This can be achieved through careful examination, taking a family history, electrical tests and genetic studies on blood samples. This sort of assessment can also distinguish CMT from other non-genetic causes of neuropathy. The initial and most important tools in diagnosing CMT are electrical tests (called nerve conduction studies), which measure the patterns of electrical activity present in the nerves and record how quickly and how well electrical impulses travel along them. Children with CMT 1A will show the typical electrical abnormality from about the age of five.
Genetic tests are usually performed on a blood sample. The tests aim to identify which faulty gene is causing a condition and the precise nature of the genetic fault, in other words, the mutation. There are several different types of mutation, which are named for their effect on the DNA. For instance, a ‘deletion mutation’ is caused when some of the DNA is deleted and ‘duplications’ occur when part of the DNA is repeated. Testing for the chromosome 17 duplication, which causes most cases of CMT 1A, is widely available in most regional genetic laboratories. Some genetic laboratories or researchers have recently begun to use new sophisticated techniques to identify mutations in genes. To find out more about testing for a specific sub-type of CMT, contact your local genetic counselling centre. They may need to do a detailed assessment, including blood and electrical tests, of your close relatives.
If you have any questions, please contact us on 020 7803 4800 or info@musculardystrophyuk.org. Occasionally, members of a family with CMT, who don’t have signs of the condition or electrical abnormalities, may request a genetic test to see if they are likely to develop the condition in the future (predictive testing). In unaffected children, it is advised to wait until they are adults and can make their own decisions about testing.