A 9-year-old girl has polyostotic fibrous dysplasia, cafe-au-lait spots, and precocious puberty. Radiographs of the femur show a ground glass lesion ending in a classic 'shepherd's crook' deformity. This syndrome results from a mutation in which gene?
- A EXT1
- B GNAS ✓
- C APC
- D TP53
Correct answer: B. GNAS
Explanation
McCune-Albright syndrome comprises polyostotic fibrous dysplasia, cafe-au-lait macules with irregular borders, and autonomous endocrine hyperfunction such as precocious puberty. It is caused by a postzygotic activating mutation of the GNAS gene encoding the Gs alpha subunit, producing constitutive cAMP signalling. EXT1 mutations cause hereditary multiple exostoses, while APC causes familial adenomatous polyposis.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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