Why is genetic carrier testing important?
Genetic testing can determine whether a woman is definitely a carrier or whether she is very unlikely to be a carrier. Genetic testing is the best method for performing accurate carrier testing.
Carriers have an increased chance of having children with Duchenne or Becker, so if a woman knows she is a carrier, she can make more informed childbearing plans. There are many reproductive options available to carriers. Learn more about reproductive options for carriers.
Carriers also have an increased chance of heart problems and, sometimes, skeletal muscle weakness. If a woman knows she is a carrier, she should be evaluated regularly by a doctor who is familiar with Duchenne. Regular cardiology appointments are necessary, and referrals to other specialists may be needed. Learn more about Carrier Symptoms and Care.
Finally, genetic carrier testing is important because once one carrier is identified in a family, there could be several more carriers identified in the extended family. It is important to share this information with other females in the family so they can pursue carrier testing if desired.
PPMD’s Decode Duchenne genetic testing program provides free genetic testing and counseling to people in the Duchenne or Becker muscular dystrophy community who otherwise could not afford genetic testing. For more information regarding our free genetic testing program, click here.
Who should consider carrier testing?
Once Duchenne has been diagnosed in a family, it is important for family members to talk with a genetic counselor. A genetic counselor will take a detailed family history and will determine what other females in the family are at risk to be carriers.
In general, all women who could be carriers (based on their family history) should be offered carrier testing. This includes women with:
- sons or brothers with Duchenne,
- uncles or cousins on their mother’s side of the family who have Duchenne,
- mothers or sisters who are carriers for Duchenne, and
- aunts or cousins in their mother’s side of the family who are carriers for Duchenne.
What are the types of tests used to identify carriers?
Genetic testing is the best method for performing accurate carrier testing. It is very helpful if the mutation in the family has been confirmed first in an affected relative. However, if the mutation in the family is not known and there are no longer any living affected relatives, carrier testing can still be done but it will require analyzing the entire gene rather than looking for a specific mutation.
In the past, CK (creatine kinase) testing and/or muscle biopsy were used for carrier testing, but these are no longer the preferred methods. CK levels are not generally reflective of disease process and are often higher in child and adolescent carriers than in adult female carriers. CK levels also may be increased for reasons other than muscular dystrophy, such as strenuous activity or sickness. Muscle biopsies on carriers are generally avoided because they are invasive (a biopsy requires removing a piece of muscle tissue so it can be studied under a microscope) and less accurate than genetic testing.
How is carrier genetic testing done?
Carrier testing is done on a blood or saliva sample. There are different lab methods that can be used for carrier testing. The method for carrier testing should be determined by the woman’s family situation, including whether the mutation in the family is known and her family history.
- If the mutation in the family is known, only that mutation needs to be tested.
- If the mutation in the family is not known because the affected person has not had testing, it is best to test the person with Duchenne first, using a blood or saliva sample.
- If the mutation in the family is not known and there are no living affected relatives to test, a comprehensive testing plan can still find most (but not all) carriers.
If genetic testing was done in the past and no mutation was found, it might be appropriate to test the affected individual again using new and improved tests, which can identify more mutations. PPMD’s Decode Duchenne program provides free repeat genetic testing to individuals with Duchenne and Becker, regardless of their age.
PPMD’s Decode Duchenne genetic testing program provides free genetic testing and counseling to people in the Duchenne or Becker muscular dystrophy community who otherwise could not afford genetic testing. Our process is simple: complete our application and receive all the information and paperwork needed to have genetic testing performed through our designated laboratory, PerkinElmer Genetics. For more information regarding our free genetic testing program, click here.
When should carrier testing be done?
Carrier testing should be offered to all at-risk adult women with a family history of Duchenne. In the past, carrier testing was generally not performed on children. However, with increasing knowledge of the potential impact on carrier females, and with genetic testing in general becoming more prevalent, carrier testing on children and adolescents is now more common.
For adolescents, it is important to consider their maturity and to provide adequate pre- and post-test counseling. Adolescent assent and parental consent should be obtained prior to carrier testing. If you are interested in carrier testing for a minor in your family, please speak with their doctor or a genetic counselor to review the pros and cons of testing.
For more information regarding genetic testing of minors, please click here to read the 2015 ASHG Position Statement on Genetic Testing of Children and Adolescents.
For more information regarding PPMD’s free genetic testing program, Decode Duchenne, click here.
What do results from carrier testing mean?
- If carrier testing finds a mutation, the woman is a carrier.
- If the mutation in the family is known and carrier testing is done but the lab does not find the known mutation, that means that the woman is very unlikely to be a carrier.
- If the mutation in the family is not known and appropriate carrier testing does not find any type of mutation, it reduces the chance that the woman is a carrier, but does not make the chance zero. This is the most difficult type of result for healthcare providers and patients to interpret. A genetic counselor can help women understand this result and what additional testing might be useful.
If you have a child with Duchenne and they already have a registry account, you can add yourself to their account in the Family Member box and you both would share the same username and password. Carriers can also register themselves separately by creating a new account with a unique username and password.
Either way, the data you share will help us advance research by providing a better understanding of the impact of being a carrier and the significance of different types of genetic changes.
Can carrier testing identify germline mosaic carriers?
Women with germline mosaicism will not be found to be carriers via genetic carrier testing, because carrier testing is done on blood or saliva cells. Women with germline mosaicism have mutations in some of their egg cells, which will not show up on a blood or saliva test.
Because lab testing does not identify germline mosaic carriers, healthcare providers are left to assume that germline mosaicism explains most cases where women have no mutation found on carrier testing but have more than one affected child.
All women who have an affected child and no mutation found on carrier testing have a small chance to have germline mosaicism. It is not known exactly how often this happens, though some studies have suggested up to 15%. Learn more about germline mosaicism.