Hemophilia is a genetic disorder caused by a change in the DNA of either the factor VIII or factor IX gene. This change is called a mutation. There are many different mutations that cause hemophilia. Through genetic testing, we can usually identify the mutation in individuals with hemophilia. The testing will not usually result in a change in treatment for a boy with hemophilia, but can help us better estimate risk for inhibitor formation, since inhibitors are more common with certain mutations. In the future, it is possible that we may use this information to help guide clinical care.
Why test female family members?
Once the mutation for a family is identified, accurate testing can easily be done for female relatives who could be carriers, including sisters, maternal aunts and cousins of the person with hemophilia. This testing can be very helpful for girls and women for many reasons. First, learning that one is not a carrier can be reassuring, and a letter will be provided to keep as part of a permanent health record.
If a test is positive for carrier status, it can be important for the health of the female. A factor VIII or IX level may be done to make sure the levels are high enough to prevent bleeding. Some carriers have lower-than-normal factor levels and need treatment for some events, such as dental procedures and surgery. If a female is found to be a carrier, this information is very helpful at the time of any future pregnancies. Special precautions will be taken for both the mother and the baby during pregnancy, labor and delivery. Of course, knowing if one is a carrier or not may help in planning pregnancies. However, the purpose of carrier testing is NOT to discourage having children, but rather to promote better health for the mother and baby.
It is not clear what the best age is for carrier testing. It should be done well before becoming pregnant, and may be useful earlier to help prevent bleeding if factor levels are low. Genetic education is important, even without testing, to make sure all female relatives are aware of the family history of hemophilia, how it is inherited and if they have a chance of being a carrier. It is important for these girls and women to tell their healthcare providers about a family history of hemophilia to help prevent serious complications for any baby boys. The Hemostasis and Thrombosis Center (HTC) at CHOP will provide written guidelines for labor and delivery precautions for pregnant relatives to help ensure a safe delivery for mother and baby, even if the carrier status is not known.
Carrier testing for mothers and sisters of CHOP patients is available at the HTC in Hematology Clinic and is usually covered by insurance. Genetic education is provided in clinic for every person tested, and genetic counseling is available by referral. Please ask your hematologist or call the hemophilia nurses at 215-590-2199 to arrange an appointment at CHOP for carrier testing for sisters 21 and under. For adult sisters or other female relatives, please call the same number and we will help arrange the testing at an adult hemophilia treatment center near them.
The HTC staff is happy to discuss any questions you may have regarding the inheritance of hemophilia, genetic testing for hemophilia and female relatives at risk.