A 16-year-old Korean boy presents to the emergency department with acute onset of lower-extremity weakness. He woke up from sleep, had several episodes of emesis, and found he was unable to move his lower extremities. He recalls eating half a dozen doughnuts earlier in the day. His parents found him struggling to get up and brought him in for evaluation.

He reports intermittent palpitations and an unintentional weight loss of 40 lb over the past year. He has had similar episodes of lower-extremity weakness with no loss of sensation. These past episodes would last approximately 3 to 4 hours, resolve spontaneously, and always occur at night. The patient was adopted at 6 months of age and, therefore, family history is unavailable.

On physical examination, his vital signs are temperature of 36.5°C (97.8°F), heart rate of 78 beats per minute, respiratory rate of 16 breaths per minutes, and blood pressure of...

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