X-linked hypophosphatemia (XLH) is a metabolic bone disease which is the result of renal phosphate wasting. It is the most common form of genetically inherited rickets. Instead of being absorbed into bone, phosphate is lost in urine. The clinical symptoms and manifestations of XLH are diverse and vary in severity, but generally include childhood leg bowing, lower leg rotation/torsion, and short stature. In addition, some patients with XLH are prone to dental abscesses and if it is determined that severe bowing or tibial torsion is unlikely to improve with medical therapy alone, surgery might be necessary.
The diagnosis of XLH requires long term medical therapy with vitamin D metabolites and phosphate salts. Most children with XLH are treated from the time of diagnosis until growth is complete. Due to the chronic nature of the disease and the need for continual medical therapy, a definitive diagnosis of XLH through evidence of renal phosphate wasting is critical to obtain before beginning patients on treatment. Treatment during the growing phase of childhood targets and corrects leg deformities, (hopefully) decreases the number of surgeries, and improves the outcome of adult height. Early diagnosis and treatment are key to optimizing these effects.
Later in life dental abscesses, arthritis, and calcifications of the tendons and ligaments (enthesopathy) are often associated with XLH in adulthood. The goals of medical treatment in adults are to reduce pain symptoms, to reduce osteomalacia (the presence and abundance of unmineralized osteoid present in the skeleton), and/or to improve fracture healing or surgical recovery.
In the last 60 years, much has been learned about XLH; however, there are still many questions yet to be answered. Great strides have been made recently in the treatment of the disease and we look forward to the future for continued research, improved medical outcomes, and happy and healthy patients with XLH.