FGF

FGFs are heparin-binding growth factors that signal through receptor tyrosine kinases (FGFR1-4), activating RAS/MAPK and PI3K/AKT pathways. Key clinical correlations: FGFR3 activating mutation causes achondroplasia (most common cause of dwarfism, AD with full penetrance, paternal-age effect) by inhibiting chondrocyte proliferation at growth plates, producing short limbs with normal trunk and large head; thanatophoric dysplasia (lethal) is another FGFR3 mutation. FGFR2 mutations cause craniosynostosis syndromes (Apert, Crouzon, Pfeiffer). FGF23 from bone is a phosphaturic hormone — excess (X-linked hypophosphatemic rickets, tumor-induced osteomalacia) causes renal phosphate wasting and rickets/osteomalacia. FGF2 (bFGF) promotes angiogenesis and wound healing. FGF8 patterns limb buds during embryogenesis.