If a patient experiencing severe anaphylaxis despite epinephrine administration has a genetic defect preventing conversion of histidine to histamine, why does the allergic reaction still occur?

💡 Explanation

Anaphylaxis involves mast cell degranulation, which releases preformed histamine. Even if new histamine synthesis is blocked, the pre-existing stores are still released, because the mast cells were already sensitized. Therefore, the allergic reaction still occurs, rather than being prevented by blocking new histamine production.

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