Here’s an informative article from Charcot-Marie-Tooth News about current best practices in genetic diagnosis of CMT. A lot of examples are given of people with less common subtypes who waited a long time to get properly diagnosed — sometimes after many years of wrong diagnoses or none at all.
Today the best path to a diagnosis starts with testing for a duplication or deletion of the PMP22 gene. A PMP22 duplication causes CMT1A, which accounts for as much as 50% of all CMT cases (GeneReviews). (The Charcot-Marie-Tooth News article says it’s one third, but it correctly identifies CMT1A as the most common type.) If that test is negative, current GeneReviews guidance is to use a multigene panel of the most commonly involved genes next, and then Whole Exome Sequencing (WES) or genome sequencing to look for less common subtypes if no cause has been found.
If this doesn’t come up with a positive match, it would make sense to screen for types of CMT2, since it’s the second most common: between 12% and 35.9% of CMT cases, depending on the country (according to a systematic review). Unfortunately there are many subtypes of CMT2, and each is caused by a different gene mutation.
CMT1 and 2 (but not a specific subtype) have long been identifiable through Nerve Conduction Velocity tests, which entail a series of brief electrical stimuli that are uncomfortable, but it’s not too bad.1 (Needle EMG, often done at the same visit, is a separate component.2) That still seems like a good place to start, at least for people old enough to tolerate the discomfort. That’s as far as I’ve gotten, and it wasn’t too bad as a test, but I’d hesitate to put young children through it.
Correction, October 10, 2026: The article linked in the first paragraph was published by Charcot-Marie-Tooth News, not the Hereditary Neuropathy Foundation (HNF); the attributions have been corrected. The description of nerve conduction tests has also been corrected: they use brief electrical stimuli, and needle EMG is a separate component.
Notes
- Johns Hopkins Medicine, “Nerve Conduction Studies.” “A mild and brief electrical shock, given through the stimulating electrode, will stimulate your nerve.” ↩︎
- Johns Hopkins Medicine, “Electromyography (EMG).” In EMG, small needle electrodes are inserted through the skin into the muscle; nerve conduction studies are often performed at the same time. ↩︎
Sources
- Johns Hopkins Medicine. “Electromyography (EMG).” n.d. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/electromyography-emg.
- Johns Hopkins Medicine. “Nerve Conduction Studies.” n.d. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/nerve-conduction-studies.
What’s your CMT diagnosis story? Let me know in the comments or send me an email if you’d rather keep it private.
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