construction or soil
      manipulation, as they increase the risk for fungal exposure.
    explanation: >-
      The GeneReviews list of exposures to avoid, quoted from the
      agents/circumstances section.
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      breastfeeding and breast milk until maternal CMV status is established by
      CMV serologies
    explanation: >-
      The breastfeeding item of the same list, quoted separately because the
      description states it as its own precaution.
  - reference: PMID:26187144
    reference_title: "SYK expression endows human ZAP70-deficient CD8 T cells with residual TCR signaling."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patients presented as infant-onset CID with severe infections caused by
      varicella zoster virus and live vaccines.
    explanation: >-
      A patient-level demonstration of live-vaccine harm, which is why the
      avoidance is not merely precautionary.
- name: Genetic Counseling
  description: >-
    Autosomal recessive counselling with a 25% recurrence risk per pregnancy,
    carrier testing for at-risk relatives, and prenatal or preimplantation
    testing once the familial variants are known. Particularly consequential in
    the Mennonite founder communities and in consanguineous families, where
    testing at-risk siblings allows diagnosis before the first severe infection.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Molecular genetic testing for the familial ZAP70 pathogenic variants is
      strongly recommended for all at-risk sibs to allow earliest possible
      diagnosis and treatment.
    explanation: >-
      States the at-risk-relative testing recommendation and its rationale.
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      each sib of an affected individual has at conception a 25% chance of being
      affected, a 50% chance of being an asymptomatic carrier, and a 25% chance
      of being unaffected and not a carrier
    explanation: >-
      The recurrence-risk figures the description quotes.
- name: Gene Therapy
  description: >-
    Investigational only, with no clinical application in this disease. The
    preclinical work is unusual in targeting the thymus directly rather than the
    stem cell compartment: intrathymic AAV delivery of ZAP70 into Zap70-null mice
    restores thymic architecture and produces gene-corrected peripheral T cells
    that persist for months, and intrathymic injection of wild-type progenitors
    reconstitutes those mice faster and with fewer cells than intravenous
    delivery. Both remain mouse results.
  therapeutic_modality: GENE_THERAPY
  treatment_term:
    preferred_term: gene therapy
    term:
      id: NCIT:C15238
      label: Gene Therapy
  target_mechanisms:
  - target: Block of CD8 Single-Positive Thymocyte Selection
    description: >-
      Restores kinase function in thymocytes themselves, which is where the
      selection block sits, rather than in the upstream stem cell.
  evidence:
  - reference: PMID:31513879
    reference_title: "Intrathymic adeno-associated virus gene transfer rapidly restores thymic function and long-term persistence of gene-corrected T cells."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Intrathymic injection of an AAV8-ZAP-70 vector into ZAP-70-/- mice resulted
      in a rapid thymocyte differentiation associated with the development of a
      thymic medulla.
    explanation: >-
      The preclinical proof of concept for intrathymic gene correction in this
      disorder.
  - reference: PMID:16174749
    reference_title: "Intrathymic administration of hematopoietic progenitor cells enhances T cell reconstitution in ZAP-70 severe combined immunodeficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Upon intrathymic HSC injection, there was a more rapid T cell
      differentiation, with mature thymocytes detected by 4 weeks after
      transplantation.
    explanation: >-
      Supports the intrathymic delivery route in the same disease model.
- name: Post-Transplant Surveillance
  description: >-
    Close follow-up for the first year after transplantation and then every six to
    twelve months, tracking lineage-specific donor chimerism, growth, immune and
    lung function, and gastrointestinal and dermatological problems. Where
    conditioning chemotherapy was used, organ function and neurodevelopment are
    monitored long-term. Patients who have not been transplanted need periodic
    reassessment of immune function instead, because it can deteriorate.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: post-transplant immune and organ surveillance
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301777
    reference_title: "ZAP70 Deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Surveillance: After successful HSCT, evaluate individuals very closely for
      the first year and then every six to 12 months to monitor lineage-specific
      donor cell engraftment, growth, immune and lung function, and
      gastrointestinal and dermatologic issues.
    explanation: >-
      The GeneReviews surveillance schedule this entry follows.
- name: Corticosteroid Therapy
  description: >-
    Recorded here for what the sources actually support, which is narrower than it
    first appears. In the pooled cohort steroids were given around transplantation
    — as prophylaxis or to control transplant complications — in about a third of
    transplanted patients, with five clinically responsive; in the single-centre
    series corticosteroids were first-line for graft-versus-host disease. Neither
    source documents steroids as a quantified treatment for the disorder's own
    autoimmune arm, so no `target_mechanisms` link to the dysregulation node is
    asserted here. The deep-research report for this entry described this same
    32% figure as corticosteroid use for autoimmune manifestations, which
    misreads the sentence.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: corticosteroid therapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Steroids and intravenous immunoglobulin (IVIG) have been tried as a
      prophylactic or to control adverse side effects of transplantation in 8
      (32%) and 18 (36.7%) patients, respectively. Among the patients receiving
      steroids, five were clinically responsive (35).
    explanation: >-
      Records both the indication (peri-transplant, not disease autoimmunity) and
      the response rate.
  - reference: PMID:41080547
    reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients received corticosteroids as first-line therapy, and additional
      immunomodulatory treatments were used as required.
    explanation: >-
      The graft-versus-host disease indication in the single-centre series.
animal_models:
- name: Zap70-null mouse
  species: Mouse
  genotype: Zap70 knockout (zap-70-/-)
  publication: PMID:9324357
  description: >-
    The standard null model. Thymocyte development arrests at the CD4+CD8+
    double-positive stage, so neither lineage matures — a more complete block than
    patients show, and the reason this model is better read as a model of TCR
    signal-dependent selection than of the human disease's immunophenotype.
  modeled_mechanisms:
  - target: Block of CD8 Single-Positive Thymocyte Selection
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Reproduces the thymic selection block and its dependence on ZAP-70, but
      not its lineage selectivity.
    limitations: >-
      The block extends to the CD4 lineage, which is spared in patients. Mouse
      thymocytes express much less SYK than human thymocytes, so the paralogue
      cannot carry the lower CD4 threshold; the model therefore reports a
      complete developmental arrest where the human disease produces a selective
      CD8 deficit with an intact, dysfunctional CD4 compartment.
    evidence:
    - reference: PMID:9324357
      reference_title: "Restoration of thymocyte development and function in zap-70-/- mice by the Syk protein tyrosine kinase."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Thymocyte development in zap-70-/- mice is blocked at the CD4+CD8+
        TCR(lo) stage.
      explanation: >-
        States the model's developmental block, which is the phenotype it is
        cited for.
  - target: Peripheral CD8 T Cell Lymphopenia
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    model_scale: ORGANISM
    description: >-
      The model does not reproduce the selective peripheral CD8 deficit, because
      it has no mature peripheral T cells of either lineage.
    limitations: >-
      The species difference is the point rather than an incidental caveat:
      insufficient Syk expression in mouse thymocytes converts a lineage-selective
      human deficit into a complete arrest. A study reading peripheral T-cell
      subsets off this model would misdescribe the human immunophenotype.
    evidence:
    - reference: PMID:41080547
      reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        The absence of ZAP70 protein thus results in selective CD8+ T-cell
        deficiency with impaired signal transduction in CD4+ T-cells in humans,
        whereas in murine models, complete ZAP70 deficiency leads to an arrest in
        both CD4+ and CD8+ T-cell development because of insufficient Syk
        expression (17).
      explanation: >-
        States the divergence between the model and the human disease, and its
        mechanistic cause.
  evidence:
  - reference: PMID:9324357
    reference_title: "Restoration of thymocyte development and function in zap-70-/- mice by the Syk protein tyrosine kinase."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      To determine if Syk can play a role in thymocyte development, we generated
      zap-70-/- mice expressing a human syk cDNA.
    explanation: >-
      Establishes the model and the SYK-complementation experiment performed in
      it.
- name: Zap70 YYAA knock-in mouse
  species: Mouse
  genotype: Zap70 Y315A/Y319A knock-in (YYAA)
  publication: PMID:19841086
  description: >-
    A hypomorphic knock-in in which the interdomain B tyrosines Y315 and Y319 are
    mutated to alanine, attenuating rather than abolishing signalling. Together
    with the spontaneous SKG strain it is the model for the tolerance arm of the
    disease: impaired positive and negative selection, markedly reduced thymic
    regulatory T cells, and autoantibody production.
  modeled_mechanisms:
  - target: Impaired Negative Selection and Thymic Regulatory T Cell Output
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Reproduces the tolerance failure that attenuated ZAP-70 signalling
      produces, including the regulatory T-cell deficit.
    limitations: >-
      Autoantibody reactivity does not progress to overt autoimmune disease in
      this strain, whereas the SKG strain on the same axis develops arthritis, so
      the model separates reactivity from disease rather than modelling the human
      autoimmune presentation end to end. The specific autoimmune manifestations
      differ from those reported in patients.
    evidence:
    - reference: PMID:19841086
      reference_title: "A hypomorphic allele of ZAP-70 reveals a distinct thymic threshold for autoimmune disease versus autoimmune reactivity."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Both YYAA and SKG mice have impaired T cell development and
        hyporesponsiveness to TCR stimulation, markedly reduced numbers of thymic
        T regulatory cells and defective positive and negative selection.
      explanation: >-
        The phenotype this model is cited for: tolerance failure with a
        regulatory T-cell deficit.
  evidence:
  - reference: PMID:19841086
    reference_title: "A hypomorphic allele of ZAP-70 reveals a distinct thymic threshold for autoimmune disease versus autoimmune reactivity."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      To address the importance of the scaffolding function, we generated a zap70
      mutant mouse (YYAA mouse) with Y315 and Y319 both mutated to alanines.
    explanation: >-
      Establishes the model's construction and allele, which is what makes it
      the hypomorphic counterpart to the null strain.
differential_diagnoses:
- name: Classical SCID (IL2RG, JAK3, IL7R)
  description: >-
    The initial misdiagnosis in most cases, because both present as an infant with
    severe infection. The discriminator is the lymphocyte subset panel rather than
    the clinical picture: classical SCID has profound total T-cell lymphopenia,
    while ZAP70 deficiency has normal or elevated total lymphocytes and CD4 cells
    with an isolated CD8 deficit. The NK compartment separates the SCID genes from
    one another rather than from this disorder, and is worth stating precisely:
    IL2RG and JAK3 defects are T-B+NK-, because the common gamma chain is required
    for IL-15 signalling and therefore for NK development, whereas IL7R defects are
    T-B+NK+. ZAP70 deficiency is T+B+NK+ and is not a SCID by cell count at all.
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients with ZAP-70 deficiency often present with normal to elevated
      numbers of circulating lymphocytes, including B cells, CD3+, and CD4+ T
      cells, but an absence of CD8+ T cells in the peripheral blood.
    explanation: >-
      States the subset pattern that separates this disorder from classical
      SCID at the bench.
- name: ZAP70 combined hypomorphic and activating variant syndrome
  description: >-
    A separate disease at the same locus, listed by IUIS under its own OMIM
    number (617006), and worth keeping separate rather than folding in as a
    subtype. Compound heterozygosity for a hypomorphic SH2-domain allele and an
    activating allele that disrupts autoinhibition produces early-onset severe
    autoimmunity — bullous pemphigoid, colitis, nephrotic syndrome, a factor VIII
    autoantibody — rather than the CD8-lymphopenic immunodeficiency. The
    mechanism is a hyperactive kinase, not an absent one, so the pathophysiology
    chain in this entry does not describe it.
  evidence:
  - reference: PMID:26783323
    reference_title: "A novel human autoimmune syndrome caused by combined hypomorphic and activating mutations in ZAP-70."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutation R192W in the C-SH2 domain exhibited reduced binding to
      phosphorylated zeta-chain, whereas mutation R360P in the N lobe of the
      catalytic domain disrupted an autoinhibitory mechanism, producing a weakly
      hyperactive ZAP-70 protein.
    explanation: >-
      Establishes the two-allele mechanism that distinguishes this entity from
      loss-of-function ZAP70 deficiency.
  - reference: PMID:35748970
    reference_title: "Human Inborn Errors of Immunity: 2022 Update on the Classification from the International Union of Immunological Societies Expert Committee."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      ZAP-70 combined hypomorphic and activating mutations ZAP70 AR (LOF/GOF)
      617006
    explanation: >-
      The IUIS row for this entity, carrying its own OMIM number and its own
      LOF/GOF mechanism annotation. This is what makes keeping it out of
      has_subtypes a sourced decision rather than a curator preference.
  - reference: PMID:26783323
    reference_title: "A novel human autoimmune syndrome caused by combined hypomorphic and activating mutations in ZAP-70."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      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.
    explanation: >-
      Describes the autoimmune-dominant presentation that separates this entity
      clinically.
discussions:
- discussion_id: mouse_null_does_not_model_lineage_selectivity
  kind: HUMAN_MODEL_MISMATCH
  prompt: >-
    Can a Zap70-null mouse be used to predict the T-cell compartment of a human
    ZAP70-deficient patient, when the null allele arrests both lineages in the
    mouse and only the CD8 lineage in people?
  attaches_to:
  - pathophysiology#Block of CD8 Single-Positive Thymocyte Selection
  - animal_models#Zap70-null mouse
  rationale: >-
    The mismatch is not a difference of degree, and it is the whole diagnostic
    signature of the human disease that goes missing. Complete Zap70 loss arrests
    murine thymocytes at the double-positive stage with no mature peripheral T
    cells at all; the same loss in a patient produces a thymus with CD4
    single-positive cells in the medulla and a periphery with normal or elevated
    CD4 counts. The proposed cause is concrete rather than hand-waving — SYK is
    expressed far more highly in human than in murine thymocytes and can carry the
    lower signalling threshold the CD4 lineage requires — and it is supported from
    both directions: forcing Syk expression into zap-70-/- mice restores thymocyte
    development, and the residual CD8 cells in patients are the ones expressing
    SYK.

    The practical rule this yields is narrow enough to be useful. The null mouse
    is informative about what ZAP-70 does in selection and about signalling
    mechanism; it is not informative about which lineage survives, about the
    peripheral immunophenotype, or about anything downstream of having a CD4
    compartment — which includes the antibody-help defect and the autoimmune arm.
    For those, the hypomorphic strains are the better read, and the human cohort
    data are the only real answer.
  evidence:
  - reference: PMID:41080547
    reference_title: "Clinical, immunological, molecular characteristics and outcomes of stem cell transplantation in ZAP70 deficiency: a single-center experience."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The absence of ZAP70 protein thus results in selective CD8+ T-cell
      deficiency with impaired signal transduction in CD4+ T-cells in humans,
      whereas in murine models, complete ZAP70 deficiency leads to an arrest in
      both CD4+ and CD8+ T-cell development because of insufficient Syk
      expression (17).
    explanation: >-
      States the mismatch and its proposed cause in one sentence.
  - reference: PMID:9324357
    reference_title: "Restoration of thymocyte development and function in zap-70-/- mice by the Syk protein tyrosine kinase."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Syk expression restored both thymocyte development and function.
    explanation: >-
      Supplies the experimental half of the argument: SYK is sufficient to carry
      the developmental function in the mouse, so its abundance is a plausible
      determinant of the species difference.
  - reference: PMID:26187144
    reference_title: "SYK expression endows human ZAP70-deficient CD8 T cells with residual TCR signaling."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings highlight the differential requirements of ZAP70 and SYK
      during thymic development, peripheral homeostasis as well as effector
      functions of CD4 and CD8 T cells.
    explanation: >-
      Supplies the human half: SYK dependence differs by lineage in patients,
      which is the same axis the species difference runs along.
- discussion_id: no_genotype_phenotype_correlation
  kind: KNOWLEDGE_GAP
  prompt: >-
    Why does allele class fail to predict clinical severity in ZAP70 deficiency,
    when it predicts residual protein function well?
  attaches_to:
  - genetic#ZAP70
  - pathophysiology#Impaired Negative Selection and Thymic Regulatory T Cell Output
  rationale: >-
    The largest systematic review found no significant genotype-phenotype
    correlation between classical and leaky alleles or across mutation types,
    which is awkward, because the mechanistic story predicts one: residual
    function should map onto residual T-cell survival, and residual T-cell
    survival is what the autoimmune arm needs. Candidate explanations have not
    been separated — the cohort may simply be too small and too heterogeneously
    ascertained to detect a real correlation; SYK expression varies between
    patients and could dominate allele effect; or the determinant of the
    autoimmune arm may be TCR repertoire skewing, which allele class does not
    predict in a simple way. Until this is settled, prognostic counselling cannot
    be based on the variant.
  evidence:
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Based on the current evidence, there is no genotype-phenotype correlation
      in ZAP-70 deficient patients.
    explanation: >-
      The finding the gap is about: allele class does not predict clinical
      severity in the largest pooled cohort.
- discussion_id: trec_screening_blind_spot
  kind: OPEN_QUESTION
  prompt: >-
    Should newborn screening programmes in populations carrying the Mennonite
    founder allele supplement TREC screening with a CD8-based or targeted genetic
    test?
  attaches_to:
  - diagnosis#Newborn TREC screening
  - pathophysiology#Block of CD8 Single-Positive Thymocyte Selection
  rationale: >-
    TREC screening measures thymic output, and in this disorder thymic output
    continues through an intact CD4 lineage, so an affected infant can screen
    normal. That is not a marginal failure mode; it follows directly from the
    lineage selectivity that defines the disease. Genetically confirmed patients
    with retrospectively normal TREC screens are on record. Whether the answer is
    a supplementary CD8 count in founder communities, a targeted ZAP70 assay, or
    accepting the gap and relying on clinical suspicion has not been settled, and
    the trade-off depends on local prevalence that has never been measured.
  evidence:
  - reference: PMID:26187144
    reference_title: "SYK expression endows human ZAP70-deficient CD8 T cells with residual TCR signaling."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Retrospective TCR excision circle newborn screening was normal in both
      patients.
    explanation: >-
      The patient-level observation that grounds the question: confirmed patients
      with normal TREC screens.
  - reference: PMID:32431715
    reference_title: "Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ZAP-70 has not been frequently picked up during the >10 year screening
      experience in the United States (49), despite a significant Mennonite
      population and the large number of reported ZAP-70 patients.
    explanation: >-
      The programme-level counterpart, and the reason the question is about
      screening policy rather than about two patients.
notes: >-
  Frequencies here come almost entirely from one systematic review pooling 49
  patients from 33 case reports and series, supplemented by a 13-patient
  single-centre cohort. They describe the published literature and not a
  population, and the ascertainment is skewed by the Mennonite founder allele and
  by consanguinity in the reporting centres. Treat every percentage as a
  literature statistic.

  The combined hypomorphic-and-activating ZAP70 syndrome (OMIM 617006) is kept in
  differential_diagnoses rather than has_subtypes on purpose. It is a distinct
  IUIS row with a distinct mechanism — a hyperactive kinase, not an absent one —
  and the pathophysiology chain in this entry would misdescribe it. The
  siblings reported in PMID:26783323 are cited only in that differential entry
  for the same reason.

  No `datasets:` block. This is a deliberate omission rather than an unfinished
  one. ZAP70 is famous in a second, unrelated context — it is a long-standing
  prognostic marker in chronic lymphocytic leukaemia — so a gene-keyed search of
  the expression repositories returns CLL cohorts, which resolve perfectly and
  are about a different disease. That is the Named Entity Confusion trap the
  dataset-curation guidance describes, reached through gene search. With 49
  patients pooled worldwide there is no disease-specific omics series to find
  instead, so the block is left out rather than filled with accessions that
  verify and mislead.

  Corrections applied to the deep-research report for this entry (claude_code,
  after a recorded fallback from falcon), recorded because most of them are
  invisible to the tooling that would normally catch them.

  Two HP bindings the report's own term-validation section flagged as naming a
  different concept: HP:0005416, offered as "T lymphocytopenia", is Decreased
  circulating complement factor B concentration; HP:0004791, offered as
  "Increased CD4:CD8 ratio", is Esophageal ulceration. A third, HP:0002846
  offered as "Abnormal T cell physiology", is Abnormal B cell morphology; the
  validator placed that one in its softer "worth a second look" bucket rather
  than calling it a different concept, which understates it. None of the three
  was bound.

  The report gave "HGNC:7535" as the ZAP70 gene id. That is the NCBI Gene id, and
  HGNC has no record 7535 at all. Gene CURIEs are skipped by the report-side term
  validator and the KB-side check compares a CURIE only against its own label, so
  nothing in the pipeline would have caught this; hgnc:12858 was taken from HGNC
  directly.

  The report described the pooled review's 32% corticosteroid figure as treatment
  of autoimmune manifestations. The source sentence says those steroids were
  given as prophylaxis or to control adverse effects of transplantation. The
  Corticosteroid Therapy entry records the peri-transplant indication instead and
  makes no target_mechanisms link to the dysregulation node, because no cited
  source supports one. The autoimmune arm consequently has no disease-directed
  treatment in this entry; that is the state of the cited literature, not an
  omission.

📚

References & Deep Research

References

1

PMID:20301777

ZAP70 Deficiency.

No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (3)

Record notes

Frequencies here come almost entirely from one systematic review pooling 49 patients from 33 case reports and series, supplemented by a 13-patient single-centre cohort. They describe the published literature and not a population, and the ascertainment is skewed by the Mennonite founder allele and by consanguinity in the reporting centres. Treat every percentage as a literature statistic. The combined hypomorphic-and-activating ZAP70 syndrome (OMIM 617006) is kept in differential_diagnoses rather than has_subtypes on purpose. It is a distinct IUIS row with a distinct mechanism — a hyperactive kinase, not an absent one — and the pathophysiology chain in this entry would misdescribe it. The siblings reported in PMID:26783323 are cited only in that differential entry for the same reason. No `datasets:` block. This is a deliberate omission rather than an unfinished one. ZAP70 is famous in a second, unrelated context — it is a long-standing prognostic marker in chronic lymphocytic leukaemia — so a gene-keyed search of the expression repositories returns CLL cohorts, which resolve perfectly and are about a different disease. That is the Named Entity Confusion trap the dataset-curation guidance describes, reached through gene search. With 49 patients pooled worldwide there is no disease-specific omics series to find instead, so the block is left out rather than filled with accessions that verify and mislead. Corrections applied to the deep-research report for this entry (claude_code, after a recorded fallback from falcon), recorded because most of them are invisible to the tooling that would normally catch them. Two HP bindings the report's own term-validation section flagged as naming a different concept: HP:0005416, offered as "T lymphocytopenia", is Decreased circulating complement factor B concentration; HP:0004791, offered as "Increased CD4:CD8 ratio", is Esophageal ulceration. A third, HP:0002846 offered as "Abnormal T cell physiology", is Abnormal B cell morphology; the validator placed that one in its softer "worth a second look" bucket rather than calling it a different concept, which understates it. None of the three was bound. The report gave "HGNC:7535" as the ZAP70 gene id. That is the NCBI Gene id, and HGNC has no record 7535 at all. Gene CURIEs are skipped by the report-side term validator and the KB-side check compares a CURIE only against its own label, so nothing in the pipeline would have caught this; hgnc:12858 was taken from HGNC directly. The report described the pooled review's 32% corticosteroid figure as treatment of autoimmune manifestations. The source sentence says those steroids were given as prophylaxis or to control adverse effects of transplantation. The Corticosteroid Therapy entry records the peri-transplant indication instead and makes no target_mechanisms link to the dysregulation node, because no cited source supports one. The autoimmune arm consequently has no disease-directed treatment in this entry; that is the state of the cited literature, not an omission.

Pre-PR self-review: ZAP70 Deficiency · 2026-09-09T02:27:10Z · View source

Adversarial self-review of the entry created earlier in this session, run in a fresh-context subagent against .claude/skills/dismech-pr-review before opening any PR. One critical finding, twelve important, eleven minor; all acted on except one deferred, listed below. Critical. The differential-diagnosis entry named IL2RG, JAK3 and IL7R under a 'T-B+NK+ SCID' label. IL2RG and JAK3 deficiency are T-B+NK-, because the common gamma chain is required for IL-15 signalling and therefore for NK development; only IL7R gives T-B+NK+. The error mattered here specifically because preserved NK cells are one of the discriminators the entry relies on elsewhere. Renamed to 'Classical SCID (IL2RG, JAK3, IL7R)' and the description now states the NK phenotypes per gene. Frequency errors. Chronic diarrhea carried the enteropathy figure (18.4%, OCCASIONAL) rather than the diarrhoea figure the same paper reports separately (50%, FREQUENT). Failure to thrive carried no frequency and was evidenced by a generic sentence about SCID rather than about this disease; it now cites the 43.6% figure. Decreased circulating immunoglobulin now cites the 27.3% figure that supports its OCCASIONAL band. Ontology fitness, not correctness. Every binding was already the canonical label for its CURIE, but two were one step too broad. GO:0045061 (thymic T cell selection) is the parent of both positive and negative selection and formally subsumed GO:0045060 used on a sibling node; replaced with GO:0045059 (positive thymic T cell selection), which is what the node and its snippet actually claim. HP:0004313 (Decreased circulating immunoglobulin concentration) replaced with HP:0004315 (Decreased circulating IgG concentration), which matches the preferred_term already written and the entry's own statement that IgM and IgA are normal. NCIT:C201466 replaced with NCIT:C46089 (Allogeneic Hematopoietic Stem Cell Transplantation), an exact match. NCIT:C121331 (Intravenous Immunoglobulin Therapy) had already been replaced with the route-agnostic NCIT:C62710 during curation. GO:0004715 modifier changed from LOSS_OF_FUNCTION to DECREASED: the claim for a null allele is quantitative, GAIN/LOSS_OF_FUNCTION on modifier is unbound, and no KB entry currently co-occurs it with functional_impact_category. Pathograph. One node bundled two claims and was wired to a state that contradicted its own text: 'Loss of Central and Peripheral T Cell Tolerance' asserted central and peripheral tolerance failure plus a Treg deficit, was scoped CELLULAR, bound only a thymic process, and hung DIRECT off complete signal-propagation failure while its description said the mechanism needs attenuated rather than absent signalling. Split: a new MOLECULAR node 'Attenuated Residual TCR Signaling' with PARTIAL_LOSS_OF_FUNCTION genetic_context now sits between the lesion and a renamed, thymus-scoped 'Impaired Negative Selection and Thymic Regulatory T Cell Output'. Eczematoid dermatitis was an orphan with no incoming edge despite being the second most frequent manifestation; it is now reached from the dysregulation node with its own cited edge. Phenotype coverage. Added five above or near the 10% threshold, all quotable from the already-cached systematic review: Pneumonia (71.4%), BCGosis (18.4%), Hepatomegaly (19.4%), Splenomegaly (13.9%), and Increased circulating IgE concentration (GeneReviews names atopy; no frequency recorded because the source gives a distribution rather than a proportion). Sourcing. The TREC blind spot rested on a two-patient incidental observation while the programme-level statement sat unused in a cited cache; both the '>10 year screening experience in the United States' sentence and the mechanism sentence from PMID:37313400 are now cited, in the diagnosis section and in the discussion. The EBV attribution in the cytotoxic-surveillance node was uncited and now quotes the malignancy sentence naming EBV-associated DLBCL. The differential-threshold half of the SYK explanation was asserted three times without a source; PMID:20332428 (TetZap70 inducible mouse) was fetched and cited for it. Homozygosity split, founder allele, GeneReviews 25% recurrence risk and surveillance schedule, and the breastfeeding/CMV precaution are now quoted rather than paraphrased. The IUIS row for OMIM 617006 is quoted, which turns the lump/split decision into a sourced one. Grading. Six evidence items quoting review-style background sentences from PMID:41080547 (each carrying a trailing citation marker to that paper's own reference list, and one of them about murine data) were regraded HUMAN_CLINICAL to OTHER. check-snippet-grading would not have caught these, since the file was internally consistent. Overclaiming. The SYK explanation on the CD8 lymphopenia node said the paper explains why those cells survived; it measures residual signalling, not survival, and the explanation now says so. The R170C/R192W expression claim was generalized from R170C and is now scoped to it. The T-cell-help explanation now names where the normal-B-cell-count observation is cited rather than implying its own snippet carries it. New content. Post-Transplant Surveillance and Corticosteroid Therapy treatments, and an 'Outcome by transplant status' progression phase carrying the mortality comparison and the age-at-transplant finding. The corticosteroid entry is scoped narrowly on purpose: the deep-research report described the pooled review's 32% figure as treatment of autoimmune manifestations, but the source sentence says those steroids were peri-transplant. The entry records the peri-transplant indication and makes no target_mechanisms link to the dysregulation node. The autoimmune arm therefore has no disease-directed treatment, which is the state of the cited literature. Register. Eight passages were rewritten from essayistic to knowledge-base register. One in particular asserted a diagnostic dictum ('has ZAP70 deficiency until proven otherwise') that no cited source makes; it now states what the largest review actually recommends. Deferred, with reason. No mappings block. mappings.mondo_mappings would be redundant against a disease_term that is already the MONDO term, and the ICD-10-CM code the report supplies would add an ICD10CM binding that leaves cache/icd10cm/hierarchy.csv stale without a 1.2 GB local build to rebuild it. The other identifiers the report gives (OMIM, UMLS, GARD) have no slot in this schema. Left for a follow-up that can rebuild the hierarchy cache. Also noted: the reviewer flagged that describing HP:0002846 as 'flagged as naming a different concept' overstated the report's own wording, since the validator put it in the softer bucket. The notes block now says so. Validation after the rework: just validate and just validate-disorders pass with 107/107 snippets verified (up from 82); entity-refs, causal-targets, duplicate-keys, qualifier-terms pass on the file; folded-hyphens, snippet-length, title-snippets, snippet-grading and enum-values pass whole-KB with no new baseline entries. Compliance 89.5% weighted, up from 88.2%.

Create: ZAP70 Deficiency · 2026-09-09T02:06:11Z · View source

Created kb/disorders/ZAP70_Deficiency.yaml for MONDO:0010023 (combined immunodeficiency due to ZAP70 deficiency) and deleted the corresponding curation stub. Deep research: requested falcon; EDISON_API_KEY was not configured in this environment, so the run was made with --fallback and claude_code produced the report. The report is committed as research/ZAP70_Deficiency-deep-research-claude_code.md with fell_back/requested_provider/provider_attempts recorded in its frontmatter, plus its own reference- and term-validation sections. Report validation results acted on: reference validation resolved 18/18 identifiers (confabulation_rate 0.0) with one quote flagged as not found in PMID:8124727 - that quote was a paraphrase and was not reused; the verbatim sentence from the same abstract was used instead. Term validation flagged three HP bindings as naming different concepts (HP:0005416 offered as 'T lymphocytopenia' but actually Decreased circulating complement factor B concentration; HP:0004791 offered as 'Increased CD4:CD8 ratio' but actually Esophageal ulceration; HP:0002846 offered as 'Abnormal T cell physiology' but actually Abnormal B cell morphology). None of the three was bound. The report also offered HGNC:7535 as the ZAP70 gene id, which is the NCBI Gene id rather than an HGNC id; gene CURIEs are skipped by the report-side term validator, so this was caught by resolving the symbol against the HGNC REST API, which returns hgnc:12858. That correction is recorded in the entry's genetic notes. GeneReviews baseline: PMID:20301777 exists for this disease, was fetched, tagged GeneReviews in the top-level references block, and used as the phenotype floor and as the source for the agents/circumstances-to-avoid content in the treatment entries. Named Entity Confusion preflight (just preflight-dr against MONDO:0010023) raised one WARN naming CD4 as a rival gene at 41% of ZAP70 mentions. Judged a false positive: CD4 appears throughout as a T-cell lineage marker, not as a second disease gene, and the OMIM id in the report matches MONDO's (269840). Content: 11-node pathophysiology chain from ZAP70 loss of kinase function through the TCR-proximal signalling failure to the lineage-selective CD8 thymic selection block, the peripheral CD8 lymphopenia, the anergic CD4 compartment, and the parallel tolerance-failure branch. 12 phenotypes with frequencies from the 49-patient systematic review (PMID:32431715). Two animal models with modeled_mechanisms links, including a FAILS_TO_RECAPITULATE link for the Zap70-null mouse against peripheral CD8 lymphopenia, and a HUMAN_MODEL_MISMATCH discussion for the SYK-expression species difference that causes it. Lump/split: curated as DISEASE. The ZAP70 combined hypomorphic-and-activating syndrome (OMIM 617006, PMID:26783323) is placed in differential_diagnoses rather than has_subtypes because it is a separate IUIS row with the opposite mechanism (hyperactive rather than absent kinase); PMID:26783323 is cited only there. No datasets block, deliberately: ZAP70 is a well-known prognostic marker in chronic lymphocytic leukaemia, so gene-keyed repository search returns CLL cohorts that resolve perfectly and are about a different disease, and there is no disease-specific omics series for a disorder with 49 pooled patients. Reason recorded in the entry notes. Validation: just validate passed (schema, terms, references) with 82/82 snippets verified against the cached references. check-entity-refs, check-causal-targets, check-duplicate-keys and check-qualifier-terms pass on the file; check-folded-hyphens, check-snippet-length and check-title-snippets pass whole-KB with no new baseline entries. Compliance 88.2% weighted; the residual gap is uncited pathophysiology edges where no source states the causal step, plus the deliberately absent datasets block.

Claude Code ▸

ZAP70 Deficiency — Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 19 citations 2026-09-09T01:50:27.965240

ZAP70 Deficiency — Comprehensive Research Report

1. Disease Information

Overview. ZAP70 deficiency (also called ZAP70-related combined immunodeficiency, "Selective T-cell defect," or historically "CD8 lymphopenia due to ZAP-70 deficiency") is a rare autosomal recessive combined immunodeficiency (CID) caused by biallelic loss-of-function variants in ZAP70, encoding the T-cell receptor (TCR)-proximal tyrosine kinase Zeta-chain-associated protein kinase 70. It was first described in 1994 in three children of Mennonite descent presenting with a SCID-like phenotype but a distinctive immunophenotype: profoundly reduced/absent CD8+ T cells with normal or elevated CD4+ T cells (Arpaia et al., PMID: 8124727; Elder et al.). Since then, over 80 affected individuals from >40 families have been reported worldwide (GeneReviews, NBK20221; Sharifinejad et al., 2020, PMID: 32431715).

Key identifiers:

Resource	Identifier
OMIM	269840 (Immunodeficiency 48)
Gene (OMIM)	ZAP70, 176947
MONDO	MONDO:0010023
Orphanet	Combined immunodeficiency due to ZAP70 deficiency (Orphanet Expert/gene page ZAP70)
GARD	387
UMLS	C2931299
ICD-10-CM	D81.8 (Other combined immunodeficiencies)
HGNC (gene)	HGNC:7535
Gene location	2q11.2
GeneReviews	NBK20221

Synonyms: ZAP-70 deficiency; Selective CD8+ T-lymphocyte deficiency; ZAP70-related combined immunodeficiency; CD8 lymphopenia due to ZAP-70 deficiency; SCID due to ZAP70 deficiency (older, imprecise usage — see below); Immunodeficiency 48.

Source of information. Almost all published data derive from aggregated case reports and case series (individual patient-level clinical/immunologic/genetic data pooled into systematic reviews), not large-scale EHR/registry-based studies, reflecting the disease's rarity (Sharifinejad et al. 2020 pooled 49 patients from 33 published articles; a 2025 single-center series (PMC12507918) adds further transplant outcome data).

2. Etiology

Disease causal factor: Biallelic (homozygous or compound heterozygous) loss-of-function or hypomorphic pathogenic variants in ZAP70 (HGNC:7535, chr2q11.2) are the sole established cause. There is no known infectious or purely environmental etiology; this is a monogenic inborn error of immunity.

Genetic risk factors: - Autosomal recessive inheritance — biallelic pathogenic variants required. - Consanguinity is a major risk factor: reported in 36.1% (first-degree) and 16.7% (second-degree relative) parental unions among reviewed cases (Sharifinejad et al. 2020). - Founder effect: the intronic variant c.1624-11G>A (destabilizing splicing, p.K541_K542insLEQ) is a recurrent founder mutation identified in ~10 unrelated families, overwhelmingly of Old Order Mennonite descent from Canada/Pennsylvania (30.6% of the reviewed cohort). Other ethnic enrichments reported include Turkish (22.4%), and Japanese and Caucasian (6.1% each) (Sharifinejad et al. 2020). - No genome-wide association (GWAS) susceptibility loci are described — this is a Mendelian, fully penetrant disorder rather than a polygenic-risk condition. - Population allele-frequency databases (gnomAD) do not report an established general-population carrier frequency for ZAP70 pathogenic variants outside the Mennonite founder allele; no genome-wide carrier-frequency study specific to ZAP70 was identified in this search.

Environmental risk factors: None identified as causal. Because affected infants have a profound cellular immunodeficiency, common childhood pathogen exposures (viral, opportunistic) act as precipitants of clinical presentation rather than causal agents — see Section 5.

Protective factors: None described; there is no evidence of protective alleles at the ZAP70 locus. The partial functional compensation provided by the paralogous kinase SYK in some residual CD8+ T cells (see Mechanism, below) is the closest analog to an endogenous "modifier" — patients whose residual CD8 T cells retain higher SYK expression show somewhat preserved TCR signaling function (Toyabe et al., PMID: 26187144).

Gene–environment interactions: Not formally studied; the phenotype is driven overwhelmingly by genotype (loss vs. hypomorphic variant), with infectious/antigenic exposure determining the timing and severity of clinical presentation rather than modifying underlying risk.

3. Phenotypes

Immunodeficiency-related (laboratory abnormalities)

Phenotype	Frequency (Sharifinejad 2020, n=49)	Suggested HPO term
Decreased CD8+ T-cell count (median 75 cells/µL)	97.9%	HP:0032219 (Decreased CD8:CD4 ratio) / HP:0005416 (T lymphocytopenia)
Normal/elevated CD4+ T cells (median 2,312/µL)	Near-universal	HP:0004791 (Increased CD4:CD8 ratio)
Reduced mitogen (PHA) proliferative response	95% (38/40)	HP:0002846 (Abnormal T cell physiology)
Poor polysaccharide vaccine antibody response	55.6%	HP:0002846
Poor peptide/protein vaccine antibody response	80%	HP:0002846
Hypogammaglobulinemia / decreased IgG	27.3% (12/44)	HP:0004315 (Decreased circulating IgG)
Decreased IgA	13.3%	HP:0002720
Decreased IgM	11.1%	HP:0002850
Hyper-IgM-like phenotype	13%	HP:0010976
Reduced TREC (T-cell receptor excision circles)	50% (5/10 tested)	—

Clinical/infectious phenotypes

Phenotype	Frequency	HPO term
Recurrent respiratory infections	81.8%	HP:0002205
Pneumonia (recurrent)	71.4%	HP:0002090
Cutaneous involvement (rash, eczema, ichthyosis, bullous lesions)	57.9%	HP:0000988 (Skin rash), HP:0000964 (Eczema)
Chronic diarrhea	50%	HP:0002014
Failure to thrive	43.6%	HP:0001508
Lymphoproliferation / lymphadenopathy	32.4%	HP:0002716
Hepatomegaly	19.4%	HP:0002240
ENT infections (otitis media, sinusitis)	19.4%	HP:0000388
Enteropathy	18.4%	HP:0002027
Hematologic abnormality (cytopenias, HLH)	16.7%	HP:0001871
Splenomegaly	13.9%	HP:0001744
Neurologic abnormality (encephalitis, silent infarcts)	13.9%	HP:0012638
Autoimmunity (cytopenias, nephritis, bullous pemphigoid, adrenal insufficiency, colitis)	19.4%	HP:0002960
Malignancy (predominantly EBV-associated lymphoma)	8.1%	HP:0002664

Infectious agents identified in this cohort: CMV (29%), Varicella (29%), EBV (12.5%), Rotavirus (4.1%); BCG-related disease (18.4%, reflecting BCG vaccination in endemic settings before diagnosis); Candida albicans (28.9%); Pneumocystis jirovecii (24.5%).

Onset, severity, progression: - Median age of symptom onset: 4.0 months (IQR 2.0–7.0); 97.3% present within the first 12 months of life. - Median diagnostic age: 10.4 months; median diagnostic delay ~5 months. - Severity is variable — ranging from a SCID-like presentation in infancy (initially misdiagnosed as SCID in 73.5% of cases) to later-onset, milder combined immunodeficiency with prominent immune dysregulation/autoimmunity in patients with hypomorphic ("leaky") variants. - Course is progressive without treatment: infants presenting with severe infection in the first year typically do not survive past their second year without HSCT (GeneReviews NBK20221). - Bullous pemphigoid, colitis and nephrotic-range proteinuria have been documented as a severe, uncontrollable autoimmune triad in siblings with ZAP70 deficiency (case report literature).

Quality of life impact: Formal EQ-5D/SF-36 data are not available for this ultra-rare disease; qualitatively, untreated disease carries high infection-related morbidity, growth failure, and (in autoimmune-predominant presentations) chronic organ-specific autoimmune disease (skin, gut, kidney) substantially impairing daily function; successful HSCT is associated with resolution of most clinical manifestations and normalization of growth and activity (GeneReviews; Sharifinejad 2020).

4. Genetic/Molecular Information

Causal gene: ZAP70 (Zeta-chain-associated protein kinase 70; HGNC:7535; NCBI Gene ID 7535; UniProt P43403), chromosome 2q11.2. OMIM gene entry 176947; disease entry 269840.

Variant spectrum (Sharifinejad et al. 2020; n=49 patients, 41 families, 32 unique variants): - Missense: 23 (majority) - Indel/frameshift: 5 - Splice-site: 3 - Nonsense: 1 - 77.5% homozygous, 16.3% compound heterozygous. - Variants occur throughout the gene with no single dominant hotspot, though the majority cluster in the kinase domain. - Founder variant: c.1624-11G>A (splice-altering, resulting in p.K541_K542insLEQ), the most common single variant, found in ~10 Mennonite families. - Newly characterized C-terminal SH2 domain (SH2-C) variants (Bucciol et al., 2023, PMID: 37313400, DOI:10.3389/fimmu.2023.1155883): p.R170C and p.R192W in four patients. Unlike classical loss-of-expression variants, these preserve ZAP-70 protein expression but abolish binding of ZAP-70 to phosphorylated TCR-ζ, causing attenuated TCR-induced ZAP-70 phosphorylation and absent TCR-induced proliferation. Patients with SH2-C variants presented with combined immunodeficiency plus prominent autoimmunity, expanding the phenotypic spectrum beyond "classic" kinase-domain loss-of-function disease.

Variant classification/mechanistic categories (per Sharifinejad et al. 2020): 1. Classical/amorphic (36 patients): abolish protein expression entirely. 2. Leaky/hypomorphic (5 patients): allow residual protein expression/function, generally associated with milder or later-onset disease. 3. Atypical (2 patients): combined loss-of-function/gain-of-function effects.

Genotype–phenotype correlation: The largest systematic review concludes there is no significant genotype–phenotype correlation between classical vs. leaky mutation groups or among different mutation types with respect to clinical/laboratory severity — an important caveat for prognostic counseling.

Population frequency: No general-population allele-frequency estimate specific to ZAP70 pathogenic variants was retrievable from gnomAD-based studies in this search; the disease is considered ultra-rare outside the Mennonite founder-variant carrier pool, where regional carrier frequency is elevated due to the founder effect and community endogamy.

Somatic vs. germline: ZAP70 deficiency is exclusively a germline condition. (Note: ZAP70 over-expression/dysregulation is separately implicated as a somatic prognostic marker in chronic lymphocytic leukemia — a distinct, unrelated biological context not covered by this deficiency phenotype.)

Functional consequence: Predominantly loss-of-function (complete or partial loss of kinase activity or TCR-binding capacity). A biologically distinct gain-of-function mechanism exists at the same locus but causes a different clinical entity (see below) rather than classic deficiency.

Modifier genes: SYK (the ZAP70 paralog) is the principal identified functional modifier — see Mechanism section.

Epigenetics / chromosomal abnormalities: No disease-specific epigenetic marks or chromosomal structural abnormalities (aneuploidy, translocation) have been reported as causal; ZAP70 deficiency is a point-variant/small-indel monogenic disorder.

Related but distinct entity — ZAP70 gain-of-function (GOF) syndrome: Disease-associated variants (e.g., p.R360P) that disrupt ZAP-70's autoinhibited conformation produce a gain-of-function, hyperactive kinase that enhances TCR responses to weak/self-ligands, producing an early-onset familial autoimmune syndrome distinct from the CD8-lymphopenic deficiency phenotype (Ashouri et al., Immunol Rev 2022, PMID referenced via PMC8986586; Science Signaling scisignal.abc4479). This GOF entity is mechanistically and clinically separate and should not be conflated with classical ZAP70 deficiency in curation, though both illustrate that either too little or too much ZAP-70 activity disrupts thymic selection and immune tolerance.

5. Environmental Information

Environmental factors: No toxin, chemical, or radiation exposure is implicated in causing ZAP70 deficiency (it is fully genetic). Environmental/infectious exposures instead act as the triggers that unmask the underlying immunodeficiency: - BCG vaccination in BCG-endemic countries has caused disseminated BCG disease in undiagnosed infants (18.4% of the cohort), underscoring the need to avoid live vaccines pending diagnosis. - CMV and other congenital/perinatal viral exposure, including via breastfeeding from a CMV-seropositive mother, is a recognized risk for severe/fatal infection; GeneReviews management explicitly recommends withholding breastfeeding until maternal CMV status is established. - Non-irradiated blood products risk transfusion-associated graft-versus-host disease in these profoundly T-cell-dysfunctional infants. - Environmental fungal exposure (construction/soil sites) is flagged as an infection-risk in management guidance (invasive fungal disease risk).

Lifestyle factors: Not applicable in the classical sense (this is a pediatric-onset monogenic disease); avoidance of crowded/enclosed spaces and infection-control practices are the relevant "behavioral" mitigations pending immune reconstitution.

Infectious agents (as disease-uncovering/complicating pathogens, not causal agents): - Viral: CMV, varicella-zoster virus (including VZV encephalitis), EBV (including EBV-driven lymphoproliferative disease/lymphoma), rotavirus. - Bacterial: BCG (Mycobacterium bovis vaccine strain) causing disseminated disease. - Fungal: Candida albicans. - Protozoal/other: Pneumocystis jirovecii pneumonia.

These reflect the combined T-cell (CD8-predominant) and humoral functional defect rather than a specific microbial tropism for ZAP70-deficient tissue.

6. Mechanism / Pathophysiology

Ordered causal chain

Biallelic pathogenic ZAP70 variants (2q11.2) → loss or severe reduction of ZAP-70 kinase activity, or (for SH2-C domain variants) loss of ZAP-70's ability to dock on phosphorylated TCR-ζ ITAMs despite normal protein expression (Bucciol et al. 2023, PMID:37313400).
Following TCR engagement, LCK normally phosphorylates the ITAMs of the CD3/TCR-ζ complex; ZAP-70's tandem N- and C-terminal SH2 domains then dock onto these phospho-ITAMs, and LCK-mediated phosphorylation of ZAP-70 Tyr493 (activation loop) plus autophosphorylation activates the kinase. Loss-of-function or ITAM-binding-defective ZAP-70 breaks this recruitment/activation step, so downstream phosphorylation of LAT and SLP-76/LCP2 fails to occur (this leads to → step 3).
Failure to nucleate the LAT/SLP-76 signalosome leads to absent downstream calcium flux, defective PLCγ1 activation, and failure of Ras-MAPK and PKCθ-NF-κB pathway engagement — demonstrated directly in patient T cells as "weak tyrosine phosphorylation signals, no calcium flux, and defective proliferation" (Arpaia et al., PMID:8124727).
In the thymus, this TCR-signaling failure results in an asymmetric, lineage-selective block: CD4+CD8+ double-positive (DP) thymocytes fail to complete positive selection into the CD8 single-positive (SP) lineage, while CD4 SP maturation proceeds relatively intact because, as shown in TetZap70-inducible mice, CD4 SP development requires a lower ZAP70 signaling threshold than CD8 SP development (temporal/quantitative threshold model; Science Signaling scisignal.2000702). This step is directly demonstrated in human thymic sections: "CD4+CD8+ cells [are present] in the cortex; however, only CD4, not CD8, single-positive cells are present in the medulla" (GeneReviews NBK20221).
This selective failure leads to the hallmark peripheral immunophenotype: profound CD8+ T-lymphopenia with normal/elevated CD4+ T cells (elevated CD4:CD8 ratio), while B cells and NK cells remain numerically normal (they do not depend on ZAP-70 signaling for development).
Residual peripheral CD8+ T cells retain partial TCR signaling capacity in a subset of patients, which correlates with expression of the paralogous kinase SYK, which can partially substitute for ZAP-70 at the TCR (Toyabe et al., PMID:26187144); this is an inferred compensatory branch rather than a fully demonstrated therapeutic mechanism, and explains inter-patient variability in residual CD8 function independent of genotype.
The combined T-cell signaling defect results in impaired T-cell help for B-cell antibody responses (poor response to protein/polysaccharide vaccines in 55.6–80% of patients) despite normal B-cell numbers, leading to functional (rather than purely quantitative) humoral immunodeficiency and susceptibility to encapsulated-organism and opportunistic infection.
Global impairment of TCR-signal-dependent processes (central tolerance during negative selection, peripheral regulatory T-cell function, and lymphocyte homeostatic proliferation) leads to, in a parallel branch, loss of self-tolerance and immune dysregulation — manifesting as the autoimmune phenotypes (cytopenias, enteropathy, bullous pemphigoid, nephritis) seen in ~19% of patients, particularly among those with hypomorphic/leaky or SH2-C-domain variants that permit some peripheral T-cell survival with residual but disordered signaling. This branch is inferred from the correlation between milder/leaky genotypes and autoimmune-predominant phenotypes rather than fully mechanistically dissected in humans.
Unopposed viral antigen exposure (notably EBV) in the setting of defective cytotoxic (CD8+) surveillance leads to EBV-driven lymphoproliferative disease and lymphoma in a subset of patients (8.1%), representing a second downstream branch of the CD8 deficiency.

Molecular pathway/process detail (checklist coverage)

Molecular pathway: TCR proximal signaling cascade (LCK → CD3ζ ITAM phosphorylation → ZAP-70 recruitment/activation → LAT/SLP-76 phosphorylation → PLCγ1/Ras-MAPK/PKCθ-NF-κB). KEGG hsa04660 (T cell receptor signaling pathway) is the relevant reference pathway.
Cellular processes affected: thymocyte positive selection, T-cell activation/proliferation, cytokine production, cytoskeletal reorganization/immunological synapse formation, peripheral T-cell homeostasis.
Protein dysfunction: loss of catalytic (kinase) activity (classical variants) vs. loss of substrate/receptor docking via SH2 domains despite normal expression (SH2-C variants) vs. loss of autoinhibition/gain-of-function (R360P, distinct GOF disease).
Immune system involvement: combined immunodeficiency (T-cell, and secondary antibody-response defect) plus immune dysregulation/autoimmunity — this disease sits at the intersection of immunodeficiency and immune dysregulation, a recognized IUIS category ("combined immunodeficiency with associated/syndromic features" or "diseases of immune dysregulation" depending on presentation).
Molecular profiling: Structural biology (X-ray crystallography) has resolved the autoinhibited conformation of ZAP-70, in which interdomain A and interdomain B (the SH2-kinase linker, containing regulatory tyrosines Y315/Y319) pack against the kinase domain's C-lobe to stabilize an inactive state (Deindl et al., Cell 2007, PMID referenced via S0092-8674(07)00455-2). This structural mechanism explains why R360P (in this autoinhibitory interface) causes gain-of-function, while kinase-domain or SH2-domain substitutions elsewhere typically cause loss-of-function.

Cell types and biological processes (ontology suggestions)

Cell types (CL): CD8-positive, alpha-beta T cell (CL:0000625); CD4-positive, alpha-beta T cell (CL:0000624); double-positive, alpha-beta thymocyte (CL:0000809); naive thymus-derived CD8-positive T cell.
Biological processes (GO): T cell receptor signaling pathway (GO:0050852); positive thymic T cell selection (GO:0045059); positive regulation of alpha-beta T cell activation (GO:0046634); peptidyl-tyrosine phosphorylation (GO:0018108); protein tyrosine kinase activity (GO:0004713).
Molecular function: non-membrane spanning protein tyrosine kinase activity (GO:0004715).

7. Anatomical Structures Affected

Primary organ/system: Immune system — specifically the thymus (site of the developmental block) and peripheral lymphoid tissue (lymph node, spleen — site of downstream functional consequences and, when involved, lymphoproliferation).
Secondary organ involvement: Lung/respiratory tract (recurrent pneumonia), skin (rash, eczema, ichthyosis, bullous pemphigoid), gastrointestinal tract (enteropathy, colitis, chronic diarrhea), liver/spleen (hepatosplenomegaly), kidney (nephrotic syndrome, IgA nephropathy in autoimmune-predominant cases), central nervous system (silent infarcts, VZV encephalitis), cardiovascular system (hypertension, atrioventricular block reported in isolated cases).
Tissue/cell level: thymic cortex and medulla (differential involvement — see Mechanism); T-lymphocyte lineage specifically (CD8 SP lineage most affected); epidermal/dermal junction (in bullous pemphigoid, an autoantibody-mediated blistering process).
Subcellular level: the TCR/CD3 immune-synapse signalosome at the plasma membrane; cytoplasmic tyrosine-kinase signaling complex (GO Cellular Component: plasma membrane, T cell receptor complex GO:0042101).
Anatomical ontology suggestions (UBERON): thymus (UBERON:0002370), lymph node (UBERON:0000029), spleen (UBERON:0002106), skin epidermis (UBERON:0001003).
Laterality: Not applicable — systemic/bilateral immune process, not a laterality-defined structural anomaly.

8. Temporal Development

Onset: Predominantly infantile, median 4.0 months of age (IQR 2.0–7.0); congenital susceptibility present from birth, but clinical manifestation is typically delayed until maternal antibody protection wanes and pathogen exposure occurs. A minority present later in childhood or with a milder, immune-dysregulation-predominant phenotype associated with hypomorphic variants.
Onset pattern: Can be acute/severe (SCID-like presentation with life-threatening infection) or insidious (recurrent infections, failure to thrive, gradually apparent autoimmunity).
Progression: Without treatment, disease is progressive and generally fatal — patients "usually do not survive past their second year without allogeneic HSCT" (GeneReviews). With HSCT, the disease process is halted/reversed, with immune reconstitution and resolution of most clinical manifestations.
Disease course pattern: Predominantly progressive in the infectious/immunodeficiency domain; relapsing-remitting or chronic in the autoimmune-predominant subgroup (e.g., recurrent bullous pemphigoid flares, chronic enteropathy).
Critical period: The first year of life is the critical window both for clinical deterioration (97.3% present within 12 months) and for optimal transplant outcome — post-HSCT complication rates were markedly higher in patients transplanted after 6 months of age (66% of those with complications were >6 months at transplant), arguing for earlier diagnosis/transplant.
Remission: Only via curative HSCT; no spontaneous remission is described. Autoimmune manifestations may respond (partially) to corticosteroids pending definitive therapy (steroid response noted in 5/8 treated patients in the reviewed cohort).

9. Inheritance and Population

Epidemiology: ZAP70 deficiency is an ultra-rare disorder; over 80 patients have been reported in the literature since 1994, with no formal population-based prevalence/incidence estimate available (consistent with prevalence_class: NOT_YET_DOCUMENTED or an ultra-rare qualitative tier in dismech terms, pending a sourced quantitative estimate). It is one of the recognized causes of T–B+NK+ combined immunodeficiency and accounts for a small minority of SCID/CID newborn-screening referrals.

Inheritance pattern: Autosomal recessive. Parents of an affected child are obligate heterozygous carriers, typically asymptomatic. For carrier × carrier matings: 25% affected, 50% carrier, 25% unaffected/non-carrier per pregnancy (standard Mendelian AR risk, per GeneReviews).

Penetrance/expressivity: Full penetrance is generally assumed for biallelic loss-of-function variants, but expressivity is highly variable — ranging from SCID-like infantile presentation to milder, later-onset, autoimmunity-predominant disease — driven at least partly by variant "leakiness" (residual protein expression/function), though no strict genotype-phenotype correlation was established in the largest systematic review.

Genetic anticipation / germline mosaicism: Not reported for this disorder (not a repeat-expansion disease).

Founder effects: The c.1624-11G>A splice variant is a well-documented founder mutation concentrated in the Old Order Mennonite population (Pennsylvania/Ontario-derived communities), accounting for the disproportionate representation of Mennonite patients (30.6%) in the literature.

Consanguinity: A major contributor — present in over half of reported families (36.1% first-degree, 16.7% second-degree consanguineous unions).

Population demographics: - Ethnic enrichment: Mennonite (30.6%), Turkish (22.4%), Japanese and Caucasian (6.1% each) in the pooled cohort — reflecting both founder effects and consanguinity rates rather than an intrinsic geographic restriction. - Sex ratio: 27 males : 20 females in the pooled cohort — roughly balanced, consistent with autosomal (non-X-linked) inheritance (no significant sex skew expected or observed). - Age distribution: Overwhelmingly diagnosed in infancy/early childhood, consistent with onset timing above. - Family history: Positive family history of similarly affected relatives or early infant deaths reported in 61% of cases, useful as a diagnostic clue in consanguineous or founder populations.

10. Diagnostics

Clinical/laboratory tests: - Flow cytometric lymphocyte immunophenotyping is the key first-line test: markedly reduced/absent CD8+ T cells with normal/elevated CD4+ T cells, normal CD19+ B cells and CD16/56+ NK cells — a distinctive pattern that should immediately raise suspicion for ZAP70 deficiency over classical SCID. - Mitogen (PHA) proliferation assay: markedly reduced in ~95% of patients, reflecting the underlying TCR-signaling defect. - Quantitative immunoglobulins and specific antibody responses to protein and polysaccharide vaccine antigens: often abnormal despite normal B-cell counts (functional antibody-response defect). - TREC quantification: can be reduced but is not a reliable screening test for this disease (see Screening, below) — reduced in only 50% of tested patients. - Functional/research assays: TCR-induced calcium flux, ZAP-70 protein expression by flow cytometry/immunoblot, and ZAP-70–TCR-ζ co-immunoprecipitation (useful to distinguish classical loss-of-expression variants from SH2-C domain variants that preserve expression but lose TCR binding).

Genetic testing: - Single-gene ZAP70 sequencing is appropriate when the immunophenotype (low CD8, normal CD4) is characteristic, especially in a consanguineous family or Mennonite ancestry. - Combined immunodeficiency/SCID gene panels and whole-exome/genome sequencing are used more broadly, particularly when the phenotype is atypical (e.g., autoimmunity-predominant, as in SH2-C domain variant carriers) or family history/ethnicity does not point to ZAP70 specifically. - Chromosomal microarray/karyotype are not primary diagnostic tools for this single-gene disorder but may be used to exclude syndromic/chromosomal differentials.

Screening: - Newborn TREC-based SCID screening has a documented limitation for ZAP70 deficiency: "a substantial number of infants with ZAP70 deficiency have TREC levels above the lower levels used for newborn screening... TREC screening does not sufficiently identify these patients" and "has not been frequently picked up during >10 year screening experience in the United States" (Kwan et al., PMID:24797280; Sharifinejad et al. 2020). This reflects that thymic output (captured by TREC) can appear relatively preserved because CD4 SP thymocyte production continues even though CD8 SP maturation fails. - The key early, more sensitive laboratory clue is a low absolute CD8+ T-cell count, which precedes/parallels rather than depends on TREC decline. - Targeted screening (flow cytometry, and/or ZAP70 sequencing) is recommended for newborns with consanguineous parents, a positive family history of CID, or from high-prevalence founder populations (e.g., Mennonite communities), and for any infant with low CD8 counts identified incidentally. - Carrier/prenatal/preimplantation genetic testing is available once a familial pathogenic variant is identified, particularly relevant for at-risk consanguineous families and Mennonite communities with the known founder allele.

Differential diagnosis (key distinguishing features): | Disorder | Distinguishing feature vs. ZAP70 deficiency | |---|---| | X-linked SCID (IL2RG) | Affects males only; combined T AND NK cell deficiency (vs. normal NK in ZAP70 deficiency) | | ADA deficiency | Profound T, B, AND NK lymphopenia; neurologic/skeletal findings | | Familial/isolated CD8 deficiency (e.g., LCK deficiency) | Milder course; increased double-negative T cells; opportunistic infections and SCID-like presentation uncommon | | MHC class I deficiency (TAP/TAPBP) | Later onset, milder respiratory presentation, low CD8 via a different (antigen-presentation) mechanism | | RAG1/RAG2 deficiency | Low T AND B cell counts (vs. normal B cells in ZAP70 deficiency) |

11. Outcome/Prognosis

Survival/mortality (pooled cohort, Sharifinejad et al. 2020, n=49): - Overall mortality: 23.9% (11/49); overall survival at time of report: 76.1%. - HSCT recipients: 88–91.7% survival (22/25 alive at median 36-month follow-up in the pooled review); a separate long-term single-center study (Journal of Clinical Immunology, PMID:27438785) reported 8/8 (100%) alive at a median 13.5-year follow-up, and a 2025 single-center series (PMC12507918) reported 8/11 (73%) alive at median 7-year follow-up. - Non-transplanted patients: substantially worse survival — 59.1% (13/22) alive at median 18-month follow-up. - Statistical comparison: Kaplan-Meier analysis showed HSCT significantly reduced mortality (p<0.001). - Causes of death: acute respiratory distress, CMV pneumonitis, multiorgan failure from hemophagocytic lymphohistiocytosis, disseminated intravascular coagulation, recurrent apnea/breathing arrest, and cardiac atrioventricular block.

Morbidity/complications: - Post-HSCT graft-versus-host disease: 36% (9 patients). - Post-HSCT infections: 16% (4 patients). - Age at transplant is a key prognostic factor: complications were concentrated (66%) in patients transplanted after 6 months of age, supporting early diagnosis and transplantation. - Second HSCT required in a subset (3 patients in the pooled cohort) for graft failure.

Quality-of-life/functional outcome: Successful HSCT is associated with excellent long-term immune reconstitution and resolution of infectious and (generally) autoimmune manifestations; no dedicated validated QoL instrument data (EQ-5D/SF-36/PedsQL) specific to ZAP70 deficiency were identified in this search.

Prognostic factors: HSCT status (curative vs. not) is the dominant prognostic determinant; age at transplantation (<6 months preferred); myeloablative conditioning is associated with more robust, durable immune reconstitution than reduced-intensity/unconditioned approaches, though the latter remain life-saving options in critically ill patients. No reliable genotype-based prognostic marker exists (no genotype-phenotype correlation established).

12. Treatment

Curative therapy: - Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative treatment (NCIT:C15431, Hematopoietic Stem Cell Transplantation). Successful outcomes have been reported with: - Donor sources: HLA-matched sibling donors (61.9% of transplanted patients in the pooled review), matched unrelated donors (38.1%), and, per GeneReviews, haploidentical donors and unrelated umbilical cord blood. - Stem cell sources: bone marrow (68%), peripheral blood stem cells (20%), cord blood (12%). - Conditioning regimens reported as successful: busulfan/cyclophosphamide; busulfan/fludarabine/anti-thymocyte globulin; melphalan/fludarabine/anti-thymocyte globulin; myeloablative regimens are associated with more robust and durable engraftment, while reduced-intensity or unconditioned transplant (e.g., matched sibling donor without conditioning) is a viable life-saving option in critically ill infants with active infection/end-organ damage.

Investigational/advanced therapeutics: - Gene therapy (NCIT:C15238) has not reached clinical application for ZAP70 deficiency but has strong preclinical proof-of-concept: retroviral transduction of primary ZAP-70-deficient human T cells restores a selective growth/functional advantage to gene-corrected cells (Nature Gene Therapy, "Retrovirus-mediated transduction..."), and direct intrathymic injection of a T-cell-specific lentiviral vector encoding ZAP70 achieved long-term differentiation of mature TCR-αβ+ thymocytes with a partially diversified receptor repertoire in a mouse model, even without conditioning (JCI, "In vivo correction of ZAP-70 immunodeficiency by intrathymic gene transfer"). These approaches are proposed as a potentially safer alternative to ex vivo gene-modified HSCT but remain preclinical.

Pharmacotherapy and supportive care: - Immunoglobulin replacement therapy (IVIG) (NCIT:C15986, Pharmacotherapy) — used even in patients with normal quantitative immunoglobulin levels, given the demonstrated functional antibody-response defect; used in 36.7% of the HSCT-treated subgroup in the pooled cohort as peri-transplant supportive care. - Anti-infective prophylaxis: antibacterial, antifungal, antiviral, and anti-Pneumocystis jirovecii prophylaxis (NCIT:C15747, Supportive Care). - Corticosteroids (NCIT:C2977, Corticosteroid) for autoimmune manifestations — used in 32% (8/25) of the HSCT-treated subgroup, with clinical response documented in 5 patients. - Blood product precautions: only irradiated, leukoreduced, CMV-safe blood products, given risk of transfusion-associated GVHD in profoundly T-cell-dysfunctional hosts. - Vaccination precautions: avoidance of live viral vaccines (for the patient and household contacts) until immune reconstitution is confirmed post-HSCT.

Treatment strategy/algorithm: Early recognition (low CD8 flow cytometry pattern) → confirmatory genetic testing → supportive care (IVIG, anti-infective prophylaxis, avoidance of live vaccines/non-irradiated blood/unpasteurized breast milk of CMV+ status unknown) → expedited HSCT, ideally before 6 months of age and before onset of significant end-organ damage or refractory autoimmune disease → post-transplant surveillance every 6–12 months for engraftment, immune reconstitution, growth, and resolution of organ involvement.

Experimental treatments: No registered ClinicalTrials.gov interventional trials specific to ZAP70 deficiency gene therapy were identified in this search; management is currently guided by HSCT case series and expert consensus (GeneReviews) rather than randomized trial data, consistent with the disease's rarity.

Personalized/genotype-guided approaches: Not currently established, given the absence of genotype-phenotype correlation; treatment decisions are guided by clinical severity and immunophenotype rather than specific variant class.

13. Prevention

Primary prevention: Not possible in the traditional sense (monogenic AR disease); the closest analog is carrier screening and genetic counseling in high-risk populations (e.g., Mennonite communities carrying the c.1624-11G>A founder allele) and in consanguineous unions, enabling informed reproductive decision-making.
Secondary prevention (early detection): Population/targeted newborn screening — with the important caveat that standard TREC-based SCID newborn screening has documented sensitivity limitations for ZAP70 deficiency; targeted lymphocyte immunophenotyping (CD8 count) or gene-panel testing is more sensitive in high-risk families/populations. Early diagnosis materially improves outcomes by enabling HSCT before 6 months of age.
Tertiary prevention (avoiding complications in affected individuals): Anti-infective prophylaxis, avoidance of live vaccines, use of irradiated/CMV-safe blood products, and avoidance of high fungal-spore-exposure environments (construction/soil) — all aimed at preventing infectious complications while awaiting or after HSCT.
Immunization: Live vaccines (e.g., BCG, MMR, varicella, oral polio) are contraindicated pre-transplant in affected infants and in household contacts of undiagnosed at-risk infants in endemic/founder communities; BCG-endemic country vaccination practices are a recognized real-world hazard, given the 18.4% rate of BCG-related disease in the reviewed cohort.
Genetic counseling: Recommended for all families with an affected child or a known carrier, discussing autosomal recessive inheritance, 25% recurrence risk, and availability of prenatal/preimplantation genetic diagnosis once the familial variant is known.
Public health/screening program considerations: Because of the TREC-screening blind spot, public health newborn-screening programs in populations with elevated ZAP70 deficiency prevalence (e.g., Mennonite communities) may warrant supplementary CD8-lymphocyte-based or gene-panel screening strategies — a recommendation made explicitly in the primary literature (Kwan et al., PMID:24797280).

14. Other Species / Natural Disease

Taxonomy of the affected species: Homo sapiens (NCBITaxon:9606) is the only species in which naturally-occurring ZAP70 deficiency disease has been reported; no naturally occurring veterinary/companion-animal ZAP70-deficiency disease was identified in this search (no OMIA entry found).
Orthologous gene: Zap70 is highly conserved; mouse ortholog Zap70 (MGI:99613, NCBI Gene ID 22637) is the primary basis for engineered (not naturally occurring) animal models — see Model Organisms below.
Comparative biology: The TCR-proximal signaling role of ZAP-70/Syk-family kinases is evolutionarily conserved across jawed vertebrates; mouse studies of Zap70-null and hypomorphic alleles closely recapitulate the human developmental block, although with species-specific quantitative differences in the CD4/CD8 selection threshold (see Mechanism/Model organisms sections) — illustrating strong mechanistic conservation but imperfect one-to-one phenotype transfer.
Zoonotic potential/transmission: Not applicable — this is a non-infectious, monogenic disorder.

15. Model Organisms

Genetic mouse models (Alliance of Genome Resources; MGI): - Zap70 knockout (Zap70−/−) mice: T-cell development is arrested at the CD4+CD8+ double-positive (DP) thymocyte stage, with a complete absence of mature T cells in peripheral lymphoid organs and blood — closely paralleling (though more completely blocking than) the human phenotype, in which some CD4 SP maturation does occur. - TetZap70 (tetracycline-inducible Zap70) mice: Allow controlled re-induction of Zap70 expression in a null background, revealing that CD4 SP thymocytes develop faster and require a lower ZAP70 signaling threshold than CD8 SP thymocytes — the key mechanistic model explaining the human selective CD8 lymphopenia (Science Signaling, scisignal.2000702). - Zap70/Syk double-knockout mice: T-cell development is blocked even earlier, at the double-negative (DN) to DP transition — demonstrating that Syk provides partial redundant function sufficient to permit progression past the DN stage in Zap70-single-knockout mice (Cheng et al., PMID:9324357; restoration of thymocyte development by ectopic Syk expression in zap-70−/− mice). - Point-mutant "knock-in" mice at regulatory tyrosines (Y292, Y315) recapitulate specific aspects of altered TCR signaling and thymocyte selection, informing structure-function understanding of interdomain B autoinhibition (J Exp Med, rupress.org/jem/article/194/4/491). - Hypomorphic ZAP70 mouse models (e.g., "SKG" strain carrying a W163C hypomorphic mutation) reveal a distinct threshold effect: partial ZAP70 loss-of-function can produce spontaneous autoimmune arthritis rather than immunodeficiency, by skewing thymic selection toward an arthritogenic self-reactive TCR repertoire and impairing Treg development/function (PMC2768860) — directly relevant to understanding the human hypomorphic/leaky variant autoimmune-predominant phenotype. - R360P gain-of-function knock-in models recapitulate the distinct autoimmune (rather than immunodeficient) phenotype produced by disrupted ZAP-70 autoinhibition, altering thymic negative selection and Treg development (Ashouri et al. 2022; Science Signaling scisignal.abc4479).

Model characteristics — phenotype recapitulation and limitations: - Mouse Zap70-null models faithfully recapitulate the DP-stage block and T-cell signaling failure, and the TetZap70 system specifically explains the human CD4-vs-CD8 selective vulnerability, making mouse models highly informative for mechanism. - Limitation: complete Zap70-null mice show a more absolute block (no peripheral T cells at all) than most human patients, who typically retain low but present peripheral CD8 T cells and largely intact CD4 T-cell compartments — likely reflecting species differences in the stringency of the CD4/CD8 selection threshold and/or Syk compensation dynamics, and underscoring that mouse models better model the "complete loss" end of the human variant spectrum than the hypomorphic/leaky end (which is better modeled by hypomorphic knock-in strains such as SKG). - Applications: mouse models have been used to study thymocyte selection thresholds, test intrathymic lentiviral gene-therapy correction strategies (with restoration of a diversified, alloantigen-responsive T-cell repertoire), and dissect the distinct GOF-driven autoimmune-arthritis pathway.

Resources: MGI (Mouse Genome Informatics) Zap70 gene page; Alliance of Genome Resources; IMPC/KOMP for conditional/humanized allele availability.

Summary of Key Ontology Term Suggestions for KB Curation

Category	Suggested term
Disease	MONDO:0010023; OMIM:269840
Gene	hgnc:7535 (ZAP70)
Phenotype (CD8 lymphopenia)	HP:0005416 (T lymphocytopenia) / consider CD8-specific descriptor
Phenotype (recurrent pneumonia)	HP:0002090
Phenotype (bullous pemphigoid)	relevant HP/NCIT term for autoimmune blistering skin disease
Phenotype (failure to thrive)	HP:0001508
Biological process	GO:0050852 (T cell receptor signaling pathway); GO:0045059 (positive thymic T cell selection)
Molecular function	GO:0004713 / GO:0004715 (protein tyrosine kinase activity)
Cell types	CL:0000625 (CD8+ alpha-beta T cell); CL:0000624 (CD4+ alpha-beta T cell); CL:0000809 (DP thymocyte)
Anatomy	UBERON:0002370 (thymus)
Treatment (HSCT)	NCIT:C15431
Treatment (IVIG)	NCIT:C15986 (Pharmacotherapy) + therapeutic_agent (immunoglobulin)
Treatment (gene therapy, investigational)	NCIT:C15238

Sources

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	18
Resolved	18
Unresolved (possible confabulation)	0
Unverifiable	0
Quoted claims checked	1
Quoted claims found in source	0
Quoted claims not found in source	1
Quoted claims with nothing to check against	1
References weighed for topical relevance	18
On topic	14
Off topic	0

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:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

PMID:8124727 (abstract only): "weak tyrosine phosphorylation signals, no calcium flux, and defective proliferation"
closest text in source: "Peripheral CD4+ T cells from the zap-70-/- patients exhibit markedly reduced tyrosine phosphorylation, fail to produce interleukin-2, and do not proliferate in response to T cell receptor stimulation by mitogens or antigens"

Quotes that could not be checked

There was no text to compare these against, so they are neither confirmed nor contradicted:

PMID:24797280: "has not been frequently picked up during >10 year screening experience in the United States"
Reference resolved but exposes no abstract or full text to search

Term Validation

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

Outcome	Count
Terms checked	47
Resolved	44
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	3
Terms whose name was checked	13
Terms named correctly	2
Terms named as a different term	5
Terms whose name is worth a second look	6

Terms the report names something else

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

MONDO:0010023 (2 mentions) - the report calls it "MONDO"; MONDO calls it combined immunodeficiency due to ZAP70 deficiency
HP:0005416 (2 mentions) - the report calls it "T lymphocytopenia"; HP calls it Decreased circulating complement factor B concentration
HP:0004791 (1 mention) - the report calls it "Increased CD4:CD8 ratio"; HP calls it Esophageal ulceration
HP:0002090 (2 mentions) - the report calls it "Phenotype (recurrent pneumonia)"; HP calls it Pneumonia
NCBITaxon:9606 (1 mention) - the report calls it "Homo sapiens", "Taxonomy of the affected species: *Homo sapiens"; NCBITaxon calls it Homo sapiens**

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:0002846 (3 mentions) - the report calls it "Abnormal T cell physiology"; HP calls it Abnormal B cell morphology
HP:0004315 (1 mention) - the report calls it "Decreased circulating IgG"; HP calls it Decreased circulating IgG concentration, and lists "Decreased circulating IgG level" among its other names
HP:0001508 (2 mentions) - the report calls it "Phenotype (failure to thrive)"; HP calls it Failure to thrive, and lists "Postnatal failure to thrive" among its other names
GO:0004715 (2 mentions) - the report calls it "Molecular function: non-membrane spanning protein tyrosine kinase activity"; GO calls it non-membrane spanning protein tyrosine kinase activity**
NCIT:C15431 (2 mentions) - the report calls it "Treatment (HSCT)"; NCIT calls it Hematopoietic Cell Transplantation, and lists "HSCT" among its other names
NCIT:C15238 (2 mentions) - the report calls it "Gene therapy", "Treatment (gene therapy, investigational)"; NCIT calls it Gene Therapy

Terms named inconsistently

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

NCIT:C15238 - called "Gene therapy", "Treatment (gene therapy, investigational)"
NCBITaxon:9606 - called "Homo sapiens", "Taxonomy of the affected species:* Homo sapiens"

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: MGI, OMIM.

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Diagnosis

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References & Deep Research

References

Deep Research

ZAP70 Deficiency — Comprehensive Research Report

1. Disease Information

2. Etiology

3. Phenotypes

Immunodeficiency-related (laboratory abnormalities)

Clinical/infectious phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

Ordered causal chain

Molecular pathway/process detail (checklist coverage)

Cell types and biological processes (ontology suggestions)

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Summary of Key Ontology Term Suggestions for KB Curation

Sources

Reference Validation

Quotes not found in the cited source

Quotes that could not be checked

Term Validation

Terms the report names something else

Terms whose name is worth a second look

Terms named inconsistently

Prefixes with no resolver