What are the pathophysiologic pathways of severe combined immunodeficiency (SCID)?

Updated: Aug 11, 2020
  • Author: Francisco J Hernandez-Ilizaliturri, MD; Chief Editor: Emmanuel C Besa, MD  more...
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There are 4 characterized pathways that can result in SCID, as follows:

  • Premature cell death caused by the accumulation of purine metabolites (seen in adenosine deaminase (ADA) deficiency)

  • Defective V(D)J rearrangements of the T-cell and B-cell receptor genes (accounts for 30% of SCID cases)

  • Defective cytokine-dependent survival signaling in T-cell precursors and sometimes NK-cell precursors (accounts for more than 50% of SCID cases)

  • Defective pre-TCR and TCR signaling. Pure T-cell deficiencies are caused by defects in either a CD3 subunit (such as CD3 δ, CD3 ζ, CD3 ε ) or in CD45 tyrosine phosphatase, key proteins involved in pre-TCR and/or TCR signaling at the positive selection stage.

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