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Review Question - QID 211005

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QID 211005 (Type "211005" in App Search)
A 32-year-old woman is brought to the emergency department after she started convulsing in the office. She has no previous history of seizures and recovers by the time she arrives at the emergency department. She says that over the last 2 days she has also experienced insomnia, abdominal pain, and dark urine. Her past medical history is significant for asthma; however, she says that she has not experienced any of these symptoms previously. She smokes 1 pack of cigarettes per day, drinks a glass of wine with dinner every night, and is currently taking oral contraceptive pills (OCPs). On presentation, her temperature is 99°F (37.2°C), blood pressure is 140/98 mmHg, pulse is 112/min, and respirations are 11/min. Which of the following enzymes is most likely to be defective in this patient?

Aminolevulinate dehydratase

5%

3/64

Aminolevulinate synthase

9%

6/64

Ferrochelatase

8%

5/64

Porphobilinogen deaminase

55%

35/64

Uroporphyrinogen decarboxylase

19%

12/64

Select Answer to see Preferred Response

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This patient who experienced seizures, insomnia, abdominal pain, and dark urine after taking OCPs most likely has acute intermittent porphyria, which is caused by a defect in porphobilinogen deaminase.

Acute intermittent porphyria (AIP) is an inherited metabolic disease resulting from deficiency in the heme synthesis pathway enzyme porphobilinogen deaminase (PBD). AIP is the most common acute porphyria and presents with primary symptoms that can be remembered with the 5 P’s mnemonic - severe abdominal Pain without tenderness on palpation, neurological symptoms such as Polyneuropathy, Psychiatric symptoms, Port wine-colored urine, and Precipitated by an exposure. On physical exam, patients are often normal except for tachycardia and hypertension.

Incorrect Answers:
Answer 1: Aminolevulinate dehydratase is inhibited by lead poisoning; however, there is no evidence that this patient has lead poisoning (old house, lead lines, wrist drop, etc.)

Answer 2: Aminolevulinate synthase is the rate-limiting step of porphyrin ring synthesis; however, it is not defective in any of the common porphyria disorders.

Answer 3: Ferrochelatase is inhibited by lead poisoning; however, there is no evidence that this patient has lead poisoning (old house, lead lines, wrist drop, etc.)

Answer 5: Uroporphyrinogen decarboxylase is defective in porphyria cutanea tarda; however, this disease would present with skin blistering in sunlight.

Bullet Summary:
Acute intermittent porphyria is caused by a defect in the porphobilinogen deaminase enzyme.

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