T-lymphocytes (T-cells) are an essential component of the immune system. They help identify and eliminate pathogens and abnormal cells (e.g., cancerous cells). T-cell disorders increase the susceptibility to viral, fungal and opportunistic infections.
DiGeorge Syndrome
DiGeorge syndrome, also called 22q11.2 deletion syndrome, features a microdeletion in a portion of chromosome 22 that leads to a defect involving the 3rd and 4th pharyngeal pouches. One of the consequences of this is incomplete development of the thymus gland. This can result in reduced or absent T-cell production.
Features of DiGeorge syndrome can be remembered with the CATCH-22 mnemonic:
- C – Congenital heart disease
- A – Abnormal facies (characteristic facial appearance)
- T – Thymus gland incompletely developed
- C – Cleft palate
- H – Hypoparathyroidism and resulting Hypocalcaemia
- 22nd chromosome affected
Purine Nucleoside Phosphorylase Deficiency
Purine nucleoside phosphorylase (PNP) deficiency is an autosomal recessive condition. PNPase is an enzyme that helps break down purines. Without this enzyme, toxic purine metabolites (including dGTP) accumulate, damaging T-cells and leading to low T-cell counts.
Clinically, patients’ immunity to infection gradually gets worse. They become increasingly susceptible to infections, particularly viruses and live vaccines.
Wiskott-Aldrich Syndrome
Wiskott-Aldrich syndrome (WAS) is an X-linked recessive condition caused by a mutation of the WAS gene. It causes abnormal functioning of T-cells. Key features include:
- Microthrombocytopenia (small platelets and a low platelet count)
- Eczema
- Recurrent infections
It increases the risk of bleeding, infections, autoimmune conditions and cancers (especially lymphoma).
Ataxic Telangiectasia
Ataxic telangiectasia is an autosomal recessive condition caused by mutations in the ATM serine/threonine kinase gene on chromosome 11. This protein is important in several functions of DNA coding. A mutation in this gene leads to problems in the coding of many other genes.
There are various features of the condition:
- Low T-cells and immunoglobulins (especially IgA), causing immunodeficiency and recurrent infections
- Ataxia (problems with coordination due to cerebellar impairment)
- Telangiectasia (particularly in the sclera and sun-exposed skin)
- Predisposition to cancers (particularly haematological cancers)
- Slow growth and delayed puberty
- Premature aging
- Liver disease
Acquired Immunodeficiency Syndrome
AIDS is caused by infection with HIV, which reduces the number of CD4 T-cells. This is covered in detail in the HIV section here.
Last updated April 2026
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