Thyroid Disorders USMLE Step 1 Practice Question
A 10-year-old boy presents with short stature, round facies, and shortened fourth and fifth metacarpals. Vital signs show BP 102/68 mmHg, HR 78/min, RR 18/min, temperature 37°C. Laboratory studies reveal calcium 7.2 mg/dL (hypocalcemia), phosphate 5.8 mg/dL (hyperphosphatemia), PTH 156 pg/mL (elevated), and normal TSH. Physical examination shows no thyroid abnormalities. Which of the following best explains his condition?
Answer choices
- AParathyroid adenoma with autonomous secretion
- BLoss of parafollicular C cells
- CDefective Gs protein signaling causing end organ resistance to PTHCorrect answer
- DActivating mutation of the RET proto oncogene
- EVitamin D intoxication
- FActivating GNAS mutation causing McCune-Albright syndrome
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