Burosumab Therapy in a Paediatric Patient with McCune-Albright Syndrome: A Case Report.

Introduction: McCune-Albright syndrome is characterized by the triad of fibrous dysplasia, café au lait skin pigmentation, and hyperfunctioning endocrinopathies. It is a sporadic condition caused by a missense mutation in the GNAS locus, located on chromosome 20q13.3, resulting in mosaic activation of the G protein alpha subunit.

Case Presentation: We pre‑sent a paediatric patient diagnosed with McCune-Albright syndrome at the age of 5 years. During the course of his condition, he was medically managed for a number of complications, such as peripheral precocious puberty and growth hormone excess, and monitored for hyperprolactinaemia. Due to fibroblast growth factor 23-mediated phosphate wasting, the patient was commenced on oral phosphate supplements and alfacalcidol. After 2 years of treatment, this therapy did not optimize his bone biochemistry (phosphate 0.96 mmol/L, alkaline phosphatase 1,172 IU/L, and parathyroid hormone 9.1 pmol/L), and the patient was started on two-weekly burosumab therapy via subcutaneous injection. His bone biochemistry soon normalized (phosphate 1.52 mmol/L, alkaline phosphatase 358 IU/L, and parathyroid hormone 6.9 pmol/L) following this, and he remains on burosumab without any adverse effects.

Discussion: This case shows the positive effect that a short-term course of burosumab has on bone health in a paediatric patient with McCune-Albright syndrome. Further research is required to assess long-term effects. Our patient also presented with precocious puberty and growth hormone excess, a coexistence that can be challenging to diagnose and is less common in males. He received medical management for both conditions, but due to the similar presentations, this case highlights the importance to investigate and diagnose associated complications as early as possible, so they can be managed in a timely manner.