X-Linked Hypophosphataemic Rickets and Growth.

X-linked hypophosphataemia (XLH) is the most prevalent form of hereditary rickets characterized by an alteration of phosphate metabolism which frequently leads to the appearance of fractures, bone deformities and growth delay. Although the mechanism of growth impairment in patients with XLH still needs to be clarified, it is known that this alteration is not due to genetic or endocrine factors. A potential explanation for the impairment of growth in this disease is the alteration of the growth plate, a structure responsible for longitudinal growth of bones. Some of the findings in the growth plate of patients with XLH include atypical organization of chondrocytes due to low rates of proliferation and apoptosis and disturbance of chondrocyte hypertrophy, overactivation of the mitogen-activated protein kinase (MAPK) signalling pathway and upregulation of phosphorylated extracellular signal-regulated kinase (pERK). Conventional treatment of XLH (consisting of oral phosphate supplements and active vitamin D analogues) is often insufficient for the longitudinal growth of bone, but other strategies based on recombinant growth hormone or therapies targeting fibroblast growth factor 23 (FGF23) or its receptor, such as burosumab, have shown promising results. This article briefly describes the relationship between XLH and growth retardation, and how to address this alteration in patients with XLH.