This question is testing your knowledge on Severe Combined Immunodeficiency (SCID). When considering a SCID diagnosis consider these aspects:

Defect:

• IL-2R gamma chain (most common, and x-linked recessive).
• Adenosine deaminase deficiency (Autosomal recessive)..
• RAG mutation --> VDJ recombination defect.

Presentation:

• Patients will present with features such as failure to thrive, chronic diarrhea, and thrush.
• Patients will present with recurrent viral, bacterial, fungal, and protozoal infections.

Findings:

• Decreased T-cell receptor excision circles (TRECs)
• Part of newborn screening for SCID
• Absence of a thymic shadow (CXR), germinal centers (on lymph node biopsy), and T cells (flow cytometry)