Types of CMT

CMT is classified by the way the nerves are affected.

Electromyography (EMG) is the diagnostic procedure used to assess the health of muscles and the nerve cells that control them and determine the classification.


Demyelinating CMT

Directly damages the myelin around the peripheral nerves. The nerves can then not transmit signals as quickly or efficiently as they should.

The axon is eventually damaged, as well, due to the long-term damage to the myelin, but CMT Types 1, 4, and X are still classified as demyelinating CMT.

Axonal CMT (Type 2)

Directly damages the peripheral nerve axon. The damage to the peripheral nerve axon caused by CMT affects the strength of the signal sent by the nerve, but the speed of the signal can still remain normal. Since the peripheral nerves are longer, the impairment can be more severe at the end of the peripheral nerve because the weakened signal does not make it all the way to the end.

Intermediate CMT

By nerve conduction traits, neither demyelinating nor axonal.

An EMG would reveal a combination of both strength and speed abnormalities.


The most common CMT

CMT1A is caused by the duplication of the Peripheral Myelin Protein 22 (PMP22) gene, which leads to the demyelination of the peripheral nerves. These patients have overexpression (too much) PMP22 protein.

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PMP22del – HNPP

HNPP is caused by a deletion of the Peripheral Myelin Protein 22 (PMP22) gene, which leads to the demyelination of the peripheral nerves. Unlike CMT1A, these patients have too little PMP22 protein.

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The GJB1 gene protein is affected and is called connexin 32.

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Caused by mutations in the Myelin Protein Zero (1q22) gene caused by mutations in the MPZ gene (1q22).

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Is axonal and caused by mutations in the MFN2 gene, which encodes Mitofusin 2, a transmembrane protein of the outer mitochondrial membrane.

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GDAP1 (CMT4A or 2k)

Can be either a demyelination, axonal or intermediate sensorimotor neuropathy labeled as CMT4A. GDAP can also be an axonal peripheral sensorimotor polyneuropathy labeled as CMT2K.

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C12or65 or MTRFR (CMT6)

A rare axonal hereditary motor and sensory neuropathy which present with a series of diseases that cause blindness and cognitive impairment. C12or65 may result with CMT Neuropathy, Leigh’s Syndrome, Spastic Parapheligia and Ataxia.

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SORD Deficiency

Also labeled as a CMT2 is a genetic metabolic disease resulting in CMT neuropathy. (SORD) Deficiency patients are missing a key enzyme needed to metabolize a sugar called sorbitol.

Information on SORD

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GAN - Giant Axonal Neuropathy

Giant axonal neuropathy (GAN) is recessive and severe resulting in progressive nerve death. It generally appears in early childhood. The protein that isn’t functioning in GAN is called gigaxonin.

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CMT2C is axonal peripheral sensorimotor neuropathy with onset as early as infancy and is characterized by the association of vocal cord paresis including respiratory (diaphragm) muscle impairment, hearing loss, leg, arm and hand weakness and paralysis. CMT2C is closely related to allelic disorders Scapuloperoneal Spinal Muscular Atrophy and Congenital Distal Spinal Muscular Atrophy, with many shared and overlapping symptoms (these three clinical disorders are often considered one disorder, TRPV4 related Hereditary Neuropathy, with a spectrum of severity).


CNTNap1 is a recessive mutation in CNTNAP1 that leads to a loss of this gene and its protein product CASPR. The loss leads to disruption of the myelinating cells from the signal transmitting nerve cell axons. This has profound negative effects on the development and maintenance of many nerve fibers in the central and peripheral nervous system. The effect on the peripheral nerves is a profound demyelination that presents with severe CMT syndromes.

For ALL CMT Genes

Search for information in the Portal for Rare Diseases and Orphan Drugs.

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Genetic Testing – CMT Genie

Wish there was an easy guide for genetic testing?

Now there is with the CMT Genie!
HNF’s CMT Genie is designed to assist you and your health care provider determine what the best option is for you!

If you don’t know your CMT type, you can find out from the HNF through The CMT Genie Program.