CMT1A, or Charcot-Marie-Tooth disease type 1A, is the most common form of inherited peripheral neuropathy. It is caused by an extra copy of a gene called PMP22 on chromosome 17, which leads to gradual damage to the myelin sheath that insulates peripheral nerves. The condition accounts for roughly 60 to 70 percent of all Charcot-Marie-Tooth (CMT) cases and typically produces slowly worsening weakness and sensory loss in the feet and hands over a person’s lifetime.1PubMed. Treating PMP22 gene duplication-related Charcot-Marie-Tooth disease: the past, the present and the future The progression is slow enough that many people remain ambulatory throughout life, but the degree of disability varies enormously from one person to another, even within the same family.
The Genetic Cause
CMT1A results from a duplication of a 1.5-megabase stretch of DNA on chromosome 17p11.2. That stretch contains the gene for peripheral myelin protein 22, or PMP22, so people with CMT1A carry three copies of the gene instead of the usual two.2Brain. PMP22 duplication dysregulates lipid homeostasis and plasma membrane organization in developing human Schwann cells The extra copy means Schwann cells, the cells that wrap myelin around peripheral nerve fibers, produce too much PMP22 protein. Myelin formation is exquisitely sensitive to PMP22 levels; even a modest increase disrupts the process.1PubMed. Treating PMP22 gene duplication-related Charcot-Marie-Tooth disease: the past, the present and the future
The duplication is inherited in an autosomal dominant pattern, meaning a child needs only one affected parent to have a 50 percent chance of inheriting the condition. Not every case runs in the family, though. An estimated 10 percent or more of autosomal dominant CMT1 families carry a duplication that arose spontaneously, meaning neither parent has the condition.3PubMed Central. Prevalence and origin of de novo duplications in Charcot-Marie-Tooth disease type 1A: first report of a de novo duplication with a maternal origin So a person can be the first in their family to have CMT1A.
How Myelin Damage Leads to Symptoms
Schwann cells overloaded with PMP22 form defective myelin sheaths. The insulation around nerve fibers becomes thinner, irregular, or fails to form properly. Over time, this leads to slower nerve signaling and, eventually, damage to the nerve fibers (axons) themselves.4PubMed Central. Characterising PMP22-Proximal Partners in a Schwann Cell Model of Charcot–Marie–Tooth Disease Type1A It is the axonal loss, more than the myelin damage itself, that drives the progressive muscle weakness and sensory deficits people experience. Recent research has also found that the PMP22 overexpression disrupts lipid balance and the structural organization of Schwann cell membranes, adding another layer to how the disease damages nerves.2Brain. PMP22 duplication dysregulates lipid homeostasis and plasma membrane organization in developing human Schwann cells
The damage follows a length-dependent pattern: the longest nerves in the body are affected first. That is why the feet and lower legs show problems before the hands, and why symptoms tend to creep upward over decades.
Symptoms and How They Develop
CMT1A usually becomes noticeable in childhood or adolescence, though some people do not recognize symptoms until adulthood. The earliest signs typically involve the feet. Children often develop high arches (pes cavus), hammertoes, and difficulty walking. Foot deformity, weakness, pain, cramps, and ankle instability are common features, and foot structure tends to evolve toward increasingly high arches from early childhood through adolescence, though a subset of patients retain flat or normal-arched feet.5PubMed. Evolution of foot and ankle manifestations in children with CMT1A
As the disease progresses, weakness of the muscles that lift the foot (the ankle dorsiflexors) causes foot drop, making it hard to clear the toes during walking. People often develop a characteristic high-stepping gait to compensate. Muscle wasting in the lower legs can give them a so-called “inverted champagne bottle” appearance. Hand weakness and loss of fine motor skills typically develop later, making tasks like buttoning a shirt or opening jars more difficult.
Sensory loss follows a similar pattern, starting in the toes and feet and gradually moving upward. People may lose the ability to feel light touch, temperature changes, or vibration in the affected areas. Small nerve fiber loss worsens with age: skin biopsies show a progressive, length-dependent drop in nerve fiber density in the legs, along with reduced sweating capacity in the feet.6PubMed Central. Small nerve fiber involvement in CMT1A
In surveys of how daily life is affected, weakness in the lower limbs ranks as the most disruptive symptom overall. For older patients and those with greater disability, balance impairment becomes the dominant concern, while younger patients tend to report sleep disturbance as particularly bothersome.7PubMed Central. The impact of symptoms on daily life as perceived by patients with Charcot-Marie-Tooth type 1A disease
Pain Is More Common Than Many Expect
CMT1A has historically been described as a motor and sensory neuropathy with relatively little pain. That characterization is misleading. In one study of 49 CMT1A patients, 88 percent reported pain, most commonly in the feet.8PubMed. Pain and small fiber function in Charcot-Marie-Tooth disease type 1A The majority of that pain was musculoskeletal, stemming from foot deformities, altered gait mechanics, and muscle cramps rather than from nerve damage directly. Only about 18 percent of patients had neuropathic pain, the burning or shooting type associated with damaged sensory nerves. Still, over half of patients in that study had elevated cold detection thresholds, meaning they could not feel cool temperatures as well as expected, which lines up with the small fiber loss seen in skin biopsies.
The distinction matters for treatment. Musculoskeletal pain from foot deformity and abnormal gait can improve with physical therapy, orthotics, and sometimes surgery. Neuropathic pain, when present, typically requires a different approach using medications aimed at nerve pain.
How CMT1A Is Diagnosed
Diagnosis usually begins with a clinical exam: a neurologist looks for the characteristic pattern of distal weakness, sensory loss, reduced reflexes, and foot deformities. A family history of similar symptoms raises suspicion, though as noted, some cases arise from new mutations.
Nerve conduction studies play a central role. CMT1A produces uniformly slowed motor nerve conduction velocities (MNCVs), typically averaging around 20 meters per second, compared to the 50 or more meters per second seen in healthy nerves.9PubMed Central. Nerve conduction velocity in CMT1A: what else can we tell The slowing is remarkably consistent across different nerves in the same person and tends to remain stable over time, which helps distinguish CMT1A from acquired demyelinating neuropathies where the slowing is patchy and uneven.10PubMed. Electrophysiological characterization of Charcot-Marie-Tooth disease type 1A in Taiwan That uniformity is a hallmark: if a nerve conduction study shows diffuse, symmetric slowing in the demyelinating range, CMT1A jumps to the top of the differential.
Genetic testing confirms the diagnosis. The standard first-line test is MLPA (multiplex ligation-dependent probe amplification), which detects the PMP22 duplication. In one UK study, MLPA identified the duplication in about 73 percent of confirmed CMT cases, making it the single most productive genetic test.11Brain. Whole genome sequencing increases the diagnostic rate in Charcot-Marie-Tooth disease When MLPA comes back negative but clinical suspicion remains, next-generation sequencing panels can identify rarer CMT-causing gene variants.12PubMed Central. High Diagnostic Yield of Next-Generation Sequencing in Charcot-Marie-Tooth Patients and a Novel Variant in the NDRG1 Gene
Why Severity Varies So Much Between People
One of the most puzzling features of CMT1A is how differently it affects people who carry the exact same genetic duplication. Two siblings can inherit the same PMP22 duplication and yet one walks without aids while the other needs braces or a wheelchair. Researchers have spent years trying to figure out why.
The leading explanation is that modifier genes outside the PMP22 region influence how the disease manifests. A genome-wide association study identified the gene SIPA1L2 as a potential modifier of CMT1A severity, offering a new pathway that could eventually be targeted by therapies.13PubMed Central. Variation in SIPA1L2 is correlated with phenotype modification in Charcot-Marie-Tooth disease type 1A Another study found that a common polymorphism in a small RNA molecule called miR-149 was associated with both the age when symptoms first appear and their severity: certain genotypes were linked to later onset and milder disease.14PubMed. Association of miR-149 polymorphism with onset age and severity in Charcot-Marie-Tooth disease type 1A This area of research is still in its early stages, but these modifier genes and regulatory molecules help explain why a single, uniform genetic duplication produces such a wide spectrum of outcomes.15PubMed Central. Modifier Gene Candidates in Charcot-Marie-Tooth Disease Type 1A: A Case-Only Genome-Wide Association Study
Physical Therapy and Orthotics
There is currently no cure for CMT1A. Management focuses on preserving function, reducing symptoms, and preventing complications. Physical therapy is the foundation. Targeted exercises, particularly those strengthening the ankle dorsiflexors and hip muscles, along with stretching and balance training, have been shown to improve gait and postural stability. A randomized controlled trial found that a 12-week home-based program combining balance training and proximal muscle strengthening significantly improved balance and walking function, and was safe enough to do at home.16PubMed Central. Clinical Characteristics of Gait Disturbance in Charcot-Marie-Tooth Disease and Future Directions in Physical Therapy
Ankle-foot orthoses (AFOs) are one of the most commonly prescribed tools for CMT1A. Lightweight, flexible AFOs help compensate for foot drop and ankle instability, keeping the foot in a better position during walking. Research has shown that AFOs reduce not just the foot drop itself but also the compensatory movements people develop at the hip and knee to work around their weak ankles.17PubMed. Foot drop splints improve proximal as well as distal leg control during gait in Charcot-Marie-Tooth disease For people with sensory deficits, the contact pressure from the brace may also provide a sensory input that improves balance.16PubMed Central. Clinical Characteristics of Gait Disturbance in Charcot-Marie-Tooth Disease and Future Directions in Physical Therapy
Surgery for Foot Deformities
When foot deformities become severe enough that braces and therapy can no longer manage them, orthopedic surgery enters the picture. The specific procedures depend on the patient’s age and the nature of the deformity. In children, the most common surgical approaches include calcaneal osteotomy (reshaping the heel bone), peroneal tendon transfer, first metatarsal osteotomy, and plantar fascia release. Adult surgical management looks similar, with calcaneal osteotomy being the most widely performed procedure among orthopedic surgeons surveyed.18PubMed Central. Prevalence and orthopedic management of foot and ankle deformities in Charcot–Marie–Tooth disease
Surgery does not stop the underlying nerve disease from progressing, so deformities can recur. The goal is to restore a more plantigrade (flat-on-the-ground) foot position, reduce pain, and make bracing more effective. Timing matters: surgeons generally prefer to intervene before bony deformities become fixed, when soft-tissue procedures alone can still achieve a correction.
Medications to Avoid
People with CMT1A need to be cautious about certain medications that can worsen peripheral nerve function. The most well-known example is vincristine, a chemotherapy drug used in some cancers. In people with CMT1A, even relatively low doses of vincristine can trigger severe, sometimes irreversible nerve damage. Case reports describe children with undiagnosed CMT1A who developed devastating neuropathy after starting vincristine-containing chemotherapy regimens.19PubMed Central. Acute neurotoxicity following vincristine due to Charcot–Marie–Tooth disease in a young child with medulloblastoma Clinicians are advised to take a thorough personal and family history of neuropathy before prescribing any neurotoxic medication.
Beyond vincristine, several other drugs are considered potentially neurotoxic for CMT patients, including certain other chemotherapy agents, some antibiotics, and high-dose vitamin B6. The Charcot-Marie-Tooth Association maintains a list of medications that CMT patients should discuss with their doctors before taking. If you have CMT1A and are facing any medical treatment, making sure every treating physician knows about your diagnosis is one of the most important safety steps you can take.
Investigational Treatments Targeting the Root Cause
Because CMT1A is caused by too much PMP22 protein, the most promising experimental therapies aim to dial that protein back down. Several approaches are being pursued.
The furthest along in clinical development is PXT3003, a combination of three repurposed drugs (baclofen, naltrexone, and sorbitol) designed to reduce PMP22 expression. In a randomized, placebo-controlled trial, the high dose of PXT3003 produced a modest but statistically significant improvement in disability scores compared to placebo, and both doses were well tolerated.20PubMed Central. A double-blind, placebo-controlled, randomized trial of PXT3003 for the treatment of Charcot–Marie–Tooth type 1A A larger, confirmatory trial (PREMIER) is ongoing.
Gene therapy represents a more direct attack on the problem. Researchers have developed artificial microRNAs packaged in a viral vector (AAV9) that silence the PMP22 gene in Schwann cells. In a mouse model of CMT1A, a single injection of this therapy reduced PMP22 levels, improved nerve conduction, reversed myelin damage, and improved functional measures, even when treatment was started after disease onset.21PubMed Central. A translatable RNAi-driven gene therapy silences PMP22/Pmp22 genes and improves neuropathy in CMT1A mice A similar approach using a different viral vector (AAV2/9) in a rat model of CMT1A prevented motor and sensory deficits, maintained near-normal nerve conduction for at least twelve months, and preserved myelin structure.22Nature Communications. AAV2/9-mediated silencing of PMP22 prevents the development of pathological features in a rat model of Charcot-Marie-Tooth disease 1 A
Antisense oligonucleotides (ASOs), short pieces of synthetic DNA designed to reduce PMP22 messenger RNA, have shown similarly striking results in rodent models. When given to mice that already had established disease, ASOs restored myelination and nerve conduction to near-normal levels.23PubMed Central. PMP22 antisense oligonucleotides reverse Charcot-Marie-Tooth disease type 1A features in rodent models The ability to reverse damage that has already occurred, not just prevent future damage, is particularly encouraging, though the leap from rodent models to human patients is always uncertain.
None of these therapies are available outside of clinical trials yet. The challenge of delivering gene therapies or ASOs efficiently to Schwann cells throughout the peripheral nervous system remains a significant hurdle. But the field has moved from having no disease-modifying treatments even in the pipeline to having multiple distinct strategies that work in animal models, which is real progress for a disease that went untreated for over a century.
Tracking Progression
CMT1A progresses slowly enough that changes can be hard to detect over short periods, which is a problem both for individual patient care and for clinical trials trying to prove a treatment works. The CMT Neuropathy Score (CMTNS) is one of the most widely used clinical scales. In a natural history study, it increased by an average of about 0.7 points per year, confirming that the disease does worsen measurably but at a glacial pace.24PubMed. Neuropathy progression in Charcot-Marie-Tooth disease type 1A That slow rate makes it difficult to distinguish drug effects from natural variation in one- or two-year trials.
Researchers are developing blood-based biomarkers that could track the disease more sensitively. Proteins like neurofilament light and growth differentiation factor 15 can reliably distinguish CMT patients from healthy controls, though whether these markers respond to effective treatment is still being tested.25PubMed Central. Clinical Outcome Assessments and Biomarkers in Charcot-Marie-Tooth Disease Separately, a study of skin biopsy gene expression identified a panel of six genes whose expression changed over time in CMT1A patients, and a machine-learning model trained on these genes could classify patients as progressive or non-progressive with high specificity.26PubMed Central. Biomarkers predict outcome in Charcot Marie Tooth Disease 1A Reliable biomarkers would not only speed up clinical trials but could eventually help clinicians identify which patients are most likely to deteriorate and might benefit most from emerging therapies.
Living with CMT1A Over a Lifetime
CMT1A does not shorten life expectancy, and most people remain able to walk throughout their lives, though many need some form of assistive device as they get older. The psychological burden deserves attention: adapting to a progressive loss of function, dealing with chronic pain, and coping with visible differences like foot deformity and altered gait take a toll that clinical scales do not always capture. Fatigue is also a pervasive and underappreciated symptom, distinct from the weakness itself and often more disabling than patients or clinicians expect.
Pregnancy and general anesthesia are two areas that sometimes worry people with CMT1A. Pregnancy generally does not worsen CMT1A permanently, though some women report temporary increases in symptoms, possibly related to weight changes and fluid retention. General anesthesia is usually safe, but anesthesiologists need to know about the diagnosis to avoid certain muscle relaxants and to position the patient carefully to prevent pressure injuries on already-vulnerable nerves.
Exercise is safe and encouraged. There was once concern that overexertion could worsen nerve damage, but this has not been borne out. Moderate exercise, especially low-impact activities like swimming, cycling, and strengthening programs tailored to the patient’s abilities, helps maintain muscle mass and cardiovascular health without accelerating the disease. The key is working with a physical therapist who understands CMT to design a program that challenges the muscles you still have without overstressing the ones that are already weak.