Fig. 2.

Regulation of FGF23 expression and secretion in XLH. Inactivating mutations in PHEX increase fibroblast growth factor 23 (FGF23) expression by increasing levels of acidic serine aspartate-rich-MEPE-associated protein (ASARM) peptide. This leads to increased release of FGF23 into the serum, and increased levels of FGF23-mediated signalling. These processes are also regulated by a wide range of other mechanisms. Green lines indicate upregulation and red lines indicate repression. For simplification, feedback loops have been represented as linear pathways centred around FGF23