Similarly, impaired resorption of phosphates in the proximal renal tubules can lead to hypophosphatemia that results in impaired vitamin D metabolism and hypovitaminosis D. X-linked hypophosphatemia (XLH), a rare disorder, is the most common cause of inherited phosphate wasting due to a mutation in the PHEX gene that predominantly affects osteoblast activity and FGF23 production.15 The gene discussed is FGF23; the disease is X-linked hypophosphatemia.