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Adam MP, Bick S, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2026.
This publication is provided for historical reference only and the information may be out of date.
Thomas D Bird, MD.
Author Information and AffiliationsInitial Posting:August 31, 1998; Last Revision:March 26, 2015.
Estimated reading time: 46 minutes
NOTE: THIS PUBLICATION HAS BEEN RETIRED. THIS ARCHIVAL VERSION IS FOR HISTORICAL REFERENCE ONLY, AND THE INFORMATION MAY BE OUT OF DATE.
Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a demyelinating peripheral neuropathy characterized by distal muscle weakness and atrophy, sensory loss, and slow nerve conduction velocity. It is usually slowly progressive and often associated with pes cavus foot deformity and bilateral foot drop. Affected individuals usually become symptomatic between age five and 25 years. Fewer than 5% of individuals become wheelchair dependent. Life span is not shortened.
CMT1A (70%-80% of all CMT1) involvesduplication ofPMP22. CMT1B (6%-10% of all CMT1) is associated with single-nucleotide variants inMPZ. CMT1C (1%-2% of all CMT1) is associated with pathogenic variants inLITAF, and CMT1D (<2% of all CMT1) is associated with pathogenic variants inEGR2. CMT1E (<5% of all CMT1) is associated with single-nucleotide variants inPMP22. CMT2E/1F (<5% of all CMT1) is associated with pathogenic variants inNEFL.
Treatment of manifestations: Treatment by a multidisciplinary team including a neurologist, physiatrist, orthopedic surgeon, physical and occupational therapists; special shoes and/or ankle/foot orthoses to correct foot drop and aid walking; surgery as needed for severe pes cavus; forearm crutches, canes, wheelchairs as needed for mobility; exercise as tolerated.
Prevention of secondary complications: Daily heel cord stretching to prevent Achilles' tendon shortening.
Surveillance: Regular foot examination for pressure sores.
Agents/circumstances to avoid: Obesity (makes ambulation more difficult); medications (e.g., vincristine, isoniazid, nitrofurantoin) known to cause nerve damage.
Pregnancy management: Affected pregnant women may experience worsening symptoms during or after gestation; a higher occurrence of presentation anomalies, use of forceps, and operative delivery; and/or an increased incidence of post-partum bleeding.
CMT1 is inherited in anautosomal dominant manner. About two thirds of probands with CMT1A have inherited thePMP22duplication; about one third have CMT1A as the result of ade novopathogenic variant. Similar data are not available for the other subtypes of CMT1. The offspring of an individual with any of the subtypes of CMT1 have a 50% chance of inheriting the alteredgene. Prenatal testing is possible if the pathogenic variant has been identified in the family. Requests forprenatal testing for typically adult-onset diseases that do not affect intellect or life span are uncommon.
| Charcot-Marie-Tooth Neuropathy Type 1: Included Disorders |
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For synonyms and outdated names seeNomenclature.
Charcot-Marie-Tooth neuropathy type (CMT1) is diagnosed in individuals with the following:
Genes. The CMT1 subtypes and the genes associated with them are summarized inTable 1. The complicated genetic diversity of hereditary neuropathies with emphasis on CMT syndrome has been addressed byBaets et al [2014],Pareyson et al [2014] and Bird [Charcot-Marie-Tooth Hereditary Neuropathy Overview.] Many genetic testing strategies have been proposed including that ofSaporta et al [2011a].
Clinical testing
Summary of Molecular Genetic Testing Used in Charcot-Marie-Tooth Neuropathy Type 1 (CMT1)
| CMT1 Subtype | Gene 1 | Proportion of CMT1 Attributed to Pathogenic Variants in This Gene | Test Method |
|---|---|---|---|
| CMT1A | PMP22 | 70%-80% | Targeted analysis for pathogenic variants 2 |
| CMT1B | MPZ 3 | 5%-10% | Sequence analysis 4 |
| Deletion/duplication analysis 5 | |||
| CMT1C | LITAF 3 (previously known asSIMPLE) | 1%-2% | Sequence analysis 4 |
| Deletion/duplication analysis 5 | |||
| CMT1D | EGR2 3 | <2% | Sequence analysis 4 |
| Deletion/duplication analysis 5 | |||
| CMT1E | PMP22 3 | <5% | Sequence analysis 4 |
| Deletion/duplication analysis 5 | |||
| CMT2E/1F | NEFL 3 | <5% | Sequence analysis 4 |
| Deletion/duplication analysis 5 | |||
| Unknown 6 | NA | NA |
SeeTable A. Genes and Databases forchromosomelocus and protein. SeeMolecular Genetics for information on allelic variants detected in thisgene.
Detects a1.5-Mbduplication at 17p11.2 that includesPMP22 resulting in the presence of three copies ofPMP22 in all individuals with CMT1A. The test method is adeletion/duplication analysis targeted specifically at thePMP22 duplication; a variety of test methods can be used (see footnote 5) in addition toFISH.
Each of these subtypes is identified based on detection of apathogenic variant in the associatedgene; hence, the variant detection rate is 100%.
Sequence analysis detects variants that are benign,likely benign, ofuncertain significance,likely pathogenic, or pathogenic. Pathogenic variants may include small intragenic deletions/insertions andmissense,nonsense, andsplice site variants; typically,exon or whole-gene deletions/duplications are not detected. For issues to consider in interpretation ofsequence analysis results, clickhere.
Testing that identifiesexon or whole-gene deletions/duplications not detectable bysequence analysis of the coding and flankingintronic regions ofgenomic DNA. Included in the variety of methods that may be used are:quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), andchromosomal microarray (CMA) that includes this gene/chromosome segment.
To confirm/establish the diagnosis in aproband with slow nerve conduction velocities, one genetic testing strategy is serial singlegenemolecular genetic testing based on the order in which pathogenic variants most commonly occur.
Because CMT1A (caused by the 1.5-Mbduplication at 17p11.2 includingPMP22) is by far the most common type of CMT1, it is appropriate to test aproband with very slow nerve conduction velocities for this duplication first [Klein & Dyck 2005].
If noPMP22duplication is identified, the next step ismolecular genetic testing ofMPZ andGJB1 (a cause ofX-linked CMT). Note: If the family history shows male to male transmission, testing ofGJB1, mutation of which causesCharcot-Marie-Tooth Neuropathy X Type 1, is not appropriate.
If noPMP22duplication,MPZpathogenic variant, orGJB1 pathogenic variant is identified, considersequence analysis ofLITAF, EGR2,PMP22 (single nucleotide variants) andNEFL [Saporta et al 2011a].
Note: This testing strategy is different from that for axonal neuropathies andautosomal recessive neuropathies.
An alternative genetic testing strategy is use of amultigene panel that includesPMP22,MPZ,GJB1, and other genes of interest (seeTable 1 andDifferential Diagnosis). Note: The genes included and the methods used in multigene panels vary by laboratory and over time. Success of this approach is demonstrated byKlein et al [2014], who were able to identify the genetic cause of CMT in five of 15 kindreds (usingexome sequencing) who had escaped earlier detection by single-gene analysis. For an introduction to multigene panels clickhere. More detailed information for clinicians ordering genetic tests can be foundhere.
Individuals with CMT1 usually become symptomatic between age five and 25 years [Marques et al 2005,Houlden & Reilly 2006,van Paassen et al 2014]; age of onset ranges from infancy (resulting in delayed walking) to the fourth and subsequent decades. Clinical severity is variable, ranging from extremely mild disease that goes unrecognized by the affected individual and physician to considerable weakness and disability.
The typical presenting symptom of CMT1 is weakness of the feet and ankles [Ferrarin et al 2012]. The initial physical findings are depressed or absent tendon reflexes with weakness of foot dorsiflexion at the ankle. The typical affected adult has bilateral foot drop, symmetric atrophy of muscles below the knee (stork leg appearance), atrophy of intrinsic hand muscles, and absent tendon reflexes in both upper and lower extremities.
Onset in the first year of life often suggests anautosomal recessive cause of CMT butautosomal dominant types of CMT caused byduplication ofPMP22 (CMT1A) and pathogenicmissense variants inPMP22 (CMT1E),MPZ (CMT1B), andNEFL have been reported in this age group [Baets et al 2011].
Proximal muscles usually remain strong.
Mild to moderate sensory deficits of position, vibration, and pain/temperature commonly occur in the feet, but many affected individuals are unaware of this finding. Pain, especially in the feet, is reported by 20%-30% of individuals [Carter et al 1998,Gemignani et al 2004,Carvalho et al 2005]. The pain is often musculoskeletal in origin but may be neuropathic in some cases [Pazzaglia et al 2010].
Poretti et al [2013] have shown that the vestibular impairment may contribute to the poor balance often present in CMT1.
In a study of 61 subjects with CMT1,Boentert et al [2014] found that 37% had obstructive sleep apnea and 40% had restless leg syndrome. If these findings are confirmed they would represent an important newly recognized aspect of the CMT1phenotype.
Episodic pressure palsies have been reported [Kleopa et al 2004].
In CMT1A, prolonged distal motor latencies may already be present in the first months of life, and slow motor nerve conduction velocities (NCVs) have been found in some individuals by age two years [Krajewski et al 2000]. However, the full clinical picture may not occur until the second decade of life or later [García et al 1998]. In a study of 57 individuals with CMT1A, three had floppy infant syndrome, two had marked proximal and distal weakness (one requiring a wheelchair), one had severe scoliosis, five had calf muscle hypertrophy, and three had hand deformity [Marques et al 2005].
Some individuals with CMT1B have onset in the first decade of life; others have a much later onset. The age of onset trend tends to run true in families [Hattori et al 2003].
CMT1 is slowly progressive over many years. Affected individuals experience long plateau periods without obvious deterioration [Teunissen et al 2003]. NCVs slow progressively over the first two to six years of life and are relatively stable throughout adulthood. Early onset of symptoms and severity of disease show some correlation with slower NCVs, but this is only a general trend. Muscle weakness correlates with progressive decrease in the compound muscle action potential (CMAP) and suggests that developing axonal pathology is of considerable clinical relevance [Hattori et al 2003,Pareyson et al 2006].
In a study of persons with CMT1A over a five-year period,Verhamme et al [2009a] found increasing disability at least partially related to “a process of normal aging.” In a study of a large family with CMT1A over two decades,Berciano et al [2010] found that deterioration varied from mild to marked. It remains unclear why such a wide range of severity is observed in persons with CMT1A with the samepathogenic variant (PMP22 dup).
In CMT1A,Kim et al [2012] found that severity of weakness and sensory loss correlated with CMAPs and SNAPs (sensory nerve action potential), but not with conduction velocities.
The disease does not decrease life span.
Other findings in individuals with CMT1. A few men with CMT1 have reported impotence [Bird et al 1994].
Pes cavus foot deformity is common (>50%) and hip dysplasia may be under-recognized [Walker et al 1994,McGann & Gurd 2002].
Pulmonary insufficiency and sleep apnea are sometimes seen [Dematteis et al 2001].
Deafness has been occasionally reported in the CMT1phenotype. Impaired auditory perception and processing has been reported as common (>60%) both in children with CMT1 and in those with CMT2 [Rance et al 2012]. Hearing loss has been associated with single-nucleotide variants inPMP22 (CMT1E) [Kovach et al 1999,Sambuughin et al 2003,Postelmans & Stokroos 2006] andMPZ (CMT1B) [Starr et al 2003,Seeman et al 2004].
Vestibular abnormalities have been reported both in persons with CMT1A and in those with CMTX [Poretti et al 2013].
Lower-limb muscle atrophy and fatty infiltration can be demonstrated by MRI and followed longitudinally [Gallardo et al 2006].
Chanson et al [2013] reported MRI findings of decreased white matter volume in both CMT1A and hereditary neuropathy with liability to pressure palsies (HNPP). This was confirmed in one pathologic examination of a brain from a subject with CMT1A.
Colomban et al [2014] reported earlier onset of symptoms (8.6 vs 14 years) and higher deterioration of quality of life in affected women compared to affected men.
People with CMT1A can have symptoms that mimic those of HNPP [Mathis et al 2014].
Quality of life from the affected individual’s perspective has been studied byJohnson et al [2014]. Foot and ankle weakness, impaired balance, pain, and fatigue were viewed as important disabling symptoms and tended to be more prevalent in affected women.Ramdharry et al [2012b] also reported a high prevalence of fatigue as a symptom in persons with CMT.
Pregnancy. SeePregnancy Management.
The CMT1 subtypes, identified solely by molecular findings, are often clinically indistinguishable.
CMT1A. NCVs vary. Mean median motor NCVs were 21±5.7 m/s in one study [Hattori et al 2003] and 16.5 m/s (range: 5-26.5 m/s) in another [Carvalho et al 2005]. In a third study, the range was 12.6-35 m/s [Marques et al 2005]. CMAP is decreased [Hattori et al 2003].
CMT1B. The NCV shows a bimodal curve, with some families having slow median motor NCV (mean: 16.5 m/s) and others having normal or near-normal NCV (mean: 44.3 m/s). The individuals in this latter "normal" NCV group tend to have lower CMAP, later age of onset, and more frequent hearing loss and pupillary abnormalities. These findings suggest the existence of two types of CMT1B: primarily demyelinating and primarily axonal. The two types probably reflect functional differences (early onset gain of function versus late onset loss of function of the MPZ protein) caused by different pathogenic variants inMPZ (seeGenotype-Phenotype Correlations) [Hattori et al 2003,Shy et al 2004,Grandis et al 2008].
CMT1C. This subtype appears to be clinically identical to CMT1A [Bennett et al 2004,Saifi et al 2005,Latour et al 2006]. NCVs range from 7.5 to 27 m/s with occasional temporal dispersion [Bennett et al 2004] and conduction block with variable age of onset including early childhood [Gerding et al 2009]. Using ultrasound,Luigetti et al [2015] found enlarged peripheral nerves in individuals with CMT1C.
CMT1D. A few families with CMT1D have been identified [Warner et al 1998,Nelis et al 1999b,Numakura et al 2003,Shiga et al 2012].
CMT1E. An amino acid substitution inPMP22 inexon 3 (p.Ala67Pro) is associated with deafness in a family with CMT1 previously reported byKousseff et al [1982],Kovach et al [1999],Kovach et al [2002].
The amino acid substitutionp.Trp28Arg was associated with profound deafness in one family [Boerkoel et al 2002].
The amino acid substitutionp.Ser22Phe inPMP22 is associated with pressure palsies as well as the CMT1phenotype in a Cypriot family [Kleopa et al 2004].
In addition to the above, the following findings in affected families demonstrate further heterogeneity in the CMT1phenotype:
CMT1A. Microscopically, the enlarged nerves show hypertrophy and onion bulb formation thought to result from repeated demyelination and remyelination of Schwann cell wrappings around individual axons [Carvalho et al 2005,Schröder 2006].
CMT1B. Individuals with slow NCVs tend to have demyelinating features on nerve biopsy, whereas those with normal NCVs have more axonal pathology with axonal sprouting [Hattori et al 2003]. Onion bulb formation has been seen [Bai et al 2006]. Excessive myelin folding and thickness were reported in a family with ac.336delAnull variant inMPZ [De Angelis et al 2004].
CMT1A. A relativegene dosage effect exists regardinggenotype-phenotype correlation:
Severe neuropathy has been reported in persons with CMT1A and a second neuropathy-causing disease such as CMT1C [Meggouh et al 2005],CMTX1,myotonic dystrophy type 1 (DM1) or adrenomyeloneuropathy (seeX-Linked Adrenoleukodystrophy) [Hodapp et al 2006].
CMT1B
CMT1C
CMT1D
CMT1E
CMT1F. Two different pathogenic variants in codon 22 ofNEFL (p.Pro22Thr andp.Pro22Arg) have been reported with demyelinatingautosomal dominant CMT1F [Shin et al 2008]. Thep.Pro22Serpathogenic variant inNEFL is associated withautosomal recessive CMT2E.
Penetrance of CMT1 is usually nearly 100%, but the wide range in age of onset and severity may result in under-recognition of individuals with mild or late-onset disease.
CMT1A/CMT1E. CMT1A refers to CMT1 caused byduplication ofPMP22; CMT1E refers to CMT1 caused by single-nucleotide variants inPMP22.
CMT2E/1F. Some individuals with pathogenic variants inNEFL, which typically cause CMT2E, may have slow NCVs, resulting in a diagnosis of CMT1F. To accommodate these two phenotypes associated with mutation ofNEFL, the designation CMT2E/1F has been used.
Dejerine-Sottas syndrome (DSS). The severephenotype associated with onset in early childhood has in the past been called Dejerine-Sottas syndrome (DSS). However, DSS is a confusing term because it no longer refers to a specific phenotype caused by pathogenic variants in a specificgene. Pathogenic variants in at least three genes (PMP22, MPZ, andEGR2) have been associated with a severe early-onset phenotype:
The overall prevalence of hereditary neuropathies is estimated at approximately 30:100,000 population. The prevalence of CMT1 is 15:100,000-20:100,000. The prevalence of CMT1A is approximately 10:100,000. These numbers hold true in a great variety of regions including China [Song et al 2006,Szigeti et al 2006].
CMT1A represents about 70% of CMT1 [Reilly & Shy 2009] and CMT1B represents about 6%-10% of CMT1 [Mandich et al 2009].
In a large study of German individuals with a CMT1phenotype (776),Gess et al [2013] found the following percentages: CMT1A (51%), CMTX1 (9%), and CMT1B (5%). Among those with a CMT1 phenotype, 66% had a genetic diagnosis.
Figure 1 shows the frequency of various genetic causes of CMT [Rossor et al 2013], indicating that thePMP22duplication onchromosome 17p is responsible for approximately 31% of all CMT cases and approximately 70% of those with the CMT1phenotype.

Genetic diagnoses in CMT and related disorders From Rossor et al [2013]; reprinted with permission
In a Chinese populationLiu et al [2013] found pathogenic variants inMPZ in 3% of individuals with CMT1 and in 6% of those with CMT2.
PMP22. Other phenotypes associated with mutation ofPMP22:
MPZ
LITAF. No phenotypes other than those discussed in thisGeneReview are known to be associated with mutation ofLITAF.
EGR2. Mutation ofEGR2 is also associated withautosomal recessive CMT4 [Warner et al 1998,Timmerman et al 1999,Warner et al 1999,Boerkoel et al 2002].
NEFL. Some individuals with pathogenic variants inNEFL, which typically cause CMT2E, may have slow NCV [Jordanova et al 2003], causing them to have been diagnosed with CMT1F [Fabrizi et al 2007]. To accommodate these two phenotypes associated with mutation ofNEFL, the designation CMT2E/1F has been used.
Acquired causes of neuropathy and other inherited neuropathies need to be considered (seeCMT Overview). The differential diagnosis includes other genetic neuropathies, especiallyCMTX, CMT2, CMT4, andHNPP, all of which show considerable phenotypic overlap [Bienfait et al 2006b].
FBLN5.Auer-Grumbach et al [2011] found pathogenic variants inFBLN5 in families with features of CMT1;FBLN5 pathogenic variants were additionally associated with age-related macular degeneration and cutis laxa.Šafka Brozková et al [2013] have found the same pathogenicmissense variant inFBLN5 in a Czech family with CMT1 and a different background haplotype compared with the Austrian family reported by Auer-Grumbach.
GJB3.López-Bigas et al [2001] have described anautosomal dominant neuropathy associated with hearing impairment caused by apathogenic variant inGJB3. Although the sural nerve pathology showed demylination compatible with CMT1, the nerve conduction velocities (NCVs) were not markedly slow and may suggest an axonal neuropathy.
Familial slow NCV (OMIM608236).Verhoeven et al [2003] have described a family with no symptoms or signs, but with slow NCVs associated with apathogenic variant inARHGEF10, encoding the protein rho guanine nucleotide exchange factor 10.
In theautosomal dominantintermediate forms of CMT, individuals have a relatively typical CMTphenotype with NCVs that overlap those observed in CMT1 (demyelinating neuropathy) and CMT2 (axonal neuropathy) [Villanova et al 1998]. Motor NCVs in these families usually range between 25 and 50 m/s. Five types are recognized to date:
It is usually not possible to differentiate between intermediate forms of CMT and most CMT2 subtypes based on clinical findings [Nicholson & Myers 2006] unless cataract and/or neutropenia (occasional findings in DI-CMTB) are present.
To establish the extent of disease and needs in an individual diagnosed with Charcot-Marie-Tooth neuropathy type 1 (CMT1), the following evaluations are recommended:
Individuals with CMT1 are often evaluated and managed by a multidisciplinary team that includes neurologists, physiatrists, orthopedic surgeons, and physical and occupational therapists [Carter 1997,Grandis & Shy 2005].
Treatment is symptomatic and may include the following:
No treatment reverses or slows the natural progression of CMT.
Daily heel cord stretching exercises to prevent Achilles' tendon shortening are desirable.
Individuals should be evaluated regularly by a team comprising physiatrists, neurologists, and physical and occupational therapists to determine neurologic status and functional disability.
Obesity is to be avoided because it makes walking more difficult.
Medications that are toxic or potentially toxic to persons with CMT comprise a spectrum of risk ranging from definite high risk to negligible risk. See the Charcot-Marie-Tooth Associationwebsite (pdf) for an up-to-date list.
SeeGenetic Counseling for issues related to testing of at-risk relatives forgenetic counseling purposes.
Rudnik-Schöneborn et al [1993] evaluated 45 pregnancies in 21 women with CMT1. Worsening of the CMT1 symptoms during or after gestation was reported in about half of pregnancies. A follow-up study of 63 pregnancies in 33 women with CMT showed no serious complications but 20% of women reported a worsening of symptoms during pregnancy [Awater et al 2012]. In a study of affected pregnant women in Norway, deliveries involved a higher occurrence of presentation anomalies, use of forceps, and operative delivery; the women also experienced increased post-partum bleeding [Hoff et al 2005].
Reilly & Shy [2009],Roberts [2012], andPatel & Pleasure [2013] have reviewed research on potential new treatments of CMT.
Dyck et al [1982],Ginsberg et al [2004], andCarvalho et al [2005] have described a few individuals with CMT1 and sudden deterioration in whom treatment with steroids (prednisone) or IVIg has produced variable levels of improvement. Nerve biopsy has shown lymphocytic infiltration. One such family had a specificMPZpathogenic variant (p.Ile99Thr) [Donaghy et al 2000].
Sahenk et al [2005] studied the effects of neurotrophin-3 (NT3) on individuals with CMT1A. This same group has shown benefit of NT3 delivered by adeno-associated virus (AAV)gene therapy in a mouse model of CMT1A [Sahenk et al 2014].
Passage et al [2004] reported benefit from ascorbic acid (vitamin C) in a mouse model of CMT1. Similar benefit was reported with a progesterone receptor antagonist in a rat model of CMT [Meyer zu Horste et al 2007]. Two high-dose (1,000-1,500 mg/day) treatment trials of ascorbic acid in CMT1A have found no beneficial effect over a period of one to two years [Verhamme et al 2009b,Pareyson et al 2011].Lewis et al [2013] also could not find a positive treatment response to ascorbic acid vs. placebo in 110 subjects with CMT1A.
Patzkó et al [2012] provided evidence for the potential use of curcumin in the treatment of individuals with CMT1B who have pathogenic variants inMPZ.
Fledrich et al [2014] suggested neuregulin-1 as a potential treatment for CMT1A based on experiments in a rat model of the disease.
SearchClinical Trials.gov in the US andEU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions.
Genetic counseling is the process of providing individuals and families withinformation on the nature, mode(s) of inheritance, and implications of genetic disorders to help themmake informed medical and personal decisions. The following section deals with geneticrisk assessment and the use of family history and genetic testing to clarify geneticstatus for family members; it is not meant to address all personal, cultural, orethical issues that may arise or to substitute for consultation with a geneticsprofessional. —ED.
Charcot-Marie-Tooth neuropathy type 1 (CMT1) is inherited anautosomal dominant manner.
Parents of aproband
Note: Although most individuals diagnosed with CMT1 have an affected parent, the family history may appear to be negative because of failure to recognize the disorder in family members, early death of the parent before the onset of symptoms, or late onset of the disease in the affected parent. If the parent is the individual in whom thepathogenic variant first occurred, s/he may havesomatic mosaicism for the pathogenic variant and may be mildly/minimally affected.
Sibs of aproband
Offspring of aproband. Every child of an individual with CMT1 has a 50% chance of inheriting thePMP22,MPZ,LITAF, orEGR2pathogenic variant.
Other family members of aproband
Testing of at-risk asymptomatic adult relatives of individuals with CMT1 is possible aftermolecular genetic testing has identified the specificpathogenic variant in the family. Such testing should be performed in the context of formalgenetic counseling. This testing is not useful in predicting age of onset, severity, type of symptoms, or rate of progression in asymptomatic individuals. Testing of asymptomatic at-risk individuals with nonspecific or equivocal symptoms is predictive testing, not diagnostic testing.
Testing of asymptomatic individuals younger than age 18 years who are at risk for adult-onset disorders for which no treatment exists is not considered appropriate, primarily because it negates the autonomy of the child with no compelling benefit. Further, concern exists regarding the potential unhealthy adverse effects that such information may have on family dynamics, the risk of discrimination and stigmatization in the future, and the anxiety that such information may cause.
In a family with an established diagnosis of CMT1, testing is appropriate to consider in symptomatic individuals regardless of age.
See also the National Society of Genetic Counselorsposition statement on genetic testing of minors for adult-onset conditions and the American Academy of Pediatrics and American College of Medical Genetics and Genomicspolicy statement: ethical and policy issues in genetic testing and screening of children.
Considerations in families with an apparentde novopathogenic variant. When neither parent of aproband with anautosomal dominant condition has the pathogenic variant or clinical evidence of the disorder, it is likely that the variant occurredde novo in the proband. However, possible non-medical explanations includingalternate paternity or maternity (e.g., with assisted reproduction) or undisclosed adoption could also be explored.
Family planning
DNA banking is the storage of DNA (typically extracted from white blood cells) for possible future use. Because it is likely that testing methodology and our understanding of genes, allelic variants, and diseases will improve in the future, consideration should be given to banking DNA of affected individuals.
If thePMP22,MPZ,LITAF,or EGR2pathogenic variant has been identified in an affected family member,prenatal testing for pregnancies at increased risk may be available from a clinical laboratory that offers either testing of thegene orcustom prenatal testing.
Requests forprenatal testing for typically adult-onset conditions which (like CMT1) do not affect intellect or life span are not common. Differences in perspective may exist among medical professionals and within families regarding the use of prenatal testing, particularly if the testing is being considered for the purpose of pregnancy termination rather than early diagnosis. Although most centers would consider decisions about prenatal testing to be the choice of the parents, discussion of these issues is appropriate.
Preimplantation genetic testing (PGT) may be an option for some families in which thePMP22,MPZ,LITAF, orEGR2pathogenic variant has been identified. Successful use of PGT for CMT1A has been reported [Lee et al 2013].
GeneReviews staff has selected the following disease-specific and/or umbrellasupport organizations and/or registries for the benefit of individuals with this disorderand their families. GeneReviews is not responsible for the information provided by otherorganizations. For information on selection criteria, clickhere.
Information in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.
Charcot-Marie-Tooth Neuropathy Type 1: Genes and Databases
OMIM Entries for Charcot-Marie-Tooth Neuropathy Type 1 (View All in OMIM)
| 118200 | CHARCOT-MARIE-TOOTH DISEASE, DEMYELINATING, TYPE 1B; CMT1B |
| 118220 | CHARCOT-MARIE-TOOTH DISEASE, DEMYELINATING, TYPE 1A; CMT1A |
| 118300 | CHARCOT-MARIE-TOOTH DISEASE AND DEAFNESS |
| 129010 | EARLY GROWTH RESPONSE 2; EGR2 |
| 159440 | MYELIN PROTEIN ZERO; MPZ |
| 162280 | NEUROFILAMENT PROTEIN, LIGHT POLYPEPTIDE; NEFL |
| 601097 | PERIPHERAL MYELIN PROTEIN 22; PMP22 |
| 601098 | CHARCOT-MARIE-TOOTH DISEASE, DEMYELINATING, TYPE 1C; CMT1C |
| 603795 | LIPOPOLYSACCHARIDE-INDUCED TUMOR NECROSIS FACTOR-ALPHA FACTOR; LITAF |
| 607678 | CHARCOT-MARIE-TOOTH DISEASE, DEMYELINATING, TYPE 1D; CMT1D |
| 607734 | CHARCOT-MARIE-TOOTH DISEASE, DEMYELINATING, TYPE 1F; CMT1F |
PMP22 (CMT1A, CMT1E)
Gene structure.PMP22 transcript variant 1 (NM_000304.2) has 1828 nucleotides and five exons, four of which encode amino acids [Patel et al 1992]. It is similar to a growth arrest-specificgene in mouse and rat. For a detailed summary of gene and protein information for the following genes, seeTable A,Gene.
Pathogenic variants
SelectedPMP22 Pathogenic Variants
| DNA Nucleotide Change | Predicted Protein Change (Alias 1) | Reference Sequences |
|---|---|---|
| c.47T>C | p.Leu16Pro | NM_000304 NP_000295 |
| c.65C>T | p.Ser22Phe | |
| c.82T>C | p.Trp28Arg | |
| c.117G>C | p.Trp39Cys | |
| c.199G>C | p.Ala67Pro | |
| c.353C>T 2 | p.Thr118Met | |
| c.469C>T 3 | p.Arg157Trp | |
| c.281dupG3 | p.Arg95GlnfsTer128 (Gly94fsTer222) | |
| (1.5-Mbduplication at 17p11.2) | -- |
Variants listed in the table have been provided by the author.GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Variant designation that does not conform to current naming conventions
Normalgene product. Peripheral myelin protein 22 is a 160-amino acid protein that is present in compact myelin and has four transmembrane domains.
Abnormalgene product. Duplication ofPMP22 is associated with increasedmRNA message forPMP22 in peripheral nerve and by an unknown mechanism that results in abnormal myelination [Gabriel et al 1997].
Most pathogenicmissense variants are localized in the transmembrane domains of peripheral myelin protein 22, indicating the functional importance of these domains. Individuals withPMP22 single-nucleotide variants tend to have more severe clinical disability than those with a single 17p11.2duplication, presumably because of adominant-negative or loss-of-protein function effect [Sereda & Nave 2006].
A mouse containing eight copies of humanPMP22 shows aphenotype similar to but more severe than that seen in individuals with CMT1A, while mice containing 16 and 30 additional copies of mousePMP22 show severe hypomyelination [Nelis et al 1999a]. This supports the hypothesis that more copies ofPMP22 result in a more severe phenotype [Giambonini-Brugnoli et al 2005].
Perea et al [2001] have generated a transgenic mouse model in which mousePMP22 over-expression can be regulated, possibly providing a system for evaluation of potential therapeutic approaches.
MPZ (CMT1B)
Gene structure.MPZ spans approximately seven kilobases and contains six exons. The reference sequence was updated in 2010 to encode the 248 amino acid proteinNM_000530.6, which should be considered when referring toMPZ pathogenic variants (for detailed information, see entry forMPZ atInherited Peripheral Neuropathies Mutation Database).
Pathogenic variants. Nearly 100 pathogenic variants inMPZ have been reported [De Jonghe et al 1997,Nelis et al 1999a,Kochański et al 2004,Lee et al 2004,Shy 2006]. More than 70% of the pathogenic variants are localized in exons 2 and 3 ofMPZ, which code for the extracellulardomain, indicating the functional importance of this domain. Intronic variants affectingMPZsplicing have been reported [Sabet et al 2006]. (For more information, seeTable A.) Aduplication of the entireMPZgene was detected in a Norwegian family with anautosomal dominant, early onset (first decade), severe, demyelinating CMT syndrome [Høyer et al 2011].
SelectedMPZ Pathogenic Variants
| DNA Nucleotide Change | Predicted Protein Change (Alias 1) | Reference Sequences |
|---|---|---|
| c.89T>C 2 | p.Ile30Thr | NM_000530 NP_000521 |
| c.131C>T 2 | p.Ser44Phe | |
| c.164G>T 2 | p.Ser55Ile | |
| c.181G>A | p.Asp61Asn | |
| c.175T>A 2 | p.Ser59Thr | |
| c.224A>T 2 | p.Asp75Val | |
| c.241C>T | p.His81Tyr | |
| c.[241C>T;337G>T] 2, 3 | p.[His81Tyr;Val113Phe] | |
| c.244T>C | p.Tyr82His | |
| c.296T>C 4 | p.Ile99Thr | |
| c.306delA 2, 5 | p.Asp104ThrfsTer14 | |
| c.347A>G | p.Asn116Ser | |
| c.337G>T 2 | p.Val113Phe | |
| c.371C>T 2 | p.Thr124Met | |
| c.389A>G 2 | p.Lys130Arg | |
| c.393C>A 6 | p.Asn131Lys | |
| c.487G>A | p.Gly163Arg | |
| c.499G>A 2 | p.Gly167Arg | |
| c.588dupT | p.Met197TyrTer38 (Met207TyrfsTer38) | |
| c.670G>T 2 | p.Asp224Tyr | |
| c.645+1G>T 2 | NA | |
| c.649C>T 2 | p.Pro217Ser |
Variants listed in the table have been provided by the author.GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
NA = not applicable
Variant designation that does not conform to current naming conventions
Nomenclature for variants incis configuration
SeeNeuropathology.
Normalgene product. P0 myelin protein is a major structural component of peripheral myelin, representing about 50% of peripheral myelin protein by weight and about 7% of Schwann cell message [Wells et al 1993]. It is a homophilic adhesion molecule of the immunoglobulin family that plays an important role in myelin compaction. It has a single transmembranedomain, a large extracellular domain, and a smaller intracellular domain. It is also expressed in glomerular epithelial cells of the kidney [Plaisier et al 2005].
Abnormalgene product. Different pathogenic variants affect all portions of the protein and may alter myelin adhesion or produce an unfolded protein response [Wrabetz et al 2006]. Either demyelinating or axonal phenotypes can result.Grandis et al [2008] found that pathogenic variants associated with late-onset disease cause a partial loss of function in transfected cells, whereas pathogenic variants associated with early-onset disease cause abnormal gain of function. AbnormalMPZ is retained in the endoplasmic reticulum of Schwann cells causing a transitory canonic unfolded protein response [Pennuto et al 2008,Saporta et al 2012].
LITAF (CMT1C)
Gene structure.LITAF has three coding exons. For a detailed summary ofgene and protein information for the following genes, seeTable A,Gene.
Benign variants. Abenign variant was reported byBennett et al [2004].
Pathogenic variants. Missense variants have been reported inLITAF [Street et al 2003,Bennett et al 2004,Saifi et al 2005,Latour et al 2006] (Table 4). (For more information, seeTable A.) The pathogenicity of some DNA changes is difficult to determine [Kochański 2006].
SelectedLITAF Pathogenic Variants
| DNA Nucleotide Change | Predicted Protein Change | Reference Sequences |
|---|---|---|
| c.332C>G | p.Ala111Gly | NM_004862 NP_004853 |
| c.334G>A 1 | p.Gly112Ser | |
| c.344C>A | p.Thr115Asn | |
| c.346T>G | p.Trp116Gly | |
| c.385G>A | p.Ala129Thr | |
| c.403C>T | p.Pro135Ser | |
| c.403C>A | p.Pro135Thr | |
| c.404C>G | p.Pro135Arg |
Variants listed in the table have been provided by the author.GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Normalgene product. The protein product ofLITAF has two names: lipopolysaccaride-induced tumor necrosis factor-α factor (LITAF) and small integral membrane protein of the lysosome/late endosome (SIMPLE) [Saifi et al 2005]. The gene may play a role in the lysosomal sorting of plasma membrane proteins [Shirk et al 2005].
Abnormalgene product. Mutation may alter the ability of the Schwann cell to degrade proteins.
EGR2 (CMT1D)
Gene structure.EGR2 spans 4.3 kb and contains two coding exons. For a detailed summary ofgene and protein information for the following genes, seeTable A,Gene.
Pathogenic variants. Selectedautosomal dominant pathogenic variants are listed inTable 5 [Timmerman et al 1999,Pareyson et al 2000]. (For more information, seeTable A.) The pathogenicity of some DNA changes is difficult to determine [Kochański 2006].
SelectedEGR2 Pathogenic Variants
| DNA Nucleotide Change | Predicted Protein Change | Reference Sequences |
|---|---|---|
| c.1075C>T 1 | p.Arg359Trp | NM_000399 NP_000390 |
| c.1076G>A 1 | p.Arg359Gln | |
| c.1142G>A 1 | p.Arg381His | |
| c.1144A>C or c.1146T>A | p.Ser382Arg | |
| c.1147G>T 1 | p.Asp383Tyr | |
| c.1160C>A 1 | p.Thr387Asn | |
| c.1225C>T | p.Arg409Trp |
Variants listed in the table have been provided by the author.GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Normalgene product. Early growth response-2 protein is a zinc fingertranscription factor. It is the ortholog of the murine Krox-2 protein. EGR2 induces expression of several proteins involved in myelin sheath formation and maintenance.
Abnormalgene product.Krox-2null mice show a block in Schwann cell differentiation.
NEFL (CMT2E/1F)
Gene structure. Both the mouse and humanNEFL have four coding exons; the 5' UTRs are highly conserved. For a detailed summary ofgene and protein information for the following genes, seeTable A,Gene.
Pathogenic variants. SeeTable 6. (For more information, seeTable A.)
SelectedNEFL Pathogenic Variants
| DNA Nucleotide Change | Predicted Protein Change (Alias 1) | Reference Sequences |
|---|---|---|
| c.23C>G | p.Pro8Arg | NM_006158 NP_006149 |
| c.64C>T | p.Pro22Ser | |
| c.64C>A 2 | p.Pro22Thr | |
| c.65C>G 2 | p.Pro22Arg | |
| c.1001A>C | p.Gln334Pro (Gln333Pro) | |
| c.293A>G | p.Asn98Ser (Asn97Ser) | |
| c.446C>T | p.Ala149Val (Ala148Val) |
Variants listed in the table have been provided by the author.GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Variant designation that does not conform to current naming conventions
Normalgene product. The protein encoded byNEFL contains 543 amino acids with a head, rod, and taildomain. Neurofilaments form the cytoskeletal component of myelinated axons.
Abnormalgene product. Knockout mice lacking neurofilments have diminished axon caliber and delayed regeneration of myelinated axons following crush injury. A mouse with asingle-nucleotide variant inNEFL has massive degeneration of spinal motor neurons and abnormal neurofilament accumulation with severe neurogenic skeletal muscle atrophy.
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