Charcot-Marie-Tooth disease (CMT) includes more than 170 genetically distinct diseases caused by mutations in more than 140 known genes. These numbers continue to increase as new discoveries are made. Each subtype name corresponds to the genetic cause behind it. When a new CMT gene is identified, the discovering scientists pick the subtype name, following established criteria within the CMT classification system. That structure keeps new findings organized in a way that makes sense both clinically and scientifically.
The CMT Name
CMT is named after the three physicians who first described the disease in 1886: Jean-Martin Charcot, Pierre Marie, and Howard Henry Tooth. According to the Charcot-Marie-Tooth Association (CMTA) and the Inherited Neuropathy Consortium (INC), CMT has evolved into an umbrella term that refers to any inheritable neuropathy, even when the genetic cause is unknown.
CMT Classifications
CMT is divided into 13 classifications that help researchers organize subtypes based on shared features, including inheritance patterns, neuropathy types, or primary symptom profiles. The 13 classifications are CMT1, CMT2, CMT4, CMTX, CMTDI, CMTRI, dHMN, dSMA, GAN, HMSN, HSAN, HSN, and SMA LEP. There is one additional group of unclassified subtypes expressed as “CMT-gene,” such as “CMT-SORD” or “CMT-TUBB3.”
CMT1 subtypes are a demyelinating neuropathy and are autosomal dominant in inheritance.
CMT2 subtypes are an axonal neuropathy and are either autosomal dominant or autosomal recessive in inheritance.
CMT4 subtypes are a demyelinating neuropathy and are autosomal recessive in inheritance.
CMTX subtypes are each X-Linked in inheritance.
Dominant Intermediate CMT (CMTDI) subtypes are an intermediate neuropathy and are autosomal dominant in inheritance.
Recessive Intermediate CMT (CMTRI) subtypes are an intermediate neuropathy and are autosomal recessive in inheritance.
Distal Hereditary Motor Neuropathy (dHMN) subtypes are a motor neuropathy affecting primarily the most distal points, have little to no sensory nerve involvement, are an axonal neuropathy, and are either autosomal dominant or autosomal recessive in inheritance. dHMN is also known as Hereditary Motor Neuropathy (HMN).
Distal Spinal Muscular Atrophy (dSMA) subtypes are a motor neuropathy affecting primarily the most distal points and have little to no sensory nerve involvement. dSMA is synonymous with dHMN (the two refer to the same thing). dSMA subtypes are either an axonal or intermediate neuropathy, and are either autosomal recessive or X-Linked recessive in inheritance.
Giant Axonal Neuropathy (GAN) subtypes affect the central nervous system and the peripheral nervous system and are an axonal neuropathy. GAN has two subtypes. GAN-1 is autosomal recessive in inheritance, and GAN-2 is autosomal dominant in inheritance.
Hereditary Motor and Sensory Neuropathy (HMSN) subtypes affect both motor and sensory nerves. The acronym has been historically used to represent CMT as a whole, and this acronym is preferred over CMT by many. Currently, six subtypes are known only by their HMSN name. Each are an axonal neuropathy and are either autosomal dominant or autosomal recessive in inheritance.
Hereditary Sensory and Autonomic Neuropathy (HSAN) subtypes affect primarily the sensory nerves and the autonomic nerves, have little to no motor nerve involvement, are an axonal neuropathy, and are either autosomal dominant or autosomal recessive in inheritance.
Hereditary Sensory Neuropathy (HSN) subtypes affect primarily the sensory nerves, have little to no motor nerve involvement, are an axonal neuropathy, and are either autosomal dominant or autosomal recessive in inheritance.
Spinal Muscular Atrophy – Lower Extremity Predominant (SMA-LEP) subtypes are a motor neuropathy affecting primarily the lower extremities, with little to no sensory nerve involvement, and are characterized as an axonal neuropathy. They are autosomal dominant in inheritance.
Explore the SMA-LEP Subtypes →
The “Unclassified Subtypes” are a group known only by their gene name. These subtypes are either a demyelinating neuropathy or an axonal neuropathy, and are either autosomal dominant, autosomal recessive, or X-Linked dominant in inheritance. Examples include CMT-SORD, CMT-TUBB3, and CMT-RFC1.
Explore the Unclassified Subtypes →
Hereditary Neuropathy with Liability to Pressure Palsies (HNPP)
HNPP is a CMT subtype. It is caused by a deletion of one copy of the PMP22 gene. This deletion reduces the amount of PMP22 protein available to support healthy myelin, which makes peripheral nerves more susceptible to compression or prolonged pressure. People with HNPP may experience episodes of numbness, weakness, or temporary palsies in areas where nerves are exposed to pressure, such as the wrists, elbows, or the peroneal nerve at the knee.
Although historically associated with pressure palsies, HNPP often includes the full range of CMT symptoms, including weakness, sensory loss, balance difficulties, pain, and fatigue. Symptom severity varies widely, just as it does across other subtypes. The “pressure palsy” label reflects only one feature of the disease and does not define the overall presentation.
HNPP is an autosomal dominant demyelinating neuropathy. For these reasons, it is classified as a CMT1 subtype.
Historical Terms and Outdated Classifications
As genetic understanding of CMT has improved, several older terms have fallen out of use. Earlier classifications were based on symptoms, age of onset, or nerve conduction studies. With modern genetic testing, most individuals now receive a diagnosis that reflects the specific gene and mutation involved.
CMT3/Dejerine-Sottas Syndrome (DSS)
CMT3 and Dejerine-Sottas Syndrome (DSS) were once used to describe early-onset, severe, and usually recessive forms of CMT accompanied by very slow nerve conduction (often below 10 meters per second). This diagnosis, however, inferred no genetic cause. Today, most individuals who would have been or were diagnosed with CMT3 or DSS receive a genetically confirmed subtype instead. DSS may still appear in descriptive contexts, but the term CMT3 is archaic and abandoned.
Roussy-Lévy Syndrome
Roussy-Lévy Syndrome is not a CMT subtype but is an outdated description of a specific symptom pattern. It refers to individuals who have high arches, reduced reflexes, distal weakness, tremor in the arms, sensory loss, and gait ataxia. Kyphosis can also be present. This pattern has historically been associated with demyelinating forms of CMT, including CMT1A and CMT1B. Because these same symptoms appear across virtually all CMT subtypes, the term is has become outdated and is no longer used in clinical settings.
If you have questions about how these historical terms relate to a current diagnosis, a CMT specialist or genetic counselor can help clarify how older labels map onto today’s genetic classifications.
Explore the Experts in CMT Genetics Database
The Experts in CMT Genetics Database compiles the most comprehensive public record of CMT-associated genes and their related subtypes. It is designed to make the genetic side of CMT easier to understand, navigate, and compare. Search tools allow you to filter by classification, inheritance pattern, neuropathy type, gene symbol, chromosome, subtype, year discovered, or any combination of these options.
The structure of the database is grounded in the research behind “CMT-Associated Genes and Their Related Subtypes: The Definitive Guide,” a reference book developed by the platform’s founder, Kenneth Raymond. The guide is available as a free PDF exclusively through the Charcot-Marie-Tooth Association and remains a helpful companion for anyone seeking to understand the foundations of CMT genetics.
The platform’s database focuses specifically on genetic and subtype-level information, including inheritance patterns, neuropathy types, chromosome locations, and subtype classifications. Each record includes the original publication reference associated with that gene or subtype, but does not include the publication itself. Records also link to external resources such as symptom descriptions, research opportunities for patients, and other relevant contexts where available.
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