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Table 2 Table of suggested diagnostic tests and investigations with expected findings

From: FOXN1 deficient nude severe combined immunodeficiency

Category Test(s) Expected findings Ref.
Genetic - FOXN1 sequencing
- PCR for previously reported FOXN1 mutations
- Homozygous FOXN1 mutation
- Previously reported mutations: R255X, R320W, S188fs
[2, 23, 25, 26]
Basic Immunology Differential white cell count - Total lymphocyte count ↓/↔/↑
- ↑ Eosinophils in Omenn syndrome
[1, 23]
Lymphocyte subpopulations - ↓ T-cell count (greater reduction in CD4+ T-cells Vs. CD8+)
- ↔B-cell count (although ↓ in 1 reported case)
- ↔/↑ NK-cell count
[1, 23, 26]
Serum Immunoglobulins ↔/↓
- ↑ IgE in Omenn syndrome
[23]
Specialised Immunology TRECs Severely ↓ or absent [23]
Recent thymic emigrants (CD4 + CD31 + CD45RA+) Severely ↓ or absent [26]
Markers of T-cell memory (CD45RA & CD45RO) and activation (HLA-DR) - Severely ↓ naïve (CD45RA+) T-cells
- ↑ memory (CD45RO+) T-cells
- ↑ HLA-DR+ in Omenn syndrome
[23, 26, 30]
T-cell proliferation to mitogens - ↓ in response to anti-CD3 &/or PHA
- May be normal in response to PMA and ionomycin
[1, 23, 26]
T-cell receptor repertoire via flow cytometry or spectratyping Oligoclonal [23, 26]
Specific antibodies to exposure and immunisation antigens [1]
Thoracic imaging Chest x-ray/ultrasound scan/MRI - Absent thymus
- May show evidence of respiratory tract infection
[1]
  1. Key: Ref. References, PCR polymerase chain reaction, ↑ increased, ↓ decreased, ↔ normal, CD cluster of differentiation, Ig immunoglobulin, TRECs T-cell receptor excision circles, HLA Human leucocyte antigen, PHA Phytohaemagglutinin, PMA phorbol myristate acetate, MRI magnetic resonance imaging