Immunology · Immunodeficiencies
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 · Parathyroid glands
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) | 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.
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.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Thymus: where T cells learn
- T-cell development: positive and negative selection
- Live vaccines: who should not receive them
- Immunodeficiency: warning signs and the infection pattern by defect
- B-cell (antibody) deficiencies: XLA, CVID, IgA deficiency, hyper-IgM
Related conditions
Microorganisms
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 (MedlinePlus Genetics, U.S. National Library of Medicine, 2026); 22q11.2 deletion syndrome (MedlinePlus Genetics, U.S. National Library of Medicine, 2026); Wiskott-Aldrich syndrome (MedlinePlus Genetics, U.S. National Library of Medicine, 2026); Ataxia-telangiectasia (MedlinePlus Genetics, U.S. National Library of Medicine, 2026).
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Representative model, for educational purposes only.