ESPE Abstracts

Introduction: X-linked hypophosphatemia (XLH), due to PHEX mutation, is the most common genetic form of rickets in children. This rare disease is characterized by decreased tubular reabsorption and increased renal loss of phosphorus due to increased FGF-23 levels. In children, XLH is often manifested by short stature, rickets and bowel limbs deformity. Conventional treatment with oral phosphorus salts and calcitriol is not always well tolerated which has a progressive and profound impact on patients throughout life. Burosumab is a monoclonal antibody designed to restore renal phosphate reabsorption at proximal tubule and to stimulate endogenous calcitriol production. We report two sisters with XLH on Burosumab treatment with satisfactory

Case report: a 3 years old girl was referred due to presumptive diagnosis of Laron syndrome. Family Background: mother with extremely short stature (-7 SD), falling teeth, bone deformity in the lower limbs and healthy 6 months-old sister. She had frontal bossing, short stature (-3,3SD), genu varus and bone pain. Laboratory test: Normal calcium, Phosphorus: 2,5 mg/dl (RV: 3,3-5,5), Alkaline phosphatase (AP): 2550 UI (RV: 150-400), Normal 25 OH D values and TPR: 73 %; Severe Rickets Score (SRS) total: 8 and FGF23: >1991 pg/ml (RV:0-134). Her mother and sister were studied and showed similar features. As clinical biochemical and radiological findings were compatible with XLH, PHEX mutation was confirmed. She started conventional treatment but she had a fracture of the right femur. We decided to start Burosumab treatment and we observed significant improvement with decrease of AP values, pain scale reduced from 8 to 2 with improvement of the SRS to 4 and increased in growth velocity (height form -3.3 DS to -2 DS during first 6 months)

Case 2: Her sister was diagnosed at 6 months of age and despite starting conventional treatment early she presented bad evolution, because of this she started burosumab treatment at 3 years old and after 6 months improved her clinical symptoms, laboratory test and quality of life.

Conclusion: Burosumab treatment was a key to control the excess of FGF-23 and improvement of clinical and biochemical manifestations of XLH. Is an alternative therapy to conventional therapy in growing children with XLH and bad evolution. The greatest achievement was to improve the quality of life of two sisters but the most important thing was the improvement and attenuated evolution in the 2nd girl because of early therapy.