In androgenetic alopecia (AGA) in men, the conversion of testosterone to the active androgen responsible for miniaturisation is catalysed by which enzyme?

• A 5-alpha reductase type 2 (predominantly in scalp follicles) ✓
• B 17-beta-hydroxysteroid dehydrogenase
• C Aromatase (CYP19)
• D 3-alpha-hydroxysteroid oxidoreductase

Explanation

5-alpha reductase type 2 converts testosterone to dihydrotestosterone (DHT) in androgen-sensitive scalp follicles. DHT binds androgen receptors in dermal papilla cells with higher affinity than testosterone, triggering miniaturisation of follicles and conversion of terminal to vellus hairs in the frontoparietal scalp. Finasteride (5-AR type 2 inhibitor) and dutasteride (dual 5-AR inhibitor) exploit this mechanism therapeutically. Aromatase converts androgens to oestrogens; its relative excess in the occipital scalp may explain AGA pattern sparing. 5-AR type 1 is expressed in sebaceous glands.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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