A 5-year-old boy presents with progressive cerebellar ataxia, oculocutaneous telangiectasias, recurrent sinopulmonary infections, and elevated alpha-fetoprotein. IgA is markedly reduced. Which DNA repair pathway is defective in this condition?

• A Nucleotide excision repair
• B Base excision repair
• C Mismatch repair
• D Non-homologous end joining ✓

Explanation

This describes ataxia-telangiectasia, caused by mutations in the ATM gene. ATM encodes a protein kinase involved in DNA double-strand break repair through the non-homologous end joining pathway. The defective DNA repair leads to chromosomal instability. Nucleotide excision repair is defective in xeroderma pigmentosum. Base excision repair defects cause various conditions. Mismatch repair defects cause Lynch syndrome.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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