Charcot-Marie-Tooth (CMT) disease is the most common inherited neuropathy. In this study, we aimed to analyze the genetic spectrum and describe phenotypic features in a large cohort from Türkiye. Demographic and clinical findings were recorded. Patients were initially screened for PMP22 duplication. Targeted sequencing or whole-exome sequencing was performed in duplication-negative patients. Overall, 311 patients from 265 families were included. Demyelinating CMT (67.4%) was more common than axonal (20.5%) and intermediate subtypes (11.7%). PMP22 duplication was the most frequent mutation, followed by pathogenic variants in GJB1, MFN2, SH3TC2, and GDAP1 genes. MPZ-neuropathy was rare in our cohort (3.0%). Interestingly, CMT4 is the second most common type after CMT1. Lower extremity weakness and foot deformities were the most frequent presenting complaints. Striking clinical features included a high frequency of scoliosis in SH3TC2, peripheral hyperexcitability in HINT1, and central nervous system findings in GJB1. Autosomal recessive CMT subtypes had higher CMTESv2 scores when compared to autosomal dominant ones (12.39 ± 4.81 vs. 8.36 ± 4.15, p: 0.023). Twenty-one patients used wheelchairs during their last examination. Among them, 16 had an autosomal recessive subtype. Causative variants were identified in 31 genes, including 28 novel pathogenic or likely pathogenic changes. Our findings provided robust data regarding the genetic distribution of CMT in Türkiye, which may pave the path for building population-specific diagnostic gene panels. Rare autosomal recessive subtypes were relatively frequent in our cohort. By analyzing genotype-phenotype correlations, our data may provide clinical clues for clinicians.

Charcot-Marie-Tooth disease (CMT) is the most common inherited peripheral neuropathy by high clinical and genetic heterogeneity. Although many studies reported from East Asian countries, data from West/South Asia remain limited. The current study aimed to summarize available epidemiological, clinical and genetic data of CMT patients in Asia. We searched PubMed, Scopus, Web of Sciences, Nature, Google Scholar, Science Direct, and Willey for relevant published articles between 2003 until Feb 2023, according to PRISMA guidelines. Articles were screened for epidemiological, clinical and genetic information. Inclusion required published mutation frequency or genetic variant in CMT patients. The Q-Genie tool and Newcastle-Ottawa (NOS) were used to evaluate the quality of genetics and observational studies, respectively. Out of 320, 32 screened articles met the inclusion criteria. Most studies were reported from China (n = 12), Japan (n=7), and Korea (n=6). The axonal CMT was the frequent type (50%), followed by demyelinating (28%) and intermediate (9%) types. Autosomal dominant (AD) inheritance was observed in 62% of genetically confirmed cases. Frequently mutated genes were GDAP1, MPZ, and JGB1, which have been found mostly in the East Asia. This systematic review reports substantial knowledge gap in West/South Asian CMT research. The review emphasized the urgent need to use comprehensively of next-generation sequencing (NGS) to uncover new mutations and improve diagnostics in West/South Asian. Future region-specific cohort studies and registries can be essential to identify frequent variants and fill the diagnostic gaps.

ITPR3 encodes type 3 inositol-tri-phosphate receptor (IP3R3), a protein expressed in Schwann cells, predominantly in the paranodal region, and involved in the regulation of Ca2+ release from the endoplasmic reticulum. Dominant variants in ITPR3 have recently been recognized as a rare cause of intermediate Charcot-Marie-Tooth disease (CMT). We collected the clinical data of a family with autosomal dominant neuropathy whose proband was diagnosed with chronic inflammatory demyelinating polyneuropathy (CIDP) for many years. The genetic diagnosis was achieved by whole exome sequencing. The proband developed symmetrical sensory-motor neuropathy with demyelinating features at 32 years old. He was diagnosed with CIDP and received numerous immunomodulatory treatments. However, his condition progressed, leading to severe proximal leg and hand atrophy that confined him to a wheelchair at 60 years. The patient's two sons began to exhibit symptoms suggestive of neuropathy shortly after age 30 years, and the condition was reoriented as inherited. Exome sequencing identified a heterozygous c.4271C > T variant in the ITPR3 gene segregating with the disease. Nerve conduction studies showed a combination of demyelinating and axonal features that vary by nerve, disease duration, and patient. A uniform thickening of the nerves was identified on nerve echography, as was distal symmetric fatty infiltration in lower limb muscle imaging. The c.4271C > T ITPR3 variant causes a late onset CMT that can be considered an intermediate CMT. Considering the electrophysiological findings and the distribution of IP3R3, we hypothesize that this variant could start as nodal dysfunction that progresses to widespread nerve degeneration.

Aminoacyl-tRNA synthetases (ARSs) are essential enzymes with a critical role in protein synthesis: charging tRNA molecules with cognate amino acids. Heterozygosity for variants in five genes (AARS1, GARS1, HARS1, WARS1, and YARS1) encoding cytoplasmic, dimeric ARSs have been associated with autosomal dominant neurological phenotypes, including axonal Charcot-Marie-Tooth disease (CMT). Missense variants in the catalytic domain of YARS1 were previously linked to dominant intermediate CMT type C (DI-CMTC). Here, we report a patient with a missense variant of unknown significance predicted to modify residue 308 in the anticodon binding domain of YARS1 (p.Asp308Tyr). Interestingly, p.Asp308Tyr is associated with proximal-predominant motor neuropathy, which has not been reported in patients with pathogenic YARS1 variants. We demonstrate that this allele causes a loss-of-function effect in yeast complementation assays when modeled in YARS1 and the yeast ortholog TYS1; structural modeling of this variant further supports a loss-of-function effect. Taken together, this study raises the possibility that certain YARS1 variants cause proximal-prominent motor neuropathy and indicates that patients with this phenotype should be screened for genetic lesions in YARS1.

Neuromuscular disorders are a heterogeneous group of acquired or hereditary conditions that affect striated muscle function. The resulting decrease in muscle strength and motility irreversibly impacts quality of life. In addition to directly affecting skeletal muscle, pathogenesis can also arise from dysfunctional crosstalk between nerves and muscles, and may include cardiac impairment. Muscular weakness is often progressive and paralleled by continuous decline in the ability of skeletal muscle to functionally adapt and regenerate. Normally, the skeletal muscle resident stem cells, named satellite cells, ensure tissue homeostasis by providing myoblasts for growth, maintenance, repair and regeneration. We recently defined 'Satellite Cell-opathies' as those inherited neuromuscular conditions presenting satellite cell dysfunction in muscular dystrophies and myopathies (doi:10.1016/j.yexcr.2021.112906). Here, we expand the portfolio of Satellite Cell-opathies by evaluating the potential impairment of satellite cell function across all 16 categories of neuromuscular disorders, including those with mainly neurogenic and cardiac involvement. We explore the expression dynamics of myopathogenes, genes whose mutation leads to skeletal muscle pathogenesis, using transcriptomic analysis. This revealed that 45% of myopathogenes are differentially expressed during early satellite cell activation (0 - 5 hours). Of these 271 myopathogenes, 83 respond to Pax7, a master regulator of satellite cells. Our analysis suggests possible perturbation of satellite cell function in many neuromuscular disorders across all categories, including those where skeletal muscle pathology is not predominant. This characterisation further aids understanding of pathomechanisms and informs on development of prognostic and diagnostic tools, and ultimately, new therapeutics.