Besides blood and urine analyses, genetic testing — checking for mutations in the PHEX gene — can be used to confirm a diagnosis of X-linked hypophosphatemia (XLH).

Diagnosing XLH, a rare genetic disorder, is a multi-step process that starts with the doctor taking the patient’s family history and assessing the person’s symptoms.

XLH is caused by mutations in a gene called PHEX, which provides instructions for making an enzyme that is active primarily in bones and teeth. Mutations in this gene lead the body to abnormally process phosphate in the kidneys, which results in phosphate being lost in the urine. Without phosphate, bones and teeth are weakened, which has profound consequences for growth and development.

What is genetic testing?

Genetic testing is a medical test that detects changes in a person’s genetic material or DNA. The results of the test can confirm or rule out a suspected genetic condition. They also can help determine a person’s risk of developing the condition and passing it onto the next generation.

How is a genetic test performed?

For a genetic test, the patient will have a small blood sample collected at a hospital or clinic. This blood sample will either be tested in-house by the hospital or clinic or shipped to an independent laboratory that will perform the genetic test.

The DNA in the blood sample will be extracted and tested for mutations that can cause disease. In cases where XLH is suspected, the DNA will be tested for mutations in the PHEX gene.

The test results can take from a few days to a few weeks to be returned to the physician who ordered the test.

What happens after the genetic test?

The physician will meet with the patient and their caregivers and discuss the results of the test. It is recommended that patients and parents of children with XLH meet with a genetic counselor to discuss the risks of passing onto the next generation any genetic mutations that may have been detected during the test.


Last updated: Jan. 2, 2019


XLH News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health providers with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.