Autosomal Dominant Charcot-Marie-Tooth Research Articles

Heterozygous Seryl-tRNA Synthetase 1 Variants Cause Charcot-Marie-Tooth Disease.

Despite the increasing number of genes associated with Charcot-Marie-Tooth (CMT) disease, many patients currently still lack appropriate genetic diagnosis for this disease. Autosomal dominant mutations in aminoacyl-tRNA synthetases (ARSs) have been implicated in CMT. Here, we describe causal missense mutations in the gene encoding seryl-tRNA synthetase 1 (SerRS) for 3 families affected with CMT. Whole-exome sequencing was performed in 16 patients and 14 unaffected members of 3 unrelated families. The functional impact of the genetic variants identified was investigated using bioinformatic prediction tools and confirmed using cellular and biochemical assays. Combined linkage analysis for the 3 families revealed significant linkage (Zmax LOD=6.9) between the genomic co-ordinates on chromosome 1: 108681600-110300504. Within the linkage region, heterozygous SerRS missense variants segregated with the clinical phenotype in the 3 families. The mutant SerRS proteins exhibited reduced aminoacylation activity and abnormal SerRS dimerization, which suggests the impairment of total protein synthesis and induction of eIF2α phosphorylation. Our findings suggest the heterozygous SerRS variants identified represent a novel cause for autosomal dominant CMT. Mutant SerRS proteins are known to impact various molecular and cellular functions. Our findings provide significant advances on the current understanding of the molecular mechanisms associated with ARS-related CMT. ANN NEUROL 2023;93:244-256.

Pregnancy outcome in Charcot-Marie-Tooth disease: results of the CMT-NET cohort study in Germany.

Background and purposeSystematic research on the effect of Charcot–Marie–Tooth (CMT) disease on the outcome of pregnancy and conversely the effect of pregnancy on neuropathy is still sparse.MethodsA clinical cohort study and cross‐sectional study within the German CMT‐NET was conducted between 2016 and 2019. Inclusion criteria were a confirmed diagnosis of CMT and at least one completed pregnancy after 1990. All participants agreed to fill in questionnaires and have their medical files reviewed.ResultsThe study group comprised 54 women with a total of 98 pregnancies. The mean age at onset of CMT disease was 12.6 years (range 0–37 years). Fifty (92%) patients had autosomal dominant CMT; two patients each (4%) had X‐linked and autosomal recessive CMT. Forty patients (74%) had a PMP22 gene duplication (CMT1A). Obstetric complications did not differ significantly from a German reference population, neither in the whole group nor in the CMT1A group. Overall there was no increased newborn morbidity and mortality. About one‐third of patients reported exacerbation of CMT disease in or after pregnancy. No adverse effects of anaesthesia were reported. Most participants stressed a positive attitude and awareness of challenges associated with pregnancy. Important issues were assistance and support in caring for the family.DiscussionIn line with findings from our previous study undertaken in the 1990s, there were no increased complication rates for pregnancy and delivery. These results are reassuring for the vast majority of CMT patients and are important for family planning and clinical care.

Analysis of GDAP1 gene mutation in a pedigree with autosomal dominant Charcot-Marie-Tooth disease

To investigate the molecular genetic mechanism of Charcot- Marie-Tooth (CMT) disease in a pedigree. Genomic DNA was extracted from the peripheral blood of the family members of a pedigree with autosomal dominant CMT disease, and 65 candidate genes of the proband were screened using target exon capture and the next generation sequencing, and the suspicious genes were verified using Sanger sequencing. PolyPhen-2, PROVEAN and SIFT software were used to predict the function of the mutant genes, and PyMOL-1 software was used to simulate the mutant protein structure. A heterozygous missense mutation [c.371A>G (p.Y124C)] was detected in exon 3 of GDAP1 gene of the proband. This heterozygous mutation was also detected in both the proband's mother and her brother, but not in her father. Multiple sequence alignment analysis showed that tyrosine at codon 124 of GDAP1 protein was highly conserved. All the 3 prediction software predicted that the mutation was harmful. Molecular structure simulation showed a weakened interaction force between the amino acid residues at codon 124 and the surrounding amino acid residues to affect the overall stability of the protein. The mutation of GDAP1 gene may be related to the pathogenesis of autosomal dominant AD-CMT in this pedigree. The newly discovered c.371A>G mutation (p.Y124C) expands the mutation spectrum of GDAP1 gene, but further study is needed to clarify the underlying pathogenesis.

Identification of a Location at Chromosome 19p in a Big Chinese Family with Charcot-Marie-Tooth Disease

Background: Autosomal dominant Charcot Marie Tooth disease (CMT) diseases is an inherited peripheral neuropathies disease, the prevalence is 17-40 per 100,000 individuals 17-40 per 100,000 individuals. The complex genetic mode and large number of CMT causing genes and loci made it is very hard for clinicians and researchers when trying to determine the underlying genetic diagnosis. In this work, we want to identify the cause for a Chinese family with Charcot-Marie-Tooth disease. Methods: Family history data were recorded. Clinical and Electromyography examinations were performed on the ten affected and ten unaffected family members. All the members were genotyped with microsatellite markers at loci considered to be associated with CMT. Two-point LOD scores were calculated using the Linkage software after genotyping. Some highly suspect genes were excluded by direct sequencing. Results and Conclusions: The clinical and pathological features were relatively gently, but which became gradually worse, with the increased genetic generation, and the onset age of the affected members. Linkage analysis was obtained at markers D19S433 (LOD score [Z]=2.03, recombination fraction [θ]=0.0) and D19S916 (Z=1.6, θ=0.0). Sequencing the dynamin 2 gene (DNM2) didn’t found any variation in the translated region. There may be some other gene or loci associated with this disease.

Phenotypic Variability in a Large Czech Family with a Dynamin 2–Associated Charcot-Marie-Tooth Neuropathy

: Mutations in the Dynamin 2 gene (DNM2) cause autosomal dominant centronuclear myopathy or autosomal dominant (AD) Charcot-Marie-Tooth (CMT) disease. Here the authors report one large Czech family with 15 members affected with an AD CMT phenotype of extraordinary variability. Genetic linkage analysis using SNP arrays revealed a locus of about 9.6 Mb on chromosome 19p13.1–13.2. In this critical interval, 373 genes were located. The only gene herein known to be associated with an intermediate type of CMT was Dynamin 2 (DNM2). Subsequent sequence analysis of the DNM2 gene in the index patient revealed a novel missense mutation p.Met580Thr. This missense mutation segregated with the neuropathy, indicating the causal character of this mutation. The phenotype of CMT in this family shows mild to moderate impairment with relatively preserved upper limbs and a very broad range of the onset of clinical symptoms from an early onset around the age of 12 to the late onset during the fifth decade. Electrophysiology showed an intermediate type of peripheral neuropathy. The motor median nerve conduction velocity varied from 36 m/s to normal values with signs of asymmetrical affection of peripheral nerves. No additional symptoms such as cranial nerve involvement, cataract, and signs of neutropenia or myopathy syndrome were observed in any member of the family yet. The progression was slow with no loss of ambulation. The authors suggest that the characterization of clinical variability in a single family may help to direct the genetic analysis directly to the rarely observed DNM2 mutations.

Dominant GDAP1 mutations cause predominantly mild CMT phenotypes

Ganglioside-induced differentiation associated-protein 1 (GDAP1) mutations are commonly associated with autosomal recessive Charcot-Marie-Tooth (ARCMT) neuropathy; however, in rare instances, they also lead to autosomal dominant Charcot-Marie-Tooth (ADCMT). We aimed to investigate the frequency of disease-causing heterozygous GDAP1 mutations in ADCMT and their associated phenotype. We performed mutation analysis in a large cohort of ADCMT patients by means of bidirectional sequencing of coding regions and exon-intron boundaries of GDAP1. Intragenic GDAP1 deletions were excluded using an allele quantification assay. We confirmed the pathogenic character of one sequence variant by in vitro experiments assaying mitochondrial morphology and function. In 8 Charcot-Marie-Tooth disease (CMT) families we identified 4 pathogenic heterozygous GDAP1 mutations, 3 of which are novel. Three of the mutations displayed reduced disease penetrance. Disease onset in the affected individuals was variable, ranging from early childhood to adulthood. Disease progression was slow in most patients and overall severity milder than typically seen in autosomal recessive GDAP1 mutations. Electrophysiologic changes are heterogeneous but compatible with axonal neuropathy in the majority of patients. With this study, we broaden the phenotypic and genetic spectrum of autosomal dominant GDAP1-associated neuropathies. We show that patients with dominant GDAP1 mutations may display clear axonal CMT, but may also have only minimal clinical and electrophysiologic abnormalities. We demonstrate that cell-based functional assays can be reliably used to test the pathogenicity of unknown variants. We discuss the implications of phenotypic variability and the reduced penetrance of autosomal dominant GDAP1 mutations for CMT diagnostic testing and counseling.

Late onset autosomal dominant Charcot–Marie–Tooth 2 neuropathy in a Costa Rican family

Objective: To describe the clinical, electrophysiologic and morphologic features of a Costa Rican family with an autosomal dominant inherited Charcot–Marie–Tooth (CMT) neuropathy.Methods: The field study took place in Costa Rica, Central America. Seven patients underwent neurological examinations and standard electrodiagnostic tests, and a sural nerve biopsy was taken from one patient. Fifteen family members were screened for gene defects associated with CMT disease.Results: Characteristic features of this family were a late age of onset (35–56 years), positive sensory symptoms and muscle cramps. Based on electrodiagnostic and morphologic data, the patients were classified as having a CMT2 neuropathy. The CMT1A duplication/HNPP deletion and point mutations in genes PMP22, MPZ, C×32 and EGR2 implicated in the most common types of CMT disease were excluded. Subsequently, almost all known CMT loci were excluded by linkage analysis.Discussion: Features of this family were a late age of onset and positive sensory symptoms. This new autosomal dominant CMT neuropathy is associated with an unknown gene defect.

Spine deformities in Charcot-Marie-Tooth 4C caused by SH3TC2 gene mutations

Charcot-Marie-Tooth (CMT) disease is a heterogeneous group of inherited peripheral motor and sensory neuropathies with several modes of inheritance: autosomal dominant, X-linked, and autosomal recessive (AR) CMT. A locus responsible for the demyelinating form of ARCMT was assigned to the 5q23-q33 region (CMT4C) by homozygosity mapping. Recently, 11 mutations were identified in the SH3TC2 (KIAA1985) gene in 12 families with demyelinating ARCMT from Turkish, Iranian, Greek, Italian, or German origin. To identify mutations in the SH3TC2 gene. The authors searched for SH3TC2 gene mutations in 10 consanguineous CMT families putatively linked to the CMT4C locus on the basis of haplotype segregation and linkage analysis. Ten families had mutations, eight of which were new and one, R954X, recurrent. Six of the 10 mutations were in exon 11. Onset occurred between ages 2 and 10. Scoliosis or kyphoscoliosis and foot deformities were found in almost all patients and were often inaugural. The median motor nerve conduction velocity values (</=34 m/s) were not correlated with disease duration. The functional disability score was </=3, indicating that the patients could walk without help. Unexpectedly, typical giant axons were observed on biopsies from a large Algerian family. Charcot-Marie-Tooth type 4C (CMT4C) is less severe than other autosomal recessive (AR) CMT. Intrafamilial variability is important, making phenotype-genotype correlations difficult, but spine deformities are clearly a hallmark of CMT4C. In the presence of scoliosis, a neurologic examination is recommended. Giant axons on biopsies are also suggestive of CMT4C. For genetic analysis, the R954X mutation should be looked for before systematic sequencing of exon 11.

Disrupted function and axonal distribution of mutant tyrosyl-tRNA synthetase in dominant intermediate Charcot-Marie-Tooth neuropathy

Charcot-Marie-Tooth (CMT) neuropathies are common disorders of the peripheral nervous system caused by demyelination or axonal degeneration, or a combination of both features. We previously assigned the locus for autosomal dominant intermediate CMT neuropathy type C (DI-CMTC) to chromosome 1p34-p35. Here we identify two heterozygous missense mutations (G41R and E196K) and one de novo deletion (153-156delVKQV) in tyrosyl-tRNA synthetase (YARS) in three unrelated families affected with DI-CMTC. Biochemical experiments and genetic complementation in yeast show partial loss of aminoacylation activity of the mutant proteins, and mutations in YARS, or in its yeast ortholog TYS1, reduce yeast growth. YARS localizes to axonal termini in differentiating primary motor neuron and neuroblastoma cultures. This specific distribution is significantly reduced in cells expressing mutant YARS proteins. YARS is the second aminoacyl-tRNA synthetase found to be involved in CMT, thereby linking protein-synthesizing complexes with neurodegeneration.

Mapping of Charcot-Marie-Tooth Disease Type 1C to Chromosome 16p Identifies a Novel Locus for Demyelinating Neuropathies

Charcot-Marie-Tooth (CMT) neuropathy represents a genetically heterogeneous group of diseases affecting the peripheral nervous system. We report genetic mapping of the disease to chromosome 16p13.1-p12.3, in two families with autosomal dominant CMT type 1C (CMT1C). Affected individuals in these families manifest characteristic CMT symptoms, including high-arched feet, distal muscle weakness and atrophy, depressed deep-tendon reflexes, sensory impairment, slow nerve conduction velocities, and nerve demyelination. A maximal combined LOD score of 14.25 was obtained with marker D16S500. The combined haplotype analysis in these two families localizes the CMT1C gene within a 9-cM interval flanked by markers D16S519 and D16S764. The disease-linked haplotypes in these two pedigrees are not conserved, suggesting that the gene mutation underlying the disease in each family arose independently. The epithelial membrane protein 2 gene (EMP2), which maps to chromosome 16p13.2, was evaluated as a candidate gene for CMT1C.

Determining Gene Dosage

Numerous investigations (both clinical and basic) in today’s molecular biology laboratory require accurate quantification of DNA by the polymerase chain reaction (PCR). To name a few important examples, quantitative PCR has been used to quantify viral copy number, to perform gene expression studies, and to diagnose genetic diseases. In this issue of Clinical Chemistry , Poropat and Nicholson describe a quantitative PCR assay for the determination of gene dosage (i.e., the number of copies of a gene per somatic cell) of the PMP22 gene, a myelin gene involved in inherited neuropathies (1). The PMP22 gene is extremely sensitive to copy number; for example, it is duplicated in the autosomal dominant Charcot-Marie Tooth type I (CMT1A) disease and is deleted in the autosomal dominant hereditary neuropathy with liability to pressure palsies (HNPP). Because the expression of the disorders can be quite variable and CMT1A shows genetic heterogeneity, the DNA testing for these diseases establishes a secure diagnosis; it also permits genetic counseling and testing for high-risk family members. For molecular laboratories involved in genetic disorders, gene dosage determinations are clinically important and frequently performed. In addition to CMT1A and HNPP, there are many genetic disorders where the primary defect is due either to allelic deletions (e.g., Duchenne muscular dystrophy, spinal muscular atrophy, α-thalassemia, growth hormone deficiency, and familial hypercholesterolemia) or to duplications (e.g., Klinefelter syndrome and Down syndrome). Furthermore, for the determination of the carrier state of disorders such as Duchenne muscular dystrophy and spinal muscular atrophy, the accurate determination of heterozygous deletions is essential. Originally, gene dosage determinations were made from Southern blots. The protocol was laborious and required large amounts of DNA. Furthermore, optimal conditions were required; very high-quality blots were necessary, with consistent transfer and hybridization and low background. We have found that Southern autoradiographic bands >10 kb …

Advances in the genetics of hereditary hypertrophic neuropathy in childhood

The peripheral neuropathies constitute approximately 30% of cases seen in a pediatric neuromuscular service. Two-thirds of such cases are chronic. Of the latter group roughly 70% are hereditary, 20% indeterminate and 10% acquired. There are definite chromosomal localizations for an increasing number of the hereditary neuropathies: to the region of the centromere of the X chromosome in an X-linked form of Charcot-Marie-Tooth (CMT) disease, to chromosome 17 in the commonest form of CMT, and to the long arm of chromosome 1, close to the Duffy locus, in a few kindreds with a rarer type of CMT. A duplication of DNA on the long arm of chromosome 17 is the commonest abnormality in autosomal dominant CMT. The duplicated region contains the gene for a 22 kDa myelin protein, PMP-22. The gene for PMP-22 is the site of a mutation in the hereditary neuropathy of the Trembler mouse. Some sporadic and inherited cases of chronic hypertrophic demyelinating neuropathy have recently been shown to be associated with specific mutations of the myelin protein P0 and PMP-22 loci. By contrast, a deletion encompassing the PMP-22 locus has been found in tomaculous neuropathy (hereditary liability to pressure palsies). Finally, mutations of the gap junction protein, connexin 32, have been shown to be responsible for X-linked dominant CMT.