Severe combined immunodeficiency (SCID) is a group of inherited genetic disorders characterised by a profound deficiency in cellular and humoral immunity arising from one of many T-cell maturation defects in the bone marrow or thymus gland.
Infants with SCID usually appear healthy at birth. Over time, they may develop: recurrent or severe infections; increased susceptibility to opportunistic infections; faltering growth; and/or chronic diarrhoea.
Newborn screening for T-cell deficiency can alert for SCID before infections and other signs of SCID develop.
Early diagnosis is imperative as, without curative treatment (e.g., haematopoietic stem cell transplantation, gene therapy, enzyme replacement therapy), the condition can be fatal in the first year of life.
Key findings on examination include the absence of lymphoid tissue, poor weight gain, or diffuse erythematous rash. Other factors alerting for SCID include absolute lymphopenia and absent thymus.
Antibacterial, antifungal, and antiviral prophylaxis should be considered for patients with suspected or confirmed SCID.
Live vaccines (e.g., BCG, rotavirus, and oral polio) should not be given to infants with suspected or diagnosed SCID. Cytomegalovirus (CMV) infection by breastfeeding should be prevented when possible.
Blood or blood products should be irradiated, leukocyte depleted, and negative for CMV before being administered to patients with confirmed or suspected SCID.
Severe combined immunodeficiency (SCID) is a group of inherited genetic disorders characterised by a severe deficiency of adaptive cellular and humoral immunity arising from one of many T-cell maturation defects in the bone marrow or thymus gland.
History and exam
Key diagnostic factors
- presence of risk factors
- recurrent and unusually severe infections
- chronic diarrhoea
- failure to thrive
- absent lymphoid tissue
Other diagnostic factors
- oral or genital ulcers
- skeletal abnormalities
- radiation sensitivity
- Family history of SCID
- Family history of infant death
- Athabascan-speaking Native American people
1st investigations to order
- flow cytometry
- chest x-ray
- quantitative immunoglobulin test (IgG, IgM, and IgA)
Investigations to consider
- chest ultrasound
- CT scan of the chest
- MRI chest
- enzyme testing
- serum uric acid
- T-cell proliferation studies
- polymerase chain reaction-based viraemia testing
- radiation sensitivity of fibroblast cultures
- genetic testing
- 22q11.2 Microdeletion syndrome/DiGeorge syndrome
- Omenn's syndrome
- Zeta chain-associated protein 70 deficiency
- Guidelines on transfusion for fetuses, neonates and older children
- Strimvelis for treating adenosine deaminase deficiency-severe combined immunodeficiency
- Log in or subscribe to access all of BMJ Best Practice
Use of this content is subject to our disclaimer