Recessive GNE Mutations in Korean Nonaka Distal Myopathy Patients with or without Peripheral Neuropathy.

Autosomal recessive Nonaka distal myopathy is a rare autosomal recessive genetic disease characterized by progressive degeneration of the distal muscles, causing muscle weakness and decreased grip strength. It is primarily associated with mutations in the GNE gene, which encodes a key enzyme of sialic acid biosynthesis (UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase). This study was performed to find GNE mutations in six independent distal myopathy patients with or without peripheral neuropathy using whole-exome sequencing (WES). In silico pathogenic prediction and simulation of 3D structural changes were performed for the mutant GNE proteins. As a result, we identified five pathogenic or likely pathogenic missense variants: c.86T>C (p.Met29Thr), c.527A>T (p.Asp176Val), c.782T>C (p.Met261Thr), c.1714G>C (p.Val572Leu), and c.1771G>A (p.Ala591Thr). Five affected individuals showed compound heterozygous mutations, while only one patient revealed a homozygous mutation. Two patients revealed unreported combinations of combined heterozygous mutations. We observed some specific clinical features, such as complex phenotypes of distal myopathy with distal hereditary peripheral neuropathy, an earlier onset of weakness in legs than that of hands, and clinical heterogeneity between two patients with the same set of compound heterozygous mutations. Our findings on these genetic causes expand the clinical spectrum associated with the GNE mutations and can help prepare therapeutic strategies.

Gene Distribution in Pediatric-Onset Inherited Peripheral Neuropathy: A Single Tertiary Center in Thailand.

BACKGROUND: Inherited peripheral neuropathy presents a diagnostic and therapeutic challenge due to its association with mutations in over 100 genes. This condition leads to long-term disability and poses a substantial healthcare burden on society. OBJECTIVE: This study aimed to investigate the distribution of genes and establish the genotype-phenotype correlations, focusing on pediatric-onset cases. METHODS: Exome sequencing and other analytical techniques were employed to identify pathogenic variants, including duplication analysis of the PMP22 gene. Each patient underwent physical examination and electrophysiological studies. Genotypes were correlated with phenotypic features, such as age at disease onset and ulnar motor nerve conduction velocity. RESULTS: We identified 35 patients with pediatric-onset inherited peripheral neuropathy. Pathogenic or likely pathogenic variants were confirmed in 24 out of 35 (68.6%) patients, with 4 of these variants being novel. A confirmed molecular diagnosis was achieved in 90.9% (10/11) of patients with demyelinating Charcot-Marie-Tooth disease (CMT) and 56.3% (9/16) of patients with axonal CMT. Among patients with infantile-onset CMT (≤2 years), the most common causative genes were MFN2 and NEFL, while GDAP1 and MFN2 were frequent causes among patients with childhood- or adolescent-onset CMT (3-9 years). CONCLUSIONS: The MFN2 gene was the most commonly implicated gene, and the axonal type was predominant in this cohort of Thai patients with pediatric-onset inherited peripheral neuropathy.

Microsatellite Dataset for Cultivar Discrimination in Spring Orchid (Cymbidium goeringii).

Cymbidium goeringii Reichb. fil., locally known as the spring orchid in the Republic of Korea, is one of the most important and popular horticultural species in the family Orchidaceae. C. goeringii cultivars originated from plants with rare phenotypes in wild mountains where pine trees commonly grow. This study aimed to determine the cultivar-specific combined genotypes (CGs) of short sequence repeats (SSRs) by analyzing multiple samples per cultivar of C. goeringii. In this study, we collected more than 4000 samples from 67 cultivars and determined the genotypes of 12 SSRs. Based on the most frequent combined genotypes (CG1s), the average observed allele number and combined matching probability were 11.8 per marker and 3.118 × 10-11, respectively. Frequencies of the CG1 in 50 cultivars (n ≥ 10) ranged from 40.9% to 100.0%, with an average of 70.1%. Assuming that individuals with the CG1 are genuine in the corresponding cultivars, approximately 30% of C. goeringii on the farms and markets may be not genuine. The dendrogram of the phylogenetic tree and principal coordinate analysis largely divided the cultivars into three groups according to their countries of origin; however, the genetic distances were not great among the cultivars. In conclusion, this dataset of C. goeringii cultivar-specific SSR profiles could be used for ecogenetic studies and forensic authentication. This study suggests that genetic authentication should be introduced for the sale of expensive C. goeringii cultivars. We believe that this study will help establish a genetic method for the forensic authentication of C. goeringii cultivars.

Targeted recombination of homologous chromosomes using CRISPR-Cas9.

CRISPR mutagenesis is an efficient way to disrupt specific target genes in many model organisms. We previously devised a targeted CRISPR recombination method to generate intragenic recombinants of alleles in Drosophila. Here, we assessed the applicability of CRISPR targeting-induced recombination to different genetic loci. We compared the ectopic recombination rates in the male germline by CRISPR targeting at two neighboring genetic loci within the genomic region that consists of the repressed chromatin domain of the Lobe gene, and the transcriptionally active domain of PRAS40. Targeting around the transcription initiation of PRAS40 resulted in higher recombination rates of homologous chromosomes than targeting at the Lobe intron. Based on the efficient homologous recombination by CRISPR targeting observed around transcriptionally active loci, we further investigated targeted recombination between P-elements that are inserted at different genomic locations. Male recombination by CRISPR targeting of P-elements located proximally and distally to the ebony gene produced recombinants deficient for the intervening region of ebony transcription. Taken together, we suggest that targeted homologous recombination by CRISPR targeting may have specific genetic applications, such as generation of allelic combinations or chromosomal variations.

Whole-genome sequencing in clinically diagnosed Charcot-Marie-Tooth disease undiagnosed by whole-exome sequencing.

Whole-genome sequencing is the most comprehensive form of next-generation sequencing method. We aimed to assess the additional diagnostic yield of whole-genome sequencing in patients with clinically diagnosed Charcot-Marie-Tooth disease when compared with whole-exome sequencing, which has not been reported in the literature. Whole-genome sequencing was performed on 72 families whose genetic cause of clinically diagnosed Charcot-Marie-Tooth disease was not revealed after the whole-exome sequencing and 17p12 duplication screening. Among the included families, 14 (19.4%) acquired genetic diagnoses that were compatible with their phenotypes. The most common factor that led to the additional diagnosis in the whole-genome sequencing was genotype-driven analysis (four families, 4/14), in which a wider range of genes, not limited to peripheral neuropathy-related genes, were analysed. Another four families acquired diagnosis due to the inherent advantage of whole-genome sequencing such as better coverage than the whole-exome sequencing (two families, 2/14), structural variants (one family, 1/14) and non-coding variants (one family, 1/14). In conclusion, an evident gain in diagnostic yield was obtained from whole-genome sequencing of the whole-exome sequencing-negative cases. A wide range of genes, not limited to inherited peripheral neuropathy-related genes, should be targeted during whole-genome sequencing.

Enhancement of the CRISPR/Cas9-Based Genome Editing System in Lettuce (Lactuca sativa L.) Using the Endogenous U6 Promoter.

The CRISPR/Cas9 system has been widely applied as a precise gene-editing tool for studying gene functions as well as improving agricultural traits in various crop plants. Here, we optimized a gene-editing system in lettuce (Lactuca sativa L.) using the endogenous U6 promoter and proved that the PHOT2 gene is a versatile target gene. We isolated the LsU6-10 promoter from 10 U6 snRNA genes identified from the lettuce genome database for comparison with the AtU6-26 promoter that has been used to drive sgRNAs in lettuce. Two CRISPR/Cas9 vectors were constructed using the LsU6-10 and AtU6-26 promoters to drive sgRNA361 to target the PHOT2 gene. The chloroplast avoidance response was defective in lettuces with biallelic mutations in the targeted PHOT2 gene, as in the Arabidopsis phot2 mutant. The PHOT2 gene mutations were stably heritable from the R0 to R2 generations, and the high gene-editing efficiency enabled the selection of transgene-free lines in the R1 generation and the establishment of independent phot2 mutants in the R2 generation. Our results suggest that the LsU6-10 promoter is more effective than the AtU6-26 promoter in driving sgRNA for the CRISPR/Cas9 system in lettuce and that PHOT2 is a useful target gene to verify gene editing efficiency without any detrimental effects on plant growth, which is often a consideration in conventional target genes.

INF2 mutations in patients with a broad phenotypic spectrum of Charcot-Marie-Tooth disease and focal segmental glomerulosclerosis.

Mutations in INF2 are associated with the complex symptoms of Charcot-Marie-Tooth disease (CMT) and focal segmental glomerulosclerosis (FSGS). To date, more than 100 and 30 genes have been reported to cause these disorders, respectively. This study aimed to identify INF2 mutations in Korean patients with CMT. This study was conducted with 743 Korean families with CMT who were negative for PMP22 duplication. In addition, a family with FSGS was included in this study. INF2 mutations were screened using whole exome sequencing (WES) and filtering processes. As the results, four pathogenic INF2 mutations were identified in families with different clinical phenotypes: p.L78P and p.L132P in families with symptoms of both CMT and FSGS; p.C104Y in a family with CMT; and p.R218Q in a family with FSGS. Moreover, different CMT types were observed in families with CMT symptoms: CMT1 in two families and Int-CMT in another family. Hearing loss was observed in two families with CMT1. Pathogenicity was predicted by in silico analyses, and considerable conformational changes were predicted in the mutant proteins. Two mutations (p.L78P and p.C104Y) were unreported, and three families showed de novo mutations that were putatively occurred from fathers. This study suggests that patients with INF2 mutations show a broad phenotypic spectrum: CMT1, CMT1 + FSGS, CMTDIE + FSGS, and FSGS. Therefore, the genotype-phenotype correlation may be more complex than previously recognized. We believe that this study expands the clinical spectrum of patients with INF2 mutations and will be helpful in the molecular diagnosis of CMT and FSGS.

Biallelic mutations in pakistani families with autosomal recessive prelingual nonsyndromic hearing loss.

BACKGROUND: Nonsyndromic autosomal recessive hearing loss (DFNB) is an etiologically heterogeneous disorder group showing a wide spectrum of onset ages and severity. DFNB genes are very diverse in their types and functions, making molecular diagnosis difficult. DFNB is particularly frequent in Pakistan, which may be partly due to consanguinity. OBJECTIVE: This study was performed to determine the genetic causes in Pakistani DFNB families with prelingual onset and to establish genotype-phenotype correlation. METHODS: Whole exome sequencing and subsequent genetic analysis were performed for 11 Pakistani DFNB families including eight consanguineous families. RESULTS: We identified eight pathogenic or likely pathogenic mutations in LOXHD1, GJB2, SLC26A4, MYO15A, and TMC1 from six families. The GJB2 mutations were identified in two families each with compound heterozygous mutations and a homozygous mutation. The compound heterozygous mutations in LOXHD1 ([p.D278Y] + [p.D1219E]) and GJB2 [p.M1?] + [p.G12Vfs*2]) were novel. The four missense or start-loss mutations were located at well conserved residues, and most in silico analysis predicted their pathogenicity. In addition to causative mutations, we found compound heterozygous mutations in PTPRQ as variants of uncertain significance. CONCLUSION: This study identified biallelic mutations as the underlying cause of early onset DFNB in six Pakistani families. This study will be helpful in providing an exact molecular diagnosis and treatment of prelingual onset deafness patients.

Peripheral Neuropathy and Decreased Locomotion of a RAB40B Mutation in Human and Model Animals.

Rab40 proteins are an atypical subgroup of Rab GTPases containing a unique suppressor of the cytokine signaling (SOCS) domain that is recruited to assemble the CRL5 E3 ligase complex for proteolytic regulation in various biological processes. A nonsense mutation deleting the C-terminal SOCS box in the RAB40B gene was identified in a family with axonal peripheral neuropathy (Charcot-Marie-Tooth disease type 2), and pathogenicity of the mutation was assessed in model organisms of zebrafish and Drosophila. Compared to control fish, zebrafish larvae transformed by the human mutant hRAB40B-Y83X showed a defective swimming pattern of stalling with restricted localization and slower motility. We were consistently able to observe reduced labeling of synaptic markers along neuromuscular junctions of the transformed larvae. In addition to the neurodevelopmental phenotypes, compared to normal hRAB40B expression, we further examined ectopic expression of hRAB40B-Y83X in Drosophila to show a progressive decline of locomotion ability. Decreased ability of locomotion by ubiquitous expression of the human mutation was reproduced not with GAL4 drivers for neuron-specific expression but only when a pan-glial GAL4 driver was applied. Using the ectopic expression model of Drosophila, we identified a genetic interaction in which Cul5 down regulation exacerbated the defective motor performance, showing a consistent loss of SOCS box of the pathogenic RAB40B. Taken together, we could assess the possible gain-of-function of the human RAB40B mutation by comparing behavioral phenotypes in animal models; our results suggest that the mutant phenotypes may be associated with CRL5-mediated proteolytic regulation.

Peripheral Myelin Protein 22 Gene Mutations in Charcot-Marie-Tooth Disease Type 1E Patients.

Duplication and deletion of the peripheral myelin protein 22 (PMP22) gene cause Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), respectively, while point mutations or small insertions and deletions (indels) usually cause CMT type 1E (CMT1E) or HNPP. This study was performed to identify PMP22 mutations and to analyze the genotype−phenotype correlation in Korean CMT families. By the application of whole-exome sequencing (WES) and targeted gene panel sequencing (TS), we identified 14 pathogenic or likely pathogenic PMP22 mutations in 21 families out of 850 CMT families who were negative for 17p12 (PMP22) duplication. Most mutations were located in the well-conserved transmembrane domains. Of these, eight mutations were not reported in other populations. High frequencies of de novo mutations were observed, and the mutation sites of c.68C>G and c.215C>T were suggested as the mutational hotspots. Affected individuals showed an early onset-severe phenotype and late onset-mild phenotype, and more than 40% of the CMT1E patients showed hearing loss. Physical and electrophysiological symptoms of the CMT1E patients were more severely damaged than those of CMT1A while similar to CMT1B caused by MPZ mutations. Our results will be useful for the reference data of Korean CMT1E and the molecular diagnosis of CMT1 with or without hearing loss.

Identification and clinical characterization of Charcot-Marie-Tooth disease type 1C patients with LITAF p.G112S mutation.

BACKGROUND: Charcot-Marie-Tooth disease type 1C (CMT1C) is a rare subtype associated with LITAF gene mutations. Until now, only a few studies have reported the clinical features of CMT1C. OBJECTIVE: This study was performed to find CMT1C patients with mutation of LITAF in a Korean CMT cohort and to characterize their clinical features. METHODS: In total, 1,143 unrelated Korean families with CMT were enrolled in a cohort. We performed whole exome sequencing to identify LITAF mutations, and examined clinical phenotypes including electrophysiological and MRI features for the identified CMT1C patients. RESULTS: We identified 10 CMT1C patients from three unrelated families with p.G112S mutation in LITAF. The frequency of CMT1C among CMT1 patients was 0.59%, which is similar to reports from Western populations. CMT1C patients showed milder symptoms than CMT1A patients. The mean CMT neuropathy score version 2 was 7.7, and the mean functional disability scale was 1.0. Electrophysiological findings showed a conduction block in 22% of affected individuals. Lower extremity MRIs showed that the superficial posterior and anterolateral compartments of the calf were predominantly affected. CONCLUSIONS: We found a conduction block in Korean CMT1C patients with p.G112S mutation and first described the characteristic MRI findings of the lower extremities in patients with LITAF mutation. These findings will be helpful for genotype-phenotype correlation and will widen understanding about the clinical spectrum of CMT1C.

Therapeutic Potential of CKD-504, a Novel Selective Histone Deacetylase 6 Inhibitor, in a Zebrafish Model of Neuromuscular Junction Disorders.

The neuromuscular junction (NMJ), which is a synapse for signal transmission from motor neurons to muscle cells, has emerged as an important region because of its association with several peripheral neuropathies. In particular, mutations in GARS that affect the formation of NMJ result in Charcot-Marie-Tooth disease and distal hereditary motor neuropathy. These disorders are mainly considered to be caused by neuronal axon abnormalities; however, no treatment is currently available. Therefore, in order to determine whether the NMJ could be targeted to treat neurodegenerative disorders, we investigated the NMJ recovery effect of HDAC6 inhibitors, which have been used in the treatment of several peripheral neuropathies. In the present study, we demonstrated that HDAC6 inhibition was sufficient to enhance movement by restoring NMJ impairments observed in a zebrafish disease model. We found that CKD-504, a novel HDAC6 inhibitor, was effective in repairing NMJ defects, suggesting that treatment of neurodegenerative diseases via NMJ targeting is possible.

Genetic and Clinical Studies of Peripheral Neuropathies with Three Small Heat Shock Protein Gene Variants in Korea.

Small heat shock proteins (sHSPs) are ATP-independent chaperones that help correct the folding of denatured proteins and protect cells from stress. Mutations in HSPB1, HSPB8, and HSPB3 are implicated in inherited peripheral neuropathies (IPNs), such as Charcot-Marie-Tooth disease type 2 (CMT2) and distal hereditary motor neuropathies (dHMN). This study, using whole exome sequencing or targeted gene sequencing, identified 9 pathogenic or likely pathogenic variants in these three sHSP genes from 11 Korean IPN families. Most variants were located in the evolutionally well conserved α-crystallin domain, except for p.P182S and p.S187L in HSPB1. As an atypical case, a patient with dHMN2 showed two compound heterozygous variants of p.R127Q and p.Y142H in HSPB1, suggesting a putative case of recessive inheritance, which requires additional research to confirm. Three HSPB8 variants were located in the p.K141 residue, which seemed to be a mutational hot spot. There were no significant differences between patient groups, which divided by sHSP genes for clinical symptoms such as onset age, severity, and nerve conduction. Early-onset patients showed a tendency of slightly decreased sensory nerve conduction values compared with late-onset patients. As a first Korean IPN cohort study examining sHSP genes, these results will, we believe, be helpful for molecular diagnosis and care of patients with CMT2 and dHMN.

Phenotypic heterogeneity in patients with NEFL-related Charcot-Marie-Tooth disease.

Charcot-Marie-Tooth disease (CMT) is the most common hereditary peripheral neuropathy. Mutations in the neurofilament light polypeptide (NEFL) gene produce diverse clinical phenotypes, including demyelinating (CMT1F), axonal (CMT2E), and intermediate (CMTDIG) neuropathies. From 2005 to 2020, 1,143 Korean CMT families underwent gene sequencing, and we investigated the clinical, genetic, and neuroimaging spectra of NEFL-related CMT patients. Ten NEFL mutations in 17 families (1.49%) were identified, of which three (p.L312P, p.Y443N, and p.K467N) were novel. Eight de novo cases were identified at a rate of 0.47 based on a cosegregation analysis. The age of onset was ≤3 years in five cases (13.5%). The patients revealed additional features including delayed walking, ataxia, dysphagia, dysarthria, dementia, ptosis, waddling gait, tremor, hearing loss, and abnormal visual evoked potential. Signs of ataxia were found in 26 patients (70.3%). In leg MRI analyses, various degrees of intramuscular fat infiltration were found. All compartments were evenly affected in CMT1F patients. The anterior and anterolateral compartments were affected in CMT2E, and the posterior compartment was affected in CMTDIG. Thus, NEFL-related CMT patients showed phenotypic heterogeneities. This study's clinical, genetic, and neuroimaging results could be helpful in the evaluation of novel NEFL variants and differential diagnosis against other CMT subtypes.

HDAC6 Inhibition Corrects Electrophysiological and Axonal Transport Deficits in a Human Stem Cell-Based Model of Charcot-Marie-Tooth Disease (Type 2D).

Charcot-Marie-Tooth disease type 2D (CMT2D), is a hereditary peripheral neuropathy caused by mutations in the gene encoding glycyl-tRNA synthetase (GARS1). Here, human induced pluripotent stem cell (hiPSC)-based models of CMT2D bearing mutations in GARS1 and their use for the identification of predictive biomarkers amenable to therapeutic efficacy screening is described. Cultures containing spinal cord motor neurons generated from this line exhibit network activity marked by significant deficiencies in spontaneous action potential firing and burst fire behavior. This result matches clinical data collected from a patient bearing a GARS1P724H mutation and is coupled with significant decreases in acetylated α-tubulin levels and mitochondrial movement within axons. Treatment with histone deacetylase 6 inhibitors, tubastatin A and CKD504, improves mitochondrial movement and α-tubulin acetylation in these cells. Furthermore, CKD504 treatment enhances population-level electrophysiological activity, highlighting its potential as an effective treatment for CMT2D.

Charcot-Marie-Tooth disease type 2CC due to NEFH variants causes a progressive, non-length-dependent, motor-predominant phenotype.

OBJECTIVE: Neurofilaments are the major scaffolding proteins for the neuronal cytoskeleton, and variants in NEFH have recently been described to cause axonal Charcot-Marie-Tooth disease type 2CC (CMT2CC). METHODS: In this large observational study, we present phenotype-genotype correlations on 30 affected and 3 asymptomatic mutation carriers from eight families. RESULTS: The majority of patients presented in adulthood with motor-predominant and lower limb-predominant symptoms and the average age of onset was 31.0±15.1 years. A prominent feature was the development of proximal weakness early in the course of the disease. The disease progressed rapidly, unlike other Charcot-Marie-Tooth disease (CMT) subtypes, and half of the patients (53%) needed to use a wheelchair on average 24.1 years after symptom onset. Furthermore, 40% of patients had evidence of early ankle plantarflexion weakness, a feature which is observed in only a handful of CMT subtypes. Neurophysiological studies and MRI of the lower limbs confirmed the presence of a non-length-dependent neuropathy in the majority of patients.All families harboured heterozygous frameshift variants in the last exon of NEFH, resulting in a reading frameshift to an alternate open reading frame and the translation of approximately 42 additional amino acids from the 3' untranslated region (3'-UTR). CONCLUSIONS: This phenotype-genotype study highlights the unusual phenotype of CMT2CC, which is more akin to spinal muscular atrophy rather than classic CMT. Furthermore, the study will enable more informative discussions on the natural history of the disease and will aid in NEFH variant interpretation in the context of the disease's unique molecular genetics.

Variants of aminoacyl-tRNA synthetase genes in Charcot-Marie-Tooth disease: A Korean cohort study.

Charcot-Marie-Tooth disease (CMT) and related diseases are a genetically and clinically heterogeneous group of peripheral neuropathies. Particularly, mutations in several aminoacyl-tRNA synthetase (ARS) genes have been reported to cause axonal CMT (CMT2) or distal hereditary motor neuropathy (dHMN). However, the common pathogenesis among CMT subtypes by different ARS gene defects is not well understood. This study was performed to investigate ARS gene mutations in a CMT cohort of 710 Korean families. Whole-exome sequencing was applied to 710 CMT patients who were negative for PMP22 duplication. We identified 12 disease-causing variants (from 13 families) in GARS1, AARS1, HARS1, WARS1, and YARS1 genes. Seven variants were determined to be novel. The frequency of overall ARS gene mutations was 1.22% among all independent patients diagnosed with CMT and 1.83% in patients negative for PMP22 duplication. WARS1 mutations have been reported to cause dHMN; however, in our patients with WARS1 variants, CMT was associated with sensory involvement. We analyzed genotype-phenotype correlations and expanded the phenotypic spectrum of patients with CMT possessing ARS gene variants. We also characterized clinical phenotypes according to ARS genes. This study will be useful for performing exact molecular and clinical diagnoses and providing reference data for other population studies.

Cerebellar White Matter Abnormalities in Charcot-Marie-Tooth Disease: A Combined Volumetry and Diffusion Tensor Imaging Analysis.

Charcot-Marie-Tooth disease (CMT) is a genetically heterogeneous hereditary peripheral neuropathy. Brain volumetry and diffusion tensor imaging (DTI) were performed in 47 controls and 47 CMT patients with PMP22 duplication (n = 10), MFN2 (n = 15), GJB1 (n = 11), or NEFL mutations (n = 11) to investigate for structural changes in the cerebellum. Volume of cerebellar white matter (WM) was significantly reduced in CMT patients with NEFL mutations. Abnormal DTI findings were observed in the superior, middle, and inferior cerebellar peduncles, predominantly in NEFL mutations and partly in GJB1 mutations. Cerebellar ataxia was more prevalent in the NEFL mutation group (72.7%) than the GJB1 mutation group (9.1%) but was not observed in other genotypic subtypes, which indicates that structural cerebellar abnormalities were associated with the presence of cerebellar ataxia. However, NEFL and GJB1 mutations did not affect cerebellar gray matter (GM), and neither cerebellar GM nor WM abnormalities were observed in the PMP22 duplication or MFN2 mutation groups. We found structural evidence of cerebellar WM abnormalities in CMT patients with NEFL and GJB1 mutations and an association between cerebellar WM involvement and cerebellar ataxia in these genetic subtypes, especially in the NEFL subgroup. Therefore, we suggest that neuroimaging, such as MRI volumetry or DTI, for CMT patients could play an important role in detecting abnormalities of cerebellar WM.

Novel homozygous mutations in Pakistani families with Charcot-Marie-Tooth disease.

BACKGROUND: Charcot-Marie-Tooth disease (CMT) is a group of genetically and clinically heterogeneous peripheral nervous system disorders. Few studies have identified genetic causes of CMT in the Pakistani patients. METHODS: This study was performed to identify pathogenic mutations in five consanguineous Pakistani CMT families negative for PMP22 duplication. Genomic screening was performed by application of whole exome sequencing. RESULTS: We identified five pathogenic or likely pathogenic homozygous mutations in four genes: c.2599C > T (p.Gln867*) and c.3650G > A (p.Gly1217Asp) in SH3TC2, c.19C > T (p.Arg7*) in HK1, c.247delG (p.Gly83Alafs*44) in REEP1, and c.334G > A (p.Val112Met) in MFN2. These mutations have not been reported in CMT patients. Mutations in SH3TC2, HK1, REEP1, and MFN2 have been reported to be associated with CMT4C, CMT4G, dHMN5B (DSMA5B), and CMT2A, respectively. The genotype-phenotype correlations were confirmed in all the examined families. We also confirmed that both alleles from the homozygous variants originated from a single ancestor using homozygosity mapping. CONCLUSIONS: This study found five novel mutations as the underlying causes of CMT. Pathogenic mutations in SH3TC2, HK1, and REEP1 have been reported rarely in other populations, suggesting ethnic-specific distribution. This study would be useful for the exact molecular diagnosis and treatment of CMT in Pakistani patients.