Cutaneous skeletal
hypophosphatemia syndrome (CSHS) is a rare disorder caused by somatic mosaicism for the gain of function RAS mutations . Affected patients have segmental epidermal
nevi, dysplastic cortical bony lesions, and
fibroblast growth factor-23 (FGF23)-mediated
hypophosphatemic rickets. Herein, we describe a case of an Emirati girl with CSHS, whose
hypophosphatemic rickets and osteomalcic pseudofractures and dysplastic bony lesions failed to recover due to poor adherence to treatment with oral
phosphate supplements and
alfacalcidol (conventional treatment). Treatment with
burosumab, a fully human
immunoglobulin G1
monoclonal antibody against FGF23 for 12 months, led to normalization of serum
inorganic phosphate and
alkaline phosphatase levels, radiographic healing of
rickets, partial healing of pseudofractures, improvement in 6-minute walk test, and the physical scale of the Pediatric Quality of Life Inventory. We conclude that
burosumab is effective in treatment of CSHS, however results of the ongoing phase 2 trial in adults (NCT02304367) are awaited.