A newborn has short limbs, narrow chest, and 'trident hand' on examination. X-ray shows rhizomelic shortening, metaphyseal flaring, and a champagne glass pelvis with horizontal acetabular roofs. The diagnosis is achondroplasia. Which mutation underlies this condition?
- A COL1A1 mutation
- B FGFR3 gain-of-function mutation ✓
- C EXT1/EXT2 mutation
- D FBN1 mutation
Correct answer: B. FGFR3 gain-of-function mutation
Explanation
Achondroplasia is caused by a gain-of-function mutation in FGFR3 (fibroblast growth factor receptor 3), which constitutively inhibits chondrocyte proliferation. The radiological hallmarks include rhizomelic (proximal) limb shortening, tombstone iliac wings with horizontal acetabular roofs (champagne glass pelvis), narrowed interpedicular distance in the lumbar spine, and 'trident' hand configuration. COL1A1 causes osteogenesis imperfecta; EXT1/EXT2 cause multiple exostoses; FBN1 causes Marfan syndrome.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.