Genetic Disorders - X-Linked Hypophosphatemia and Treatment

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Dr. Mark Paskewitz is the vice president of clinical operations at the National Institute of Clinical Research in Los Angeles. Earlier in his career, Dr. Mark Paskewitz served as the senior director of clinical development with Kyowa Hakko Kirin Pharma, where he contributed to the creation of burosumab, the first-of-its-kind drug treatment for X-linked hypophosphatemia (XLH)

When a person has XLH, their blood does not have enough phosphorus due to an underlying problem with the kidneys. Without enough phosphorus, the patient’s bones weaken. Symptoms of XLH include bow-leggedness, slow growth, and pain in the teeth, bones, and joints. 

XLH is a genetic disorder; the genes involved are essential for the proper regulation of blood phosphate. Mutated copies of these genes in patients with XLH result in the overproduction and/or persistence of a protein that prevents the kidneys from introducing phosphate into the blood. In patients with XLH, the phosphate is excreted in the urine. 

Until recently, no drug existed specifically for XLH. In 2018, the Food and Drug Administration approved burosumab, marketed as “Crysvita,” to treat patients with the disorder. In clinical trials, Crysvita restored blood phosphate levels to normal in the vast majority of XLH patients.