Diagnostic criteria for severe combined immunodeficiency (SCID)

Definitive diagnosis*

Patient less than 2 years of age with either (a) an absolute CD3 T cell count of less than 300/mm³, or (b) an absolute CD3 T cell count of greater than 300/mm³ with absent naïve CD3/CD45RA T cells, and at least 1 of the following:

Male with deleterious pathogenic variant in the X-linked IL2RG gene encoding the cytokine receptor common gamma chain (gamma-c).

Male or female patient with deleterious homozygous or compound heterozygous pathogenic variants in any of the genes listed in the Gene Defects table other than IL2RG.

ADA activity of less than 2% of control or pathogenic variants in both alleles of the ADA gene.

Engraftment of transplacentally acquired maternal T cells.

Probable diagnosis*

Male or female patient less than 2 years of age with (a) less than 20% CD3+ T cells, an absolute lymphocyte count of less than 3000/mm³, and proliferative responses to mitogens less than 10% of control or (b) the presence of maternal lymphocytes in the circulation.

IL2RG: interleukin 2 receptor gamma chain, also called the cytokine receptor common gamma chain; ADA: adenosine deaminase.
* Patients with a definitive or probable diagnosis are assumed to have a greater than 98 and 85% probability, respectively, that in 20 years they will still have the same diagnosis.

Data from: Tangye SG, Al-Herz W, Bousfiha A, et al. Human inborn errors of immunity: 2019 update on the classification from the International Union of Immunological Societies Expert Committee. J Clin Immunol 2020; 40:24.

Graphic 67948 Version 7.0

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Diagnostic criteria for severe combined immunodeficiency (SCID)