In medical contexts, CMT most commonly refers to Charcot-Marie-Tooth disease, a group of inherited conditions that damage the peripheral nerves connecting the brain and spinal cord to the rest of the body. It’s the most common inherited nerve disorder, affecting roughly 10 to 82 people per 100,000 depending on the country studied. CMT can also stand for Certified Medical Transcriptionist, a healthcare documentation role. This article covers both meanings.
Charcot-Marie-Tooth Disease: The Basics
CMT disease isn’t a single condition. It’s a family of genetic disorders that progressively damage peripheral nerves, the long cables that carry signals between your brain and your muscles, skin, and organs. Because those nerves deteriorate over time, people with CMT experience a mix of sensory and motor problems: numbness, tingling, pain, muscle weakness and wasting, and foot deformities that gradually worsen.
Symptoms typically start in the feet and legs before eventually affecting the hands. Early signs often include difficulty lifting the front of the foot (called foot drop), frequent tripping, and a noticeable change in foot shape such as high arches or curled toes. The progression is slow, usually unfolding over years or decades, and severity varies widely even within the same family. CMT does not typically shorten life expectancy, but it can significantly affect mobility and fine motor skills over time.
What Causes CMT
CMT is caused by mutations in genes that produce proteins essential for peripheral nerve function. More than 100 different genes have been linked to various forms of the disease. The most common culprit is the PMP22 gene, which is responsible for 70 to 80 percent of CMT type 1 cases. Most of the time, the problem isn’t a broken gene but an extra copy of it, created by a small duplication of genetic material on chromosome 17. Other genes involved include MPZ (10 to 12 percent of CMT1), MFN2 (about 20 percent of CMT2), and GJB1 (roughly 90 percent of X-linked CMT).
The inheritance pattern depends on the type. Most forms of CMT1 and CMT2 follow an autosomal dominant pattern, meaning you only need one copy of the altered gene to develop the disease. If one parent carries it, each child has a 50 percent chance of inheriting it. Some rarer forms require mutations from both parents (autosomal recessive). X-linked CMT, caused by a mutation on the X chromosome, tends to produce more severe symptoms in males than in females because males have only one X chromosome.
CMT1 vs. CMT2: Two Main Types
The two broadest categories of CMT differ in what part of the nerve is damaged. CMT1 is a demyelinating form, meaning it attacks the protective insulation (myelin) that wraps around nerve fibers. Without that insulation, electrical signals slow dramatically. In nerve conduction testing, people with CMT1 typically show speeds below 38 meters per second in the median nerve, with an average around 23 m/s. Healthy nerves conduct signals much faster.
CMT2 is an axonal form. The insulation stays relatively intact, but the nerve fiber itself (the axon) degenerates. Because the myelin is mostly preserved, nerve conduction speeds stay closer to normal, averaging about 46 m/s. The real giveaway on testing is reduced signal strength rather than reduced speed. In practice, both types produce similar day-to-day symptoms, though the age of onset, rate of progression, and specific pattern of weakness can differ.
How CMT Is Diagnosed
Diagnosis usually starts with a neurological exam and a detailed family history. If CMT is suspected, the first step is electrodiagnostic testing, which measures how fast and how strongly electrical signals travel through your nerves. During the test, small electrodes are placed on the skin over various nerves. The pattern of results helps distinguish between demyelinating and axonal types and separates CMT from other causes of nerve damage, such as diabetes or autoimmune conditions.
Genetic testing confirms the diagnosis and identifies the specific subtype. DNA testing for the PMP22 duplication (CMT1A) is widely available and catches more than 98 percent of cases caused by that gene. Testing for X-linked CMT through the GJB1 gene detects about 90 percent of cases. For less common subtypes, testing availability is more limited, though next-generation gene panels have made broader screening increasingly accessible.
Managing Symptoms
There is no cure for CMT, but a combination of physical therapy, bracing, and sometimes surgery can help maintain function and quality of life. Physical therapy focuses on preserving muscle strength, flexibility, and balance, particularly in the lower legs and feet. Occupational therapy can address fine motor difficulties in the hands as the disease progresses.
Ankle-foot orthoses (AFOs) are one of the most common tools for managing CMT. These braces fit inside shoes and address specific problems like foot drop, ankle instability, or difficulty walking heel-to-toe. The right type depends on how much ankle stability you still have. People with flexible ankle instability often benefit from lightweight carbon fiber braces that allow some natural movement. Those with more rigid instability may need custom-molded solid braces with a total-contact inner boot for maximum support. A well-fitted brace improves foot and ankle alignment, restores a more natural walking pattern, and reduces the risk of falls.
Surgery is sometimes recommended for significant foot deformities, particularly when bracing alone can’t correct alignment issues. Procedures range from tendon transfers to bone realignment, and the goal is always to create a more stable, braceable foot rather than to eliminate the need for support entirely.
Treatment Research
Several clinical trials are exploring new approaches to CMT. A phase 3 trial is testing an oral drug designed to block the conversion of glucose to a sugar alcohol called sorbitol, targeting a specific enzyme deficiency linked to one CMT subtype. Another phase 2 trial is evaluating a drug that enhances the signal between nerves and muscles, potentially improving strength. On the gene therapy front, an early-stage trial at Nationwide Children’s Hospital is testing a single injection that delivers a functional copy of the IGHMBP2 gene directly into the spinal fluid for patients with specific rare subtypes (CMT2S and a related condition).
CMT as Certified Medical Transcriptionist
CMT also stands for Certified Medical Transcriptionist, a credential held by healthcare documentation specialists. These professionals convert voice recordings from physicians into written medical reports, including patient histories, discharge summaries, and exam notes. A large part of the job now involves reviewing and editing drafts produced by speech recognition software, checking for accuracy, consistency, and any errors or missing information that could compromise patient care. Transcriptionists also translate medical abbreviations into their full forms and enter completed reports into electronic health record systems.
Certification is not legally required to work in the field, but some transcriptionists pursue it voluntarily. Earning the credential involves passing an exam, and maintaining it requires continuing education credits on a recurring cycle. The role demands strong knowledge of medical terminology, anatomy, and documentation standards, along with strict adherence to patient confidentiality rules.