Since CF is an inflammatory disease and circulating cytokines such as IL-1β and TNF-α have been shown to increase FGF23 expression in osteocytes28, we hypothesized that TGF-β, a known prognostic marker in CF, can activate osseous FGF23 secretion, thereby explaining the elevated FGF23 plasma levels in CF patients. The gene discussed is FGF23; the disease is cystic fibrosis.