496P Recessive missense variants in DARS2 gene as novel cause of axonal Charcot-Marie-Tooth disease.

Charcot-Marie-Tooth (CMT) disease is a heterogeneous group of genetic neuropathies, with more than 90 associated genes. While the majority of individuals with genetic diagnosis have demyelinating CMT, a significant proportion of individuals with axonal CMT remain genetically unsolved. Aminoacyl-tRNA synthetases (aaRS) have been implicated in various neurological disorders, including CMT. Here, we hypothesize that hypomorphic variations of DARS2 , which encodes the mitochondrial aspartyl-tRNA synthetase, are associated with axonal CMT. We investigated four individuals from two unrelated families with axonal CMT. We conducted clinical assessments, genetic testing, and functional studies in fibroblasts from two affected individuals. Two pairs of siblings, now adults, presented with progressive distal muscle weakness with onset during childhood, absent lower limb reflexes and normal cognitive function. Brain MRI scans showed no abnormalities. Electrophysiological studies revealed positive waves and fibrillations and was consistent with a diagnosis of axonal motor and sensory neuropathy. Genetic testing identified compound heterozygous variants in DARS2 in both families (c.713C>T; p.Ser238Phe and c.1006C>T; p.Arg336Cys in Family 1; and c.74del; p.Ile25Thrfs*38 and c.1006C>T; p.Arg336Cys in Family 2). The four individuals share the variant DARS2 : c.1006C>T, p.Arg336Cys, located in the insertion subdomain of DARS2, where very few variants have been previously reported. In Family 1, this variant is in trans with another missense variant (c.713C>T; p.Ser238Phe) located in the dimerization domain of DARS2, which is an essential region for the correct functionality of the protein, as in other aaRS. In Family 2, it is combined with a truncating variant. Functional analyses in fibroblasts revealed reduced DARS2 protein levels and altered mitochondrial localization. Additionally, we observed a decrease in both mitochondrial mass and fragmentation, consistent with a disrupted mitochondrial network morphology, suggesting the involvement of DARS2 in the disease pathophysiology. The identification of fully penetrant variants (p.Ser238Phe and p.Ile25Thrfs*38) combined with a hypomorphic variant (p.Arg336Cys) expands the phenotypic spectrum of DARS2-related disorders, establishing a novel association between DARS2 and axonal CMT. The combination of penetrant variants and hypomorphic variants distinguishes these cases from previously reported with DARS2-related leukoencephalopathy. We propose that the genotypic combination of a hypomorphic and a penetrating allele for DARS2 explains the symptoms in these two families with a pure axonal CMT. These findings underscore the importance of mitochondrial aspartyl-tRNA synthetase in peripheral nerve function and highlight potential targets for therapeutic intervention in CMT. [ABSTRACT FROM AUTHOR]