Does Dietary Phosphorus influence FGF-23 concentrations in Fibrous Dysplasia Patients?

MAROTTE C; GUERRERO L; SANCHEZ AL; SOMOZA J; BAGUR A; OLIVERI B; PARISI MS

Montreal

Congreso; 30thMeeting ASBMR; 2008

American Society for Bone and Mineral Research

High levels of fibroblast growth factor 23 (FGF-23) have been reported in Fibrous Dysplasia (FD) patients. However, whether or not phosphate physiological regulation mechanisms are maintained is unknown.Objective: to determine whether serum FGF-23 concentrations are regulated by dietary phosphorus (P) in FD patients.We studied 6 polyostotic FD patients (2M, 4W) aged 31.5±11.2 y (X± SD) (r: 20-50), and 6 healthy controls (1M, 5W) aged 33.4±15.5y (r: 20-57).Patients and controls performed a 5 days control diet with 1500mg/d of P. After a free diet period (3-27d), FD patients performed a 5 days restriction diet with 625mg/d of P. All the subjects filled a daily meals record. P and calcium total intakes were calculated. Lab tests after each diet: serum FGF-23 (C-terminal, Inmutopics), 1,25(OH)2D, P, Ca, iPTH, and creatinine; and urinary P, Ca, and creatinine. Tubular reabsorption of P (TRP) was calculated.After the control diet, P intakes were: 1145±116mg/d in patients, and 917±250mg/d in controls (ns). After the restriction diet, in FD patients, P intake was: 712±67md/d (p<0.05 vs control diet).After control diet: FGF-23 levels were higher in FD patients (118.3±48.7 vs 40.0±25.6RU/ml, p<0.02). Only patient 6 had levels in the control’ s range (17.5 to 68RU/ml). Mean TRP was lower in FD patients (81.7±8.3%) vs controls (86.7±5.6%) (ns). No differences were observed in the other studied parameters.After the restriction diet, mean FGF-23 levels dropped to 95.7±44.0RU/ml, (ns). FGF-23 values of 5 patients persisted above the control’ s range upper limit (fig 1). TRP values increased (92.2±3.4%, p<0.05). All patients had TRP >80% (fig 2). 1,25(OH)2D and iPTH did not correlate with FGF-23 or TRP levels.Our observations may suggest that physiological mechanisms involved in P homeostasis could be preserved in some, but not all, FD patients. These results are in accordance with the wide clinical expression of FD. Further studies should be conducted to confirm these results.