Correct Answer: B. Defect in DNA helicase
Werner syndrome (adult progeria) is a rare autosomal recessive disorder caused by mutations in the WRN gene, which encodes a DNA helicase with exonuclease activity. The defective helicase impairs DNA repair mechanisms, particularly nucleotide excision repair (NER) and base excision repair (BER). This leads to accumulation of unrepaired DNA damage, triggering premature cellular senescence and apoptosis. The hallmark pathophysiology involves defective unwinding of DNA strands during repair processes, causing genomic instability. Clinically, patients present with premature aging features—graying of hair, baldness, cataracts, atherosclerosis, and increased cancer risk—typically manifesting in the third to fourth decade. The WRN helicase defect directly causes accelerated telomere shortening (not lengthening) due to impaired telomere maintenance and increased replicative stress. Indian textbooks (Robbins Pathology) emphasize that DNA repair defects, not telomerase dysregulation, are the primary driver of premature senescence in Werner syndrome. This distinguishes it from dyskeratosis congenita, where telomerase deficiency is central.
Why the other options are wrong
A. Increased telomerase activity — This is wrong because Werner syndrome involves decreased telomerase activity and accelerated telomere shortening, not increased activity. Increased telomerase is seen in dyskeratosis congenita (a different telomeropathy) and cancer cells. The NBE trap conflates Werner syndrome with other aging syndromes; students may confuse telomerase upregulation with premature aging mechanisms. C. Increase in length telomere due to decrease in telomerase activity — This is contradictory and factually incorrect. Decreased telomerase activity causes shortening, not lengthening, of telomeres. While Werner syndrome does involve reduced telomerase activity, the consequence is accelerated telomere attrition, not elongation. This option conflates two opposing processes and is a classic NBE distractor for students who half-remember telomere biology. D. None of above — This is wrong because option B (defect in DNA helicase) is definitively correct. The WRN gene encodes a RecQ-family helicase, and loss-of-function mutations are the established genetic basis of Werner syndrome. Selecting 'none of above' would ignore the well-established molecular pathology documented in international and Indian pathology textbooks.
High-Yield Facts
- WRN gene mutation encodes a RecQ-family DNA helicase with 3'→5' exonuclease activity, defective in Werner syndrome
- Premature telomere shortening (not lengthening) occurs due to impaired DNA repair and replicative stress, not telomerase upregulation
- DNA repair defects (NER, BER, mismatch repair) accumulate unrepaired lesions, triggering senescence and genomic instability
- Clinical onset typically third–fourth decade with graying, baldness, cataracts, atherosclerosis, and 10-fold increased cancer risk
- Werner syndrome vs. dyskeratosis congenita: Werner = helicase defect; dyskeratosis = telomerase deficiency (opposite mechanisms)
Mnemonics
WRN = Wrong Repair Now WRN helicase defect → impaired DNA unwinding → accumulation of unrepaired DNA → premature senescence. Remember: Werner = helicase, not telomerase. RECQ family = REpair Checkpoint Quenched WRN is a RecQ helicase; when defective, checkpoint control fails, DNA damage accumulates, cells age fast. Use when comparing Werner to other DNA repair syndromes (Bloom, Cockayne).
NBE Trap
NBE conflates Werner syndrome with telomerase-related aging syndromes (dyskeratosis congenita, Hutchinson–Gilford progeria). Students who remember "telomeres + aging" may reflexively choose telomerase options, missing that Werner's primary defect is helicase-mediated DNA repair, not telomerase activity.
Clinical Pearl
In Indian tertiary centers, Werner syndrome is rare but important in differential diagnosis of premature aging. A young patient (30–40 years) presenting with early-onset atherosclerosis, cataracts, and cancer should prompt genetic testing for WRN mutations. Unlike Hutchinson–Gilford progeria (LMNA mutation, neonatal onset), Werner manifests in adulthood, making it a classic board question.
_Reference: Robbins and Cotran Pathologic Basis of Disease, Ch. 7 (Genetic Disorders); Harrison's Principles of Internal Medicine, Ch. 408 (Genetic Counseling)_