ADA-SCID (adenosine deaminase deficiency) leads to T and B lymphocyte death. The accumulating toxic metabolite that primarily causes lymphocyte apoptosis is:
- A Adenosine
- B Inosine
- C Deoxyadenosine triphosphate (dATP) ✓
- D Hypoxanthine
Explanation
In ADA deficiency, deoxyadenosine (from DNA turnover) cannot be deaminated to deoxyinosine. Lymphocytes (especially T cells) have high deoxykinase activity and phosphorylate deoxyadenosine to dATP. Massive intracellular dATP accumulation inhibits ribonucleotide reductase (blocking DNA synthesis), activates apoptotic pathways (including cytochrome c release), and inactivates S-adenosylhomocysteine hydrolase, disrupting methylation reactions. This selective lymphocytotoxicity causes SCID. Adenosine itself has some toxicity but dATP is the primary lymphocytotoxic metabolite. Inosine and hypoxanthine are downstream products that are not directly toxic.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.