New genetic diagnostics for CMT

Here’s an informative article from the Hereditary Neuropathy Foundation (HNF) 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 is screening for mutations to the PMP22 gene, which causes CMT1A — two thirds of all CMT cases. (The HNF article incorrectly says it’s one third but correctly identifies it as the most common type.) If that test is negative, then immediately use Whole Exome Screening (WES) to quickly and economically screen for several less common subtypes.

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 — a third of all CMT cases. Unfortunately there are 10 subtypes for 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 lot of uncomfortable shocks and burned leg and arm hairs, but it’s not too bad. 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.

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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