A 3-year-old child presents with recurrent pneumonia, eczema & thrombocytopenia. Which protein synthesis is abnormal in this child?
First, I need to recall the possible conditions that present with these three symptoms. Recurrent infections, skin issues, and low platelets—this sounds like an immunodeficiency disorder. The triad of eczema, thrombocytopenia, and recurrent infections is classic for Wiskott-Aldrich syndrome (WAS).
WAS is an X-linked recessive disorder. The main issue here is a defect in the WAS protein (WASP). This protein is crucial for the cytoskeletal rearrangements in hematopoietic cells. Without functional WASP, there are problems with B and T cell function, leading to immunodeficiency. The eczema is due to skin barrier defects, and thrombocytopenia comes from dysfunctional megakaryocytes producing abnormal platelets.
The other options might be other immunodeficiencies. For example, Severe Combined Immunodeficiency (SCID) could present with infections but doesn't typically include eczema and thrombocytopenia. Common Variable Immunodeficiency (CVID) usually presents later and without the eczema. Ataxia-Telangiectasia has neurological symptoms and cancer predisposition but not the same triad. So, the correct answer should be related to WASP synthesis.
Now, the options given in the question are A, B, C, D, but the correct answer isn't labeled here. However, based on the core concept, the answer is the protein defective in WAS, which is WASP. So the correct answer would be the option listing WASP. The other options would be proteins from other conditions. For example, if any option mentions ADA (for SCID), CD40L (for Hyper-IgM), or RAG proteins (for Omenn syndrome), those are incorrect. The clinical pearl here is to remember the triad and link it to WASP deficiency.
**Core Concept**
The triad of recurrent infections, eczema, and thrombocytopenia in a child points to **Wiskott-Aldrich syndrome (WAS)**, an X-linked recessive primary immunodeficiency. The disorder involves defective **WASP (Wiskott-Aldrich Syndrome Protein)** synthesis, critical for actin cytoskeleton regulation in immune cells.
**Why the Correct Answer is Right**
WAS is caused by mutations in the **WAS gene** on the X chromosome, encoding **WASP**. This protein is essential for B-cell and T-cell signaling, platelet function, and skin barrier integrity. Defective WASP leads to impaired actin polymerization, causing dysfunctional immune responses (recurrent infections), eczema (due to epidermal barrier defects), and thrombocytopenia (abnormal platelet production/structure).
**Why Each Wrong Option is Incorrect**
**Option A:** Defects in **CD40 ligand** cause Hyper-IgM syndrome (not eczema or thrombocytopenia).
**Option B:** Mutations in **RAG1/RAG2** lead to Severe Combined Immunodeficiency (SCID), presenting with severe infections but no ecz