A 14-year-old male presents with worsening drowsiness, palpitations, shortness of breath, and difficulty swallowing. As a toddler, he used his arms to climb up his thighs to attain an upright position. Since then, his progressive immobility has resulted in paralysis from the neck down. Examination reveals new pedal edema and restricted ocular motion. An X-ray demonstrates the findings seen here. As a result of his genetic disorder, which of the following conditions is least likely in this patient? Source
