Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes X-linked hypophosphatemia ?
    ### Response:
    What causes X-linked hypophosphatemia? X-linked hypophosphatemia (XLH) is caused by mutations in the PHEX  gene on the X chromosome. Nearly 300 PHEX mutations have been associated with XLH. Mutations in this gene lead to an increase in the bodily concentration of fibroblast growth factor 23 (FGF23), a growth hormone that regulates phosphate reabsorption in the kidneys.
    