FGFR1 and X-linked hypophosphatemia: Additionally, in vivo studies have reported that conditional deletion of FGFR1 specifically from the osteocytes of Hyp mice, a mouse model of X-linked hypophosphatemia (XLH) that exhibits elevated FGF23 production, improves the rickets and osteomalacia phenotype of these mice in association with a decrease in both FGF23 bone mRNA and circulating protein.