CMT Subtypes

Charcot-Marie-Tooth disease is not a single condition but a family of more than 100 genetic subtypes. They are grouped first by how the nerves are affected, then by the specific gene involved, and often down to the exact mutation within that gene. Knowing your subtype is more than a label: it shapes what to expect, guides your care, and increasingly determines which research studies and therapies you may be eligible for.

How CMT is classified

Electromyography (EMG) and nerve conduction (NCV) testing reveal how the nerves are affected, which sorts CMT into a few broad classes. Genetic testing then identifies the exact gene, which is your specific subtype.

Why knowing your subtype matters

For decades, knowing your exact gene changed little about day-to-day care. That is no longer true. Research and clinical trials are now organized by subtype, because a therapy that helps one gene defect may do nothing for another. A gene-replacement approach for one recessive subtype, an enzyme-targeting drug for SORD deficiency, an antisense strategy for CMT1A: these are subtype-specific by design.

Confirming your subtype with genetic testing can rule out look-alike conditions, help your clinician anticipate how your CMT may progress, flag medications to avoid, and tell you which studies you may qualify for. It is the single most useful step for connecting your care to the research pipeline.

CMT is caused by more than 100 genes. In a large 2014 commercial-laboratory cohort (Quest / Athena Diagnostics, with Baylor College of Medicine), four genes, PMP22, GJB1, MPZ, and MFN2, accounted for about 95% of genetically confirmed cases.

Most prevalent types

Five subtypes account for the large majority of CMT. If you have a genetic diagnosis, there is a good chance it is one of these.

1. 1
   CMT1A About 40 to 60% of confirmed cases

   PMP22 (duplication)

   An extra copy of PMP22 makes too much of the protein, which disrupts myelin. It accounts for roughly 70% of the demyelinating (CMT1) group on its own.

2. 2
   CMT1X About 10 to 13% of confirmed cases

   GJB1 (connexin 32)

   X-linked, so it runs through families differently. Often starts in childhood and tends to hit men harder, while women may be mild or have no symptoms at all.

3. 3
   HNPP About 3 to 15% of confirmed cases

   PMP22 (deletion)

   A missing copy of the same gene behind CMT1A, causing episodes of numbness or weakness after pressure on a nerve. Mild cases are easily missed, so it is likely under-diagnosed.

4. 4
   CMT1B About 5 to 10% of confirmed cases

   MPZ

   Changes in myelin protein zero. Demyelinating and usually dominant, with severity that varies a lot depending on the specific variant.

5. 5
   CMT2A About 3 to 7% of confirmed cases

   MFN2

   The most common of the type 2 (axonal) forms. Often earlier onset and can be more severe, and some people develop optic-nerve involvement.

Shares are of genetically confirmed CMT, and are shown as ranges because large patient cohorts in different countries report different proportions. No single study gives one worldwide number.

Subtypes we cover in depth

The subtypes with a full HNF page of their own, covering how each one behaves, how it is inherited, and what to expect. Your genetic report is the authoritative source for your own diagnosis.

Every CMT subtype, by type

147 recognized subtypes across 119 genes, grouped the way the naming system groups them. Use it to place your own result: find your gene, and you will see which family your subtype belongs to and how it is inherited. Newer discoveries are named after the gene rather than given a type number, which is why the last group looks different.

Research moves fast and new subtypes are named every year, so treat this list as a snapshot rather than a final word. Ask your neurologist or genetic counselor about anything that affects your own care.

Frequently asked questions

Sharing your subtype and symptoms in GRIN helps researchers understand each form of CMT and design the trials that target it.