What causes XLH?
Mutations in a gene called PHEX are known to cause XLH. This gene encodes for an enzyme that regulates the synthesis of a protein called fibroblast growth factor 23 (FGF23), though researchers do not fully understand this process.
Mutations in PHEX mean that circulating blood levels of FGF23 are higher than normal, which lowers phosphate reabsorption by the kidneys. In turn, more phosphate — which is essential to bone mineralization — is secreted in the urine and lost.
Patients with the disease tend to have bone abnormalities, among other symptoms.
When may I need genetic testing?
Doctors can use genetic testing to find out whether you or your child have mutations in the PHEX gene, possibly to confirm a diagnosis of XLH.
If you or your spouse have XLH and you are expecting, you may want a prenatal genetic diagnosis for the fetus. This type of genetic test can determine before birth whether the child is likely to inherit the disease.
You may also be interested in a preimplantation genetic diagnosis with in vitro fertilization (IVF). Here, a genetic test is run on embryos that are created via IVF before they are implanted into the mother’s uterus, ensuring they do not carry a disease-causing mutation.
It’s a good idea to meet with a genetic counselor as well as your primary care physician before undergoing genetic testing. They can help you in deciding whether to be tested and in deciding among tests, and discuss reproductive options with you.
How is the test given?
For both adults and children, a small blood sample is sufficient for genetic testing. Your doctor will arrange a time for you or your child to go to the hospital or clinic for a blood draw. Some hospitals have their own testing laboratory. Most often, they send the blood sample to an independent laboratory for testing.
If you are pregnant and want a prenatal test, your doctor will discuss how samples will be collected from the fetus. There are two main methods of collection: amniocentesis or chorionic villus sampling (CVS). Each has its pros and cons, and your doctor will help guide you in choosing the method best for you and your family.
For a preimplantation genetic diagnosis, you will need to discuss genetic testing with the IVF clinic.
It can take a few days to a few weeks for results of a genetic test to arrive. These will go to your doctor, who will arrange to meet with you and discuss the results, and your options moving forward.
Are there risks or drawbacks?
Every medical procedure has some risks. However, the risks of giving a blood sample to be tested are generally very small. There is a small risk of bleeding and infection at the needle injection site, and some people can feel dizzy or lightheaded during a blood draw.
Prenatal genetic testing has some risks as well. The process of collecting DNA from the fetus has some risks for both mother and child, though complications are rare.
Last updated: Aug. 7, 2020
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.
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