Genetic testing for XP
Xeroderma pigmentosum (XP)
People who have XP are born with the condition, even if it's not diagnosed until later in life. You inherit an affected gene, which is passed from both of your parents.
We can do a blood test to find out if you or your child have XP. This is called genetic testing. The test is complex and takes up to 4 months to be completed.
Your doctor can arrange the blood test for you. It is available on the NHS.
How XP is passed on from parents to children
Genes come in pairs. 1 gene comes from your mother and the other gene comes from your father.
You have XP when an affected gene is passed from both of your parents (inherited).
You must have 2 copies of the affected gene to get XP. This is called a recessive genetic condition.
People with only 1 affected gene in their pair are called carriers. They do not have the condition, but they can pass the affected gene on to their children.
If 2 carriers have children, this can result in 3 different combinations:
If both parents pass on their unaffected gene (white boxes), their child will not have XP and they will not be a carrier. This means that they cannot pass it on if they have children in the future.
There is a 1 in 4 chance of not being affected at all.
If 1 parent passes on an unaffected gene (white box) and the other parent passes on an XP gene (grey box), the child will be a carrier. This means they do not have XP, but could pass it on to their future children.
It's most likely that parents who are carriers will have a child who's also a carrier. There is a 1 in 2 chance of being a carrier for XP.
If both parents pass on their XP gene (grey boxes), their child will have XP.
There is a 1 in 4 chance of inheriting XP.
Genetic counselling
Parents that are closely related to each other, such as first cousins, are more likely to have children with recessive genetic conditions. The parents are more likely to carry the same affected genes. This applies to all recessive genetic conditions and not just XP.
Having genetic information about yourself might change important future decisions in your life. You might need to think about this carefully. If you do have XP, we offer you genetic counselling. This is when we talk to you about how the genetic condition might affect you or your family. We answer your questions and support you.
Giving your permission (consent)
We want to involve you in decisions about your care and treatment. If you decide to have genetic testing, we ask you to sign a consent form. This says that you agree to have the test and understand what it involves.
If you would like more information about our consent process, please speak to a member of staff caring for you.
Follow-up appointment
You get a letter with the results of the genetic testing.
If you do not have XP, we refer you back to the care of your GP or referring doctor.
If you have XP, we invite you to the XP service for an appointment.
The XP service is a national rare diseases specialist service. NHS England funds this service. We aim to give people with XP the best coordinated care.
If your results are not certain, we might need to repeat the genetic testing with new samples of blood. This is very rare.
If you have any questions or concerns about your test results, please contact the XP clinical nurse specialists.
Resource number: 3512/VER4
Last reviewed: December 2021
Next review due: December 2024
