The CMTA does not endorse any form of genetic testing over others. The best way to decide which type of genetic testing is best for you is in consultation with your neurologist and a genetic counselor. To find a genetic counselor, visit www.nsgc.org, and click on “Find a Genetic Counselor.”
Genetic testing for CMT can be very complicated, as there are over 90 genes that have been found to cause CMT when mutated. However, the vast majority of people who have had a genetic cause to their CMT found have had one of five conditions, caused by mutations in four genes: CMT1A (PMP22 gene duplication), CMT1X (GJB1 gene mutation), CMT1B (MPZ gene mutation), HNPP (PMP22 gene deletion), or CMT2A (MFN2 gene mutation). Even within these five types of CMT, it is possible to narrow down the most likely gene based on a couple of things that a person with CMT presents with:
- Nerve conduction studies
- Family history
These are the two most important items to know when considering genetic testing. Flow charts have been published using nerve conduction velocities to direct genetic testing, usually with the aid of family history information (SEE: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3235845/).
Family history information can be used in a couple of ways – if a person in the family has had positive genetic testing, most likely everyone else affected in the family has the same type with the same genetic mutation. In this situation, individuals can have testing for just the mutation that was previously found. For example, if someone has an R69C mutation in MPZ, an affected daughter can have testing for just the R69C MPZ mutation and does not need to have the full MPZ gene sequenced or a full panel of tests.
Not everyone wants or needs to have a genetic diagnosis of CMT. For someone who does not already have a diagnosis of CMT, getting positive genetic testing results or an abnormal nerve conduction study could mean that s/he is no longer eligible for supplemental insurances, such as life, long-term care or disability insurances. It is important to think about the implications of a genetic test result over the long term before making the decision to be tested. Genetic testing for CMT is always optional. You have the right to decide to pursue to refrain from testing.
Not everyone who has CMT and wants to know their genetic type needs actual genetic testing, particularly if there is a family history and someone has previously had positive genetic testing results. It can be assumed that others in the family that are showing symptoms have the same type of CMT. For people who have unclear symptoms, it is possible to do a nerve conduction study in many types of CMT to determine if someone is affected. This is particularly true for the demyelinating types of CMT, such as CMT1A, where the nerve conductions are slow. If a family member also has slow nerve conduction studies, it can be assumed that person has the same genetic type of CMT as the person tested in the family.
If someone is making family planning decisions for CMT, such as prenatal or preconception options, that person will need to have their own positive genetic testing. The other family member’s positive testing would not be able to be used for family planning options.
- Family Planning For CMT – Part 2 The Second Article in a Series By Shawna Feely, MS, CGC, and Carly Siskind, MS, LCGC In the first article we presented options that people with CMT have to become biological parents without passing CMT on to ...Read more ...