Adenosine deaminase (ADA) deficiency causes SCID primarily because accumulation of which metabolite is selectively toxic to lymphocytes?

• A Deoxyadenosine and dATP ✓
• B Uric acid
• C Hypoxanthine
• D Inosine

Explanation

ADA converts adenosine to inosine and deoxyadenosine to deoxyinosine. In ADA deficiency, deoxyadenosine accumulates and is phosphorylated by deoxycytidine kinase (highly expressed in lymphocytes) to dATP. Elevated dATP inhibits ribonucleotide reductase (blocking DNA synthesis) and induces apoptosis via DNA strand breaks and cytochrome c release — selectively destroying B and T lymphocytes, causing combined immunodeficiency. This is why ADA-SCID affects both T and B cell lineages.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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