Severe combined immunodeficiency
From IDWiki
Background
Epidemiology
- Most common form of severe primary immunodeficiency
Pathophysiology
- No or almost no T-cells, and any that exist do not work properly
- Many genetic abnormalities can lead to this condition, and may cause related defects in B and NK cell lines
- However, given that T-cells are required for B-cell function, all SCID patients are functionally B-cell deficient
Clinical Manifestations
Diagnosis
- Usually diagnosed at birth with newborn screen containing a TREC (T-cell receptor excision circles) assay
- In adulthood, diagnosis is based on flow cytometry to T cell count, and T cell response to mitogens (see Definition, below)
Definition
- T-cell count <300 cells/μL and no T-cell response to mitogens (<10% compared to controls)
- Hypomorphic SCID is less severe, with a normal number of T-cells, but with T-cell function <30% compare to controls
Management
- Initially treated supportively with management of infections and replacement of immunoglomubins
- Protective isolation in hospital with positive pressure rooms
- Antibiotic and antifungal prophylaxis to reduce frequency and severity of infections
- Commonly-used antibiotics include sulfisoxazole, amoxicillin, trimethoprim-sulfamethoxazole, or azithromycin
- Avoid live-attenuated vaccines, but can continue to give killed or subunit vaccines (though they may not mount much response)
- Definitive treatment is hematopoietic stem cell transplantation, ideally from HLA-identical sibling
- Gene therapy is an area of active research
Prognosis
- Uniformly fatal in childhood unless treated
