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

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]