Narcolepsy Type 1 (with cataplexy) is pathophysiologically characterised by loss of neurons producing which neuropeptide in the lateral hypothalamus?

• A Neuropeptide Y
• B Melanin-concentrating hormone (MCH)
• C Vasoactive intestinal peptide (VIP)
• D Orexin (hypocretin) ✓

Explanation

Narcolepsy Type 1 is characterised by loss of 85–95% of orexin (hypocretin)-producing neurons in the lateral hypothalamus, resulting in undetectable or very low CSF orexin-1 levels (< 110 pg/mL). Orexin normally promotes wakefulness and stabilises sleep-wake transitions; its absence causes pathological intrusions of REM sleep elements into wakefulness (cataplexy, sleep paralysis, hypnagogic hallucinations) and excessive daytime sleepiness. This neuronal loss is believed to be autoimmune (anti-TRIB2 antibodies, HLA-DQB1*06:02 association). Narcolepsy Type 2 lacks cataplexy and typically has normal orexin levels.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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