X-linked hypophosphatemia (XLH) is a rare, genetic, progressive, lifelong phosphate-wasting disorder caused by loss-of-function mutations in the PHEX (phosphate-regulating endopeptidase homologue, X-linked) gene, leading to excess circulating levels of fibroblast growth factor 23 (FGF23) (Beck-Nielsen et al., 2019). The gene discussed is PHEX; the disease is X-linked hypophosphatemia.