Fibrous Dysplasia GNAS1 Mutation — NDEB AFK MCQ
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Correct answer: C — GNAS1
Fibrous dysplasia is caused by a post-zygotic (somatic) activating mutation in the GNAS1 gene (encoding the alpha subunit of the stimulatory G protein, Gsα), leading to constitutive activation of adenylyl cyclase and increased cAMP. This results in replacement of normal bone with fibrous tissue containing immature woven bone. Monostotic (single bone) is more common than polyostotic. McCune-Albright syndrome (polyostotic fibrous dysplasia + café-au-lait spots + precocious puberty) involves the same GNAS1 mutation affecting multiple tissues.
Reference: Neville – Oral and Maxillofacial Pathology, 4th ed., 2016