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Inborn Errors of Metabolism · USMLE Step 1

Which of the following best describes why IEMs may sometimes remain undiagnosed until adulthood in milder cases?

  1. Because they affect only hair texture and skin pigmentation
  2. Because partial enzyme function causes episodic or subtle symptoms
  3. Because they invariably cause lethal disease in the neonatal period
  4. Because they manifest only with very high-protein diets in adults
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Correct answer: Because partial enzyme function causes episodic or subtle symptoms

Partial enzyme activity may suffice under normal conditions; milder IEMs can cause intermittent or subtle symptoms that only become overt under stress (illness, fasting) — delaying diagnosis until later.

Difficulty: Medium Question 17 of 19

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