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severe combined immunodeficiency

Monday 29 November 2004

Definition: Severe combined immunodeficiency refers to a genetically and clinically heterogeneous group of disorders with defective cellular and humoral immune function.

Patients with SCID present in infancy with recurrent, persistent infections by opportunistic organisms, including Candida albicans, Pneumocystis carinii, and cytomegalovirus, among many others.

Laboratory analysis shows profound lymphopenia with diminished or absent immunoglobulins.

The common characteristic of all types of SCID is absence of T cell-mediated cellular immunity due to a defect in T-cell development.

Without treatment, patients usually die within the first year of life. The overall prevalence of all types of SCID is approximately 1 in 75,000 births (Fischer et al., 1997; Buckley, 2004).

SCID can be divided into 2 main classes: those with B lymphocytes (B+ SCID) and those without (B- SCID). Presence or absence of NK cells is variable within these groups.

The most common form of SCID is X-linked T-, B+, NK- SCID (MIM.300400) caused by mutation in the IL2RG gene (MIM.308380) on chromosome Xq13.1 (ILR2RG-associated SCID).

Autosomal recessive SCID includes:
- T-, B+, NK- SCID (600802) caused by mutation in the JAK3 gene (MIM.600173) on 19p13.1 (JAK3-associated SCID) (MIM.600802)
- T-, B+, NK+ SCID (608971) caused by mutation in the IL7R gene (146661) on 5p13, the CD45 gene (151460) on 1q31-q32, or the CD3D gene (186790) on 11q23 (IL7R-associated SCID)
- T-, B-, NK- SCID (102700) caused by mutation in the ADA (608958) gene on 20q13.11 (ADA-associated SCID)
- T-, B-, NK+ SCID with sensitivity to ionizing radiation caused by mutation in the Artemis gene on 10p;
- T-, B-, NK+ SCID caused by mutation in the RAG1 and RAG2 genes on 11p13 (RAGs-associated SCID)

Approximately 20 to 30% of all SCID patients are T-, B-, NK+, and approximately half of these patients have mutations in the RAG1 or RAG2 genes (RAGs-associated SCID)

Synopsis

- opportunistic infections

References

- Fischer A, Hacein-Bey S, Le Deist F, Soudais C, Di Santo JP, de Saint Basile G, Cavazzana-Calvo M. Gene therapy of severe combined immunodeficiencies. Immunol Rev. 2000 Dec;178:13-20. PMID: 11213798