The effects of burosumab on growth, nephrocalcinosis and cardiovascular outcomes in children with X-linked hypophosphatemia: a single-center experience

X-linked hypophosphatemia (XLH) is the most common cause of inherited rickets. It is characterized by chronic hypophosphatemia due to increased levels of Fibroblast Growth Factor 23 hormone (FGF23), renal phosphate wasting, and decreased renal vitamin D hydroxylation. Burosumab, an anti-FGF23 antibody, was approved in 2018 for XLH children. This retrospective single-center study assessed the progression of clinical, biological, renal, and cardiovascular outcomes of XLH patients who started burosumab before 18 years of age, between July 2018 and June 2022. In total, 12 children began burosumab treatment at a median age of 10.1(2.7–14.7) years, after 7.6 (1.1–11.3) years of conventional therapy. The last follow-up was 2.7(0.8–4.7) years after burosumab initiation, with 10 patients with at least 2 years of follow-up. Regarding the progression of anthropometric parameters, only height SDS significantly increased from baseline at the last follow-up. Regarding the biological parameters, as expected, at 12 months after starting burosumab and at the last follow-up, phosphate and alkaline phosphatase levels significantly improved. Although not significant, there was a trend towards an early increase of osteocalcin and crosslaps during the first months of therapy. Before starting burosumab, 5 patients (42