Bone Abstracts

Fibrous dysplasia is a mosaic disease resulting from post-zygotic activating mutations of the GNAS locus which codes for the α subunit of the Gs G-coupled protein receptor. In bone, impaired signalling results in impaired differentiation and proliferation of bone marrow stromal cells which are replaced by fibrous tissue resulting in bone fragility and dysplasia. All children diagnosed with Fibrous Dysplasia at The Royal National Orthopaedic Hospital since 2009 (103 children), excluding those with craniofacial involvement, were identified and prospectively screened for co-morbidities of the disease. Screening included clinical assessment, Whole Body MRI (WB MRI), measurement of blood and urinary phosphate levels, serum alkaline phosphatase calcium and FGF 23 levels. We correlated the levels of FGF23 with: serum and urinary phosphate levels; serum alkaline phosphatase levels; number of disease sites ie polyostotic vs monostotic; number of fractures: significant pain; and the need for surgical intervention.

Results: 56/57 patients tested had elevated levels of FGF 23, the highest values were in the 4 patients clinically identified with phosphate wasting rickets, prior to screening. 2 other patients had levels >200 (normal range 0–100) but were asymptomatic. 4/93 patients had frank hypophosphateamia with increased urinary phosphate. 24/92 patients had elevated alkaline phophatase levels, without significantly higher levels of FGF23. 89/91 patients had normal serum calcium. Approximately one third of patients thought to have monostotic disease had polyostotic disease on WB MRI, levels of FGF23 did not predict this finding. 23/102 patients sustained fractures, almost all prior to diagnosis. The levels of FGF 23 taken at the time of screening ie not at the time of fracture, were not different from patients without a history of fractures. Patients reporting significant pain at the time of clinical assessment did not have significantly elevated levels of FGF 23.

Conclusion: FGF 23 levels were elevated in all but one patient in the cohort. The highest values were found in those with phosphate wasting rickets. However the level of FGF 23 was not useful in predicting any other clinical outcome and could not be used to predict disease progress. Serum phosphate remained the most useful test.

Disclosure: The authors declared no competing interests.