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[Immunology](https://durgical.com/en/immunology/) · [Immunodeficiencies](https://durgical.com/en/immunology/#a-immunodeficiency)

# T-cell and combined deficiencies: DiGeorge, SCID, Wiskott–Aldrich, ataxia-telangiectasia

- Topic

Without working T cells, viruses and fungi cause severe infections from the first months, and B cells lose their helpers too.

Updated 2026-11-01

**See it in 3D:** [Thymus](https://durgical.com/en/anatomy/thymus/) · [Parathyroid glands](https://durgical.com/en/anatomy/parathyroid-glands/)

## Key points

- SCID: no functional T cells; most common form is X-linked (IL2RG, common gamma chain); ADA deficiency is autosomal recessive. Detected by TREC newborn screening.
- DiGeorge (22q11.2 deletion): failed 3rd and 4th pharyngeal pouches; absent thymus shadow, low T cells, hypocalcemia (no parathyroids), conotruncal heart defects, cleft palate.
- Wiskott–Aldrich (WAS gene, X-linked): small, few platelets with bleeding, eczema and recurrent infections; low IgM, high IgA and IgE; lymphoma risk.
- Ataxia-telangiectasia (ATM, autosomal recessive): ataxia before age 5, eye and skin telangiectasias, IgA deficiency, high AFP, radiation sensitivity, leukemia and lymphoma.
- Live vaccines and non-irradiated blood are dangerous in severe T-cell deficiency.

## What it is

T cells direct most of the immune response, so their failure also weakens antibody production; that is why these disorders are often called combined. They range from SCID, which is fatal in infancy without a stem cell transplant, to syndromes in which the immune defect is one part of a wider picture (heart, palate, platelets, brain).

## T-cell and combined deficiencies: the table to know

| Disease | Defect (gene, inheritance) | What is low | Infections and clues | Key test |
| --- | --- | --- | --- | --- |
| [Severe combined immunodeficiency (SCID)](https://durgical.com/en/conditions/adenosine-deaminase-deficiency/) | IL2RG common gamma chain, X-linked (most common); ADA, RAG1/2, JAK3 and others, autosomal recessive | T cells absent or nonfunctional; B-cell function lost; NK cells absent in some forms | Onset in first months: thrush, chronic diarrhea, failure to thrive, Pneumocystis, CMV, disseminated BCG; no thymic shadow | Low TRECs on newborn screen; very low CD3 T cells by flow cytometry |
| DiGeorge syndrome (22q11.2 deletion) | Deletion at 22q11.2 (TBX1); autosomal dominant, mostly new (de novo) | T cells (thymic hypoplasia); variable severity | Viral and fungal infections; hypocalcemic tetany or seizures; truncus arteriosus or tetralogy of Fallot; cleft palate; typical face | FISH or chromosomal microarray; low calcium and PTH; CD3 count |
| Wiskott–Aldrich syndrome | WAS gene (WASP, actin cytoskeleton); X-linked recessive | Platelets few and small; IgM low (IgA and IgE high); T-cell function | Bleeding and petechiae, eczema, infections with encapsulated bacteria and viruses; autoimmunity; lymphoma | Low platelet count with small platelet volume; WAS gene testing |
| Ataxia-telangiectasia | ATM gene (DNA repair); autosomal recessive | IgA (often IgG2) and T cells; variable | Progressive ataxia, telangiectasias of eyes and skin, sinopulmonary infections, leukemia and lymphoma, radiation sensitivity | High alpha-fetoprotein (AFP); ATM gene testing |
| Hyper-IgE (Job) syndrome | STAT3; autosomal dominant (Th17 failure) | Th17 response; IgE very high; eosinophils high | Cold staphylococcal skin abscesses, pneumonia with pneumatoceles, eczema, retained primary teeth, coarse face, fractures | Very high IgE; eosinophilia; STAT3 testing |

## Clinical notes

- SCID is a pediatric emergency: hematopoietic stem cell transplant, ideally before serious infections, is curative; ADA-SCID can also be treated with enzyme replacement or gene therapy.
- Children with suspected SCID receive only irradiated, CMV-safe blood products and no live vaccines (BCG at birth is part of Colombia's schedule, so a family history matters).
- The calcium problem in DiGeorge syndrome may appear as neonatal seizures and can recur during illness or surgery.

## Memory aid

For DiGeorge, think of a missing pouch pair: no thymus, no parathyroids, a misbuilt outflow tract and an open palate. For Wiskott–Aldrich, picture a boy with itchy skin, bruises and colds.

## Test yourself

Think of the answer, then tap the question to see it.

## Which test, done on newborn blood spots, screens for SCID?

The TREC assay (T-cell receptor excision circles), which is very low when the thymus makes few new T cells.

## An infant has tetany from hypocalcemia, a conotruncal heart defect and no thymic shadow. What is the likely diagnosis?

DiGeorge syndrome (22q11.2 deletion), from abnormal development of the 3rd and 4th pharyngeal pouches.

## What triad defines Wiskott–Aldrich syndrome?

Thrombocytopenia with small platelets, eczema and recurrent infections, in a boy (X-linked WAS gene).

## Which blood test is characteristically high in ataxia-telangiectasia?

Alpha-fetoprotein (AFP).

## What is the most common genetic form of SCID?

X-linked SCID, caused by mutations in IL2RG, the common gamma chain shared by several interleukin receptors.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/immunology/t-cell-and-combined-deficiencies-digeorge-scid-wiskott-aldrich-ataxia-telangiect/)

## See it in 3D

The structures of Durgical's 3D anatomy where it is found.

- [Thymus](https://durgical.com/en/anatomy/thymus/)
- [Parathyroid glands](https://durgical.com/en/anatomy/parathyroid-glands/)

## Related

- [Thymus: where T cells learn](https://durgical.com/en/immunology/thymus-where-t-cells-learn/)
- [T-cell development: positive and negative selection](https://durgical.com/en/immunology/t-cell-development-positive-and-negative-selection/)
- [Live vaccines: who should not receive them](https://durgical.com/en/immunology/live-vaccines-who-should-not-receive-them/)
- [Immunodeficiency: warning signs and the infection pattern by defect](https://durgical.com/en/immunology/immunodeficiency-warning-signs-and-the-infection-pattern-by-defect/)
- [B-cell (antibody) deficiencies: XLA, CVID, IgA deficiency, hyper-IgM](https://durgical.com/en/immunology/b-cell-deficiencies-xla-cvid-iga-deficiency-hyper-igm/)

## Related conditions

- [Adenosine deaminase deficiency (ADA-SCID)](https://durgical.com/en/conditions/adenosine-deaminase-deficiency/)

## Microorganisms

- [Pneumocystis jirovecii](https://durgical.com/en/microbiology/pneumocystis-jirovecii/)
- [Candida albicans](https://durgical.com/en/microbiology/candida-albicans/)
- [Cytomegalovirus](https://durgical.com/en/microbiology/cytomegalovirus/)
- [Staphylococcus aureus](https://durgical.com/en/microbiology/staphylococcus-aureus/)

[← All of immunology](https://durgical.com/en/immunology/)

Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.

Sources: [X-linked severe combined immunodeficiency](https://medlineplus.gov/genetics/condition/x-linked-severe-combined-immunodeficiency/) (MedlinePlus Genetics, U.S. National Library of Medicine, 2026); [22q11.2 deletion syndrome](https://medlineplus.gov/genetics/condition/22q112-deletion-syndrome/) (MedlinePlus Genetics, U.S. National Library of Medicine, 2026); [Wiskott-Aldrich syndrome](https://medlineplus.gov/genetics/condition/wiskott-aldrich-syndrome/) (MedlinePlus Genetics, U.S. National Library of Medicine, 2026); [Ataxia-telangiectasia](https://medlineplus.gov/genetics/condition/ataxia-telangiectasia/) (MedlinePlus Genetics, U.S. National Library of Medicine, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/immunology/t-cell-and-combined-deficiencies-digeorge-scid-wiskott-aldrich-ataxia-telangiect/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/immunology/t-cell-and-combined-deficiencies-digeorge-scid-wiskott-aldrich-ataxia-telangiect/